Camshaft design matters most to determine induction and exhaust lengths.

I have had good luck with 17.25" length from valve to air trumpet. About 438 mm long.

 

Today I have about 330mm from valve to trumpet. I am afraid 438 mm will make my trumpets really close to the engine room wall. I have maybe 50-60mm more room before the trumpets come to close to the engine room wall. Is it better to make them as long as I can, or should I aim for one of the induction waves

I´m using Enem E11 camshaft. New camshaft will be Highspeedracings HSR280 HighSpeed Racing Engines Sweden
This camshaft has a bit more duration, 314 compare to 308 and 1,9 mm more lift.

Oh heck, I want to know how the 43mm ITB's worked out on the 2.5L?

It´s working very well, it produce 167 whp @ 6000 rpm and 220 Nm @ 4300 rpm. I was hoping for a bit more power and torque, but I don´t know if it is the camshaft, ITB´s or both that limit the power. Personal I believe it´s the camshaft. But the motor is really drivable, it´s just like driving a stock car.

Picture is from one of the last pull

 

Oh heck, I want to know how the 43mm ITB's worked out on the 2.5L?

 

Length does mater

I would have to check my old notes for the formula, but back in the late 70s when I used to pick the brains of those who knew these things.
I was told use the formula find the length you need. then the goal was 100-104 percent efficacy (remember these were full tilt race engines) NA at peak torque usually 2000 rpm under red line (Max hp). 100 percent was when the volume of free air drawn in to the cylinder was equal to the swept volume. So the intake was designed to have that same volume from the closed intake valve to the bell mouth of the ram tube. So the shape of the intake needed to incorporate the size of the throttle body or carb while smoothly ducting the intake charge. Often a larger throttle body needed to be moved out towards the ram intake.
Long story shortened you really should in a perfect world, know the length and shape of the intake then decide what size throttle body fits.
I do this it works well but I can't really afford to experiment much I usually stick with what I know.
Sorry about the way I ramble on, I hope you can make sense of this.

 

Toyota 20V ITB?

 

You have good eyes It´s Toyota 4AGE 20V ITB´s mounted upside down on a modified DCOE manifold.

Very nice set up. if you post your intake cam specs combined with the dyno run you posted, I will do some math for you.

This dyno run is with the old camshaft, unfortunately I don´t have much data on the new camshaft. I have bought it on recommendation from the Tuner.

Would you happen to have the AFR to go along with the dyno chart?

There is a bog around the 2300rpm mark.

I don´t have picture of AFR curve. As far as I remember the bog was fixed when I adjusted Throttle Transients in the DTA. On full throttle AFR is +/- 12,8 from bottom to top.
BTW I found a picture of the last run in the dyno. Here we was testing to adjust the camshaft. We was running out of time and ended up with the camshaft a couple of degrees to much retard compared to where it produced highest power. Peak power is 500 Rpm lower than we had on max.

I was gonna get in to Helmholtz and Engleman theory, but that's complicated.

Just look at Visards rules.

To find a runner length for a certain peak torque, use 175mm for 10,000 RPM. Add 44mm for each 1000 RPM you are shooting for under that.

This seems to be an easy rule of thumb to follow I will measure more exactly how much space I have.
Do you have any idea how much this will affect power output if I miss some millimeter. I know there isn´t an accurate answer on this, but are we talking 30Hp or 5Hp?

 

Camshaft design matters most to determine induction and exhaust lengths.

Very nice set up. if you post your intake cam specs combined with the dyno run you posted, I will do some math for you.

 

Would you happen to have the AFR to go along with the dyno chart?

There is a bog around the 2300rpm mark.

 

I was gonna get in to Helmholtz and Engleman theory, but that's complicated.

Just look at Visards rules.

To find a runner length for a certain peak torque, use 175mm for 10,000 RPM. Add 44mm for each 1000 RPM you are shooting for under that.

 

You could always ask Bjorn at Highspeed Racing what he recommends. He has a lot of dyno experience with CIH engines. He designs his own camshafts too.

You'll find that its a combination of parts that makes it all work well....head porting, camshaft, induction, exhaust. He has made over 270 PS from a 2.4 CIH rally engine, so he's a good person to ask!