throttle to valve distance

[Sam_Q]

I am well aware of how the length from the intake valve(s) to the tip of the inlet opening has a harmonic affect and how it causes the engine to act,

however I have also been told that on a multiple throttle system it also has a critical effect where the throttle is in the inlet tract, so the valve to throttle distance. I assume this is related to a reversion wave that lets a multi-throttle engine be more smooth than a single throttle engine with wilder cams but I dont know anything about the topic.

So if it does make a difference then why does it? how do I find out whats ideal apart from trial and error?

[Ben Wilson]

According to Jenvey, the main factor is using the turbulence created by the throttle blade to aid in fuel mixing.

[Sam_Q]

thats it???

well that was an interesting article but I have some doubts that that is it

[jeffro ra28]

At WOT id agree with what Ben has said.

At closed to 1/2 throttle i dare say that is the only area where it will have any other sort of affect. Im guessing all its going to do is change throttle response characteristics.

So what sort of maximum effort engine gets raced around at half throttle? But if you are on and off the gas all the time, it is crucial to have good throttle response, i beleive this is what we are trying to acheive with throttle distances from valve.

Also, are we talking boosted or NA? What comes to mind is the RB26 having a plenum chamber before its multi throttle setup. Some people remove this for certain racing instances. But why? Low down torque?

[Sam_Q]

4a non turbo engine, I am guessing I should just design the throttle length as to what is convenient fabrication wise

[jezza323]

4a non turbo engine, I am guessing I should just design the throttle length as to what is convenient fabrication wise

that would be my guess as to the best way to go...i cant honestly see it making a measurable difference

wot i can see making a difference is injector placement, both in relation to the throttle plate, and the intake valve

[Sam_Q]

my thoughts exactly jezza, thats why I started this thread because I was thinking that cant do much but I wanted to make sure before I get the grinder out

[o_man_ra23]

There was a huge discussion which involved the physics of this. Cant remember the thread, but pretty sure it said tuned length intake runners or something for the title. Basically what came out of it is that there is fukall effect of harmonics on an ITB intake system. A good plenum setup can help reducing harmonic effects at a narrow rev range, but the design time, fabrication cost etc of such a system would be far outweighed by how small the gains would be. If your after throttle response, just make the runners as short as possible. If you want more torque... use longer runners with a plenum (see the foul can variable runner length system)

Of course with a 20V's high RPM power band, long runners are going to make 3/5ths of fukall difference to your torque down low, and will just hamper high RPM throttle response. So in conclusion, for your system, make the runners as short as practically possible.

[Billzilla]

Put the butterflys as far away from the head as you can.

[Sam_Q]

thanks Bill that makes things really practical for me

[o_man_ra23]

Put the butterflys as far away from the head as you can.

A scientific reason for this Bill?? (not trying to be a pain in the arse... just trying to understand better)

[Billzilla]

A scientific reason for this Bill?? (not trying to be a pain in the arse... just trying to understand better)

Simply to let the airflow stablise as much as possible at part throttle.
That's why I don't like a lot of aftermarket throttle bodies that copy Weber DCOE's - they are the same length and that's often too long. The ones I use are about 15mm long.

[jezza323]

so you would normally run a very thin throttle plate with the shortest possible bell mouth then bill? and make up the runner length all in the post throttle plate runner?

[Billzilla]

so you would normally run a very thin throttle plate with the shortest possible bell mouth then bill? and make up the runner length all in the post throttle plate runner?

Yep, have the butterflys right out near the end, like this ->

[Kyosho]

Tissue please.

That's GORGEOUS!