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oldcorollas
Forums Junkie

Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003

Re: Garrett T51S Turbo on JZA70 Supra

Fri, 21 May 2004 02:17

LOL

i'm sure i'm now the last person you will want to listen to about this but.... Wink

twin charge has already been done by toyota.
it has already been done by many people.

it's a good idea in theory

Quote:

I am open to any critism and ideas that people may have.

i hope so

where do we start....
it IS an academic problem. you have two sources of air. one is slow to start, the other is suddnely switched off.

you can run them with SC blowing into turbo, turbo blowing into SC, or parallel.

for my money, the best results will come from parallel setup.

idea being that the SC provides constant boost, and when turbo comes up to speed, it takes over, right?

it's not all about boost, it's about flow. with SC making sayy 14psi, when turbo is making 14psi, thats just the pressure in the inlet manifold, and is not relative to flow. when the SC turns off, the pressure will plummet and you have a massive dip. the turbo is still spinning, but if it's too big, it can 'fall off' and thats baaad.

we can go into numbers for arguments sake but i cbf right now.

and remember that with 1 bar SC boost, you are only doubling the engine capacity. how much capcity is needed to spool the turbo into it;s efficiency region?

what you NEED to do, is have a system that progressively changes from SC to turbo. what you WANT is for the turbo to be flowing enough air, at a high enough pressure, to make it worth swapping... if you have the SC running full, and turbo equalling the pressure, the turbo has almost ZERO airflow.

so. throttle the input to the SC, so that as presure in the manifold rises above a set limit, the SC pushes less air.
throttle the output of the turbo, so that when it is not up to pressure, air is not blown backwards thru it... you can also throttle the turbo inlet so it initially spools faster (since it has less resistance as it's not actually pushing air)

you go thru three stages.
SC pushing full amount of air.
SC and turbo providing half the required air each
turbo providing full amount of air.

this way you never have the dip that EVERYONE seems to get from twin charging... all you need is a way to control the throttles Wink

based on pressure differentials. ie a stepper or PWM controller... OR you can use manifold pressure, a few PWM IAC valves, and normal wastegate actuators.

anyhoo, i have crunched some numbers, and i have a nice design to implement, but for me it's not worth the effort... it is a lot of stuffing around for minimal gains... the main problem will always be the turbo size.

on a drag strip, you have time to spool the turbo.
on the road, if you have a fuckoff big turbo, that NEEDS an SC to spool it up, what happens at part throttle? twin charge is great for WOT acceleration, but what makes and breaks a system like this is the transient response.

you also need to consider switching points, when the SC kicks in and out based on what parameters, and also... something that most ppl don't consider... is the SC's inertia when switching on... it's a pretty solid little thing Wink

anyhoo, just a few ideas (as always)

if you have come up with a better way, i'd be very interested to hear more about it... i can't say i'm keen on the whole "wow i've found this awesome snake oil" stuff..

everyone has twin charge ideas at sometime Wink

not many ppl go thru with it...most falter at the design stage, and those who get past that start to think.. wow thats a lot of weight and complexity for what?

surely a later generation turbo (more efficient, faster spooling) would be a more viable option? Norbies car seem to have best of both worlds.....

Cya, Stewart

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