How much HP?

[chopthebass]

I am still at the planning stage of a Roadster and haven't totally decided on the engine. I like the idea of the Coyote but, my question is this...
I have been told by a few people that 350 to 400HP is the sweetspot for the Roadster and any more will give a great show of smoke and less acceleration! and it makes the front too heavy and messes with the handling! I see Lazrcng and others have used a 427CI 535HP motor and was wondering if the extra 100HP is really that useable?

Thanks.

[68GT500MAN]

You will get many answers to this question. Depending on your intended use and budget, you can never have too much HP. Not saying that all of it will be useable at all time, just nice to know that it is there.
Doug

[chopthebass]

I guess so. I DO like the idea of a 427 though!

My car will only be used on street, so I am guessing no more than 400HP should still make the car fairly quick.

[dforthof]

I went with an Aluminator Coyote NA, should be somewhere around 425-450 at the crank when all said and done. Still building, haven't driven it yet. If it's too much power, I plan on not stepping on the gas pedal so hard, but something tells me it won't be enough because I like to talk a big game!

[riptide motorsport]

435 hp is just right.............

[lazrcng]

I can tell you that 300hp would still be enough in these cars to be fun. However, I wanted to have as much as I could afford for this build. I wanted it to sound awesome and this motor definitely sounds great. And it is very cool to say its has a 427 in it.

That said, yes it might be a bit over motored. It does drive very nicely on city streets an highway. I have about 230 miles so far. I have not been to the floor with it, but have been in the pedal enough to know it could go bad very quickly. And I got my first ticket already, lol!

I have been drag racing for 28 years and love speed and power. I also know that this car can kill me faster than any other car I have owned.

I wish you well on your build and any way you go you will have one awesome car!

[skullandbones]

I think the "sweet spot" probably is around 350 to 400 hp with the right gearing. That's what I have done. But as you get used to it, there is a tendency to want more just to see over the next horizon so to speak. I love the sound of my little 302. It's loud enough to be obnoxious but not enough to hurt your ears until reved up past 4k. 400 to 450 hp is probably on the bubble for getting hairy in these things. I feel comfortable having mine at the power level it is right now for a while. Another consideration is to know what hp is being put out there. If not specified, it usually means hp at the flywheel or crank. RWHP should be mentioned if that is the case. 15 to 20 % is a significant difference. For example, 350 to 375 hp at the rear wheels could be pretty hairy!

Good luck on your choice. It's fun having a problem like this.

WEK.

[Unicoiman]

In my Roadster I installed a 1968 429. Motor was totally gone thru including boring .030" over. Motor should be putting out around 400 HP. Exhaust sound is great both at idle and in power. Motor has plenty of HP and torque is great. Don't think I would want any more power as the car can get away from you in a heartbeat. If you are not used to driving a light weight/powerful car use caution until you get used to it. Also watch out for the law. Good luck on your decision.

[efnfast]

I made 490RWhp and (I believe) 485RWtq and I can not imagine having less in my car....sluuuuuuuuuuuuuuuuuuug. If I were to build another cobra I would want at least 600RWhp next time.

Do what you want to do in your build - I find a lot of people are ninnies when it comes to component selection. For example, when I was researching gearing 98% of people told me I would be retarded to use 4.10s, 2% of people (who actually had them) told me I would love them. So, I went with 4.10s and have no regrets. I love the gearing.

The biggest tip is to modulate the throttle (i.e., roll onto it, don't just stab it to the floor .... at just half throttle I can walk my 04 cobra (ported/pullied/etc....) without even trying) and do a proper suspension setup (e.g., a 5link rear .... I drove a 300hp 4link car and was like :/ :/ :/ :/ :/ whereas with my 5link it's planted at all times and I've never felt like I was going to lose it)

[Mesa Mike]

It really depends on how you intend to use the car. Street only, 370-400 crank HP is good. If you track the car you will want more. I have about 450 crank hp and I could use more, especially on the straight sections of the track. You just have to be careful on how quickly you apply the throttle. Never, ever go WOT with the wheels and the nose not straight to the roadway ahead. I think you also need to address the amount of stopping power you have. Track cars need better brakes than street cars, for the most part. I believe the higher the H P the better the braking needs to be. Good luck.

[chopthebass]

Thanks Mike. After reading that some builders are using the Ford Racing 427 535hp I am thinking maybe 450hp might be about right. Plenty of power. I did build a Dax Cobra in the UK with a 345hp chevy crate 5.7 HO engine, and that was pretty potent. I believe their cars weigh more than the FFR so I am expecting performance will be better! I totally understand the 'be gentle with the throttle' policy with these cars.

[David Hodgkins]

My crate Ford (Windsor) Boss 302 makes 340 rated and I can bolt a 125 HP supercharger on if if I need more HP (forged internals).

Mine is 98% street driven and I've been on the road 3 years with no overwhelming desire to add the supercharger. My car feels balanced, not nose heavy, and corners well.

I also needed more drivers footbox room and the 302 allows that. When people ask if it's a 427 I say it's a 302 making as much as the mid 60's big blocks with better handling.

:)

[Kalstar]

I would agree, 350whp is nearly perfect. To much and it becomes a beast.

[GloP]

I am curious if anyone has any concrete numbers to compare to. For example skid pad, slalom mph, braking 60-0, obvious 0-60 and quarter mile with some of these engine/components combo. Often we see a lot of opinions and/or single measurements that make it hard to know what we're optimizing for. I'm an engineer so I tend to want to measure everything and I understand everything is a compromise, I just don't understand by how much and which decision really impacts which result. I'm sure that if someone is looking to build a well rounded car, and not a straight line beast or if someone is looking to drag race, they'll go for different things to take a super obvious example, but I think actual measurements would be helpful to better understand the compromises we're making. I'd love to see the same tests some of the car sites/magazines do applied to our cars and see which parts were used.

[tirod]

First, these days, HP and weight ratio front to rear are actually unrelated.

In the day, a 350+ hp 289 in the leaf spring chassis would just get edged out by the coil spring 427. The block weight difference was 150 pounds or more, the torque that and more, too. A lot of stuff was written about the 427 being a nose heavy slug, but in terms of percentages in front/rear weight ratio, they were pretty close - much better than the Mustang.

What the A-arm front end was missing was having unequal length control arms, and a lot more development time on the track to trickle down to the street cars. Overall, they both turned within about two seconds a lap. The 289 wasn't hampered by brute torque overdoing the rear grip, that torque was the edge on a short straightaway.

What we really saw was the leaf spring to A arm conversion offering some improvement, but not really all that. It wasn't done well. 1965 understanding of chassis dynamics wasn't advanced.

These days, you can drop in a 5.0 stroker block - which might be the lightweight Ford casting with 70 pounds of iron missing, or a 351 based stroker, which kept it for truck use. The latter is what is used on most modern 427 builds now, and it's relatively light compared to an FE with deep iron skirts with crossbolts. But those are rare blocks and hard to get.

So, going 427 doesn't involve a significant weight penalty. In fact, there are those who balance the chassis and put the battery back up front where it evens out the rear heavy bias even more. That's the major issue with the kits - they are too light up front, and it's the reason the donor brakes don't work as well as installing front calipers all the way around.

This stuff goes further than just picking a hp number and being happy. That is actually the easy part. Overall handling is what makes the car have a sweet spot, and it also gets into polar moments, roll, sway bars, spring rates, shock valving, etc. Most of which doesn't get discussed on a daily basis, because most kit owners are engine centric and chassis development escapes them.

For many, it's really a matter of hood clearance, too - the taller blocks have interference issues with the scoop and carburetor, the high rise manifolds we have today were not included in the styling issues of a 1954 six cylinder British sports car. A lot of guys like the air gap drag race style manifolds, at best. a low riser 180 was the factory choice. The race cars used Webers on what amounted to a valley plate.

More issues.

It gets involved.

[Plebeian]

As long as your car is set up properly including tires, gearing, and suspension, you can use 500 hp just fine. Whether or not that is enough or too much is more a matter of driver preference. Cheers.

[chopthebass]

As long as your car is set up properly including tires, gearing, and suspension, you can use 500 hp just fine. Whether or not that is enough or too much is more a matter of driver preference. Cheers.

Thanks Pleb. That is the conclusion I have reached after hearing people's own thoughts on the matter. I have decided on a 351W based 427. I found a local guy here in Calgary that can build me a new one cheaper than if I use the Ford Racing 427 535HP crate engine. Only 'downside' is it will have slightly more HP than the crate engine at around 560.

[Bob Cowan]

There's no such thing as too much power, only not enough control.

Control means control of your right foot, AND having the chassis set up well enough to use that power. These are not snap-tite models. Once assembled, you need to spend time tuning the engine and tuning the chassis.

Getting to certain power level is fairly easy, but you need to use your head about it. It's pretty easy to build a 600hp 302 engine. But that's pretty radical, and would a difficult car to drive on the street. For a fuel injected engine, you can build an easy to drive car that makes about 1.2-1.3hp/cube. If you want about 500 hp, plan on using a 408.

I drive mine on the street pretty regularly, and I don't find it difficult to drive at all. I wouldn't let an amateur drive it, though. That much power does take some practice.

[FormulaGod]

Dave Smiths Coyote MK4 went a best of 11.4 in the 1/4 on STREET TIRES. For a street car, that will wipe 99.9% of anything you run into. I like speed as much as the next guy, but I think anything over 450hp on a 2k lb car is overkill. Its all subjective, this is just my two cents.

[Kalstar]

Dave Smiths Coyote MK4 went a best of 11.4 in the 1/4 on STREET TIRES. For a street car, that will wipe 99.9% of anything you run into. I like speed as much as the next guy, but I think anything over 450hp on a 2k lb car is overkill. Its all subjective, this is just my two cents.

Agreed with above post. I would even venture to say a well set up 400hp car will walk a loose big cubed build every day of the week. Sure straight line hi-way roll on would be a different story but the around town, quick burst blasts, steetlight king type driving (99% of sport driving) the lower hp, no traction limited car will walk the hp monster up to well above legal speeds.

Flame suit on.

[CraigS]

One thing to keep in mind is where will you use more power. When you can't use full throttle in 1st and 2nd, where is the gain for a street driven car. Depending on rear gear, engine redline etc, 2nd gear gets you to 60-65 or so. So, if you can't go to full throttle until you are already over the speed limit what do you do w/ the power? OTOH, even though I won't be able to use it except in autocrosses I am planning on upping my current 400 engine hp.

[Richard Oben]

Just opinion on my part.

Do not over cam or over carb. I prefer EFI generally for drivability, different topic. Build as big a power plant as you want. 500 HP is only good if it is usable. What you really want is torque. A decent windsor based motor is great, 427 windsor is a great idea. Just do not build it so it makes all its power at 3k RPM and up. Use a cam intake and fuel delivery that makes torque from about 1800 to 6K.

WHY, simple side pipes at 3k hurt your ears. Not running around town with a few blasts of the throttle but on the highway you will hate a car that bucks at 2k it will be awful to drive. We have been doing this since 98 the guys that drive their cars a lot all have mild motors. All the FE powered cars sit a little more than the 302 or 351 cars.

That being said the coyote car we did is just the best of all worlds but it takes up a lot of foot box room. HTH, Richard.

[Plebeian]

Agreed with above post. I would even venture to say a well set up 400hp car will walk a loose big cubed build every day of the week. Sure straight line hi-way roll on would be a different story but the around town, quick burst blasts, steetlight king type driving (99% of sport driving) the lower hp, no traction limited car will walk the hp monster up to well above legal speeds.

Flame suit on.

So you're saying a well set up 400 fwhp car will walk a not well set up (loose) 500 fwhp car in a quick low speed burst, no surprise there. Like I said before, it's all about having a well balanced set up. Personally, I just enjoy the low end torque (without needing to downshift) on country roads outside of town, no streetlight king stuff for me. Cheers.

[chopthebass]

Hell this is confusing me now! So I may go back to my original plan of a Coyote but I really wanted the old school look and sound. Maybe a 347 is the way to go or stick with the 427 idea, but maybe very mildly tuned?. I have plenty of time to decide, so I will do some more investigation.

[Kalstar]

Hell this is confusing me now! So I may go back to my original plan of a Coyote but I really wanted the old school look and sound. Maybe a 347 is the way to go or stick with the 427 idea, but maybe very mildly tuned?. I have plenty of time to decide, so I will do some more investigation.

Let me put this another way....Picture your car as a 5'7" 120lbs model.

150-250Whp = Sports bra
251-325Whp = 34B
326-400Whp = 38C
401-475Whp = 44D
476-550Whp = 48DD
551Whp+ = 54EE

I am a solid C-cup guy. Too big and they just get in the way. But different "strokes" for different folks (pun intended).

Oh, one more thing, an IRS rear-end is like a pair of nice fitting yoga pants. Nothing wrong with that no matter what you have on the "top end'.

[narkosys]

^^ That is such a great analogy! and it works! guys discussing cars as if they where boobs. go figure :P

P

[chopthebass]

Mwahaha!! So funny.

I think I will go for 44D. I guess any more is a waste!

[Plebeian]

My car is a 54EE, that is just plain gross.

Chopthebass, I think your plan for a 427 is great. As Richard Oben stated, you just want to make sure it has good driveability. I will reinterate, if your car is set-up correctly, you can use 500 hp just fine. There are many of us running that high and much higher. I will post an extreme example. Steve Berg's turbo FFR Cobra is running over 800 rwhp. He drives it on the street whenever weather allows, including to work. He drove it to the track, ran the 1/8th mile in 5.5 seconds at 125 mph, then drove home. Not exactly useless or "just a smoke show".

FYI, I noticed that Kalstar started stating rwhp numbers in his boob analogy relating to appropriate hp. Rwhp numbers are a far far cry from fwhp numbers. A Ford crate 427 with 535 hp is around 450 rwhp (or less) on a Mustang dyno.

FYI, Dave Smith (owner of FFR) runs a 500 fwhp engine (Ford crate 363) in his type 65 coupe.

Just trying to help. Cheers.

[Plebeian]

I just noticed you're in Canada. Cold temps could effect your traction. Cheers.

[chopthebass]

I just noticed you're in Canada. Cold temps could effect your traction. Cheers.

Is RWHP that much less than the flywheel?
Yes I am in Canada but I don't plan on winter driving, and if I do it will be very cautiously! My UK cobra (DAX replica) had a Chevy 345hp crate engine and that caught me out a couple times in the wet, so I got pretty good at driving very carefully.

I have noticed a lot of you guys have lots of HP. I am planning to build the kit as per the build manual, but are there modification I should consider with 500+ HP? I will be adding 12" rear disc brakes and they will be power brakes too.

Cheers

[Bob Cowan]

Is RWHP that much less than the flywheel?
Yes I am in Canada but I don't plan on winter driving, and if I do it will be very cautiously! My UK cobra (DAX replica) had a Chevy 345hp crate engine and that caught me out a couple times in the wet, so I got pretty good at driving very carefully.

I have noticed a lot of you guys have lots of HP. I am planning to build the kit as per the build manual, but are there modification I should consider with 500+ HP? I will be adding 12" rear disc brakes and they will be power brakes too.

Cheers

You generally lose about 18-20% of your power through the drive line. Takes power to make all those parts spin.

Of course, it's Canadian HP, so you need more of it to get the same effects. :)

Don't forget altitude losses. You lose about 2-3% per thousand feet.

I think the only big issue with lots of power is the IRS axles. Standard axles may or may not hold up to that. I would suggest upgrading to better quality from The Drive Shaft Shop or Disc Brakes R Us. I'v been using the DBRU heavy duty axles for years.

The solid axle with stock Mustang parts will take a LOT of abuse. Unless you're drag racing with sticky tires, I wouldn't upgrade that. If you are drag racing, better axles and a worm gear would be a good idea.

Some people would also recommend upgrading to racing brakes. Unless you're going to be road racing, I think that's a waste of money. Design a good brake system with off the shelf parts (or the complete kit parts) and you'll be fine. The only advantage to the racing brakes is that you can abuse them lap after lap.

[chopthebass]

Thanks Bob. Interesting about the altitude thing. Had no idea about that. I am definitely going with higher HP in that case!
Looking like a 54EE now!!