Thread: 2.5 vs 3inch exhaust on 35-40psi of boost

At that boost level you’d certainly be struggling with 2.5”.

That’s a lot of gas to eject!

For context, 35psi is almost the equivalent of a 7.5l engine

Ok thanks I am upgrading to a 3inch system in Jan

Originally Posted by Kaaaiju

Hi, having hit a brick wall with my current turbo running standard 2.5inch system on 35psi of boost but doesn’t want to go any more

turbo has a pressure ratio of 3.7 so good for a lot of boost but wondering now if it’s the exhaust holding it back

if anyone has any experience with this I’d be keen to hear more

Thanks

Pressure ratio of 3.7 @ what flow rate?

3.7 doesn't tell you anything without the accompanying flow and turbine drive pressure requirements.

Originally Posted by shack

Pressure ratio of 3.7 @ what flow rate?

3.7 doesn't tell you anything without the accompanying flow and turbine drive pressure requirements.

yes sorry I forgot to add that

“The compressor wheel is a 57 trim and the Compressor housing A/R is 0.59 A/R. This turbocharger can support up to 29 lbs/min of airflow and up to 3.7 pressure ratio.”

Originally Posted by Kaaaiju

yes sorry I forgot to add that

“The compressor wheel is a 57 trim and the Compressor housing A/R is 0.59 A/R. This turbocharger can support up to 29 lbs/min of airflow and up to 3.7 pressure ratio.”

Ok thanks.

The following only applies to diesel engines...

That turbo should "come on boost" pretty quick but will possibly be limited at the top end.

However, without a turbo flow map to reference you are looking at about 240 HP... Not to be sneezed at!

It may/should flow more air at lower pressure ratios.

Every turbo needs to be matched for engine size and required power and fuel type.

If you have a large engine, pressure ratio is obviously far less important.

With only 2.5l displacement to make high power, you need high PR and the equivalent flow... AT that high PR.

For reference, a gt2056 will flow 30 lb/min @ 2.5 PR.

It will however be very laggy and possibly undriveable under 2000 RPM....

Unless you're tuner has some mad skills.

Post up a flow map and that will tell the whole story, my figures are only based on 3.7PR and 29lb/min.

Originally Posted by shack

Ok thanks.

The following only applies to diesel engines...

That turbo should "come on boost" pretty quick but will possibly be limited at the top end.

However, without a turbo flow map to reference you are looking at about 240 HP... Not to be sneezed at!

It may/should flow more air at lower pressure ratios.

Every turbo needs to be matched for engine size and required power and fuel type.

If you have a large engine, pressure ratio is obviously far less important.

With only 2.5l displacement to make high power, you need high PR and the equivalent flow... AT that high PR.

For reference a gt2056 will flow 30 lb/min @ 2.5 PR.

It will however be very laggy and possibly undriveable under 2000 RPM....

Unless you're tuner has some mad skills.

Post up a flow map and that will tell the whole story, my figures are only based on 3.7PR and 29lb/min.

Here is the Turbo i run, all the info should be here for you

GBC20-300 39mm – Garrett Motion

Originally Posted by Kaaaiju

Here is the Turbo i run, all the info should be here for you

GBC20-300 39mm – Garrett Motion

At a PR of 3.7, that turbo flows 26lb.

That's enough for about 220hp.

I'm not going to run the math on the rest of it tonight, but 35 psi might be at the upper end already.

Do you have a nano log of it at 35 psi? I should be able to extrapolate a bit from that.

Don't forget that high pressure ratios require high drive pressures, the only way to get that is with flow and fuel, lots of fuel!

Just because a turbo can hit certain specs, doesn't mean that it will do it easily, or on every engine.

All factors need to be correct, and yes, the exhaust also.

Even the MAF reading and RPM at the 35psi will help.

Originally Posted by shack

At a PR of 3.7, that turbo flows 26lb.

That's enough for about 220hp.

I'm not going to run the math on the rest of it tonight, but 35 psi might be at the upper end already.

Do you have a nano log of it at 35 psi? I should be able to extrapolate a bit from that.

Don't forget that high pressure ratios require high drive pressures, the only way to get that is with flow and fuel, lots of fuel!

Just because a turbo can hit certain specs, doesn't mean that it will do it easily, or on every engine.

All factors need to be correct, and yes, the exhaust also.

Even the MAF reading and RPM at the 35psi will help.

Sent you a PM with the log