decided to try ITBs
 

just out of curiosity decided to build a little diy itb kit for my all-motor build. acquired a set of complete throttle bodies from '06 gsxr 750. getting spare intake manifold next week (thanks levnubhin!)

im pretty sure it will be a complete ghetto setup but i just want to see if it actually does anything versus my tuned intake mani. whole thing will cost me under $200 and ill dyno both setups on same day at same place with same tuner.

if they dont work i can always sell it on clubroadster :)

anyone knows what length runners i should make? im shooting for high top end and i dont really care about low end

just some specs on the overall setup:

'01 block
slightly ported '99 head
+1mm supertech valves all around
85.5mm 11.5:1 supertech pistons
m-tuned rods
ebay header (temporary until i can get custom one made)
2.5" exhaust w/ high-flow cat

still need to measure clearance on head to see how much lift i can get on cams. also unsure about duration on cams.

Unless your going to run velocity stacks I would try to shoot for like ~7 inch straight runners, which i think is about as long as they can be with enough rooms for filters

i give it 3 weeks before this up in the shit in the classifieds so tell him well guys youl buy it for cheap later.

finish your build first...

miataTURBO.aids

He said hes shooting for high end.... short runners are better for high end, long for low end torque

7 inch runners would be pretty aimed at peak power on this engine since it cant rev very high, Ive done a lot of work with tuned runners in the past.

also, thats not entirely true, to have runner's tuned for absolute peak power at 7000 rpm would be much longer than 7 inches but it would create a very small power band. shorter runners will oscillate at more rpm's creating a very linear power band. Depending on the circumstances you could very easily make more low end and less top end with short runners and the complete opposite with slightly longer runners.

touché

should i try velocity stacks? if i will ever run these on my car it will only be at the track

If you wish to know about runner calculations I suggest you read the Honda IRTB forums as they have calculations for it all. They are mostly log calculations but attached is my IRTB.xls from when I did the math for it and realised there aint enough room to DIY it unless I get laser cut stuff.
Tract length (because its not just the runner that is in the calculation) is done for optimum use not absolute power or torque, to tune for them you gotta get tinkering with a dyno to see the changes. Also a set of vernier pulleys would help.

Shorter = higher up
Longer = lower down
But believe me when I say going no stack may place the critical flow outside your redline.

If you feel like spending lots of money for the hell of it, go for it.

but if youre just messing around I would suggest just making the runners between the throttles and the head long enough that you have a usable power band.
Plus its easier to run filters if you intend to.

yeah, ill try several configurations from 5" to 10" to see what will be better

Updates on this? I'm all curious and such.

sending out itbs to BMC tomorrow morning so they can make me a sexy manifold flange with short runners that will hook up to throttle bodies.

ps: anyone knows of a solution to make oem suzuki idle control (stepper motor) work? if not then ill create a small pcb to make it happen or remove idle butterflies completely