intake flow numbers

gtxrt

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doe's anyone know the flow numbers for a stock 440 intake, read 200 cfm but then on hughes engines they have a ch4b at 273 cfm. can't be that much difference 200 cfm vs 273 cfm. thinking stock should flow more than 200 cfm.
 

PRHeads

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Personally, I don’t feel what the “manifold” flows on its own is all that important.
I think it’s more useful(although still not all that useful) to see how much the head flow diminishes when the intake and a carb are installed.

I did some tests like that a number of years ago, and the stock BBM intake knocks the flow down quite a bit..... especially on a ported head.

I’ll see if I can dig up an example.
 

PRHeads

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Okay, here’s one example.
It’s a nicely ported 906 head with a 2.14 valve, tested @.700 lift.
All 4 ports tested, then averaged. Then the intake was bolted to the head, and both runners of the manifold that corresponded to that position of the head were tested.
1&8, 3&6, 5&4, 7&2.
A 1000cfm Holley carb main body and baseplate were mounted to the manifold.
All eight results for each manifold runner were averaged, and that number can be compared to the average flow for the head with only the radius plate.

The 8 cylinder avg for the head alone for this test was 286.7cfm.

The 8 cylinder average for a stock 383 intake #301, with the 1000cfm carb attached was 212.8cfm(-73.9cfm)

The 8 cylinder avg for an ootb low deck RPM, with the carb attached was 250.6cfm(-36.1cfm)

The 8 cylinder avg for a mildly gasket matched RB M1 single plane with carb attached was 263.1cfm(-23.6cfm)

The manifold installed nearly always causes a reduction of flow through the head(unless it helps fix a turbulence/separation issue).

The very M1 manifold that knocked this 906 head from 286 down to 263......... flowed well over 300cfm........ when attached to a ported std port Indy SR head......... that flowed 340 with a radius plate.
So, it will pass 300cfm....... yet still shows a flow reduction when attached to a 286cfm head.
 
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gtxrt

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i guess that is why Hughes engines says intake needs 15-20 percent more then the head. so the intake you tested should be 330-340 cfm flow not to hurt the head flow.
 

PRHeads

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That very same M1 single plane that flowed over 300cfm on the Indy SR head......... will still show a reduction in flow....... even on a stock 906 head flowing around 230.

I’ve formed my own views on the importance of manifold flow numbers from dyno testing all sorts of different engine combos for the past 32 years.
And on a few occasions I’ve had the chance to do some manifold swaps where I did have some flow data for the pieces being tested........ and more than once the best flowing manifold was not the one making the most power.

It’s not that the flow doesn’t matter at all........ it’s just not the “last word” in gauging how good a particular manifold is or isn’t.

Especially in terms of the “better” aftermarket manifolds, I need to see what it does on the dyno, or in the car....... to assess its suitability for a particular combo.

I’m not all that concerned with what it flows.
 
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gtxrt

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PRHeads, so you said the 383 intake flows 212.8, would a stock 440 intake flow about the same ? how much cfm gain would you guess with a ported stock iron intake ?
 

PRHeads

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Using my limited number of samples(in this case.... 2 square flange 440 intakes), the 440 intake seems to be a few cfm better than the 383 version.
Taking one of those stock 383(301) intakes, spending a fair amount of time cutting out the dividers and opening up the plenum area, then port matching it to a std valley pan gasket and going in as far as is easily accessible..........brought it from 212cfm to 230cfm(8 cyls avg).
This was for a 12:1 511 running in FAST.
That configuration helped at the dragstrip, but the big plenum doesn’t help low speed operation.
430A785A-05FD-4017-BEC9-909345F93646.jpeg


When the manifold is a big cork in the induction system, then the flow numbers are probably a more reliable indicator of what will happen when the better flowing manifold is installed.
 
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PRHeads

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Here’s the bottom of an extensively modified 301 intake.
You’ll just have to look at it close to see how it’s been redesigned.
All that work resulted in an 8 cylinder average of 245cfm.
It was used on a 511 that had quite a few very high end parts in it, including some pretty trick 906 heads and an .800” lift cam, via a Jesel 1.7 rocker system, that made very good power(for a 4bbl BBM with an iron intake) and ex manifolds.
9C3DAEBA-1243-4410-B775-4DF351EBD279.png


A couple of the individual runners of this manifold outflowed their counterparts of an RPM, but there were two that were no better than the mildly reworked 301, which brought the avg down below the RPM(250 vs 245).
 
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Gunner1

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I use to work the flow bench at Extrude Hone back when the EFI ford 5.0 craze was going full swing. We pumped a lot of heads and manifolds. I got to flow them seperate and together. We would find the weak holes and try to balance them out by blocking the putty from the high flow runners and just pump the low ones. PR Heads your right on target. It's the total combo not just flow alone. We did make some really monster long runner chevy efi manifolds flow 290 to 300 per runner. But a short runner manifold flowing less would still spank one in a 1/4 mile run.
 

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