I posted this on RSOC BB but its relevant to yall to so here goes...

Heres one I never understood----

Obvioulsy the larger the compressor wheel, the higher the air flow.
To let the exhaust gas out to create big power, the exhaust side of that large compressor wheel turbo also needs to be v.big (T4 for example).
The side effect of this though is big lag.

Why then cant you have a small exhaust housing, but with a HUGE wastegate (external one would b easier), so the lag isn’t there, but the huge amount of exhaust gas can can still escape to create the big power????

I mean a T4 compressor wheel, joined to a T2 exhaust housing, with a say, 3inch diameter external wastegate could flow 500+bhp of air easily n have no lag.

I don’t see the problem, but there must be one, otherwise someone would have made em like this.

Any ideas?

Cheers
Steve

I thought the problem is simply torque. The torque provided by the gas flowing past the small impeller is simply not enough to turn the compressor to generate the boost.

[Edited by Adam M - 12/20/2001 11:32:32 AM]

Smaller exhaust housings, don't mean smaller impellers, just like the VF turbo's with either a P18, or P20 housing.

The engine will be producing the same amount of gas at low rev's, but trying to force it through a smaller housing will increase gas speed, and spool up.

Steve, a 3" wastegate is MASSIVE, I think 45mm is average, and these are rated at about 900bhp.

I'm currently using a Garrett GT35, and the exhaust housing has an AR of 1.06, it's pretty laggy, and will only produce 8psi @ 3500rpm, 27psi @ 4000rpm :D.

I'm thinking of changing the housing to a .83 AR, but don't know just how badly this will effect the mid/top end. It's a BIG change.

Guess you could always try two external wastegates :D

Mark.

MARK-

2 wastegates- v.v.good idea.

Im so glad u understood my point- the RSOC people dont seem to (very stuck in their ways, cossie owners- apart from me!).

Nice one

Steve

Steve,

Well they are "Cossie" owners :D.

It all comes down to space, and cost. I've got a Turbonetics "Racegate", bit naff compared to a very nice Greddy one I sold to Pat a while ago. Just wish I'd known then, what direction I'd end up going in.

Even the Turbonetics WG cost about £350 +, compared to £500~600 for some of the others. Seems to do the job though.

Then, you'll also need some air injectors to control it (them ?) properly. Ahmed does a nice set.

To be honest, you won't need two WG's for 500bhp.

What turbo's are the 550bhp Cossie Escorts using (Martin, etc') their setups work well, and they still get good boost from 3k.

Who's the best person to find out what effects I'll get changing to the .83, from 1.06.

Mark.

All the 500+ bhp cossies have normal huge exhaust housing T4's (they come on boost bout 4000rpm).

This idea is getting shot down in flames on the RSOC board with some quite good techy reasons why this idea wont work, go looksie, its well worth a look....

steve

There is a way of doing this: Volvo use it on the S/V40 T4 and 2.0T. It has two small impellers in separate chambers, one served by a 2 into 1 manifold for 1&3 cylinders, the other by 2&4 cylinders. That way you can have a biggish compressor that spins up quickly without too much lag from a big impeller.

The Mitsubishi charger from those cars won't give you 500bhp tho' ...