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Discussion Starter · #1 ·
wondering if anyone has any insight/articles on this?

Goals:
peak power at about 7500rpm and starts at 5000RPM

Setup:
JDM d15b VTEC
Akmee type S kit
stock 9.2:1 CR
CRB1000 ITB's
Y8 many stock runners cut, porting
stock CRB injectors/ placement
Vacume log
 

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I recommend about 13.5" from head to tip of velocity stack ( around 16.5" from valve to tip of stack). I've tried all ranges from 10"-14.5" and 13.5 is the optimum length for my 8000 rpm motor. I noticed that too short of length hurts the powerband dramatically. Going a little too long is not as detrimental (you just lose a little peak power) The overall taper and size also determines the length. 1000rr ITB's are also what I run as well :).
 

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my brother was saying something about an inaccuracy with the above link bone posted, this was when he built ITBs for a SOHC nissan KA24E, i can't remember the details however.
 

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Here's one of the best links i have found a long time ago about ITB's dimensions, Rep me if found useful :) >>>> Jenvey Throttle Bodies
 
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Discussion Starter · #7 ·
good stuff guys! thanks.
 

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seems to me that the toda http://www.toda-racing.jp/product/onemake_e/b16/b16-07.html one, doesnt look like it conforms to the calculator.
- Im in the process of building some cbr954 itb's and ive been contemplating runner length. Toda says the short runner does " improvement of the accelerator response is due to the
reduction in volume of air within the manifold."
Which to me makes since. Motorcycle throttle bodies are as close to the head as they can get. And yes i know they avg. 14,000 rpm, but still.
- Im studying engineering and know about equations and calculations. But ive seen that in dynamics of engines and air speed and how everything works, sometimes getting everything what is supposed to be perfect doesnt work. I mean look at the rotary engine, they designed for years on how to build it and when they finally did, it ran like crap. Simply because not everything matched how that motor SHOULD work.
- my dad races sportsmen v8 race cars and somethings they put on there shouldnt make power the way it does. Just like if you get to big of a plenium on your intake it slows everything and isnt as functional.
-so i guess waht im sayin is maybe we should just experiment and see what works...instead of relying on calculators.
-just my 2 cents
 

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I found the "optimum" length of intake system (excluding the intake port) to be 9" in computer simulation for my engine (using Engine Analyzer Pro 3.3). IIRC port length is 2.8", so my total intake tract length is around 12". It seems to work very well, pulls hard 4500-8000 in my Z6 and in old D15 w/ A6 cam too.

According to my dynosheet and especially the torque curve, the whole system seems to work very well.
 
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