Opinions on 1.28 exhaust housing

[jpowel29]

Once my new motor is broke in and I have some baseline data to compare against, I am considering moving up from my .98 exhaust housing to a 1.28.

With the new motor (ported heads, big cam, good valve springs, lightweight valvetrain) I will be able to reliably turn over 4500rpm and keep my shift points up as well.

Anyone have feedback on how well a GT4202 responds with a 1.28 on the track? My current stall is around 2600rpm - how well can I expect to light it off the line?

 

[MAXLLY]

looking for opinions, I have one it aint worth much here. :rofl:

I think its a bit big, can you get some more tire for the 2 wheel?

Only a couple guys here (that i know of) can speak to that GT42 and the housing you are interested in.

She'll turn some RPM and resist backpressure if thats what you want.

Good luck Man, sounds like a sweet build!

 

[never satisfied]

With the right converter and tuning, you wont have any trouble lighting the turbo. I ran the 1.28 without any trouble.

 

[Josh2002cc]

I know of a guy who runs a larger exhuast housing on his gt4202 and has no problems at all, and it is much larger He is also running what seems to be similar mods to what you listed as on your "new" engine.

 

[never satisfied]

If you want 4500 rpm, the GT42 is not your turbo. JMO

 

[JOHNBOY]

If you want 4500 rpm, the GT42 is not your turbo. JMO

X2 The turbine wheel is done right around 3500 IMHO. It just cant flow enough to make good power much higher.


With the right converter and tuning 1.28 should not be a problem. That is what is on mine right know and I have no issues lighting it. I tryed 1.01,1.15, 1.28 and really did not notice much difference.

 

[jpowel29]

I am seeing the power drop off pretty steep above 3500rpm on my dyno charts so what you all are saying makes sense. Thanks for the input.

 

[never satisfied]

The GT4208 might work at the higher rpm. You may even be able to turn one of your 42's into a 4208.

 

[super diesel]

The Gt4202 and the GT4208 have the same turbo wheel I thought (all GT42 stuff)? The differance is the compressor wheel (GT4508 wheel) and an opened up GT42 compressor housing. Still just as restrictive on the exhaust side, just harder to spin with the bigger compressor wheel (pushing more air).

 

[never satisfied]

Ok, never mind then. Thanks

 

[McRat]

Yup, a 4202 will start to fade well before it gets to 4500. It will run up there, but it will be off it's map. 4508, 42mag (4208), would be the smallest that will get there and survive.

I personally like the 1.15 housing on the 4202.

 

[never satisfied]

Have you tested a 1.28 on a 4202?

 

[McRat]

Have you tested a 1.28 on a 4202?

Not that I remember.

I have tuning customers with them, and sometimes they will have spooling issues.

 

[never satisfied]

Interesting. I guess at a higher elevation I could see it being an issue.

JP, what elevation are you?

 

[McRat]

A turbine and it's housing is nothing but a motor to get power from. A turbocharger is two separate animals, a turbo (turbine) and supercharger geared together. They even use the turbine by itself to drive the crankshaft on certain engines. The new Volvos are one of them. There is a second turbine that is hooked to the crankshaft with no compressor on it, and upriver there is a normal turbocharger. They call that turbo-compound technology. WWII aircraft engines used it.

The turbine wheel is designed around a specific housing A/R, then they make bigger and smaller ones to adjust for different flows that are delivered to it. A bigger A/R won't supply as much torque to the supercharger at lower exhaust flow rates, but will carry the torque out further. A smaller A/R will supply more torque at the lower flow rates, but will cause more backpressure in higher flow areas.

But the compressor itself controls how much boost will be possible. Supplying the compressor with good turbine power when it's already off it's map, won't gain much. Any gain you'd get by overspeeding it will get eaten by the loss in efficiency. The compressor will fade at the same RPM if it starts to leave the map, no matter how much power you put into it.

 

[jpowel29]

Interesting. I guess at a higher elevation I could see it being an issue.

JP, what elevation are you?

1322ft

 

[jpowel29]

[Supplying the compressor with good turbine power when it's already off it's map, won't gain much. Any gain you'd get by overspeeding it will get eaten by the loss in efficiency. The compressor will fade at the same RPM if it starts to leave the map, no matter how much power you put into it.[/QUOTE]

Makes sense - stacking drive pressure isn't going to help anything (neither will eroding the turbine/compressor wheels or damaging the shaft). I am going to be content with the GT42 until I can get more laps on the truck. Then if I am still wanting more I will look into a T6 set-up. The prospect of adding a cage does not excite me but I have already started down that path...