Interesting dyno test (cats and boost)

[illtal]

Yes, just one. It was a Hellion with 62s on a 9.5/1 aluminator and made 1100 on e85.

big tuning window on the low compression....
I'm guessing the tq loss from the lower compression wasn't that much with more timing added in and/or boost added in?

Edit
Was that a gen3 car?

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[engineermike]

big tuning window on the low compression....
I'm guessing the tq loss from the lower compression wasn't that much with more timing added in and/or boost added in?

Was that a gen3 car?

Yes, Gen3.

I'm looking at some of my dyno data from calibrating and a PD blown setup at 9.5/1 made about 7% less power and 4% more torque vs a 12/1 combo, both hitting the airflow limit of the blower up top. I was originally assuming 4% loss for every compression number but this was more like 3%, which is within the 3-5% accepted range. If you aren't airflow limit, it's pretty easy to offset the loss with more airflow (and timing) as long as you have the fuel system to go along with the increased airflow.

When turbo'd, it appeared as though compression ratio reduced the overall efficiency and power less than with a blower. [Unfortunately, I found 35-40 more hp AFTER the following dyno's were done using "unlikely" cam and spark timing, so take it for what it's worth.] 904/745 at 13 psi and 1000/825 at 17.5 psi. SAE corrected. My theory is that the higher EGT resulting from the lower CR increased the exhaust gas energy, which lead to less drive-pressure required and less resulting pumping losses. F1 learned something similar and balanced combustion efficiency vs system efficiency by optimizing compression ratio.

 

[illtal]

Yes, Gen3.

I'm looking at some of my dyno data from calibrating and a PD blown setup at 9.5/1 made about 7% less power and 4% more torque vs a 12/1 combo, both hitting the airflow limit of the blower up top. I was originally assuming 4% loss for every compression number but this was more like 3%, which is within the 3-5% accepted range. If you aren't airflow limit, it's pretty easy to offset the loss with more airflow (and timing) as long as you have the fuel system to go along with the increased airflow.

When turbo'd, it appeared as though compression ratio reduced the overall efficiency and power less than with a blower. [Unfortunately, I found 35-40 more hp AFTER the following dyno's were done using "unlikely" cam and spark timing, so take it for what it's worth.] 904/745 at 13 psi and 1000/825 at 17.5 psi. SAE corrected. My theory is that the higher EGT resulting from the lower CR increased the exhaust gas energy, which lead to less drive-pressure required and less resulting pumping losses. F1 learned something similar and balanced combustion efficiency vs system efficiency by optimizing compression ratio.

Does the higher egt affect the response of the turbo(s)? I guess you'd need a 12:1 setup with the same turbos to see a difference.

 

[engineermike]

Really hard to say and it would be another trade-off. Assuming the egt spooled the turbos quicker, you still have 7% less torque on tap, but for a shorter period of time during lag.

 

[GregO]

My theory is that the higher EGT resulting from the lower CR increased the exhaust gas energy, which lead to less drive-pressure required and less resulting pumping losses. F1 learned something similar and balanced combustion efficiency vs system efficiency by optimizing compression ratio.

Bam

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