Blow through intake manifold flow testing

Carnut1 · Post by **Carnut1** » Sat May 26, 2018 8:20 am

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Not my idea but looks like a fast way to get an idea how similar the flows are without bolting to the head. I figure Pitot speeds at exit may be helpful too. Input welcome. Thanks, Charlie

Post by **NormS** » Sat May 26, 2018 9:24 am

To be a little closer to a real configuration, do think it would be worth trying a 4 hole carb spacer, to simulate a 4 barrel carb bolted directly to the manifold? Norm @ CFS

Post by **pcnsd** » Sat May 26, 2018 9:34 am

All entry and exits have a respective CD. The exit CD as mounted will not exist in application. My preference would be to mount to a head. I am not sure what this can tell you other than giving a baseline capacity to compare other manifolds to. This will work if you already know what your target range for capacity and area is, but not if it is new to you.

Carnut1 · Post by **Carnut1** » Sat May 26, 2018 9:45 am

NormS wrote: ↑Sat May 26, 2018 9:24 am To be a little closer to a real configuration, do think it would be worth trying a 4 hole carb spacer, to simulate a 4 barrel carb bolted directly to the manifold? Norm @ CFS

I thought about that but the only spacer I have like that is on the old pickup and not tearing into that today. Thanks, Charlie

Carnut1 · Post by **Carnut1** » Sat May 26, 2018 9:48 am

pcnsd wrote: ↑Sat May 26, 2018 9:34 am All entry and exits have a respective CD. The exit CD as mounted will not exist in application. My preference would be to mount to a head. I am not sure what this can tell you other than giving a baseline capacity to compare other manifolds to. This will work if you already know what your target range for capacity and area is, but not if it is new to you.

Paul, I thought this might speed me along since the difference between ports was more than I expected when bolted to the head. This way I can get them closer before the nightmare of testing on a head. Thanks, Charlie

Carnut1 · Post by **Carnut1** » Sat May 26, 2018 9:52 am

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Tape lasted .1 seconds without a plate clamped to the manifold. Cfm on left of port rest of numbers ft/sec and the top of the port is down. Interesting test. Thanks, Charlie

Scotthatch · Post by **Scotthatch** » Sat May 26, 2018 10:07 am

I have done this ..... first off the duck tape is no good as it leaks air ..... second is it helps but is not the whole picture .. flow without the head will show what the intake is capable of which is a good piece of information .. just on this info I have found intakes that are low ... once you flow this way if you put it on a head at full valve lift and see what you get as compared to the no head number you can sometimes see that the interface point is a problem .... sbc is not to bad but some motors and intakes the runner is coming into the port at a angle that is not the same as the port bias and you see a big drop ...

Post by **GARY C** » Sat May 26, 2018 2:32 pm

I made a fixture for my bench that would allow me to flow one port at a time, I just don't know what cfm # you would use to validate it.

Post by **NormS** » Sat May 26, 2018 3:29 pm

If nothing else, this may be a way to show how a manifold plenum distributes dry air flow. Wet flow may be a different story, depending on the type of manifold and the type of fuel.

steve cowan · Post by **steve cowan** » Sat May 26, 2018 4:38 pm

Charlie,
As always you are thinking outside the box on testing which i admire and you are willing share as well,i think it is a great test for some data,do you test it on inlet side of bench and check the #s ?? and see if there is a correlation.
i would be confident that Larry has done some testing to this nature and got some results to show if it is worthy of the journey,i asked the question here some years ago of porting OEM style intakes to get the CFM the same on all runners and the general consensus was dont try it and only modify the runner CSA in equal ratio through the runner,now that may of changed and everyone has an opinion on that i spose,i read years ago when DR J airwolf was doing a nitrous BBC and he showed his CFM # s on the OEM style intake and they were the same and that motor made a rediculous amount of power on the dyno and pushed a 3600 pound camaro into the 8.0 region.
anyway good discussion Charlie and i will be interested where this goes.

BILL-C · Post by **BILL-C** » Sat May 26, 2018 5:03 pm

For getting "quickie" flow numbers for an intake manifold, i prefer to use clay radius, or better yet,same plastic flow guide used for head testing, and suck through intake. Your curves are so gradual in the middle of the runners that the flow direction doesn't matter much there. The tape stays on much better also. Also helps to speed up testing so you can spend more time on more important measuring, like cross sectional areas. Basically, the bigger you make the intake, the better it flows on the bench. This IS NOT what makes all cars fast. I believe "line of sight" and getting the cross sectional areas the right size for the intended application are the 2 most important things to spend your valuable time on when porting intakes.

turbo2256b · Post by **turbo2256b** » Sat May 26, 2018 5:49 pm

IF you are doing blow through instead of sucking myself would never do that.
Also because of pushrod locations the left side of the intake needs to be worked different than the right side.

Carnut1 · Post by **Carnut1** » Sat May 26, 2018 5:53 pm

I would love to see some pics of how you guys suck through the intake. I may not have been clear that I have the bench on exhaust and blow into the plenum. Thanks, Charlie

Carnut1 · Post by **Carnut1** » Sat May 26, 2018 5:55 pm

turbo2256b wrote: ↑Sat May 26, 2018 5:49 pm IF you are doing blow through instead of sucking myself would never do that.
Also because of pushrod locations the left side of the intake needs to be worked different than the right side.

Why would it matter if you suck or blow? Pressure differential is the same.

Carnut1 · Post by **Carnut1** » Sat May 26, 2018 5:58 pm

BILL-C wrote: ↑Sat May 26, 2018 5:03 pm For getting "quickie" flow numbers for an intake manifold, i prefer to use clay radius, or better yet,same plastic flow guide used for head testing, and suck through intake. Your curves are so gradual in the middle of the runners that the flow direction doesn't matter much there. The tape stays on much better also. Also helps to speed up testing so you can spend more time on more important measuring, like cross sectional areas. Basically, the bigger you make the intake, the better it flows on the bench. This IS NOT what makes all cars fast. I believe "line of sight" and getting the cross sectional areas the right size for the intended application are the 2 most important things to spend your valuable time on when porting intakes.

Bill, this reads like you install the radius on the intake and then flow air from the runner into the plenum. Is that what you do? Thanks, Charlie

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