Compression Ratio and Boost Query

RustyRatRod said
The "real world" reason you can do that with the Eclipse is called electronic fuel injection. Were that a carbureted build, it would act completely different. Also as you pointed out yourself, alloy heads are much better at dissipating heat, so there's another score for less detonation. I'm in the preliminary stages of a slant 6 turbo build, myself. I plan to try some unorthodox (read dirt cheap) timing control and I plan to make it work, even though some say I cannot. That just makes me want to do it even more and I will.

I don’t wholly disagree. But, I do think a properly setup blow-through carburetor can deliver fuel just as efficiently/safely in a drag/wot situation. I do agree that the injection, in cooperation with the ECM and the sensor compliment working in unison gives a huge safety margin. Just not FI alone.

I got to thinking the main reason may be low speed cylinder pressure.

RustyRatRod said
The "real world" reason you can do that with the Eclipse is called electronic fuel injection. Were that a carbureted build, it would act completely different. Also as you pointed out yourself, alloy heads are much better at dissipating heat, so there's another score for less detonation. I'm in the preliminary stages of a slant 6 turbo build, myself. I plan to try some unorthodox (read dirt cheap) timing control and I plan to make it work, even though some say I cannot. That just makes me want to do it even more and I will.

I agree in part. I don’t think its the injection alone though. Its the injection and timing being controlled by the compliment of sensors via the ECM.

I got to thinking about it last night, and I think the primary difference between a 4G63T and an LA handling boost is low-speed cylinder pressure.

The eclipse made 14psi from about 6000-7200 rpm. I don’t think it made boost at all until at least 3800 from a cruising WOT pull.

My point is. That 318 will be lucky to reach 6500 N/A with those heads and springs. To have useable boost, it will need to come on lower in the rpm range. That means more pressure during less rpm = more dwell time = more heat soak. I suspect that is the primary limitation/advantage here. There isn’t much dwell @7200rpm compared to 5800rpm.

If you are building a 225, this is going to be something to consider. I don’t think the one I had would exceed 4200 rpm. (But it was a little sick)
A cam with a very late intake closing might help. But.. it might cause other issues with boost?