Plenum volume Indy t ram

[mopardave]

Anyone know the plenum volume of the Indy 400-4I-15 tunnel ram and whats needed for a 12.5:1 511? Mine looks small.

[mag2555]

What cid motor are we talking about and it intended peak rpm?

[mopardave]

I have a 12.5:1 511 and shift at 6800rpm

[F-BIRD'88]

You can try out carb spacer which add both plenum volume and carb height, which are different thingies.
Use what works.

[rebelrouser]

Several years ago I built a manifold for my NSS engine, and some of the reading I did before the design, the manifold needed a plenum volume of two cylinders. If it was more it may run better at Higher RPM's but might be soft down low, if less the opposite. I think this kind of points to why a lot of single carb manifold often benefit from a spacer, they have a small plenum. But just from what I see the runner length and camshaft specs should be set for the max rpm you want the engine to run, that is a bigger slice of the combination to get max performance.

[mopardave]

Some have told me this t ram needs a 1/2" plenum spacer under the lid. I guess its just a try and see deal.

[panic]

Bill Jenkins said that the plenum volume (SBC probably TR1) that gave the best dyno power was always too large to launch the car. For best ET, deduct 10% volume with a stuffer (wood block contoured to match the floor, height to make the volume you want, varnished).
Since the visual is untouched, also confuses observers...

How does carburetor CFM factor in? Only as a trend, no math known to me. Small carbs > large plenum volume, etc.
As mentioned above, spacers increase volume, but also pull the venturis up and away from the intake ports.

[gunt]

i have posted it here before , but look at the import guys there double the capasity no of 2 cylinnders , there putting 5l manifolds on 2.0l engines , and there making serious power and times

[pcnsd]

In the Helmholtz equation, reducing only the number of cylinders from 8 to 4 increases the Helmholtz volume because the frequency has been reduced by 50%. So yeah, doubled volumes.

[Stan Weiss]

In the Helmholtz equation, reducing only the number of cylinders from 8 to 4 increases the Helmholtz volume because the frequency has been reduced by 50%. So yeah, doubled volumes.

Paul,
Can you post up that equation?

Stan

[pcnsd]

In the Helmholtz equation, reducing only the number of cylinders from 8 to 4 increases the Helmholtz volume because the frequency has been reduced by 50%. So yeah, doubled volumes.

Paul,
Can you post up that equation?

Stan

Stan,
It was previously posted here:
viewtopic.php?f=1&t=4977&sid=af3338ad85 ... b&start=15

The phrasing is in MS Excel format. There is an included spreadsheet at the end of the thread. I use a massaged version of that spreadsheet today as my understanding of application has grown. However, the base equation given is the same.

Helmholtz volume=Average intake runner CSA*Ncyl/(Intake runner length*(2*PI()*TargetRPM*Ncyl/(60*Nrev)/(SOS fps*12*Harmonic#))^2)

Ncly = number of cylinders supported by the volume.
Nrev = number of revolutions for a complete cycle (2)
Target RPM is a number between PT and PHP and generally 25-33% the difference biased to PT. (This is also usually applied to the runner design)
SOS FPS = Speed of sound in Feet Per Second at your target inlet temperature.
Harmonic# is either 2 or 3, Whichever produces the largest practical volume. For V8's it depends on intake type: tunnel ram (2) or sheetmetal (3)

[Stan Weiss]

In the Helmholtz equation, reducing only the number of cylinders from 8 to 4 increases the Helmholtz volume because the frequency has been reduced by 50%. So yeah, doubled volumes.

Paul,
Can you post up that equation?

Stan

Stan,
It was previously posted here:
viewtopic.php?f=1&t=4977&sid=af3338ad85 ... b&start=15

The phrasing is in MS Excel format. There is an included spreadsheet at the end of the thread. I use a massaged version of that spreadsheet today as my understanding of application has grown. However, the base equation given is the same.

Helmholtz volume=Average intake runner CSA*Ncyl/(Intake runner length*(2*PI()*TargetRPM*Ncyl/(60*Nrev)/(SOS fps*12*Harmonic#))^2)

Ncly = number of cylinders supported by the volume.
Nrev = number of revolutions for a complete cycle (2)
Target RPM is a number between PT and PHP and generally 25-33% the difference biased to PT. (This is also usually applied to the runner design)
SOS FPS = Speed of sound in Feet Per Second at your target inlet temperature.
Harmonic# is either 2 or 3, Whichever produces the largest practical volume. For V8's it depends on intake type: tunnel ram (2) or sheetmetal (3)

Paul,
Thanks.

Stan

[mopardave]

I spoke with Wilson Manifolds about this. They suggest leaving the volume alone and adding a couple shear plates. Said extra plenum volume is good for full on race packages, but no so much for my mainly street driver and once a year to the track deal. Adding plenum volume takes away from low end performance and moves it up.

[Erland Cox]

Plenum volume dampens pulsing.
If the engine runs rich at high RPM more plenum volume helps.

Erland

[Rick!]

In my brother's BBM 598, there is some MAP "wobble" between 6600-6800 but it doesn't affect performance and the driver can't hear it.
This is with EFI and twin 2000cfm throttle bodies with thin spacers to fit the throttle enhancer and no plenum spacer on the same Indy tunnel ram.
If this it the Cuda still, I still recommend putting a proper scoop on instead of deflecting air away from the rear carb. JMHO.