Do you have a part number?

What size are the chambers on the 243 head?

How much cam do you have?

What is your quench?

Do you run 87 octane?

 

Runs on 89
10.5 to 1 compression
61cc chamber on heads
224r cam
Quench idk

Ordered pistons from summit

 

With the 243 heads, you will have to run dished pistons. Quench suffers though because of it. Remember they are a ~64cc chamber vs the 317's ~72cc chamber. Running a flat top with the 243's is going to run compression up around 11:1 with a stock gasket. It would essentially be an iron LS2 at that point and you would def. need to run 93 or severely hamper timing in the tune which is a waste. Best bet is to do like I did and you'll be right where you want to be with the right cam choice. I'll bet with just a light deck on the block to true them up, you'll be very close to zero deck and then you can run a ~.04ish thickness gasket to achieve your desired compression as well as have proper quench.

 

Thanks for the input fellas.

I have never built a LS motor as this is the first. I have built several sbc and bbc. It does appear that the LS motors have a different feel to them by it appears that the pistons stick out of the hole or are very close as compared to the tradational .025 uncut deck of a sbc and bbc.

Several reports on here and a google search rendered that most lq4's pistons stick out of the deck at .006 to .008. Is that true or are the pistons in the hole a little as BottledSausage is reporting?

If the pistons are out of the hole that amount with the 4.080 and .051 gasket then the quench is going to be right at .043 to .045.

Im assuming the pistons we have talked about receive a 0 for reliefs, since there are none. For example in the old sbc, a -5 flat top piston.

I can then see that that combo would be very 87 octane friendly.

However, if the pistons are down in the whole a tad, would it be cheaper to switch to a different gasket such as the Fel Pro 1041. Its thinner and has a bigger bore, so you can control the quench and compression ratio better to acheive the need for 87 octane.

Here is a link to the two gaskets.

http://www.summitracing.com/parts/fel-1041/overview/

and here is the chevrolet ls3 gasket we are talking about

http://www.summitracing.com/parts/na...0046/overview/

 

ALL the Piston in all the Iron motor LS based engines stick out of the hole about that much.

They all have the same compression height.

 

On looking for a piston then.

A compression height of 1.338 is what your looking for?