Voith

Piston crown must look similar to Wossner 3.0T after it is done, flat spot is def. going bye bye.

333pg333

Would think 8:8.1 would be ok unless you're on really low oct fuel?

Raceboy

This cannot be done, it ruins every engine this method is applied

Voith

100 octane fuel on every pump here. Ill see what can be done. 8.5:1 would probably be good enough.. I just don't want to go 9.x:1 and pull the head every now and then, its an old school turbo, it should have some lag.

V2Rocket

you've unlocked the pandora's box of this engine...

how far down (the rabbit hole ) can we go, if it doesn't seem to matter under a 16v head?

i was reading on some DSM forums about their quench stuff since DaveW mentioned they have .080" or more from factory...they all seemed to think it's a more critical design feature on wedge-heads (like the 8v 944) but largely a non-issue on DOHC pent-roof center-plug stuff...although it still can help, but not necessary

edit..
doing some reading of "other marques" ive found some interesting info...Ford supercharged modular engines are about 0.100" in the hole to lower compression. the old Chrysler Slant-6 225ci usually is in the hole between 0.140-0.180" depending on machining tolerances. the Ford 5.4 2v engine runs about 0.120" in the hole...all of these are very reliable long-lived engines, and in the case of the 5.4 4v, very powerful!!

also, here is a picture stolen from a magazine of a Dodge Neon SRT-4 engine...this is the stock setup...the piston flat at TDC sits over 8.5mm below deck, with the lump there to fill the head chamber and promote tumble for idle and cruising conditions...

Voith

In progress

Voith

Raceboy

Nice! Even though I would have taken a bit less material from the piston

Voith

Its actually still a bit too shallow. As it sits calculator is saying with 1.9mm HG this is 8.85:1..

What CR are you running?

Raceboy

I am running 9.6:1. 9:1 would be least CR on 16v motor unless the goal is 2bars of boost and/or endurance racing.

Voith

Hm hm. Have to think this trough.. I could go with 8.8:1 I guess..

What was the CR on Joulalalmi 968 turbo on his alusil engine?

Raceboy

it is Jõujaam In English it means "powerplant".

They had in the region of 9.2-9.3 iirc.

rluciano

My 8 valve engine is 8.7:1 cr. I'd think you'll be fine with the 16 valve head.

blade7

The Alusil engine that apparently cracked a cylinder before liners were fitted...

Raceboy

That was after the boost was raised, it held up fine for almost three years of constant use, both street driving and racing (circuit, top speed, drag etc).

People blow up even standard engines, does that mean stock power levels are too much for the hardware?

When exploring the limits, things can and will go wrong, but then you just know where the limit is, that's it. it is always the easiest way just not to do anything and just be negative towards everything.