So, Machine Shop came back with some bad news and I have to go .030" over on my Turbo 5.3 Build. There is not a great selection when it comes to .030" Pistons for the LM7. So after calling Summit I went with these:

http://www.summitracing.com/parts/SLP-H1132CPA75MM

It is a flat top piston and per my calculations on the stock heads (61cc 852 Heads) I will be around a 10.5:1 Compression Ratio. Will I be able to safely run a S400 on 8-10 pounds of boost on 93 Gas using these heads or should i be looking at swapping for 241 or 243 Heads ?

Thank You.

 

I would swap heads.

 

There is plenty of e85 stations in my neighborhood. .. would the stock heads work if I ran e85,10lbs,10.5:1 CR ?? Or went to a 93/Meth setup?

 

Am i looking for top secret information or something, lol ? Someones gotta have done a flat top boosted 5.3 on stock heads ... that ran e85 and it worked like magic ? lol ... any advice would help, thank you.

 

Who's doing your tune? I would be on the horn with him asking these questions.. You are at his mercy lol

But yes plenty of guys run mid to high 10's CR on E85.... Since it will still have good drivability out of boost..

 

to be honest I do not know ... YET! ... my first priority is get this motor together, into the car to fab up the piping. so this is the bridge I am at now ... HELP ME CROSS IT !!!! I also was thinking maybe have the machine shop machine a 7cc dish into the piston... that is if the e85 on 10.5:1 is a no go...

 

Just an FYI, did you calculate how much the piston would come out of the bore? I know back when i looked at those pistons, the CH was off, the piston would actually be below the deck, not above like the stockers. This assumes a 9.240 deck height. Just double check it, you may be lower on CR than you think with those flat tops.
If i remember correctly, i think i was coming up with 9.234 with those pistons, which with a 9.240 deck height, it will sit .006 in the hole.

 

So just going off specs without physical measurement (motor is not together) compressiom height on thr speed pro pistons is 1.325 so using that number the poston will sit 0.025 in the hole... with those numbers using a ls9 gasket and 61.15 cc head i am at 9.8:1.... i am much more comfortable with that then 10.5:1... still think going e85 would be a good idea.