14psi on turbo = 14 psi on supercharger?

[CHB]

now i'm a bit sick of the turbo lag on my 3T-C turbo. now came out with an idea to change the turbo to supercharger so that it will responce faster and good for street. fabrication is not a problem for me, but i want to know if 14psi of turbo boost does it feels the same on supercharger too? i'll opting for a SC12 or SC14(if available) and i guess it will support from low revs until 7000RPM without having to switch the supercharger off? my MS-II will be able to control a relay so switching the supercharger on is not a problem for me.
idea please...

[willwal98]

Basically it will just feel like a bigger engine, no sudden increase in power like the turbo. Also 14psi on a blower will probably give a little bit less power than on a turbo because it uses a bit of power to turn it over.

[oldcorollas]

according to the docs put up earlier, max power draw will be like 15 or 16kw for an SC14?
but.. no lag.. down low it will still not make full pressure, but whatever pressure it does make will be no lag.
14psi is abotu the limits of the SC12/14 tho, from a heat perspective..
water/methanol injection in front of the turbo? MS should be able to switch it for high throttle

[CHB]

i plan to plum the supercharger to my existing intercooler piping. so cooling is not a problem with the 600x300x76mm intercooler i guess. here is the photo of my current setup



i've think to do a twin charged setup, where i can relocate the alternator onto the intake side of the block, where as the SC will be mounted just underneath the turbo. SC -> Turbo -> Intercooler -> inlet throttle.
what do you guys think?

[oldcorollas]

need larger exhaust housing on turbo, as you only want it to make maybe 5psi or so. also want to resize the compressor, to be more efficient at larger flow and lower pressure...
cos the SC will multiply the boost if in series.

but could be good option.

i was meaning heat produced in the SC.. making it inefficient..

[CHB]

ok may be i need to switch the supercharger off in this case to reduce the heat it produce.
but here rise another question, when the SC is off, can the turbo still drawing thru the off SC? or it will choked to death?

[JustenGT8]

A SC (especially a roots) will produce alot less HP than pretty well any turbo on the same boost. Not only does it take crank HP to drive, it's a far less efficient mover of air which means more heat and less mass airflow for the same boost.

To run your twincharge setup as described i would set 2 off triggers for the SC. One is as per stock which is a vac single i believe so when you are on cruise it's off. Ad a slight time delay circuit so gear changes and spirited on/off throttle doesn't trigger in. In the case of cruise the interanl SC bypass provide enough bypass.

The 2nd trigger is for when the turbo is handling all the top end. A bit tricky to trigger as a boost reference alone will be no good (will have to think about this one). For this you would have to supplement the SC internal bypass and i think a big arse WG would do the job nicely. As it's also boost referenced you would just use MAP to trigger i think?

Easier to run the turbo thru the SC and obnly deactivate the SC on cruise as per stock.

No the SC won't be a restriction.

A Stu says, you will want to run a much bigger turbo than current

[oldcorollas]

sorry, i missed the Sc runnign thru turbo...
much better to run turbo thru SC as Justen said. that way you are reducing the pressure differential across both chargers, so they both don't work so hard.
ie, if you have 1:1.5 ratio across turbo (7psi) and 1:1.5 ratio across SC (7psi with no turbo, 18psi with the rubo going), then you reduce your SC losses, and get back from turbo..
and still have 18psi boost (or 7psi when turbo hasn't spooled yet)

switching stuff off is difficult, but can be done, but there are fundamental differences in flow vs pressure between the two devices.

[CHB]

ok let say it will be Turbo -> SC -> Intercooler -> inlet manifold
when the SC stop spinning when it is off, there screws inside the SC is not moving at all, is there any room for the turbo charged air to flow thru the off SC?

[JustenGT8]

You don't turn the SC off...leave it running as you would with SC only.

The SC is off on cruise, stationary etc just like factory....only difference is it's getting fed by a turbo instead of ambient...it won't know the difference

[Duk]

A SC (especially a roots) will produce alot less HP than pretty well any turbo on the same boost. Not only does it take crank HP to drive, it's a far less efficient mover of air which means more heat and less mass airflow for the same boost.

While I won't argue the efficiencies (or lack there of) of the SC12/14, it's a bit wrong to call all Roots type SC's inefficient. The new Eaton/Magnuson TVS SC can be as high as 75+% efficient. That's centrifugal levels.
The back pressure on the engine caused by the turbine housing and turbine wheel rob the engine of power and potentially (probably) cause more heat and exhaust gas retention in the combustion chambers. The higher combustion chamber temps can obviously cause detonation issues, typically countered with retarded ignition timing (less power) and the exhaust gas contamination also reduces the available volume for fresh air/fuel.

Theoretically , a supercharged engine should tollerate more ignition advance per pound of boost if the air entering the engine is at the same temp as that supplied by a turbo and if the exhaust system starting at the headers/exstractors can flow well enough.

[oldcorollas]

the TVS is effectively a twinscrew with no internal compression.

the SC12/14 and a ROOTS blower (straight lobed) IS inefficient...

back pressure on turbine is one thing, but the worst it will do is to prevent the cylinder from scavenging properly, or dilute the new air with exhaust = EGR = more efficiency... (not more power tho)

[Duk]

The TVS is still considered a Roots SC. I did ask this question of a SC guru on another car forum and he assured me it is still a Roots SC.
The twin screws use internal compression.
Back pressure on the pistons will still cost power.
How can exhaust gas recirculion in an engine on boost achieve more efficiency? I can see how when it has manifold vacuum (lower pumping losses), but not how when on boost .

[oldcorollas]

what is the definition of a Roots SC?
the real roots had 2 lobes per rotor, straight lobes, and no internal compression.
then was "twisted lobe" roots, with 60deg? twist (current eatons).
TVS has 4 lobes with progressive pushing of the air. the only thing stopping it from having internal compression is length.

same as you can make a "twinscrew" shorter and have no compression.
the lysholm design (imo) refers to the type of male/female lobe engagement style...

i don't profess to be an SC guru.. but that guru is wrong .... or maybe all SC's are roots? or maybe none?
anyway, SC12/14 are Roots SC. 2 straight lobes.

it depends what efficiency you are talking about? VE? fuel per kw, fuel per engine cycle etc etc...

[CHB]

ok let me try to find a SC14 and plumb it up as SC-> Turbo -> Intercooler and set it off while at cruise or idle. we'll see how it goes..