Modern Engines & Static CR vs. Boost Levels?

[BLSTIC]

ptuomov - Would this high tumble port be of use to your Porsche build?

[ptuomov]

ptuomov - Would this high tumble port be of use to your Porsche build?

Yes, but it’s not the next thing to try. Next thing is to try to get the bottom end to run safely to 8000 rpm. John Kuhn is working on a couple of short blocks for that purpose.

[Bazman]

Well I'm a dumbass but I grabbed a near new LS99, converted it to LS3, dropped in a 040 Cometic gasket and a 222/226 cam, then ran 13.7psi boost on pump gas.

Best I can figure, static compression is 10.9:1ish with a quench in the low 30's. It's never detonated that I can tell. It can get hot though but just drops power as timing is pulled. It's run a few 1000 miles like that and done several track laps and closed road days, so in all seen a lot of WOT.

In theory it should detonate and have blown up. It made 663rwhp and still runs.

The LS3's aren't too bad for old tech.... though the high ring land worries me. Will be dropping boost on a freshen up until I can build a new forged and darton sleeved LS9 unit with squirters then lean on it a bit harder... or buy an LT5 and ditch the blower for turbos.

[ptuomov]

We are now running 8.3:1 compression, street cams with good idle, and 8000 rpm. The piston dish shape with its near circular dish that promotes tumble and high volume piston oil squirters allow for about 19 degrees of ignition advance with 93 octane pump gas and 1.5 bar boost. It’s not the “modern way” but seems to work for us.

[BLSTIC]

Where this modern high tumble port excels in my opinion is with long stroke turbocharged four valve engines. Long stroke compared to bore allows for a high combustion chamber without a piston dome, as does turbocharging and the associated lower compression ratio.

Also check this screenshot out. It's a time lapse of tumble flow breakdown in different piston positions. An undersquare engine has an average volume closer to the top for a lot longer than a square or oversquare engine, so you'd expect any tumble generated to hang around a lot longer in such an engine.

This is making me think of other engines i could apply this to.