Flow test results of my Front Facing Plenum

[B-Man]

Hi Guys,

I just got the flow bench test results back for my front facing plenum. This is a custom plemum that bolts on to the standard runners.

Since there had been a bit of a debate over front facing plenums and my engine is being rebuilt, I took the opportunity to get it tested.

I know this is a static test, on a flow bench so it doesn't represent exactly what is happening in the head with valve movement etc - But it's a good start for a bit of empirical analysis.

1 275.4 cfm

2 283.1 cfm

3 307.2 cfm

4 272.4 cfm

5 277.2 cfm

6 298.3 cfm

(1 being front, 6 being rear - Throttle body = XF)

So I am getting a 34.8 cfm difference between 3 & 4 - Which is interesting as one might speculate that most of the flow goes to 5 & 6.

BTW I am no engineer - but 11.3% difference in air flow betwen runners seems a lot to me ??

Has anyone got any comparative bench flow tests for standard or GReddy/Trust plenums ?

Now I gotta decide what I am going to do about this -

a) Try and fix the current plenum (a bit hit & miss)

B) Replace with standard plenum

c) Replace with after market (Trust/GReddy)

d) Just keep in and richen it up a bit

Opinions and feedback welcomed folks. Keep in nice though OK ?

Cheers,

[GTS-t VSPEC]

B-man, Good to see someone putting the effort into looking at this issue scientifically. I'd be interested to see how well a non-modified stock one does for flow distribution:D

[elbee111]

Ditto to that re testing the standard.

Why would it flow in a sawtooth ascending 1-2-3 and 4-5-6??

Interesting.

El bee

[walkoau]

keep us posted b-man

[B-Man]

Originally posted by elbee111

Why would it flow in a sawtooth ascending 1-2-3 and 4-5-6??

Interesting.

Might have something to do with the shape of the plenum ??

[B-Man]

Another

[Roy]

Any pics of the internals?

On an RB25 if you remove the top half of the plenum, are all the lower runners the same length?

On an RB20 the runners are only the same length when top & bottom halves of plenum are bolted together.

Ie say runner no.1's top sectoin equates to say 50% of its length and so does the bottom section. On runner no.6 though top section equates to 65% of runner length, and bottom equates for the remaining 35% of length (rough numbers only).

So if you only use the bottom section of the plenum then some runners are shortened by 50% others by 65%... making sense?

[T0nyGTSt]

How much was the testing?

And would they do a stock one as well for education purposes?

T.

[B-Man]

Roy - by sight, they all look the same length.

Anyone got a standard plenum (the top bit only, not runners and all) and I will get it tested for a side by side comparison. Can use my runners etc - The test wasn't that much, so I'd be happy to pay for it , if someone donates the standard plenum....... I might even buy it off you , if the results are good !

Cheers,

[sidewaymambo]

I can lend you my standard plenum, PM me..

[Freebaggin]

sidewaymambo & B-Man, that would be excellent to do a flow test in the same way on the standard plenum. As we know, a number of guys have problems with no 1 and no 6 cylinders (possibly due to fuel reasons as well) but to have the baseline flow data would be excellent.

grepin, if you read this you should invest in flow testing your Greddy plenum whilst it is still off the motor.

[sidewaymambo]

Originally posted by Freebaggin

sidewaymambo & B-Man, that would be excellent to do a flow test in the same way on the standard plenum.  As we know, a number of guys have problems with no 1 and no 6 cylinders (possibly due to fuel reasons as well) but to have the baseline flow data would be excellent.

grepin, if you read this you should invest in flow testing your Greddy plenum whilst it is still off the motor.

That's exactly what I am thinking..if someone can lend it for test..I wish ..

[B-Man]

Sidewaymambo & I have just spoken and I'll pick up his standard plenum on the weekend -

So I'll get the same people to do the bench flow test on it and then post the results back !

Thanks Phillip !

Good stuff !

[GTS-t VSPEC]

Top work guys, will be waiting for the results:D

[Roy]

B-Man when you pick up the plenum dont be tempted to look under the bonnet of sidewaymambo's car...mmm very strong is the power of the darkside (in my best yoda voice)

...and great work for the trouble your going to, a case of Crownies for the man!

[Bo0sT_JuNkY]

If someone has a stock plenum with the throttle moved to the front,Then it would be good to see how that flows compared to stock too.

[sidewaymambo]

B-man..

Don't you dare to chop off my plenum throttle from side and weld to from after you done the normal plenum test..

LOL...

[B-Man]

No way man ! I'll look after it - I promise !

Does someone want to donate a GReddy Plenum ? And I'll get that flowed at the same time .. . . I promise I won't put it on my car and give you back my old one.... he he he joking !

But yeah, I am serious about flow testing a GReddy if someone else is willing to help.

[T0nyGTSt]

If you ask nicely maybe Peter at Advan will lend you his shop display unit

T.

[Sydneykid]

Hi B-man it is good to have someone confirm our on car results. But be careful, how a manifold reacts (flows) under vacuum (ie; on the flow bench) is very different to how it flows under boost. Did you do it at 1 bar or 2 bar vacuum? We find head flowing for a turbo engine gives more boost friendly results at 2 bar vacuum.