Intake Plenum Volume

[damienkennedy]

What is a good base line to start with your plenum volume? I am finding loads of conflicting data, some say 1.5 times the engine capacity. . . some say 60% the engine capacity. . . whats a good base line to start with for runners and plenum?

The engine we are running is a 03 gsxr 600, the stock airbox held approx 11-12 litres which is massive!

[damienkennedy]

What is a good base line to start with your plenum volume? I am finding loads of conflicting data, some say 1.5 times the engine capacity. . . some say 60% the engine capacity. . . whats a good base line to start with for runners and plenum?

The engine we are running is a 03 gsxr 600, the stock airbox held approx 11-12 litres which is massive!

[murpia]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by damienkennedy:
The engine we are running is a 03 gsxr 600, the stock airbox held approx 11-12 litres which is massive! </div></BLOCKQUOTE>
Yes, but it had individual throttles downstream of that airbox...

The reason you find conflicting data is that there is no single right answer. If you design for extra volume, you can always fill up some volume with packers when you dyno test to see when power drops off.

Then, if the throttle response is still poor when you track test, you can add more packers to improve it and trade-off power against response to get the best laptime.

Regards, Ian

[exFSAE]

60% of engine capacity? That would be 360cc, or approximately the size of a soda can. Does that seem right or feasible?

[BrendonD]

60% is way too small. We're running a 2L plenum on our 450cc single. It runs pretty smoothly through the powerband, but we have yet to do our fine tuning for power.

[Mbirt]

There's tons of information available on this forum on intake design and loads more with a quick googling.

Remember the plenum is your source of capacitance to smooth out the intake pulses traveling through the restrictor. Unrestricted engine intake plenum "safe ranges" may not apply. In 1D simulations of our thumper, I found that, compared to the 3l plenum setup, the 1l plenum simulation was down about 10hp at the peak torque rpm (7500) and cut its loss to 5hp at 10000 rpm. The thumper's steadier flow at higher speed helped narrow the gap between the large and small plenums. Since you have a 4-cylinder, a gain this great won't likely appear unless the small plenum is 360cc. I think you'd be hard-pressed to find an engineered plenum on a 4-cylinder car of less than a liter. Wesley, a popular poster on here has stated that his team felt a 2.5l plenum did not decrease the driveability of their 4-cylinder.

For your runners, calculate the runner lengths required for your intake cam duration and desired peak torque rpm to take advantage of the 2nd or 3rd wave reflection to the face of the valve and see what you can manufacture and package.

[Mazur]

I have heard that a team tested very large plenum volumes and kept increasing in power up to 500% engine displacement.

Throttle response begins to suffer after a certain point.