robertbartsch

What size dished pistons do I need for the following set up that would yield 11.4 compression:

60CC chambers LS6 heads milled .055
4.125 crank
6.125 connecting rods
Stock LS1 alumium block
Stock head gasket

Thanks..

ls1290

iTrader: (20)

-7cc dish pistons will give you 11.4 with the listed setup.

robertbartsch

Really: thinks.. I thought it would be more...

I assume that is not too bad and that these pistons will not impact the fast burn combustion chamber too much....

robertbartsch

Hey LS1290:
Somehow I don't think -11CC is the right dished pistion for a 60CC head and 4.125 crank with a 6.125 rod since:

The Lunati web page indicates 10.6 compression ratio with the following dementions:

Head chamber 67CC (BONE STOCK)
Crank = 4.125
rod = 6.125
Piston = -11CC
Stock head gasket

*****************************
To arrive at a 10.4 compression ratio with a 60CC milled head shouldn't the piston dish be around -15CC - 18CC?

robertbartsch

Really?

ls1290

iTrader: (20)

http://www.appletreeauto.com/engcalc.htm

bore: 3.9
stroke: 4.125
deck height: 0.054 <- stock gasket thickness
chambers: 67 ( 60cc for the heads 7cc for the pistons )

compression: 11.4

robertbartsch

Thanks..

I'm confused about the variable measurement for the pistons.

If the 7CC adjustment is designed to capture the fact that Gen 3 motors have pistons that are "out-of-the-hole," shoudn't I deduct 7CC from the chamber size instead of adding 7CC to the chamber size?

Using this logic, my chamber size would be 57CC (60cc - 7cc) and not 67 (60CC + 7CC)

Thanks...

robertbartsch

I think I have the general idea now.

If the dish is 7CC and the piston is at zero deck hieght, my chamber size is 67 (60CC + 7CC)

Question:
When I buy pistons is it assumed that they will be zero decked even though the stock pistons are out-of-the-whole?

Pro Stock John

iTrader: (34)

Try:

cgelineau@diamondracing.net

strokedls1

iTrader: (1)

With a stock size .052 head gasket, zero out of deck height, and 3.905 bore I get -8 cc at 11.35, and -7.5 at 11.42 to 1 ratios. Things will change if you want to go a little out of bore with a different head gasket. Ross pistons web page has a great calculator that I always use.

robertbartsch

thx stroked one...

Question: Is this engine a bad combo - some have said the stroke is too long for the stock bore....

your view please///

Pro Stock John

iTrader: (34)

I don't like the 4.125 x 3.900 bore idea, but I'd probably offset things by running a 114 LSA camshaft maybe straight up to keep the power peak up. My 114 LSA camshaft peaked 200 rpms than my 112 cam.

robertbartsch

Pro Stock:
Was your iron motor a 4.0 stroke?

So you believe the 4.125 stroke is too much for a 3.9 bore; any particular concern?

Pro Stock John

iTrader: (34)

My old motor was an iron block, 4.060 bore x 4.075 stroke. With a S1 244/244/112 cam it make peak tq at 4400 rpms...

IMO I would not want truck like torque, so I'd run a a 114 or even a 115 lsa cam.

robertbartsch

Well maybe a 4.0 stroke with a stock bore (383CI) would be the better choice?

ls1290

iTrader: (20)

Or going with a 4.125" stroke crank on a 4.0" bore block; 415 CID. The LQ4 blocks go for about $650 new.

robertbartsch

The LQ4 block is iron. Most here seem to think aluminum is the better choice...

strokedls1

iTrader: (1)

I would stick with the aluminum and do a 4" stroke. Thr 383ci is a nice setup that makes good power. I have the iron block and have had to lose some things and swap suspension to reduce the weight.