Aaron, would you mind running one more....

I've got a low compression FI engine that's taking a gob of timing, that I got about 2 years ago, but just got on the road this year. I never did know the compression ratio on it for sure. So I'm trying to figure out if the amount of timing I'm running is reasonable for this engine or not. (22 degrees at torque peak, 24 at max rpm, on 11 psi, no kr)

Stock displacement (347). -16cc Mahle dished pistons. Heads are 241 castings, first generation TEA stage 1's, with "just a clean-up", but I don't know the cc's on them. Stock graphite head gasket. Comp cam 224/228 .581/.588 on 115.

Any help on this is much appreciated!!

 

Hi John_D,
Do you know if the cam is ground with any advance or do you know the intake center line? Do you know the piston to deck height clearance? I can estimate with stock short block but with aftermarket pistons all bets are off.

 

I really appreciate you looking into this.
I looked all over and finally found the cam card.

It is a 115 +4. Part# 54-000-11.

Valve timing at .050 (open close):
Int: 1 BTDC 43 ABDC
Exh: 53 BBDC 5- ATDC

Does 5- ATDC = 5 BTDC ?

The ICL is 111.


I don't know the story on the piston to deck... I can try to get that info from the builder. Could you run it as stock, and as zero, just in case?

 

John_D.:
I looked up the specs for the Mahle pistons that you most likely have. According to Mahle, the specs are as follows:
Part #:LS1314898I16
Bore:3.898
Stroke:3.622
Rod Length:6.125
Dish:-16cc
Piston Pin Dia:.927
Compression Height:1.314
Weight:400 grams

So, assuming the deck height is stock at 9.240" the pistons would be .010 out of the hole. If the block is decked, the pistons would be further out of the hole increasing compression ratio.

I used a stock LS1 piston ring depth, because I can't find that spec. If the top piston ring is lower it will lower compression slightly.

All that said, this should be very close:

 

Thanks!!!!!

I was thinking we were shooting for "around" 9:1, possibly lower with the thought of possibly going with a different head later on.

That helps a bunch!

 

Mahle advertises 9:1 with those pistons and a 64cc head, so it sounds like your where you want to be.