What is best exhaus size for 2.7L Turbo

[bb]

Most of you know that I am running a2.7 Turbo with a custom made exhaust I had bought a used set of headers, shortenned them and made the cross over pipe to the turbo. Las winter I made the cross over pipe of a smaller diameter to increase velocity and I think that I went backwards, now boost comes on even later.

now the question: What is the best exhaust size,( I mean for the headers and for the crossover pipe), for my 2.7 turbocharged motor? It is supposed to get around 250 HP at 7psi.

Please throw some suggestions.

Thanks
Oscar

[Lukesportsman]

Is this a low compression turbo engine or a turbo conversion of a NA engine?

Depends both on size of engine, rpm, and primary size on the headers. If your primarys are large and the collector is small then you get bad evacuation and yet still backpressure.

What size did you start off with and where are you now? The pipe size after the turbo must be virtually without backpressure to minimize spool time.

[beepbeep]

Hello!

Turbo engines live off heat and exhaust pulses. Mached length primaries don't do much at all, headers are pressurized to roughly double boost and very little exhaust pulse tuning can be made. Long mached headers usually do more harm than good, as they allow gases to cool. Turbocharger spins beacuse of pressure difference between turbine intake and exhaust. The hotter the gases, the greater volume they have (PV=nRT) and the better turbo spins. Crossover pipes, long headers etc. are not needed. Keep heders as short and stubby as possible, with smooth bends. Usual N/A exhaust tuning tweaks are waste of time. Keep heat inside headers by wrapping them with thermal blanket. You can use same size for primaries as OEM. IO think they were 1.5 och 1.75 inch or so. Try to get muffler as free flowing as possible.

I don't believe 250hp from 7psi is possible without some very hot cams and good FI. Certainly not with stock 2.7 cams and CIS.

Cheers!

[bb]

the motor is the original 2.7s. Bae never changed the CIS pistons... I only say 250 because on the original literature and install installations that is what it said. I made a run with the GTECH PRo and am around 230HP?... I am trying to tune the EFI this week. I will try and find out the size of the headers that I bought. the crossover pipe is 2" o.d.

Oscar

[bb]

and, I had to use the cross over pipe to connect the two headers to the turbo.

Oscar

[beepbeep]

Originally posted by bb
and, I had to use the cross over pipe to connect the two headers to the turbo.

Oscar

OK, I didin't quite understand what you meant with "crossover pipe". There is a N/A engine construction where you connect two downpipes with "crossover pipe" to enchance torque curve at certain rev range.

[bb]

I did some checking and here is what I found... the headers have an o.d. of 1-3/4". The pipe that connects the headers to the turbo is 2" o.d.

The boost is coming on at 3500 rpm but never seems to hit above 5PSI at 6300 rpm.

suggestions?

[sammyg2]

Waste gate is my guess.
Either that ir a damaged turbo and that is unlikely.
You need to make sure the waste gate is closing properly and isn't opening too soon.

My engine starts developing boost at around 2900 depending on what gear I'm in, and hits 5 psi before it gets to 3600 rpm.
Something is wrong with your set up.

You aren't running it supper-rich, are you? that would cool the exhaust gasses and make the turbo less efficient.

[bb]

yeah, I am running pretty rich. I have been working to tune megasquirt and am almost to the point where it is tuned better, yet still pretty rich in the High RPM/High KPA. I should have it close by this weekend. I was just wondering if the small pipe from the headers to the turbo(2") was restricting the flow. I was at 2-1/4" last year and it seemed to come on a little better. Another factor is that I did install a new wastegate and boost controller that "Might" be openning?

Oscar