Intake/throttle Body/Plenum - Need info

[down4glamis]

I have an idea, and i am almost ready to just do it. I am now being told im not as cool as i think, but not a real reason "how" err... "why"

i want an intake like the one i am posting, similar to the "hillborn" system, and close to a "carburator" style air intake. 3 webbers, with a "plenun" underneath them, that feed each carb to 2 cylinders.


why cant the runners just shoot straight into the intake side of the head? why is there a need for a plenum? how can i control the amount of air i may need?

By down4glamis at 2010-03-11

By down4glamis at 2010-03-11

 

[chazzone]

That'd probably work if you were designing something that was going to run at 10,000 rpm or higher, but if you want something that you can drive, the runners are too short.

Read up on intake design, there really isn't enough time or space to teach a class in this forum.

 

[Big Jim M]

The reason for a plenum is to mix the mixture from all the carbs so one that is a bit rich or lean might be able to be compensated by the other two carbs.
A rig like you drew might work on a 1/4 mile track.. But as far as streeting something like that...not a chance.
The length and diameter of the runners mean LOTS AND LOTS to the velocity of the fuel and the amount of standoff.. Just drawing something and expecting it to work is a dream.. one that is most likely a nightmare.
Big JIm

 

[chazzone]

The reason for a plenum is to mix the mixture from all the carbs so one that is a bit rich or lean might be able to be compensated by the other two carbs.
A rig like you drew might work on a 1/4 mile track.. But as far as streeting something like that...not a chance.
The length and diameter of the runners mean LOTS AND LOTS to the velocity of the fuel and the amount of standoff.. Just drawing something and expecting it to work is a dream.. one that is most likely a nightmare.
Big JIm

Yeah, webers are a bear to tune. You could spend all morning on a set, and have the pressure change at lunch, then be right back to square one.

Runner length, runner diameter, and plenum volume all work together to effect the intake charge. The cam has to be designed to allow for the appropriate valve timing, etc.

Even on a F.I. engine, these all have major impacts on cylinder filling.

It's not about the shortest length = best overall performance, just like cutting an exhaust system off your truck will not increase performance, but will decrease performance.

Seriously, take some time and study the design aspects of intakes. The information is available, and you never know what it might lead to.