Author Topic: Flow numbers: Cylinder head vs Intake manifold?  (Read 4134 times)

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Joe-JDC

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Re: Flow numbers: Cylinder head vs Intake manifold?
« Reply #15 on: November 15, 2020, 05:08:55 PM »
If I put your 320 cfm head on my flow bench, and flow it at .700" and 28", then bolt a stock RPM to it, depending on which port, the flow may drop to 270 cfm.  Same head, same intake, but #1, #4, #6, or #7, and the flow may be 300 cfm.  Bolt your 401 cfm on it, and it may or may not flow 320 cfm, but it will be close.  Now take that same 320 cfm head and bolt the stock RPM on it, and pull the flow bench up to 34", and check flow, pull it up to 40" and check the flow.  Did it reach 320?  Probably, but just barely.  Now put that 401 cfm intake on the same port, and pull the flow bench up to 34", and it may be flowing 330 cfm through the head.  40", it may be 340 cfm.  The 28" is an industry standard, and it just measures how much something has improved, or is capable of being improved.  Take this example.  I have had some of these FE heads that just will not flow above .650" and goes turbulent.  Put an intake manifold on that head, and it continues to flow to .750"----go figure.  Another example: a head goes turbulent at .500", and I pull the flow bench up to 32", it is still turbulent.  Pull it up to 40", and it does not clean up.  That engine will be a dog.  Another example:  a head goes turbulent at .650", flow drops to 20 cfm at. .700", and drops even more at .750".  The port  had some work done but it was in the wrong place, and you can't fix it.  The best answer for this question, is than on my 2018 EMC engine, the heads flowed 303 cfm upper/290 cfm lower/210 cfm exhaust, and the intake manifold flowed 338 cfm.  Increased the intake manifold flow to 360 cfm, no difference.  375 Y, 561tq/595 hp.  Joe-JDC
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plovett

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Re: Flow numbers: Cylinder head vs Intake manifold?
« Reply #16 on: November 15, 2020, 06:30:30 PM »
If I put your 320 cfm head on my flow bench, and flow it at .700" and 28", then bolt a stock RPM to it, depending on which port, the flow may drop to 270 cfm.  Same head, same intake, but #1, #4, #6, or #7, and the flow may be 300 cfm.  Bolt your 401 cfm on it, and it may or may not flow 320 cfm, but it will be close.  Now take that same 320 cfm head and bolt the stock RPM on it, and pull the flow bench up to 34", and check flow, pull it up to 40" and check the flow.  Did it reach 320?  Probably, but just barely.  Now put that 401 cfm intake on the same port, and pull the flow bench up to 34", and it may be flowing 330 cfm through the head.  40", it may be 340 cfm.  The 28" is an industry standard, and it just measures how much something has improved, or is capable of being improved.  Take this example.  I have had some of these FE heads that just will not flow above .650" and goes turbulent.  Put an intake manifold on that head, and it continues to flow to .750"----go figure.  Another example: a head goes turbulent at .500", and I pull the flow bench up to 32", it is still turbulent.  Pull it up to 40", and it does not clean up.  That engine will be a dog.  Another example:  a head goes turbulent at .650", flow drops to 20 cfm at. .700", and drops even more at .750".  The port  had some work done but it was in the wrong place, and you can't fix it.  The best answer for this question, is than on my 2018 EMC engine, the heads flowed 303 cfm upper/290 cfm lower/210 cfm exhaust, and the intake manifold flowed 338 cfm.  Increased the intake manifold flow to 360 cfm, no difference.  375 Y, 561tq/595 hp.  Joe-JDC

Thanks Joe,

Hopefully I will get to test my combo on the dyno with the different intakes.  I am super curious about it and I don't know the right answers.  I probably don't know the right questions.

paulie

plovett

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Re: Flow numbers: Cylinder head vs Intake manifold?
« Reply #17 on: November 15, 2020, 06:42:54 PM »
Well think about this:

I have two intake manifolds:

#1 has a smaller CSA and a smaller overall volume, yet flows much more.  All of that sounds great.

#2 has a larger CSA and larger overall volume, yet flows much less.   That sounds bad.  But is it? I dunno.

Just based on that #1 would be the easy choice, but of course there is more.  #2 is a dual plane with a split plenum and has much longer runners. 

pl


My427stang

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Re: Flow numbers: Cylinder head vs Intake manifold?
« Reply #18 on: November 15, 2020, 07:44:23 PM »
Paulie,

Some good reading

https://www.speed-talk.com/forum/viewtopic.php?f=1&t=1163&start=15

Could take days but lots of good info buried in some other stuff






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plovett

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Re: Flow numbers: Cylinder head vs Intake manifold?
« Reply #19 on: November 15, 2020, 07:47:14 PM »
Paulie,

Some good reading

https://www.speed-talk.com/forum/viewtopic.php?f=1&t=1163&start=15

Could take days but lots of good info buried in some other stuff

Thanks Ross! 

I will read it.

pl

427John

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Re: Flow numbers: Cylinder head vs Intake manifold?
« Reply #20 on: November 15, 2020, 09:52:18 PM »
A case of quality being as important as quantity,while quantity is measurable with access to a flow bench quality not so much.

Hmmm.  I'm listening.  I'm not trying to be funny here, but how would one describe this quality?  Highest density of air/fuel in the cylinder at spark, at any given rpm?  I think it would it ultimately be "measured" by the dyno and/or the dragstrip? 

A big plenum short runner intake might affect this quality negatively at low rpm and vice versa with a small plenum long runner intake.  But a flow bench just takes a "snapshot" at 28" and gives you one number.  Engine rpms, loads, throttle positions, etc.  can all vary at that same snapshot of info. 

Like I said,  I am just trying to wrap my mind around the significance of intake manifold flow numbers with respect to cylinder head flow numbers. 

pl
Yes I would agree that the dyno/dragstrip would be the measurement.with regards to the intake port flow vs cylinder head port flow based on pure speculation with no supporting evidence,you would think that an intake port with a flow surplus to that of the head port would tend to have an effect similar to that of an increased volume with the added benefit of increased velocity but like I said that is pure speculation,do you intend to test both intakes?It would be interesting to find out how wrong my thinking is.

plovett

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Re: Flow numbers: Cylinder head vs Intake manifold?
« Reply #21 on: November 15, 2020, 11:45:14 PM »
A case of quality being as important as quantity,while quantity is measurable with access to a flow bench quality not so much.

Yes I would agree that the dyno/dragstrip would be the measurement.with regards to the intake port flow vs cylinder head port flow based on pure speculation with no supporting evidence,you would think that an intake port with a flow surplus to that of the head port would tend to have an effect similar to that of an increased volume with the added benefit of increased velocity but like I said that is pure speculation,do you intend to test both intakes?It would be interesting to find out how wrong my thinking is.

Yes, I plan to test both intakes.  I may have to sell one to fund the project, but hopefully not.  I don't even know what my thinking is, but I would love to see the comparison.  I think the engine will be stout enough to make it a good test.  A 400 hp engine wouldn't be a good comparison, nor would a 750 hp engine.  But a 600 hp engine might overlap the ideal ranges of both intakes.