How do you pick the correct flow rate for a intake manifold? - Chevelle Tech
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  #1  
Old Feb 26th, 09, 9:40 PM
Mikeys69 Mikeys69 is offline
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Default How do you pick the correct flow rate for a intake manifold?

How do you pick the correct intake manifold (single plain in my case), with so many to select from. Most do show RPM ranges. So other than that, just ask around and find out what works?

My combo is in my sig.
Thanks.
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Old Feb 26th, 09, 11:26 PM
WHT/73 WHT/73 is offline
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Default Re: How do you pick the correct flow rate for a intake manifold?

Are you talking flow rates for each cyl ?

If you are, do a search on this site there is a guy who ports them so each runner flows very close to the same cfm.

A little pricey but... if your looking for that last few HP it's priceless.
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  #3  
Old Feb 26th, 09, 11:30 PM
trmnatr trmnatr is offline
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Default Re: How do you pick the correct flow rate for a intake manifold?

Quote:
Originally Posted by big_red View Post
How do you pick the correct intake manifold (single plain in my case), with so many to select from. Most do show RPM ranges. So other than that, just ask around and find out what works?

My combo is in my sig.
Thanks.
learn VooDoo like Bryce and Mark when it comes to porting the intake
OR
off knowledge of what works

Dart 4150 or Motown
Victor Jr.

Dart 4150 or Motown are almost identical and would be best, Victor Jr. would be good

Get the heads ported and use intake you have and the car will accelerate down the track with your rear gear
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Old Feb 27th, 09, 7:18 AM
Mikeys69 Mikeys69 is offline
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Default Re: How do you pick the correct flow rate for a intake manifold?

Here's what I'm thinking.
Look at any intake and it looks like the runners are more than big enough to support any size head intake port/valve size/cam lift/exhaust port. Providing the carb/ventures are up to the task . But as RPM increases, more air flow increases.

I understand the straighter the shot to the intake valve via the intake manifold is best. And the length of the intake runner must be of a length that will effectively mix the incoming air/fuel. And each intake runner must flow as close as possible to each other to supply equal amounts of mixed air/fuel to each cylinder.

Is there a point were a intake can't support this demand?
I think there is. But how do you pick the manifold that's correct for you application?

I'm not looking for anything for my build. Just trying to learn something here.
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  #5  
Old Feb 27th, 09, 7:22 AM
VORTECPRO VORTECPRO is offline
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Default Re: How do you pick the correct flow rate for a intake manifold?

Quote:
Originally Posted by big_red View Post
Here's what I'm thinking.
Look at any intake and it looks like the runners are more than big enough to support any size head intake port/valve size/cam lift/exhaust port. Providing the carb/ventures are up to the task . But as RPM increases, more air flow increases.

I understand the straighter the shot to the intake valve via the intake manifold is best. And the length of the intake runner must be of a length that will effectively mix the incoming air/fuel. And each intake runner must flow as close as possible to each other to supply equal amounts of mixed air/fuel to each cylinder.

Is there a point were a intake can't support this demand?
I think there is. But how do you pick the manifold that's correct for you application?

I'm not looking for anything for my build. Just trying to learn something here.
Theres a lot more to it than just flow, runner length, and cross section, there is tuning envolved.
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Old Feb 27th, 09, 7:35 AM
Mikeys69 Mikeys69 is offline
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Default Re: How do you pick the correct flow rate for a intake manifold?

Quote:
Originally Posted by VORTECPRO View Post
Theres a lot more to it than just flow, runner length, and cross section, there is tuning envolved.
You aren't talking tuning as in a screw driver/distributor.
Your talking cam selection and the above?
The complete package.
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http://www.chevelles.com/forums/showthread.php?t=386745

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  #7  
Old Feb 27th, 09, 11:54 AM
Mikeys69 Mikeys69 is offline
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Default Re: How do you pick the correct flow rate for a intake manifold?

Judging by all the views verus replys. No one really knows.
Thanks guys..
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  #8  
Old Feb 27th, 09, 12:43 PM
mirage2991 mirage2991 is offline
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Default Re: How do you pick the correct flow rate for a intake manifold?

^ you know, I've not seen that many intake comparison on a flow bench or even on a given set of heads with different intakes. I recall a Vic JR 4150 flange vs a dual plane air gap bolted on to the flow bench on a 315 (maybe it was 305) head. The diff between the two were about 15-20cfm. The single was outflowing it, but, on the motor the intakes made close hp (496 I think it was). Of course the single plane made more on top, but on average, they were pretty darn close...if I recall correctly.
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  #9  
Old Feb 27th, 09, 2:53 PM
1989GTA 1989GTA is offline
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Default Re: How do you pick the correct flow rate for a intake manifold?

Ideally you want the intake manifold to act like an extension of the intake runners in your head. So when you bolt on the intake manifold there will be no loss of flow into head or at least kept to a minimum.

I doubt there will be any out of the box intake manifold that will fit that description. What you should of done when you purchased your heads was to also talk to a porter and ask him which intake manifold would work best for your application and have him work both the head and intake manifold at the same time in order to match them up.
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  #10  
Old Feb 27th, 09, 3:11 PM
Scotch Scotch is offline
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Default Re: How do you pick the correct flow rate for a intake manifold?

Is this purely a track deal, or will it see street time too?

You decide on the manifold design based on what rpm the engine will spend the most time at. Honestly.

For most street cars, a tall dual-plane like the Air Gap you've got are the best choice. The Air Gap loses less at high RPM than others, and the design is really good in the low/midrange as well.

If you want more peak high rpm power, by all means- look at the single-planes that are out there. The models suggested already are all good, and by having one ported to match your heads, you'll be doing about all you can do.

It also depends on how much torque and traction you've got. I've run single-plane intakes on street cars with big cubic inch engines because they had all the torque I could possible get traction with on the street. Even though they were not optimized for low rpm use, it didn't matter because I could overpower the tires at any moment just by hammering the throttle. I could use the high rpm power, and I didn't lose anything down low.

You've got a 406 in a relatively-heavy '69 Chevelle. I'd guess you could use the torque, but you know your combo and car better than any of us. Can you sacrifice a little low end to get more top end? Is traction an issue?
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  #11  
Old Feb 27th, 09, 3:18 PM
trmnatr trmnatr is offline
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Default Re: How do you pick the correct flow rate for a intake manifold?

Quote:
Originally Posted by 1989GTA View Post
Ideally you want the intake manifold to act like an extension of the intake runners in your head. So when you bolt on the intake manifold there will be no loss of flow into head or at least kept to a minimum.

I doubt there will be any out of the box intake manifold that will fit that description. What you should of done when you purchased your heads was to also talk to a porter and ask him which intake manifold would work best for your application and have him work both the head and intake manifold at the same time in order to match them up.
We all wish that
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  #12  
Old Feb 27th, 09, 11:21 PM
Bomber '67 Bomber '67 is offline
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Default Re: How do you pick the correct flow rate for a intake manifold?

This is not such an easy question once you get beyond the single four barrel basics of single plane/dual plane, low rise/mid rise/high rise. You will find that even a lot of pro builders will try several different intake manifolds to find the best one for that combo of engine/drivetrain and car. And even then, they still fine tune with different size carb spacers.

It is too bad that there is no standardized rating of the runner and the plenum volumes.

If you really wanted to do the math. I would expect that you should match the intake manifold and intake port runner volume to the engine size and camshaft duration - and then size the plenum to match the sum total flow of those runners.

Thomas
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  #13  
Old Feb 28th, 09, 12:40 AM
Dr J's Performance Dr J's Performance is offline
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Default Re: How do you pick the correct flow rate for a intake manifold?

Quote:
Originally Posted by VORTECPRO View Post
Theres a lot more to it than just flow, runner length, and cross section, there is tuning envolved.



Mr VortecPro is right there is a lot more than just CFM when it comes to picking the right Manifold for your Combination. After you have done some of the number crunching and pick a manifold that meets your specs, the cfm of every runner plays a roll. With the testing I've done on the flow bench and dyno, a manifold seams to make the best over all power and TQ when the runners flow 30- 45cfm more than the head. At this level when you flow the manifold and head together on the bench the Manifold will show the least reduction in total flow. The more the manifold flows the less flow you lose through the head.
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  #14  
Old Feb 28th, 09, 12:57 AM
trmnatr trmnatr is offline
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Default Re: How do you pick the correct flow rate for a intake manifold?

Quote:
Originally Posted by Dr J's Performance View Post
Mr VortecPro is right there is a lot more than just CFM when it comes to picking the right Manifold for your Combination. After you have done some of the number crunching and pick a manifold that meets your specs, the cfm of every runner plays a roll. With the testing I've done on the flow bench and dyno, a manifold seams to make the best over all power and TQ when the runners flow 30- 45cfm more than the head. At this level when you flow the manifold and head together on the bench the Manifold will show the least reduction in total flow. The more the manifold flows the less flow you lose through the head.
The Dr. J's Performace Motown flows 40-45cfm more than the heads

Bryce and Mark, What about if we have a head that flows 250 for example and the manifold flows 350. Is that just an over kill or wasted torque ?

Mike, take a look at this link
http://s510.photobucket.com/albums/s...townPlenum.jpg
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  #15  
Old Feb 28th, 09, 1:09 AM
Dr J's Performance Dr J's Performance is offline
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Default Re: How do you pick the correct flow rate for a intake manifold?

Quote:
Originally Posted by trmnatr View Post
The Dr. J's Performace Motown flows 40-45cfm more than the heads

Bryce and Mark, What about if we have a head that flows 250 for example and the manifold flows 350. Is that just an over kill or wasted torque ?
IF the manifold flows 100 or even 200 cfm more than the head it's not over kill on my opinion. The key to manifold air flow is the efficiency(coefficient of flow) based on the exit size of the runner. Most single plane manifolds in the as-cast form are in the 65-75% coefficient range and flow 100-110 cfm per sq inch. Ported the will be in the 90-95% range and flow 135-140 cfm per sq inch. The more efficient the runners are the better the fuel atomization you'll have.
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