when do you detect the need of a bigger aftermarket plenum and on what application

[renxun]

as per title above. i would like to know that at what situation do you guys face before decide to go aftermarket plenum wid bigger throttle body. well generally yes i know its bigger can accomodate more air and so on ... but at what application when this plenum will come to a need? for example. i dun run circuits but i do drag racing and occasionally drift and weekend drive wid my Rona.

i see alot of pl run good times even without the aftermarket plenum wid bigger throttle and making big output at dyno but im sure it has its own set of advantages. would like to know for my own knowledge.

[radaris]

I've done a bit of research on phlenum design because I put a 3vz-fe in an obscure home. Speaking to many people the only rule in making one That made sense was that the volume of the phlenum should be 3 times that of the capacity of the engine. So if it was a 3 litre engine the phlenum should be 9 litres.

Basically the phlenum is a presurised air tank with the presure governed by the MAP or AFM. That being said it is allways full and being under pressure I don't think shape plays a major part in performance either.

[woggin]

i have heard 1.5X the engine capacity!

[jonathan yee]

.....i dont think it's possible to make over genrallizations with plenum sizes.

sizes would come down to a lot of variables like what response, NA or forced induction, turbo sizes and wether it's straight topend your goin for etc.

i'm in the process of making my plenum for my 3sgte and the mech i went and spoke to (and yes he know's what he's talking about with high P 3s's) recommended only 1.5-2L volume. thats for my aim of a turbo 3S making good power thru to 8000rpm.

also i think side feed plenums what the opposite end to the TB tappered down to provide a more equal fill of cylinders.

[Cuts]

I made one recently, and found a lot of conflicting informantion with regards to volume etc.

Mine is also on a 3s (gen3) Im using velocity stacks, with equal legnth runners to the factory (with an increase in OD). Plenum volume of just under 4 litres, 2zz-ge throttle body (68mm as opposed to the stock 205's 60mm) picked up responce (obviously with stacks and bigger tb). Also side mounted the tb so dont have to have pipes over hot engines.

Most notable improvment was the drop in temperature, i never see inlet temps over 25 on the highway, hot day traffic situations it goes up to 30-35, but once you get some boost and airflow again drops back down, the plenum chamber itself doesnt get anywhere near as hot as the factory cast ally ones used to.

[renxun]

thanks for the input guys.. beside the response. when is the time do u guys felt the stock plenum had reach its limitation?

[Cuts]

when the poor design of the plenum has become an issue, when the tb is too small, when you need to re route intercooler piping, when your fed up with the stock one.

pick one

[ed]

Basically the phlenum is a presurised air tank with the presure governed by the MAP or AFM. That being said it is allways full and being under pressure I don't think shape plays a major part in performance either.

thats basically all incorrect

[The Real Roadrunner]

lol

fn10char

[jonathan yee]

sorry to be blasphemous...does anyone know the volume of the greddy plenums for the sr20 motors....? they only look smallish about 2-2.5L and they seem to be popular and big enough for over 300rwkw...? even on throttle bodies under 70mm

[The Real Roadrunner]

So is the stocker, what is the point?

the Greddy plenums will lose a shitload of lowend (have graphs to prove it) and dont do bugger all unless your running 268+* cams. the only time id use one would be if it ran a GT3582r and i was chasing 350+rwkw for drag purposes.

You should be measuring from the back of the TB to the back of the valve to work out plenum sizes etc but the majority dont bother and just asume the "log" section is what makes the grunt.

[fixeruperer]

i detect i need a bigger aftermarket plenum becuase i dont have one yet haha, tho my stocker 4ag16v manifold modded to rwd seems to work great anyway, i cant imagine making much more power with a custom one.

[renxun]

thats what im tinking.. i saw alot of people having them in their drag car.. and im still running on stock plenum wid stock tb....

and the reason im considering tis is basically just that i dont have one yet.. and curious of what is the gain to expect whether its worth the amount spent or not.

[jonathan yee]

So is the stocker, what is the point?

the Greddy plenums will lose a shitload of lowend (have graphs to prove it) and dont do bugger all unless your running 268+* cams. the only time id use one would be if it ran a GT3582r and i was chasing 350+rwkw for drag purposes.

You should be measuring from the back of the TB to the back of the valve to work out plenum sizes etc but the majority dont bother and just asume the "log" section is what makes the grunt.

reason i asked was becuase i was looking thru one of my ol car mags recently and on a write up for the project car they where changing their custom plenum for a greddy, obviuosly their custom one was way over sized cuase the greddy plenum was loads smaller and they were goin from an 80mmTB down to 66 or there abouts.

point being that i was asking what size the plenum was in volume. to me doesnt look like it'd be all that big and is the size that i'd be looking at for my 3S.

runner length and design determines where your power band is at.

wild generalization- shorter runners allow pull thru to redline, where as long runners will produce low end tourque but your power will drop of in the top rpm.

also if you know so much about what plenum/inlet manifold volumes are required for what power levels care to share some info...?

[Shifty]

i have heard 1.5X the engine capacity!

+1

Where the hell are you going to find eight litres in an engine bay with a 1UZ? Six litres is bad enough!

Applying some common sense as long as it's forced induction it's not that much of a concern, and if it's atmo then as long as the intake path is fairly short and low-restriction again it's not that much of a concern. Obviously this is only relevant if you're not chasing every last sceric of horsepower, but at the end of the day we're amateurs playing in the field of billion dollar development budgets so I doubt we'll be nailing much perfectly anyway.