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

[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

[Tombie]

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

[Kaaaiju]

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

[shack]

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

ThanksPressure ratio of 3.7 @ what flow rate?

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

[Kaaaiju]

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.”

[shack]

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.

[Kaaaiju]

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 (https://www.garrettmotion.com/racing-and-performance/performance-catalog/turbo/garrett-boost-club-line-gbc20-300/)

[shack]

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

GBC20-300 39mm – Garrett Motion (https://www.garrettmotion.com/racing-and-performance/performance-catalog/turbo/garrett-boost-club-line-gbc20-300/)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.

[Kaaaiju]

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

[TonyC]

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

GBC20-300 39mm – Garrett Motion (https://www.garrettmotion.com/racing-and-performance/performance-catalog/turbo/garrett-boost-club-line-gbc20-300/)

Hi Kaaaiju,
Why did you chose that turbo?
The Garrett link you posted suggests the it is suited to a 0.8-2.0 litre motor, were as the next size up is suited to 1.0-2.5 litre motors.
Is it about trying to keep low down torque, rather than all out power?
Also why a fixed geometry turbo rather than variable.

Thanks

Tony

[Kaaaiju]

Hi Kaaaiju,
Why did you chose that turbo?
The Garrett link you posted suggests the it is suited to a 0.8-2.0 litre motor, were as the next size up is suited to 1.0-2.5 litre motors.
Is it about trying to keep low down torque, rather than all out power?
Also why a fixed geometry turbo rather than variable.

Thanks

Tony

my mate has the GCB 22 in his defender and it’s insane with power, these have the same oil and drain locations like the factory turbo so it’s easy to install and can run very high boost and power at a really low cost $1100 vs $3500-$6400 for a vnt

I chose this on my daily as I try 3 different vnts and it’s very hard to setup correctly with low down power and power up top, had one vnt wastegate break on me with was disappointing and another vnt had been messed around with the settings and drove like rubbish

vnts are harder to dial in to what you want, my circumstances are much different to most

plus fix geometry is easy to setup and tune for the most part

[Pedro_The_Swift]

When the US Army wanted more power for their latest Tank, they went to see Mr Banks...


How much HP are you losing to backpressure? - YouTube (https://www.youtube.com/shorts/k7yYY_hy250)