bluehawk2

iTrader: (74)

I purchased a forged 347 shortblock with 28cc dish pistons for my turbo build.

I am going to run my 243 patriot cnc ported heads...........they havn't been milled any

what compression will this give me with gm mls gaskets??



thanks

TURBO6.0L

iTrader: (1)

You should be right around 8.0:1.
Numbers used in case someone wants to check my calc.
Gasket thick = .051
Gasket bore = 3.92
Stroke = 3.622
Bore = 3.905
Chamber = 64cc
Deck clearance = .006 in hole. Average number, would help if you knew what yours was for sure. Every .0075 is good for about .1 in compression.

8:1 is a little lower than most folks are running. Most builders suggest 9.5:1 for turbo car. They say that you lose a lot on the lower end but if you mostly just race you probably would never notice since you would be spooling the turbos before you launch. You cold mill .042 off the heads but that will only get you to 8.5:1. Once you mill more than that you will have to mill the intake surface as well as start to worry about piston to valve clearance if you decide to use a big cam. You can use a .040 head gasket to bump it up to 8.7:1 but the cometics are the only ones I know of that are thinner but they are known to leak unless block and heads are freshly machined with a very fine finish which most machine shops don't do.

Paint_It_Black

iTrader: (1)

You lose on the low end with lower compression, not higher. Nothing wrong with 8 to 1. The lower your compression the more boost and timing you can run on pump gas. Lower compression + more boost is more power than higher compression and less boost (within the limitations of the gas/timing you're running).

TURBO6.0L

iTrader: (1)

Thanks for the correction. I should have clarified that was for the 8:1 CR. So yes you will lose some power on the lower end with a lower compression engine. I think at some point with lowering the compression you will start to lose enough low end power it would not be worth it otherwise folks would be running 7:1 like they did 10 years ago. Local tuner here said that 9.5:1 forged LS1 is good to around 650 to 700 HP on his mustang dyno with 92 octane. Guys are probably going with a higher ratio so they have a more responsive setup.

bluehawk2

iTrader: (74)

I didn't realize I was getting that low of a compression shortblock.

I got a really good deal on it from a member here.


i am running a thunder racing cheater cam, so maybe I could mill some off the heads to get some compression back.

I am going to run a vig 4000 converter with a 2-step, so maybe spool-up will be a little better

TURBO6.0L

iTrader: (1)

What ever compression you go with you will still be able to make good numbers. Are you going to run the APS twin kit in your signiture?

bluehawk2

iTrader: (74)

yes, I have it on the car now...............i'm going to swap to gt35r's this winter


I guess with that compression ratio I will be able to run some aggressive timing

TURBO6.0L

iTrader: (1)

Yes lots of timing and boost. I would still probably shave the heads some though. The APS kit is what I really would have liked to have gotten but did not want to modify the car that much to make the kit fir. That kit makes some killer numbers at least based on what I have seen others say. Probably one of the best IMHO. How much power did you end up making or what did APS say it was it supposed to make?

bluehawk2

iTrader: (74)

I am running it really safe right now because i have the stock shortblock, but it made 480 hp and 47x torque on a mustang dyno with the converter unlocked through a 12 bolt. 8 psi


I'm running 15 degrees of timing and afr is no more than 11.0


I ran 10.92 at Memphis a couple of weeks ago.


I'm happy with the kit right now, but i know i can't turn the boost up until i get the new turbos on the kit

TURBO6.0L

iTrader: (1)

Pretty good numbers for such low boost especially through unlocked torque converter. And I do know how tight those MD's are. Nice track time!!

bluehawk2

iTrader: (74)

i don't really think that i have a 28cc dish. When i purchased the engine it was supposed to be 9:1

I had a local builder look at the pistons and he said there is no way that what I have a 28cc dish

What do you think?