Understanding the merits of turbo engines and NA engines

[bazza]

HP being equal, I can't think of a single reason that's important to me that would cause me to want the turbo...

400 hp NA will have far less torque as it is relying purely on RPM to make it's power and will most likely have peak torque at a high rpm - it would be gutless down low compared to the turbo.

The 400 hp turbo on the other hand would make peak torque at 3000-4000 depending on turbo selection and most likely carry the power to redline.

I wouldn't run the EZ series... given the timing cover alone has 120 odd bolts, the build / rebuild time is rather lengthy due the complexity of the engine, tuning is expensive as you need to deal with AVCS / AVLS then the stock internals are weak... although I'm a big fan of the KISS principle so I'd use either EJ / turbo or EG / turbo.

[el_jefe]

400 hp NA will have far less torque as it is relying purely on RPM to make it's power and will most likely have peak torque at a high rpm - it would be gutless down low compared to the turbo.



Depends a lot on turbo selection, and what is "gutless" in a 3500lb AWD might be just right in a 1800lb RWD.

[Turboguy]

Plus- we get that sound which can only be achieved with a flat-6 :)

[Xusia]

400 hp NA will have far less torque as it is relying purely on RPM to make it's power and will most likely have peak torque at a high rpm - it would be gutless down low compared to the turbo.

The 400 hp turbo on the other hand would make peak torque at 3000-4000 depending on turbo selection and most likely carry the power to redline.

I wouldn't run the EZ series... given the timing cover alone has 120 odd bolts, the build / rebuild time is rather lengthy due the complexity of the engine, tuning is expensive as you need to deal with AVCS / AVLS then the stock internals are weak... although I'm a big fan of the KISS principle so I'd use either EJ / turbo or EG / turbo.

Hi bazza,

Welcome to the forum!

I mean no offense when I say your post makes absolutely no sense to me.

Turbo's make their power using exhaust gasses to spin up the turbine. At low RPMs, there is little to no boost, so they make pretty much the same torque as a normally aspirated version of the same engine. At higher RPMs, of course they will make more power; than the same engine without a turbo! However, as stated previously (by me) the comparison isn't between 2 engines of the same size; one with a turbo and one without. It's a comparison of 2 engines that make the same peak HP; one with a turbo and one without. In order to have equal power, the NA engine would need additional displacement (which is why we are comparing/discussing the H6 vs. a turbo H4...). This would mean at lower RPMs, the NA engine will have more torque because the turbo isn't yet spun up.

I would add to this that those of us that prefer NA engines, the reason is generally NOT related peak HP. It's two things, primarily:

Linearity of throttle response, which is more predictable
Lack of turbo lag


At this point I think the message has been well presented that the EJ (turbo H4) is highly tuneable to just about any realistic HP goal. But that doesn't address the 2 points above. Lots of folks have said the stock turbo has no lag. I haven't driven a WRX, so I comment on it directly, but I can say I've NEVER driven any turbo car with NO lag. There is always some. And even if true, it doesn't address the throttle response.

As for keeping it simple, that's definitely me - I'm a huge fan of simple. To me, a NA engine is inherently less complicated than a turbo engine. I guess the argument could be made the H6 has more cylinders, whereas the H4 has a turbo, so they are equally complicated. I personally wouldn't agree, but that's me. I'll take a couple more pistons and spark plugs over an intercooler, exhaust plumbing, etc. any day.

EDIT: I should add - just in case you feel compelled to try - there probably isn't anything you can say about a turbo engine that will cause to change my opinion. That said, I've already consigned myself to building my 818 with a WRX engine. The H6 - while I would definitely prefer it - is just too much of a hassle (and expense) for me. And you know what? Despite not really liking turbos, I think I'll love my 818 all the same! :)

[el_jefe]

Turbo's make their power using exhaust gasses to spin up the turbine. At low RPMs, there is little to no boost, so they make pretty much the same torque as a normally aspirated version of the same engine.

I beg to differ sir.

http://i9.photobucket.com/albums/a86/orionis996/Car%20stuff/331522_68_full.jpg

(sorry about the speed instead of RPM, the shop printed it that way)

It's all about sizing the turbo appropriate to your needs. That particular car has a smallish turbo, and blows the tires off in the first three gears above 2000 rpm, and lag is nonexistent unless you are lugging it at 1500 rpm in 5th.

Personally, I'm a fan of high cylinder compression, low boost turbo motors. Instant throttle response, plenty of power, no lag. The only drawback is that if you get a bad batch of fuel, the chances of exploding your motor are pretty high.

Again, torque isn't going to be a big concern for this car, in fact it's about the last thing you will want in a mid engine RWD chassis. Unless you like driving backwards on corner exits. Look at ferrari and lambo motors, decent hp, low torque. They did that for a reason. As stated, linear powerband will be key, although I have no doubt that someone will drop in a holset turbo off of a diesel and have a skijump dyno chart with stupid power. http://i9.photobucket.com/albums/a86/orionis996/gif/supragif.gif

[bazza]

Depends a lot on turbo selection, and what is "gutless" in a 3500lb AWD might be just right in a 1800lb RWD.

I'm talking apples v apples. So same car... 400 hp NA vs 400 hp turbo - both running say an EZ30. Turbo will be far better to drive assuming the turbo is correctly sized and not a mismatch.


Hi bazza,

Welcome to the forum!

I mean no offense when I say your post makes absolutely no sense to me.

Turbo's make their power using exhaust gasses to spin up the turbine. At low RPMs, there is little to no boost, so they make pretty much the same torque as a normally aspirated version of the same engine. At higher RPMs, of course they will make more power; than the same engine without a turbo!

This is not quite correct. On a 2.5L and 3.3L, at idle a GT35R for example is flowing far more air than the engine can consume, remove the BOV and you can put your hand there and feel how much air is coming past and not being consumed by the engine - it's actually quite impressive. So an engine not on boost is still getting far more air than a NA engine even at idle. Boost is just engine restriction - some people get carried away with boost and they don't really understand it but a good engine with decent turbo will make very good power and torque figures even before the turbo is running it's target boost. At higher RPM it also depends on turbo selection - small turbos can give huge midrange around 3000-4000 rpm but have nothing up top.


However, as stated previously (by me) the comparison isn't between 2 engines of the same size; one with a turbo and one without. It's a comparison of 2 engines that make the same peak HP; one with a turbo and one without. In order to have equal power, the NA engine would need additional displacement (which is why we are comparing/discussing the H6 vs. a turbo H4...). This would mean at lower RPMs, the NA engine will have more torque because the turbo isn't yet spun up.

Of course - that makes perfect sense. I was talking say EZ30 NA vs EZ30 turbo making the same power. For the same engine, the NA needs to rev and have cams to hit 400 bhp whereas the turbo setup would just need about 7-10 psi of boost.



I would add to this that those of us that prefer NA engines, the reason is generally NOT related peak HP. It's two things, primarily:

Linearity of throttle response, which is more predictable
Lack of turbo lag


At this point I think the message has been well presented that the EJ (turbo H4) is highly tuneable to just about any realistic HP goal. But that doesn't address the 2 points above. Lots of folks have said the stock turbo has no lag. I haven't driven a WRX, so I comment on it directly, but I can say I've NEVER driven any turbo car with NO lag. There is always some. And even if true, it doesn't address the throttle response.

I agree about the throttle response and the lag. My trackcar went from 2L/TD06h-20G (big turbo small engine) to a 2.5L/GT35R (big turbo, medium engine) to a 3.3L/GT35R (big turbo, big engine). The 2L was laggy and throttle response was lacking. The 2.5L gave far better throttle response but was still a touch laggy and not quite linear. The EG33/GT35R setup however is extremely linear and throttle response is ridiculous, it's actually hard to drive at low RPM as it just wants to go, it's like a light switch and my wife actually complained because it's so responsive lol. So it all depends on the setup.


As for keeping it simple, that's definitely me - I'm a huge fan of simple. To me, a NA engine is inherently less complicated than a turbo engine. I guess the argument could be made the H6 has more cylinders, whereas the H4 has a turbo, so they are equally complicated. I personally wouldn't agree, but that's me. I'll take a couple more pistons and spark plugs over an intercooler, exhaust plumbing, etc. any day.

I do agree. I'd love to ditch the turbo, intercooler and everything else turbo related as the complexity ****s me, but I'd half my power and torque and that's not acceptable when there are high powered V8's floating around :P

Example: http://www.youtube.com/watch?v=3eFnBiuQJgA


EDIT: I should add - just in case you feel compelled to try - there probably isn't anything you can say about a turbo engine that will cause to change my opinion. That said, I've already consigned myself to building my 818 with a WRX engine. The H6 - while I would definitely prefer it - is just too much of a hassle (and expense) for me. And you know what? Despite not really liking turbos, I think I'll love my 818 all the same! :)

Why would I want to change your mind? It's your car and it's not hard to change the setup if one day you decide you don't like it.

[Xusia]

I appreciate the discourse, but I don't believe for even a moment that a 2.5L engine at idle is producing more boost than the engine can consume. I'm not sure how you can prove that to me, but I've LOVE to be proven wrong! :)

[bazza]

I appreciate the discourse, but I don't believe for even a moment that a 2.5L engine at idle is producing more boost than the engine can consume. I'm not sure how you can prove that to me, but I've LOVE to be proven wrong! :)

You're mixing up airflow with boost. Boost (positive pressure) is created when an engine simply cannot consume the provided airflow from the turbo. What I've experienced is simply the turbo at idle spinning at X rpm creating more airflow than the engine can consume, it's quite common with the Garrett ball bearing turbos. The extra airflow is not enough to make any difference to the vacuum readings on the engine let alone boost but the point is a turbo doesn't start working when at full boost - it's working well below that.

This is another setup, it's an old 2.2L / GT30R that we built years ago - you can see how the turbo spins up nicely even at idle and this turbo was on the large side of things for the 2.2L engine capacity...
http://www.youtube.com/watch?v=FCpLIkb3IOQ

Anyway, hope that makes sense. I guess the issue with these RWD setups and no weight is severe lack of traction - is that the case?

[Xusia]

I'm trying to understand what you are getting at, but it still doesn't make sense to me. For instance...


You're mixing up airflow with boost. Boost (positive pressure) is created when an engine simply cannot consume the provided airflow from the turbo.

So when there is more airflow than the engine can consume, you have boost.


What I've experienced is simply the turbo at idle spinning at X rpm creating more airflow than the engine can consume

So what you've experienced is boost, by your own definition. If it were true that turbos provided boost at idle, it can't be significant because if it were significant there would be no such thing as turbo lag. I have experienced turbo lag on every turbo car I've driven or ridden in, so it seems to me there can't be any significant boost at idle.


It's quite common with the Garrett ball bearing turbos. The extra airflow is not enough to make any difference to the vacuum readings on the engine let alone boost but the point is a turbo doesn't start working when at full boost - it's working well below that.

If when you say "working" you mean it's spinning and creating some boost, I'd believe that - it seems obvious. The real question is whether or not the boost at that point is enough to provide a noticeable increase in power. At lower RPMs it isn't, so when you compare an turbo H4 and a NA H6, the H6 is going to provide more power at lower RPMs. At higher RPMs, when the turbo is providing significant boost and a noticeable increase in power, that would no longer be true.

I apologize if at any point you got the impression I meant turbos only work at full boost. That is not at all what I meant, and I know better!


I guess the issue with these RWD setups and no weight is severe lack of traction - is that the case?

I also think traction will be a real problem, especially with an engine producing more torque. That's one reason I think I'll be happy with a stock turbo H4 - even a 2.0L. This car just isn't going to need a lot of power to get up and go!

[armstrom]

Not to continue the boost at idle conversation... But we need to take a step back and think about what's going on. First, boost pressure and vacuum level are measured BEHIND the throttle butterfly, in the intake manifold. The pressure level in front of the butterfly is of no concern. The recirculation valve is meant to prevent damage to the turbo by not allowing sudden changes in pressure to cause huge changes in the forces applied to the compressor wheel, shaft and bearings. When the throttle butterfly slams shut that pressure has a place to go rather than traveling back down the intake piping as a resonance pulse and stopping the compressor wheel.
Some recirculation valves are also designed to be open at very high vacuum levels (idle) in order to reduce the exhaust backpressure and increase efficiency. In these scenarios the turbo is basically "freewheeling" and pumping most of its air in a loop. Again, if the pressure were allowed to build in front of the throttle butterfly we would increase backpressure in the exhaust and reduce engine efficiency at idle, so on and so forth.

In order to make positive boost the turbo's turbine section must be driven with enough force (due to the speed and temperature of the gasses passing through it) to spin the compressor wheel fast enough to force more air mass through the throttle body than the engine can consume at that moment. When the BSAC of the engine is insufficient to consume the air being pushed by the turbo, you get boost. The fact that the turbo is able to blow a large quantity of air through a very low restriction recirculation value at idle is of no importance. If you were to force the recirc valve closed some pressure would build up in front of the throttle butterfly, the compressor wheel would slow down and exhaust pressure would build until the system reached equilibrium. This wouldn't be ideal though. But in this situation the tiny throttle opening is the limiting factor. It will not allow enough air to pass through it to ever overcome the air consumption demands of the engine. Even if you were to build pressure in front of the throttle butterfly that pressure wouldn't be available to you when you open the throttle. As soon as more air can flow through the throttle body the vacuum level in the manifold will drop and the engine will begin drawing air through the turbo until the turbine section is able to spool up and begin providing additional airflow into the induction tract.

Try a little thought experiment.. Even if it sounds funny. Don't actually try this :)
Imagine you build a system out of PVC pipe with three inlets/outlets. One has a valve on it that can be opened and closed. Hook up a vacuum cleaner to the section with the vale so that the valve is between the vacuum cleaner hose and the rest of the system. Now switch on the vacuum and close the valve so that barely any air gets through. Now imagine you blow into one of the other two opening (I know, stick with me). You will be able to feel the air you blow into that section coming out the third whole... In actuality, most of it will come right back out... This means you are producing more air than the vacuum is able to consume through the valve! This simulates the recirculation valve system. The valve represents the throttle butterfly and the vacuum is the air-starved engine. Now, keep blowing into the end and suddenly open the valve while also closing the third outlet with your hand (simulating the recirculation valve slamming shut). Do you think the fact that you were able to blow more air than was consumed with the valve closed will make any difference in this situation? Heck no! That vacuum cleaner will empty your lungs in a fraction of a second. This is analogous to the situation being discussed here.

I hope this makes sense.
-Matt

[Desertrunner]

One thing I don't get is if turbo engines are so much better then NA why are bikes still NA. You would think with all the suggested benfits, weight & power the bike builders would be all over this idea.

Good point Matt,

Tony

[armstrom]

One thing I don't get is if turbo engines are so much better then NA why are bikes still NA. You would think with all the suggested benfits, weight & power the bike builders would be all over this idea.

Good point Matt,

Tony
Bikes have the advantage of being very lightweight. A little torque goes a LONG way. It's also easier to produce small engines that rev very high for motorcycles. Turbo systems are complex. They require additional intake piping, any reasonably high pressure system will require an intercooler, they need an oil supply, etc... It's not a simple system to just pop on to an existing engine. Also, motorcycles have a tradition of using very high compression, high revving engines. High compression is not traditionally compatible with forced induction (though this is changing with advances in direct injection technology).

With all that said, there are plenty of turbo kits for larger bikes. A turbo Hayabusa can make insane power, far beyond what is possible with other normally aspirated modifications. Lots of torque in a motorcycle can actually make the bike much harder to deal with. You might not even be able to use all the torque available to you because your weight is insufficient to keep the bike down in lower gears.
-Matt

[Xusia]

armstrom, THANK YOU for that explanation. I understand what you are saying and it makes sense to me. It also validates what I've personally experienced.

Desertrunner, There are plenty of people that would argue turbo engines are not unilaterally better - it all depends on what your goals are. While what armstrom says is true, as a long time sportbike rider, I would add that the primary reason bikes don't use turbos is throttle response. The handling of a motorcycle at lean demands precision, linearity, and predictability from the throttle. Because a turbo is driven by exhaust gasses, there is inherent a delay in it's effect. While this delay can be small, it still exists, and creates a potentially unsafe situation. For example, if you were leaned over in a corner and needed to apply a bit more throttle (for whatever reason), you need to be able to do so in a controlled and predictable manner: twist the throttle a bit more and get a specific, and instantaneous response. A delay in the response (such as caused by a turbo) could result in more power being applied than was intended. This may not seem like a big deal to some people, but on a motorcycle it can mean the difference between staying in your lane or not; or maintaining traction or losing it. It would cause you to ride the motorcycle more conservatively and therefore introduce a limiting factor to your riding. Most riders don't buy sportbikes to ride conservatively (that's what Harleys are for!!), and they sure as heck don't want some aspect of the bike to be the limiting factor (for most, the limiting factor is their skill). I hope that makes sense.

[el_jefe]

One thing I don't get is if turbo engines are so much better then NA why are bikes still NA. You would think with all the suggested benfits, weight & power the bike builders would be all over this idea.

Good point Matt,

Tony

Only benefits are power and size, turbos add weight (a lot), complexity, and a huge thermal issue. Bikes don't like weight, and have enough problems with heat (especially at idle) without adding the issues turbocharging brings. that being said, several manufactures built turbo bikes in the 70's and 80's.

[el_jefe]

armstrom, THANK YOU for that explanation. I understand what you are saying and it makes sense to me. It also validates what I've personally experienced.

Desertrunner, There are plenty of people that would argue turbo engines are not unilaterally better - it all depends on what your goals are. While what armstrom says is true, as a long time sportbike rider, I would add that the primary reason bikes don't use turbos is throttle response. The handling of a motorcycle at lean demands precision, linearity, and predictability from the throttle. Because a turbo is driven by exhaust gasses, there is inherent a delay in it's effect. While this delay can be small, it still exists, and creates a potentially unsafe situation. For example, if you were leaned over in a corner and needed to apply a bit more throttle (for whatever reason), you need to be able to do so in a controlled and predictable manner: twist the throttle a bit more and get a specific, and instantaneous response. A delay in the response (such as caused by a turbo) could result in more power being applied than was intended. This may not seem like a big deal to some people, but on a motorcycle it can mean the difference between staying in your lane or not; or maintaining traction or losing it. It would cause you to ride the motorcycle more conservatively and therefore introduce a limiting factor to your riding. Most riders don't buy sportbikes to ride conservatively (that's what Harleys are for!!), and they sure as heck don't want some aspect of the bike to be the limiting factor (for most, the limiting factor is their skill). I hope that makes sense.


Haven't ridden a 2-stroke much? lol

[Desertrunner]

armstrom, THANK YOU for that explanation. I understand what you are saying and it makes sense to me. It also validates what I've personally experienced.

Desertrunner, There are plenty of people that would argue turbo engines are not unilaterally better - it all depends on what your goals are. While what armstrom says is true, as a long time sportbike rider, I would add that the primary reason bikes don't use turbos is throttle response. The handling of a motorcycle at lean demands precision, linearity, and predictability from the throttle. Because a turbo is driven by exhaust gasses, there is inherent a delay in it's effect. While this delay can be small, it still exists, and creates a potentially unsafe situation. For example, if you were leaned over in a corner and needed to apply a bit more throttle (for whatever reason), you need to be able to do so in a controlled and predictable manner: twist the throttle a bit more and get a specific, and instantaneous response. A delay in the response (such as caused by a turbo) could result in more power being applied than was intended. This may not seem like a big deal to some people, but on a motorcycle it can mean the difference between staying in your lane or not; or maintaining traction or losing it. It would cause you to ride the motorcycle more conservatively and therefore introduce a limiting factor to your riding. Most riders don't buy sportbikes to ride conservatively (that's what Harleys are for!!), and they sure as heck don't want some aspect of the bike to be the limiting factor (for most, the limiting factor is their skill). I hope that makes sense.

I never figure this out but it just supports what I have felt for a long time. Bazza is a friend and we are developing EG33 engines together but I have suggested to him on a number of occussions that when I watch his car going around the track it doesn't look smooth. I had thought it was because of the way he drove it, now after your comment I am convinced the car is losing traction when the turbo kicks.

If the car is at its handling limits a sudden change in torque will be a problem, it would be like walking on egg shells.

By the way its a brilliant discussion, I am learning heaps.

Tony

[el_jefe]

If the car is at its handling limits a sudden change in torque will be a problem, it would be like walking on egg shells.



Especially in a mid engine car, where most of the weight is on the rear. They handle brilliantly up to the limit, but when you oversteep that limit watch out. Go to a track day with a bunch of Lotus Elise's, 90% of the accidents are the cars going tail first into a barrier.

[armstrom]

Just FYI, using a turbo does not have to mean poor throttle response. It all comes down to proper sizing. If you have a huge turbo then yeah, anything other than WOT and high RPM will mean significantly lower torque output followed by the turbo "hitting" like a freight train and sending you spinning wildly out of control. This is fine for a drag setup where all your time is spent at WOT and in a straight line. A properly sized turbo will provide nice, linear torque output within the "performance" RPM range. If you're driving the car correctly you should still be on boost even when powering out of a corner. Just have to keep the revs up enough. With a properly sized turbo you should still have a wide range of revs to play with.

[bazza]

I never figure this out but it just supports what I have felt for a long time. Bazza is a friend and we are developing EG33 engines together but I have suggested to him on a number of occussions that when I watch his car going around the track it doesn't look smooth. I had thought it was because of the way he drove it, now after your comment I am convinced the car is losing traction when the turbo kicks.

If the car is at its handling limits a sudden change in torque will be a problem, it would be like walking on egg shells.

By the way its a brilliant discussion, I am learning heaps.

Tony

Tony, you've seen it happen only once in one of the videos where it was simply driver error?!!? It had nothing to do with the turbo spool, setup or grip. I came into a corner a bit hot and I mashed the throttle a bit early while turning and the rear got a bit excited and lit up. You're simply mixing up pure power with spool. At 3500 rpm and above - there is no lag. WOT = instant 7 psi. You see the 600 bhp V8's have the same issue but they're power is all NA - it's simply getting on the throttle to early.

Example of a pretty clean lap:
http://www.youtube.com/watch?v=u7aIcTAK5jQ

[Xusia]

Haven't ridden a 2-stroke much? lol

Nope! I don't like them either!! LOL


I never figure this out but it just supports what I have felt for a long time. Bazza is a friend and we are developing EG33 engines together but I have suggested to him on a number of occussions that when I watch his car going around the track it doesn't look smooth. I had thought it was because of the way he drove it, now after your comment I am convinced the car is losing traction when the turbo kicks.

If the car is at its handling limits a sudden change in torque will be a problem, it would be like walking on egg shells.

By the way its a brilliant discussion, I am learning heaps.

Tony

This is what I am trying to avoid and why I prefer NA engines. I don't plan on doing a lot of track time - mostly "spirited" street driving - but it's still a concern. Since I've consigned myself to using a WRX donor, my plan is to leave the stock turbo in hopes of maintaining as much linearity as possible.


Just FYI, using a turbo does not have to mean poor throttle response. It all comes down to proper sizing. If you have a huge turbo then yeah, anything other than WOT and high RPM will mean significantly lower torque output followed by the turbo "hitting" like a freight train and sending you spinning wildly out of control. This is fine for a drag setup where all your time is spent at WOT and in a straight line. A properly sized turbo will provide nice, linear torque output within the "performance" RPM range. If you're driving the car correctly you should still be on boost even when powering out of a corner. Just have to keep the revs up enough. With a properly sized turbo you should still have a wide range of revs to play with.

I've just not personally seen linear throttle response from a turbo engine. It could be the cars I've driven, or it could be that I'm more sensitive to throttle response issues because of motorcycling. I honestly don't know.

That said, I think it really boils down to use case. For track use, you can stay on [at least some] boost, so what you are saying makes sense. The same could probably apply to spirited street driving, but wouldn't apply to normal daily driving which my 818 will be doing a lot of. So for my use case, it's not ideal and I'm certain I will notice the lag. I honestly hope I'm wrong!

When it comes to track driving or spirited street driving, even though you can stay on boost, that is simply one more thing to need to think about and manage. Doable, yes, but having less to think about and manage allows me to focus more on the fun. And at the end of the day, I really don't care what my lap times are. I just want to push it hard - as safely as that can be done - and have fun. For that, I think a NA engine is the superior experience and would allow me to push it harder more safely than a turbo engine.

[BrandonDrums]

Not to continue the boost at idle conversation... But we need to take a step back and think about what's going on. First, boost pressure and vacuum level are measured BEHIND the throttle butterfly, in the intake manifold. The pressure level in front of the butterfly is of no concern. The recirculation valve is meant to prevent damage to the turbo by not allowing sudden changes in pressure to cause huge changes in the forces applied to the compressor wheel, shaft and bearings. When the throttle butterfly slams shut that pressure has a place to go rather than traveling back down the intake piping as a resonance pulse and stopping the compressor wheel.
Some recirculation valves are also designed to be open at very high vacuum levels (idle) in order to reduce the exhaust backpressure and increase efficiency. In these scenarios the turbo is basically "freewheeling" and pumping most of its air in a loop. Again, if the pressure were allowed to build in front of the throttle butterfly we would increase backpressure in the exhaust and reduce engine efficiency at idle, so on and so forth.

In order to make positive boost the turbo's turbine section must be driven with enough force (due to the speed and temperature of the gasses passing through it) to spin the compressor wheel fast enough to force more air mass through the throttle body than the engine can consume at that moment. When the BSAC of the engine is insufficient to consume the air being pushed by the turbo, you get boost. The fact that the turbo is able to blow a large quantity of air through a very low restriction recirculation value at idle is of no importance. If you were to force the recirc valve closed some pressure would build up in front of the throttle butterfly, the compressor wheel would slow down and exhaust pressure would build until the system reached equilibrium. This wouldn't be ideal though. But in this situation the tiny throttle opening is the limiting factor. It will not allow enough air to pass through it to ever overcome the air consumption demands of the engine. Even if you were to build pressure in front of the throttle butterfly that pressure wouldn't be available to you when you open the throttle. As soon as more air can flow through the throttle body the vacuum level in the manifold will drop and the engine will begin drawing air through the turbo until the turbine section is able to spool up and begin providing additional airflow into the induction tract.

Try a little thought experiment.. Even if it sounds funny. Don't actually try this :)
Imagine you build a system out of PVC pipe with three inlets/outlets. One has a valve on it that can be opened and closed. Hook up a vacuum cleaner to the section with the vale so that the valve is between the vacuum cleaner hose and the rest of the system. Now switch on the vacuum and close the valve so that barely any air gets through. Now imagine you blow into one of the other two opening (I know, stick with me). You will be able to feel the air you blow into that section coming out the third whole... In actuality, most of it will come right back out... This means you are producing more air than the vacuum is able to consume through the valve! This simulates the recirculation valve system. The valve represents the throttle butterfly and the vacuum is the air-starved engine. Now, keep blowing into the end and suddenly open the valve while also closing the third outlet with your hand (simulating the recirculation valve slamming shut). Do you think the fact that you were able to blow more air than was consumed with the valve closed will make any difference in this situation? Heck no! That vacuum cleaner will empty your lungs in a fraction of a second. This is analogous to the situation being discussed here.

I hope this makes sense.
-Matt

Thanks for posting this, reading through the thread I was hoping someone pointed this out. Most modern engines idle with the throttle plate closed and instead idle off of recycled emissions air and/or an idle air control valve or perhaps a few vacuum hoses routed here and there. Any air a turbo blows at idle results in positive pressure because the system is sealed aside from a blow off or re-circulation loop.

On my WRX I always see a negative boost pressure reading at idle. I'm not entirely sure why but I think when the re-circulation valve is open, the hole for the boost gauge is partially blocked or something, the vacuum hose for the boost gauge connects directly to the waste gate re-circulator assembly. On another old old thread we were talking about turbo lag and how an un-spooled turbo would cause negative manifold pressure at partial throttle and this came up. The negative manifold pressure continues for a little bit at low rpm and partial throttle until the turbo spools up enough to reach atmospheric so the negative pressure at idle and partial throttle are two different things apparently.

Anyway, all the posts saying a turbocharged engine will feel better on an 818 than an N/A one are off. That's A. just an opinion and B. in theory you actually would benefit tremendously by having lower torque and higher revvs to make the same amount of power on a lightweight 2wd vehicle. It would be easier to control, traction would be easier to maintain and would have more flexibility with your gearing because you'd have a wider power band to work with, you could have much shorter gearing with wider spread between gears.

[David Hodgkins]

Guys, I spun this off into it's own thread.

As you were...

:)

EDIT: Just in case you missed this in the other thread...

I - and I believe everyone here - understands that sometimes someone posts something off topic in a thread. Let's agree that if it can be dealt with faily quickly (ie a response or 3 ) that it's part of a discussion. The Turbo/non-Turbo diversion had 23 posts and there were another 13 or so posts that were chatter about the thread going OT. No biggie, the OP and others requested that it be move to it's own thread and it has been.

One more thing. If a thread is created for a very specific topic let's agree that we'll try to keep it on topic. But, if a more generic thread is created like my SEMA thread or Dave's feedback thread let's try to recognize the difference and let the thread flow more freely. I'm not going to start jumping in everytime a thread has 5 posts off topic. Let's agree to use some logic to decide what's what.

[Desertrunner]

Tony, you've seen it happen only once in one of the videos where it was simply driver error?!!? It had nothing to do with the turbo spool, setup or grip. I came into a corner a bit hot and I mashed the throttle a bit early while turning and the rear got a bit excited and lit up. You're simply mixing up pure power with spool. At 3500 rpm and above - there is no lag. WOT = instant 7 psi. You see the 600 bhp V8's have the same issue but they're power is all NA - it's simply getting on the throttle to early.

Example of a pretty clean lap:
http://www.youtube.com/watch?v=u7aIcTAK5jQ

Okay I agree that lap is far more controlled. I think your right.

[metalmaker12]

I am not even going to comment on this thread other than 400 whp na, is not going to happen. I mean maybe with like 15-25k in a stroked 3.6L motor.
What I have learned from 12 years of Subaru repairing, tuning etc experience, the 2.0-2.5 ej engines like turbos, last with turbos, and make serious power with turbos. No 2.0-2.5 ej na will make 400whp unless it is fully race built, running on like jet fuel, and has a magic powers

If you want Na with some grunt a EZ36D: 3629CC DOHC, 260ps (191 kW) @6000 rpm, 335Nm@4400 rpm. Bore 92 mm, Stroke 91 mm. Compression 10.5:1. Problem; It probable wont fit in the 818 and will grossly unbalance the car.

Why go on about boost rpm points and etc etc, get a turbo or na, its your choice, both will be great in this car

[Silvertop]

I am not even going to comment on this thread other than 400 whp na, is not going to happen. ............

Why go on about boost rpm points and etc etc, get a turbo or na, its your choice, both will be great in this car

Or for that matter, even 400 flywheel horsepower is not going to happen. The nice thing is that it doesn't need to. Even a stock 165HP NA 2.5 will propel this 1800 lb lightweight fast enough to scare your passenger. And with the 190 to 200HP that I hope to extract with cams, intake and exhaust for my NA 818, it will be borderline stupid fast, but still completely drivable by us ordinary humans. And that's all I need.

[Xusia]

For me the point is learning. Based on my experience, I don't like turbos, yet that is what I am planning for my 818. Perhaps I'd feel differently if I understood them better. Perhaps not. But regardless, there is no shame in attempting to understand that which you do not. :)

[Desertrunner]

Not sure if I agree on the 400hp, its possiable for a EG33 to do it with NA you just need to get the revs up and maintain the torque. With Subaru engine I think the area of NA is totaly uncharted waters. There are plenty of drag motor developing high HP NA but next to none of the 9 to 10K NA engines. From my stand point I get so frustrated because so many people think that a NA Subaru engine is going to set the world because they ported the head, changed the cams, installed new piston and rods even maybe changed the injectors. When in the real world they haven't got a clue as to what works and what doesn't. In all this engine talk on the various threads no one has even mentioned the need for a dry sump on the 818R. With a car as light and as fast as these the GForce on the curves is going to starve the engine of oil.

Tony

[Xusia]

The 400hp discussion is causing the smart @$$ in me to want to come out. I'm struggling contain myself, but so far I've been successful. Oh snap! I just lost...


Um yeah... This thread here is for discussing the merits of turbo vs. non-turbo engines. It's not about whether 400hp is realistic, or how to do it. So, if you all could take that discussion elsewhere, that'd be g r e a a a a a t... Thanks...





JUST KIDDING!!! Seriously, discuss it if you like. I was just making a light-hearted funny based on how this thread came to be. I mean no offense to anyone and hold no grudges (though obviously it's open season on teasing!). :)

[flynntuna]

Isn't true that to prevent detonation in a Subi engine with over 300hp, 110 octane fuel or e-85 needs to be used?

[armstrom]

Isn't true that to prevent detonation in a Subi engine with over 300hp, 110 octane fuel or e-85 needs to be used?

That's a much bigger question than you might think :) Let me start by saying that I've never tuned a subaru engine so I can't say if there's something specific about them that would cause what you say to be true, but I doubt it.

First, what is detonation? Most people mean pinging or knock when they say detonation. Pinging or knocking occurs when the flame front/pressure wave of a combustion event impacts the top of the piston too early. This puts huge stresses on the piston/rings and if it is severe enough or is left uncorrected for too long it will cause physical damage to the piston. Sometimes as severe as blowing a hole right through the top of the piston!

Knocking/Pinging can be caused by two primary things.

Detonation or Pre-ignition... this means you have lost control of the combustion process and some of your air fuel mixture is igniting BEFORE the spark plug fires.
Improper timing map tune.


Pre-ignition itself can be caused by many factors

Air charge temperature too high
Insufficient cooling of the combustion chamber (too hot of a spark plug, poor coolant circulation, carbon build-up hot spots, etc...)
Cylinder pressure too high (too much boost or too much compression)
Ignition timing that is is too advanced, causing combustion temperatures that are too high and cause combustion chamber heating
A/F ration that is too lean, causing high combustion temperatures that are too high, blah blah blah..
Fuel with too low of an octane rating


While adding octane can generally compensate for/cover up any of these problems, it should really only be used as a last resort or a temporary measure.

Adding a larger intercooler or changing to air/water might help with high charge temperatures. If that's not enough you can always look into using water injection as it provides a huge charge cooling effect and helps to regulate the combustion process overall. Also, using a turbo with a larger/more efficient compressor wheel can reduce charge temperatures. More extreme options involve reducing compression ratio with different pistons or a thicker headgasket, so on and so forth. Double check that you don't have carbon build-up, and that you're not running too lean. Don't underestimate the cooling ability of adding extra fuel :) Many cars run pig rich under high boost/load just for the cooling effect on the charge temperature.

Finally, make sure your timing map is good. It's entirely possible that the timing advance is too aggressive in some load cells so what you might think is detonation is simply timing that is advanced too far. In other words the combustion event is NOT occuring before the spark, you're just firing the ignition too soon! Ignition tuning is really the magic sauce to a good overall tune. The engine will run on pretty much A/F ratio within reason. Just don't get too lean and it will make safe power. Your REAL power is made with the timing map. Keep in mind you're trying to ignite the charge at just the right time so that the flame front impacts the top of the piston at just the right time to ensure as much force as possible goes into accelerating the piston down the cylinder. Too early and you slam into the piston while it's still on the way up, wasting energy slowing down the piston, too late and the pressure has decreased too much to impart much force. Think of it like pushing a kid on a swing. If you try to push too soon the chains jerk around and the swinging person generally gets upset with you (this is like pinging!) too late and you don't impart much force and they don't swing any higher. You need to hit that sweet spot every time. Now, complicate that by the fact that flame front propagation rate varies due to MANY different factors and you begin to see the complexity of getting a proper ignition tune :)

[Etos]

I think it's kinda silly to try to compare a doable 400hp turbo 4 to an undoable 400hp H6 NA. Well maybe not undoable but it would cost a ton and require more then 93 octane. Regardless, it's not about peak HP or even under the curve that people wanting NA are looking for. It's throttle response, linear power delivery, early torque and maybe just something unique. Hell even doing H4 NA is extremely viable since it's a 1800 car. I personally am abandoning H4 NA due to not meeting my power requirements without being outright exotic. I'll most likely go with an EZ36, put some high compression pistons in, valve springs, cams, bearings, BnB, slight porting of heads and port exhaust manifold.

I also am not concerned about weight of the H6 as a turbo H4 has it's own aspects that add weight from obviously the turbo and intercooler. The added weight difference an H6 will make won't be significant at all.

I'm also gonna wait a while for someone else to fit an H6 in, deal with all the headaches figuring everything out then start doing my build when a coupe version comes out :D



Isn't true that to prevent detonation in a Subi engine with over 300hp, 110 octane fuel or e-85 needs to be used?

Definitely not. There's plenty of people in the 500hp+ on 93 octane pump.

[Racebrewer]

BnB ? ? ? Subies already have too many acronyms.....<LOL>

Thanks.
John

P.S. Maybe we need a Sticky with Subie acronyms?

[narkosys]

Blueprint and Balance I think. One of the few I remember :P

P

[philly15]

this thread makes me laugh people who have never owned/tuned subarus are going to be in for a surprise

[metalmaker12]

I agree it is funny to me to... a big surprise for sure

[smitch]

I'm going to chime in on here about the turbo lag and the instant power of the h6.

My EG33 swap is a pooch until after 4 grand. It has something to do with the iris closing in the intake manifold. My NA car feels like it has more lag than my turbo car because of the iris set up. I've heard others on another board complaining of the same issues. My friend that drove the car said the same thing about the lack of bottom end. I rallyx'd the car and if in the right gear there was never problem. Also because EG33 revs above 7k it doesnt seem to be an issue. Compared to my other swapped impreza 2.0 avcs turbo car pulls harder pre boost than the na car. I think its simply technology playing a roll. The EG33 is twenty years old.

All that being said, the people that are complaining about turbo lag need to go and drive a version 8 2.0 sti twinscoll turbo car with avcs mated to a six speed transmission. Car revs to 8k and when driven at speed you're never out of the power band unless it's the drivers fault and the torque curve is very flat.

I've owned two 04 sti's. The EJ257 motors feel like a NA motor to me. There is very little lag because of the little turbo. Very nice daily drivers if it wasnt for the six speed trans. That being said I dont know if the EJ257 would be that great of a choice in a light weight car because of the instant torque.

Good luck with everyone's builds.
I can't wait to start reading some build journals.

I need a garage before I can start another project. The wife is all gun ho about building another project. Just a matter of time and money. If I have my way a version 8 2.0 sti motor will find its way into the 818 mated to a 4.44 five speed. I absolutely love these motors.