[6spdhyperblue]

The gmpp hotcam tune has the master switch for vvt set to NONE

[cmitchell17]

Originally Posted by 6spdhyperblue

The gmpp hotcam tune has the master switch for vvt set to NONE

Yes, but on my LT1 OS it ignores that switch, you have to zero out the tables. Not saying that it doesn't work on the OS that the GMPP crate motor runs though?

[MeanGreen1LE]

Been a long road with this project to say the least, (I’ll elaborate in a journal thread) and since I’m forever waiting on parts it seems I thought I’d bump this thread.
I’m actually considering milling my heads now and have the same question pretty much.

Curious to see those running pump gas especially 91; what compression ratio did you end up with and specifically what dynamic compression ratio do you have with your cam. And how does it run?

I don’t want to leave performance on the table unnecessarily but I don’t want detonation.

[cmitchell17]

Originally Posted by MeanGreen1LE

Been a long road with this project to say the least, (I’ll elaborate in a journal thread) and since I’m forever waiting on parts it seems I thought I’d bump this thread.
I’m actually considering milling my heads now and have the same question pretty much.

Curious to see those running pump gas especially 91; what compression ratio did you end up with and specifically what dynamic compression ratio do you have with your cam. And how does it run?

I don’t want to leave performance on the table unnecessarily but I don’t want detonation.

I think the ideal is as much compression as you can get without abnormal combustion. The ideal compression ratio is infinity with ideal cycles but we don't have ideal cycles so there becomes some optimal critical point at which you get decreasing returns in efficiency going higher. I think its might be one reason modern/post DEF diesels went down to the 16:1s from the 17s, although the reason probably had to do with Nox emissions.

I calculate mine to be around 12:1 but the big question is I don't know the relationship between head milling and combustion chamber volume. But then again I've never ran my engine with any other compression ratio. I don't remember it ever knocking (besides what I think is false knock) but I almost never ran 93 in mine since I ran E85 basically 100% of the time. Then again I haven't had my car running in 6 months.

I want to get to at least the 14s but I just don't see a way to get there without spending a huge amount of money with a completely aftermarket bottom end.

My controversial opinion is about dynamic compression ratio is that it dosen't matter and doesn't have a true scientific meaning, its more a tool for racers building motors to have some metric as to octane requirements. Its not like detonation/abnormal combustion only happens at low rpms.

[s346k]

direct injection was implemented for use in engines seeing 18:1+ compression.

the answer is: the most you can

[cmitchell17]

Originally Posted by s346k

direct injection was implemented for use in engines seeing 18:1+ compression.

the answer is: the most you can

What engine was that? I know the Mazda engines have 14:1 (I think 13.5:1 for the US version) with direct injection and they made it work on 87. Their new HCCI engine I think is like 16:1.

Mazda and Toyota seem like the only ones making reasonable statements nowadays. All GM is doing is caving in and admitting their supposed "sins" of building trucks and SUVs and going on and on about how they are going to be "part of the solution" by banning internal combustion engines and ignoring facts.

[6spdhyperblue]

Originally Posted by cmitchell17

What engine was that? I know the Mazda engines have 14:1 (I think 13.5:1 for the US version) with direct injection and they made it work on 87. Their new HCCI engine I think is like 16:1.

Mazda and Toyota seem like the only ones making reasonable statements nowadays. All GM is doing is caving in and admitting their supposed "sins" of building trucks and SUVs and going on and on about how they are going to be "part of the solution" by banning internal combustion engines and ignoring facts.

where u at with your car? I haven’t heard anything in a while

[cmitchell17]

Originally Posted by 6spdhyperblue

where u at with your car? I haven’t heard anything in a while

Still sitting there with no motor haha. I hate giving stuff to machine shops because you never know when it will be 6 months before you see it again.

The machine shop is supposedly going to replace the intake with .020 oversized seats made with some type of heavy duty chrome alloy. The exhaust seats were still good and apparently no bent valves, even though I swear the number 5 exhaust valve seamed bent.

The biggest thing is I have no idea what kind of seats to use, I couldn't find any info online. I've been talking with my uncle who talks with the shop so I'm not 100% up on all the details. I did talk with CHE about seats but honestly the guy there seemed to have a little bit of an attitude and kept questioning me running ethanol and kept telling me I should run with no exhaust valve seals for extra lubricity. Anyway my machine shop found something I guess so I am trusting them.

I bet it will be a few more months before I get the heads back, then I have to put the heads back on and measure for PTV, then finally get cam motion to start on my cam once I have that measurement. So that will be another month, then once I get the cam I can measure for pushrod length, then I guess another month to get those. So its going to be a while.

The worst part about waiting is I'm forgetting so many things, and things are setting up and im forgetting where I put tools and bolts and things like that. I did at least get my circle D in.

Anyway thanks for asking

[s346k]

Originally Posted by cmitchell17

What engine was that? I know the Mazda engines have 14:1 (I think 13.5:1 for the US version) with direct injection and they made it work on 87. Their new HCCI engine I think is like 16:1.

the diesel engine.