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Old 07-12-2007, 11:23 PM
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Intake manifold volume

One of the subjects that keeps coming up is which manifold to use for what purpose.

I was surfing, looking for info on another subject when I came across this from Nascar, showing intake manifold volumes.
http://nascarheads.com/chevy_18_sb2.html

We choose heads by intake runner volume, why shouldn't we choose intake manifolds by volume????? Inquiring minds need to know

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Old 07-13-2007, 06:57 AM
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Intake Volume

Intakes are designed for different RPM's. For example an Edelbrock Performer goes from 1500 to 5500. If it's designed for a higher RMP range the volume will also be higher.
Go to one of the intake manufactures web sites and they will give you the information you need.
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Old 07-13-2007, 08:38 AM
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Quote:
Originally Posted by Channel Cat
Intakes are designed for different RPM's. For example an Edelbrock Performer goes from 1500 to 5500. If it's designed for a higher RMP range the volume will also be higher.
Go to one of the intake manufactures web sites and they will give you the information you need.
I think TI's question goes a lot deeper than that, he's no newb. The Performer is designed around a 350, not unlike a cam or cylinder heads designed for a 350 on a smaller engine it will shift a little higher in the RPM range and on a larger engine lower. A single plane that would give a mild 350 a case of the soggy bottoms might work work very well on a similar 406. I think more thought should be given to plenum volume vs. RPM and displacement just as the port volume and flow specs and cam timing. We agonize over those to get the perfect setup but the general trend in thinking among average rodders when it comes to intakes is that Manifold X works good in this RPM range so that's the one we need but little thought is given to the difference in air flow requirements between a 305 and a 400. Then again I could be wrong.
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Old 07-13-2007, 09:20 AM
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Intake Volume

I agree it is a combination of components that have to be matched to get peak performance from any engine. But putting an intake that's rated to 6,500 RPM on an engine that only sees 5,500 RPM will not be as good as one designed to peak at 5,500. Then there is the torque curve to consider. You also should look at the vehicles purpose. If it's for a truck that's being used for pulling vs a car being used as a daily driver the set up and components are different.
I went to the web site and looked at all the intakes. They seem to be designed for all out, pedal to the floor high RPM. NASCAR engines run around 9,000 RPM. Unless you have an all out race car these may not be for you.
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Old 07-13-2007, 09:24 AM
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Tech, you are right, this is an area where we all spend a great deal of time and money on for an application that warrents it. For hard core racing or street applications there is seldom a stock type intake that calculates out perfect for plenum volume port entry or runner velocity. For the most part you are stuck with the runner length, which give you a tuning affect but the runner sizing and shape as well as the plenum volume and shaping into the runners can and will be modified to suit the application. The plenum is an area we do a lot of work on in certain applications. Runner work is based on size needed to usually get airspeed down (making them bigger) so as to not shear the fuel mix as it moves through the runner. Too small a runner is almost if not more so worse than too big.

Fully porting and optimizing an intake can run a customer up to $1000.00. On big block Ford motors with heavy hits of nitrous it's almost manditory work given the poor design of stock aftermarket manifolds for these applications.
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Old 07-13-2007, 11:29 AM
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Quote:
Originally Posted by techinspector1
One of the subjects that keeps coming up is which manifold to use for what purpose.

I was surfing, looking for info on another subject when I came across this from Nascar, showing intake manifold volumes.
http://nascarheads.com/chevy_18_sb2.html

We choose heads by intake runner volume, why shouldn't we choose intake manifolds by volume????? Inquiring minds need to know

Nice catch thanks, noted and will review later...... can never know 2 much
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Old 07-13-2007, 12:43 PM
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Quote:
Originally Posted by techinspector1
One of the subjects that keeps coming up is which manifold to use for what purpose.

I was surfing, looking for info on another subject when I came across this from Nascar, showing intake manifold volumes.
http://nascarheads.com/chevy_18_sb2.html

We choose heads by intake runner volume, why shouldn't we choose intake manifolds by volume????? Inquiring minds need to know
Most 180 degree intakes flow less, in many cases substantially less, than the head port they connect too. This is especially true of passages on the lower plane. Because of fuel drop-out issues, street driven intakes really need to be undersized, as unless you keep the revs up over 3000/4000 rpm all the time, lean/rich distortions by cylinder become a very big problem. The OEM solves this with lots of exhaust heat and smallish passages to keep mixture velocity up. This is a surprisingly big problem that port injection pretty much eliminates. The interesting part of port injection is the short distance between the injector and the valve. One would think, especially after all that's been written on fuel atomization on carbureted engines, that having the fuel injected an inch an a half above the valve wouldn't sufficiently atomize the fuel. Yet compared to a carburetor or TBI, it does a much better job of atomization and provides more consistent mixture ratios cylinder to cylinder. One has to consider that injecting fuel at 40 psi must be the reason that atomization is so good compared to that which can be achieved by a conventional carb/TBI and manifold, at least in the moderate RPM ranges.

Typical measurements on a carbureted performance street engine with a 180 intake will show flow, mixture ratio, cylinder temps, and power output varying from 10 to 20 percent between cylinders. In spite of this, the typical 180 type intake consistently shows better power output from a street engine than 360 types of IR style or common plenum intakes untill the engine is at fairly high revs. Surprising, but still it's there in the engineering data.

Messing around on the flow bench, I find that with a 180 degree intake, the port shapes should be different between the those of the upper and lower plane. The lower plane appears to function better with a less tall but wider port. Won't that make for weird looking heads. The high plane ports would look like a conventional Chevy and next to them the low plane ports would look like those of a "Y" block Ford.

Every-time I look at my Harley, I can't help but wonder what my Chevy would be like with 8 S&S Super Gs on it.

Never mind, still crazy after all these years.
Bogie
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Old 07-13-2007, 05:28 PM
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Thanks for the responses fellows. I knew there had to be more to it. That's the nice thing about being on a forum like this one, you get to pick the brains of those who have found out and done things that maybe you haven't. This is a great forum and I feel at home here, as there is an immense amount of knowledge to be gained from you guys and I'm able to pass on some of what I know to help the younguns. What goes around, comes around and 40 or 50 years from now, the guys who are newbies now will be doin' the same for youngsters coming up, although it may be with fuel cells or some other presently-unknown power source. It's a good thing.

Rick, I never considered there would be a need to slow down the mixture to prevent fuel shear. I had considered that a smaller runner would increase velocity and contribute to good cylinder filling, but the idea of fuel shear never occurred to me. Thank you.

Hippie, your observation concerning matching the displacement and rpm's to the volume of the intake is what compelled me to post this thread in the first place. Thank you.

Channel Cat, I agree it is the combination and application that must be taken into consideration. It makes me a little sad when I see someone post that they are going to use a Performer RPM on their 305 grocery-getter. They must be gettin' this info from the quasi-motorhead down at the Sonic. Thank you.

Bogie, again, something that never occurred to me, the idea that the flow would be different between the first and second story of a 180 manifold. Makes a lot of sense now that you've spelled it out. Thank you.

Pepi, at the age of 65, I still learn something new every day and am very appreciative that I still have the faculties to retain some of it. Thank you.

Last edited by techinspector1; 07-13-2007 at 05:38 PM.
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Old 07-13-2007, 11:43 PM
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I've often wondered what a taller single plane intake like a tunnel ram with one carb but with a smaller sized plenum would run like if the runner sizes were optimized. I'd think with the longer length and no turns there would be one heck of a sweet spot in the power curve and throttle response wouldn't be bad if the plenum was kept reasonably sized?
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