[Dougal]

All you guys who're running moderate boost (20+psi) with no intercooler, how are you finding the power improvements?

I've just got my Isuzu fuel pump sorted and am running 19psi peak to keep EGT's at 750 deg C. I'm finding it takes a reasonably large increase in boost to drop the EGT's and the power to drive the turbo is noticable.

I wound it up incrementally from 14psi and found 19 was necessary, but it was noticably faster at 14 (up to when you have to lift the foot). Calculations seem to support this, 19psi on a 65% efficient compressor gives only 10% density increase over 14psi.
The bad side is predicted turbo exit temperatures shoot from 110 deg C to 130 deg C and the power required to pump that air goes from 9 to 14kilowatts at 2000rpm.

An intercooler is next on my list, but I'm wondering how you guys without them are getting on.

 

[66gaza]

All you guys who're running moderate boost (20+psi) with no intercooler, how are you finding the power improvements?

I've just got my Isuzu fuel pump sorted and am running 19psi peak to keep EGT's at 750 deg C. I'm finding it takes a reasonably large increase in boost to drop the EGT's and the power to drive the turbo is noticable.

I wound it up incrementally from 14psi and found 19 was necessary, but it was noticably faster at 14 (up to when you have to lift the foot). Calculations seem to support this, 19psi on a 65% efficient compressor gives only 10% density increase over 14psi.
The bad side is predicted turbo exit temperatures shoot from 110 deg C to 130 deg C and the power required to pump that air goes from 9 to 14kilowatts at 2000rpm.

An intercooler is next on my list, but I'm wondering how you guys without them are getting on.

Hi Dougal, I'm surprised you don't already have an intercooler , did the isuzu truck the engine came from have one?
What do you mean by "the power to drive the turbo is noticeable" I thought free exhaust energy drove the turbo.

Gaza

 

[Dougal]

Hi Dougal, I'm surprised you don't already have an intercooler , did the isuzu truck the engine came from have one?
What do you mean by "the power to drive the turbo is noticeable" I thought free exhaust energy drove the turbo.

Gaza

I've messed around with home-made air-water intercoolers before, but currently nothing's hooked up. I have a larger XSpower air-water cooler at home which I hope to fit, but it's tight for space so it may not happen.
My engine was imported from japan years ago without the truck, but they only had intercoolers in the very later stages of that model.

While turbos feed off exhaust heat, they need pressure to work too. I've measured backpressure on this turbo before and it was almost exactly twice boost pressure. So to get my 19psi boost, I might have almost 40psi of pressure in my exhaust manifold.

With more freeflowing exhaust manifolds etc it's possible to get backpressure down close to (or even slightly under) boost pressure but it needs quite a hot exhaust to acheive that.
The power figures I mentioned were just pressure tiems airflow, what a 100% efficient compressor would need to do the same work. The actual power going through the turbine shaft would be about 1/3 higher again.