LS6

Is there a certain limit value for piston above the block deck at TDC.

I'm calculating a Stroker combination, I found the piston will be above the block deck by 0.035", is this within the acceptable limit?

With this clearance, the quench Will be 0.018"!!!

It can be solved with a connecting rod center to center 6.000", but the crankshaft spec sheet say a minimum connecting rod length is 6.098".

badazz81z28

iTrader: (6)

I don't know, but a thicker head gasket will keep the piston from smacking the head.

KCS

iTrader: (20)

It would be okay with a thicker head gasket. The top ring is usually at least .180" down so only .035" out is no big deal.

LS6

Just for understanding

Is there any issue of angular motion or major stress on the block cylinder wall and crankshaft when going with connecting rods sized smaller length (center to center) than the one is specified by the crankshaft manufacture sheet?

For example, K1 4.250" or 4.125" stroke crankshaft, the manufacture spec.sheet specified minimum connecting rod as 6.098", and if I went with 6.000", will there be an issue on the crankshaft or on the block wall cylinder, or other that I'm not aware of?

KCS

iTrader: (20)

Yes. That minimum rod length value is related to how the counterweights are cut. If you run a 6.00" rod where the crank manufacturer requires a 6.10" rod, your pistons will likely hit the counterweights/reluctor wheel hard. I would consider that a major stress.

Bill71

The piston skirt may hit the crank counter weight if you use a shorter rod. Best to use a kit where the crank, rods, and pistons were designed to work together.

Krom

Use a thicker gasket to dial in the squish to what you are looking for.

A.R. Shale Targa

iTrader: (2)

Pretty sure Cometic makes a .070"

Fraser588

Most likely the piston will hit the heads with that amount of quench. Had .030" quench setups hit the heads, the pistons do rock in the bore, forged pistons have more wall clearance than cast pistons. While that does sound bad its not catastrophic but should be avoided.

Basically the ideas of what is ok for quench with a cast piston is different than a forged piston.

The piston should be at 0 deck, with a steel rod. Look at how the OEM's are, LS factory engines are .006 above the deck.

Another option would be to cut the tops of the pistons in a lathe, which isn't difficult. Any of the piston companies could do that to an existing piston, or a machine shop or Rebco.

Bottom line, order the correct piston with the appropriate compression height.

KiwiKid

Agreed Fraser, most engine builders I know will re-machine the top of the piston to give .032" quench, which is considered about the optimum quench for a high performance engine, and exactly what I run in my LS race engine's.

Cheers,

Mark.

Fraser588

I would run .040" (or more) quench with forged aluminum 2618 type pistons. Specially if its a 4.125"+ bore size boosted motor with .005-or .006" wall clearance. If you had a naturally aspirated engine with less clearance, 4032 pistons, or cast, .030" or .032" quench could be optimal.

This isn't something I read in a book or magazine, this is from tearing down a motor and seeing the chamber imprint on the piston.

One spec doesn't work for all engines.

LivernoisMotorsports

iTrader: (1)

what your looking for is a min. of .040" piston to cylinder head deck clearance for a street car. this # is not for when things are new these #'s are for when the engine is a little worn and things start rocking a little to prevent the piston from kissing the head.
If you have a virgin deck and are going to run a much thicker head gasket you will need to mock up your intake to ensure it will still fit.
A min rod length # means anything shorter than that will hit the counterweight. So unless your having counterweights machined and spending a small fortune on heavy metal for balancing I would reconsider or have a special crank made

KiwiKid

Fair comment Fraser my Ls engines are N/A and we also run fairly tight piston to bore clearance, and .040 Cometic gaskets and I have never seen an issue at .032, but we don't push it any tighter than that, but nor do we like to see anymore than .035" quench.

A.R. Shale Targa

iTrader: (2)

Aluminum blocks grow more than iron
Room temp .032" becomes close to .040" at
Operating temp.

KiwiKid

Good point Tony, and probably why we have not seen any evidence of physical contact between the piston and the head surface.

We are also not revving these engines much above 7,000 RPM.

Cheers,

Mark.