Preturbo backpressure

[Yrkesman]

I just did a datalog yesterday with my cosworth YB engine which has Holset HX35 (54/60) bolted to it with 46mm external wastegate. I finally got around to install my vdo 5bar sensor to exhaust manifold. The boost pressure in my setup is peak 1.7-1.8bar and it settles to 1.5-1.6bar. The preturbo backpressure was less than boost to 5700rpm where it went to 2bar and after 7200rpm the backpressure went to 2.3bar. I don't know if that's too bad, but ofcourse it could be less. Would be interesting to see some other results if someone has measured backpressures in cosworth yb engines with different turbo setups. I have 3" exhaust and catalytic converter, so it could be that one restriction is there.

Here's the latest dyno graph I have.

[therealpinto]

Interesting!

I have been meaning to measure the back pressure on my turbo Pinto, that uses a turbo quite similar to yours (but exhaust housing no 12 and 54/83 mm size I think). I boost less though.

When I had the Mitsubishi 16T I measured the backpressure up to about 1.1 bar and the backpressure never rose much above the boost (0,1 bar above by the most at top revs).

Gustaf

[Yrkesman]

Interesting!

I have been meaning to measure the back pressure on my turbo Pinto, that uses a turbo quite similar to yours (but exhaust housing no 12 and 54/83 mm size I think). I boost less though.

When I had the Mitsubishi 16T I measured the backpressure up to about 1.1 bar and the backpressure never rose much above the boost (0,1 bar above by the most at top revs).

Gustaf

The compressor wheel in my hx35 is something like 54/83, turbine wheel is 60/xx? The turbine housing I have, is number 12, but I have tought of changing it to number 14 if I can find one somewhere.

[therealpinto]

Check with http://www.airtune.se, that's where I got my turbo and I think they can order almost any Holset parts you like.

Gustaf

[Yrkesman]

Check with http://www.airtune.se, that's where I got my turbo and I think they can order almost any Holset parts you like.

Gustaf

Thanks, I'll ask from there.

[BSR-Patrik]

Keep in mind that there is one rule to follow in this case, as soon as the absolute back pressure exceeds the absolute boost pressure, no more power will be gained. This is easy to understand with some elemental physics.

[Yrkesman]

I think one reason for the backpressure is my 3" catalytic converter. I'll have to measure the pressure after the turbo when I have time.

[BSR-Patrik]

Easy, measure pressure between turbo and catalyst and compare this to the current atmospheric pressure.

I think one reason for the backpressure is my 3" catalytic converter. I'll have to measure the pressure after the turbo when I have time.

[Yrkesman]

I measured today that the maximum exhaust backpressure (was measured from the downpipe) was 0.3bar, so it seems that the catalytic converter doesn't limit the flow as much as I first tought. I think I need to get bigger exhaust housing somewhere and see how it works.

[Yrkesman]

I measured today pressure from the compressor outlet. It was 0.2-0.3bar more than from the inlet plenum. So when inlet plenum had 1.6bar, compressor outlet had 1.9bar and preturbo backpressure was 2.2bar. I didn't have time to try without catalytic converter, but I hope I can check that next weekend.