GMT900 6.2 PPV Build Log

[Marky Dissod]

So you are saying that the thicker head gasket, reducing quench/compression,
will be less efficient at keeping the engine from detonation,
and therefore require higher octane to compensate for the increased chance of detonation,
if I am understanding you correctly.

Purpose of quench, especially in a wedge combustion chamber, is to enhance mixture motion.
During the squeeze, the 'flat' area of the piston rises to nearly meet the 'flat' area of the head.
They may not be truly flat, they're shaped so that combustion canNOT take place in those areas.
They instead push the air/fuel mixture toward the largest part of the combustion chamber in motion like bellows.
The further apart the 'flats' are, the less mixture motion is induced.

Other ways to avoid ping / knock are to choose the cam carefully, to write the spark tables carefully,
to choose the correct octane, and to achieve finer fuel atomization, which GM combined with more quench.
Compare the Gen5 pistons to the Gen4 pistons, then compare the Gen4 pistons to the Gen3 pistons.
As the piston chamber has evolved, so has the static compression ratio.

 

[ls3_ppv]

I noticed the PPV was burning oil and needing topped up about every two weeks. This motor didn't live an easy life, it was loud but slow and I had places to be. It came with an ebay catch can on the passenger or PCV clean side and i did what any professional idiot would do and remove that to upgrade to an even bigger catch can! As a master level internet sleuth I set to reading about catch cans, how they work and why they are needed. Since I was catching oil here but burning more oil than was caught I tried to vent to atmosphere from both valve covers based on what the internet told me. (lol)

Here is the catch can the PO put on the car. He mentioned I should upgrade this and the HPtuners guy commented it was weird to only have a can on the PCV clean side instead of the dirty and clean side or just the dirty side. Blue line connected the corsa intake to the can and provided a filtered fresh air feed. Green line routed to the PCV connection on the passenger valve cover. Let's call this PPV PCV rev. 1


Anyways, lets throw that away and install another ebay catch can! Spoiler: it didn't work BUT I did learn how to make AN lines even if they are scuffed up. Actually it did work to catch crankcase vapors, problem was it simply saturated the filter and oozed oil simply venting to atmosphere. Oh and there is no vacuum on the crankcase which helps to seal up piston rings, maybe prevent oil loss. I'd come to learn the err of my ways even if the internet told me this is the way. Lets call this PPV PCV rev. 2

 

[ls3_ppv]

I went back to the drawing board, there was improvements that needed to be made to the PCV system on this car. So I came up with this terrible drawing and this contraption of a PCV catch can setup.


I didn't realize until now that I had come up with a viable PCV system for a naturally aspirated LS motor. We have vacuum at all times pulled through the crankcase via the top connection of intake manifold, blowby cannot push into the intake tube, the catch can is now on the PCV dirty side of this motor and we can still vent excess to atmosphere after going through the catch can. Let's call this PPV PCV rev. 3

This worked, it worked well I might add. This was installed in April of 2022 and used for about 5 months. Bit of foreshadowing here but the only change needed to make this suitable for boost is an additional check valve on the connection between the intake manifold. Easy day! And unfortunately this idea of boost was also poorly executed....

 

[RooTBeeRthe1st]

Got to say, I'm interested to see what the next 2.5/3 years of your ppv's life consists of.

 

[swathdiver]

My bone stock 6.2 L9H puts down 372 rear wheel horsepower through the traps in the quarter mile.

Before you mod the motor to try and bring the power up, change the gears.

You can put a trutrac in the 8.6 or you can get a 9.5" 14-bolt out of a RWD Escalalde/Denali with 3.42 gears and then re-gear it. A P265-70-17 tire, being taller than stock PPV, will help a little in keeping the tires planted. Of course, the choice of tire is important in this endeavor. Michelin Defenders serve us well at the drag strip and on the street.

Those LS9 head gaskets by themselves would have dropped your compression ratio. We don't know if the block and heads were milled down and what pistons are in it to know for sure. L9Hs require high octane gasoline or E85.

Drivetrain losses on my 5.3 and 6.2s are just under 8%, the 6L80 and 9.5" axles are very efficient. If your circle D torque converter is a billet type, it will sap a bit more horsepower to turn it with the extra rotational weight.

Fun stuff!