Draw through vs Push through SC setups

[Invid]

What are the main advantages/disadvantages between the two types of set up, and which would be more preferable to build for an EFI set up?

[oldcorollas]

with carby?
neither

draw through,
pro: the fuel helps seal the SC and removes a bit of temp, no need to pressure seal the carby
con: when your manifold and C and engine bay explode due to the shitful fuel delivery resulting in a backfire.

push through (blow through)
pro, less likely to have explosion
con: need to pressure seal the carby

or do you mean with throttle body before or after?

before: TB meters the air, but means the SC is sucking against the TB, which increases the pressure gradient across it and may increase losses (? nto sure on that yet)
after: SC flows all the air it can and that shit needs to be vented somewhere if the TB is closed. this means the SC moves a lot more mass, but the lag is potentially lower, plus since the air is vented, the pressure gradient is lower, plus the air cools the C...

[Invid]

Sorry should have mentioned in original post, it's going on an EFI set up, so was wondering would it be better to have the SC before the TB, or in-between the TB and manifold.

[Smokey228]

I would have thought that it'd be easier and better to have the throttle as close to the manifold... I thought in general practice, for best throttle response, you want it as close to the intake as possible? That was why rb26's had individual throttles in the runners rahter than at the opening of the plenum...

Cheers,
Jase

[Invid]

To my understanding, having the SC before the TB (or a push through set up I'm assuming) would need to have a BOV installed, whereas a draw through set-up (TB before the SC) would require a relief valve eg. 1GGZE set up

Would it be better to have a lower pressure gradient?

[oldcorollas]

RB26 are turbo.. thus there is usually not much pressure before the TB.. IF the TB is not open
and when that occurs there is BOV to release it...

yup, if TB before, need to vent the air, which can be substantial if you are say, cruising at 3000rpm on highway with barely any throttle.

will you have the SC clutched?

as for the losses.. i still haven7t thought abotu it much.
(sorry for kinda OT)
loss comes from the mechanical friction to turn the SC
loss also comes from the pressure differential across the SC that is trying to turn the lobes backwards.

if you have TB closed then it is possible to get to fairly low pressure between the TB and SC. on the manifold side of the SC at cruise you migth have 0.5bar..
the pressure on the TB side of th eSC will depend on the SC ratio... if it is 1:1, then the pressure between TB and SC would be maybe 0.25 (cos it moves twice as much air as engine and gives 0.5bar in the manifold)
so the pressure drop is 0.25bar

when TB is after SC and you are cruising, the air going in is 1 bar, and the air going out is 1 bar (assuming you have big enough vent to not create back pressure), so ideally, there would be no pressure drop, and no force trying to turn the rotors backwards..

but then you are actually moving air (at 1 bar pressure, instead of 0.25 bar pressure) so the internal losses due to the lobes squishing the air around will be higher...and there will be some loss from the air leavign the SC etc....

so i'm not sure which is more efficient for the SC need to do some proper thermodynamic evalutation, which is a bit beyond me atm...



draw through will have less response, BUT, if you calculate the volume of the IC and manifold etc.. say.. 10 litres.. and you have SC set up to push 1 bar (ie 2L per SC rev), then excluding air eaten by the engine, it takes 5 revolutions to completely fill the manifold to atm, and then another 5 to fill to 1 bar pressure (it will take longer cos air is eaten by the engine but...) but even if it took 30 revolutions of the SC, thats 1 second at 1800rpm, 0.5sec at 3600rpm, 0.25sec at 7200rpm.

chances are it will be less than than.. maybe 1/3rd? 1/4? and the lag is not complete lag, but a linear increase in boost pressure = softer on engine.

same thing happens with TB after SC, but then you have less volume to fill so it takes less time.. but we are still talking in sub second amounts

[Invid]

Currently I have it clutched and going to be a Push through configuration. It's not to late to change to a draw through so was keen to hear which was better. It seems they're both pretty similar:

Push through
Pros:
Better throttle response
No back pressure

Cons:
Internal air losses
Marginally more lag/linear pressure increase

Draw through: Opposite of the above Pros and Cons.

[oldcorollas]

then again, during cruise, the SC will be turned off in both cases..

if you are at half throttle with a push through, how do you relieve the excess air? or is it more all or nothing? or is it taken care of by the BOV with a set spring pressure?

[Duk]

..but then you are actually moving air (at 1 bar pressure, instead of 0.25 bar pressure) so the internal losses due to the lobes squishing the air around will be higher...and there will be some loss from the air leavign the SC etc....

If you can use an external compression SC like an Eaton, then there will be negligable power consumption when the SC discharge is vented back into its inlet when cruising.
The Nissan March SuperTurbo used a plenum chamber mounted TB, so the SC wasn't throttled. They use a SC that is very similar to the Toyota 1s, 2 straight lobed rotors (internal compression).

[Invid]

Would the use of a plumb back BOV with the set spring pressure fix that problem perhaps?

It's a daily driver, and I'm Ms Daisy so half throttle is a very likely outcome.

[Duk]

A vacuum actuator drive butterfly valve would be the best method. It's the same method used by Eaton/Magnuson. http://www.magnusonproducts.com/bypass.htm

[Invid]

Thanks for the link Plonka, but I'm a bit unsure, according to their 'sample' SC installation diagram (http://www.magnusonproducts.com/images/samplekit.jpg) it appears they are describing a draw through set-up. From examining a 1GGZE (a factory Toyota draw through set-up) these contain relief valves which I assume would be similar to a bypass valve? Would a bypass valve still work for a blow style set-up?