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ed_ma61
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May 2002

ITBs & Port X-Sectional Areas + Lengths : Your Thoughts....	Mon, 11 October 2004 14:59

ive been doing a fair bit of resarch and maths on ITB manifold design and dimensions and id like some feedback on what ive come up with. (If possible Id also like anyone who's done a 3sge in a similar fashion to describe their assembly... the similarities would make excellent comparisons) anyway, a stock 2jzge setup looks something like this: total valve area = 16.08 cm^2 port area at head/manifold join = 11.29 cm^2 a few cm up the manifold runner, the area expands dramatically (almost a step function) from this 11.29 cm^2 to 18.85 cm^2 and this continues up into the stock plenum. now, im trying to design a nice, harmonically tuned, high velocity, individual runner intake manifold, to suit.... - redline around 8500 - power band from say 6700 to 8200 - rod stroke ratio of 1.75:1 (thus the desire for higher velocity intake style) - cams not figured out due to trying to sort out intake velocity caharcteristics and cyl filling properties - please contact me if you can help describe this to me - desire around 110-120hp/L - do NOT want a 500rpm power band 9000rpm gutless screamer of an engine!! would still like to maintina some sembelence of tourque in the lower rpms (hence details paid to good inatke design) im proposing individual 45mm throttles at ~15cm from the valve face (edit - is there data or recommendations on distance from throttle to vlave??). the area of each throttle would be 15.97 cm^2 (close enough to valve area of 16.08) this is based on my understanding that the throttle area should be as close to the valve area as possible. not only this though, but such a port cross sectional area I calculated to produce peak torque around 7000rpm. the emphasis placed on tuning cross sectional port area for tourque band seems quite significant. as a consequence, im lead to believe that i should try and maintain this cross sectional dimension all the way from the throttle to the valve??? which means id need to do some serious work on the 11.29 cm^2 bottle-neck witnessed at the head/manifold interface?? (alternatively is there some advantage to narrowing the port at this point, and increasing the intake velocity, venturi style, and simply maintinaing this 16 cm^2 area along the rest of the port length?) back to the 45mm port and throttle, mean intake velocity at 8500rpm is around 22m/sec - i figure thats fine. comments? beyond the throttle, ive read that a taper in runner diameter, up to a factor of 1.3x or 1.4x valve area is the way to go. thus id be aiming for an expansion from 45mm at the throttle to around 52mm by the end of the runner. thoughts? (bellmouth would expand again on top of this 52mm) regarding length - ive found VERY little accurate information on calculating harmonic lengths. however, one calculator suggested that for a tuned rpm of 7000-8900rpm a 16" total port length would be appropriate for 2nd harmonic resonance... ...this seems quite long!! of all the itb manifold setups ive seen, not many have i noticed to be 16" in length!! perhaps they are halving (or some other multiple) the harmonic length and accepting the lower energy of the resonance?? its all a bit much in one post, but i kind of needed to write it all down to atleast get it clear on paper. my apologies... ...now if anyone can add some useful insights, suggestions or information to what ive just spat out, please speak up! and as i mentioned earlier, if youve built an ITB setup for a 3sge (or a 2jzge!) id be interested in what youve done, what interesting things you noticed while tunig it, and what suggestions youd have to make... cheers guys! ed [Report message to a moderator]

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