Dual plane vs. single plane intake???

[Mesa Mike]

Whis will have best performance for street with my 650 holley double pumper??

[Hankl]

Mike it depends on the overall configuration of the engine. With the Dual plane you will have more torque with a smaller lower revving motor.
With the Single, the engine will need to rev higher to attain a similar power output. Things like Cam, Heads, Exhaust, etc, all play into the need for one or the other.

Hank

:cool:

[riptide motorsport]

Unless your drag racing the dual
Plane sill be the better performer....HTH steven

[AJ Roadster NJ]

Great question, and hits to one of my pet peeves with the performance hobby. Everyone (or nearly everyone) wants horsepower. A horsepower number is a meaningless mathematical derivative of torque. The scientific definition of power expressed as rotational force is torque, period, end of story.

Horsepower, which again is mathematically derived from measured torque, is a false expression that was useful in the period up to about 1920 or so, when our great grandfathers were trying to decide whether the 2 hp tractor suited their needs more than the 4 hp version, and horsepower was something they could relate to. My Roadster has maybe 420 hp, but I don't think I could get the same experience by removing the engine and hooking up a team of four hundred and twenty horses.

Whew.

OK, now to your question. Don't evaluate this on hp, evaluate your question on how you intend to use the car. More than likely you are like the rest of us, and your car will see mostly street use with perhaps an occasional track day. When the main use for the car is street driving, you want the torque curve to look like a plateau -- the curve should shoot up quickly at low rpm, and maintain a solid torque reading across the graph. Do that, and you will have a car that makes you change your shorts a lot.

A dual plane manifold will get you that gorgeous torque curve, which favors across-the-board torque over peak hp. Yes, you will be leaving peak hp on the table, but what does that mean? Guys dyno their engines and see a peak hp number at, say, 6500 or 7000 rpm and try to make that number go higher by switching out parts or whatever. DON'T DO IT. On any dyno sheet, the hp and torque numbers cross each other at 5250 rpm because of the formula used to derive the hp number from the torque number causes that to happen. Increasing hp (a derived number) past 5250 rpm means you are giving up torque, giving up true power, actual force expressed as twist. So why does that happen? Because for the guys 100 years ago that came up with this silly idea of expressing power in terms of the number of horses the power equated to (!?!?!) could not fathom the concept of an engine turning more than 5250 rpm.

I have actually seen TV shows (like the old cast of 2 guys) who were giddy with excitement at gaining 8 hp at 7000 rpm with a new intake or whatever, and on the screen, if you paused it, you could actually read the sheet and see the numbers where they took away peak torque to gain that false hp "improvement." They HURT the power, and called it an improvement.

Single plane -- other guys have already stated (and I agree with them) that single plane is best used on the track. A single plane manifold moves the power curve upwards in the rpm range, which is where you'll live if you're always on the track. But for street driving, let's say usually in the less-than-6000 rpm range, you'll be losing torque -- less power, less fun.

Good luck.

AJ

PS -- for my carbed 351W, I chose a Weiand Stealth manifold, which is a dual plane with an excellent rpm band. It is dual plane. Very tall, barely fits with a BG carb and K&N filter. But it does fit (less than 1/8" to spare).

[Mesa Mike]

I talked to a company called Pro Systems and they asked me alot of questions about engine, cam, weight, displacement, etc. They gave me a part number (carb) that will provide me with the performance I want. Under the carb they recommend a dual plane, 1/2" 4 hole spacer. Think I'll take their advice and go to a dual and give it a try. Can always go back to the single. I'll run my current carb and then (down the road) upgrade to their custom built carb, which is based off of a Holly double pumper.

Thanks for your inforation AJ, Hank and Steven

[AJ Roadster NJ]

The phenolic spacer does two things for you. First, it isolates the carb from heat, hence producing more power. It can do that but in reality the carb stays really cool until you shut off the motor anyway, because there is air (at the ambient temp) and gas (cold) running through it at high volumes, and it stays pretty cool. Even the upper portion of the intake doesn't get very warm while running the engine, but it warms up right away when the engine gets shut off. The second thing the spacer does is effectively lengthen the runners to each intake port. The longer the runner, the more torque (power) you'll get from the motor. Remember those funny looking trumpet intakes over fuel injectors back in the day? That's why they had them. (Here's an example on an old Jag...http://www.malaysianevo.com/front_website/gallery.php?o=0&id=349). A half inch doesn't sound like much, but it is. It creates velocity as opposed to volume, and the velocity of the air/fuel charge as it travels through the runner is crucial to filling the cylinder with mixture while the intake valve is open.

You didn't say which block you were building from. If you're basing your engine on a 289 or 302 block, you'll likely be fine. If you're basing on a 351W, you may need to use a dropped-base air cleaner to get room for the phenolic spacer, depending on which dual-plane intake you go with. Generally, I do not think you're going to be happy with anything that is fairly short. Those are made to accomodate under-hood clearances on muscle cars. You want as much height as you can get in your manifold and still fit under the hood, because again, height equates to runner length, and runner length equates to torque, and torque equates to performance that makes you change your shorts every so often. :eek:

AJ

[Mesa Mike]

Thanks AJ.