disco192

So this is my situation:

I have a 383 that is fully assembled ready to go in. Because of a dished piston, i decided to go with a .026" gasket to help compression, but now I am worried about quench. The piston comes up 9.005" and I am not 100% sure about how much the block was decked because I got it from a guy who built the shortblock. The guy said the block was "surfaced." What is a typical "surface" of a LT1 block?

I am just having last minute fears and dont wanna blow up this motor. If it was decked .010 then I should be fine with .036 quench, but any more and I am gonna have problems. It cant be decked more than .02 because that would bring the piston out of the hole.

Would .026 quench cause probems? I am running a cam with 236/242. The shortblock is a budget rebuild 383 (KB pistons, 6" scat I beams, Scat cast crank, total seal rings). I know .035 quench is the "minimum," but how set in stone is that? Is that just a safe zone, or can you push the limits a bit?

I just dont wanna tear this motor apart again unless I have to.

Thanks,
Stu

disco192

Im not sure what the differnece would be because I am not running forged pistons and I am running total seal rings. The KB pistons have less heat expansion than forged pistons and the rings are pretty tight.

Not sure how the Forged I beams would be any different than stock or forged H beams.

BTW I am planning on running about 6300 rpm

LT4orbust

are you saying it's .005 above the deck of the block

disco192

The total height of the piston from crank centerline to piston crown is 9.005"

I am not 100% sure about the deck height

captaindbol

Most often a "surface" is just whatever is required to true the surfaces of the block and correct any warpage or runnout. This will hopefully be less than .010. Only way to know for sure is to slap a dial indicator on it and measure. Measure every hole! A machining error can leave you with a nice clean deck surface and still not be parrellel to the crank centerline.

rskrause

Word! You need to measure the piston deck (on each cylinder) when assembling a new motor. Not only may the block deck not be parallel, you can't just assume that all the pistons have the correct compression height, etc. Anyone of a number of dimensions may be off.

The only way it is good to "push the limits" on that 35 thousanths rule of thumb is if the motor has been very carefully assembled with every relevant clearance correct and verified. For example, when you start trying to use very tight quench things like piston to bore clearance come into play. Pistons that are a little "loose" will rock in the bore and this can cause piston to head contact if the qunech is tight. But some people do build them as tight as 25 thousanths (with steel rods).

Rich

SStrokerAce

As captaindbol said, MEASURE IT! You can't know these things without measuring them.

On a Iron block motor your quench at full operating temp will shrink about .004-5", on an aluminum block it will grow that much.

http://www.ls1tech.com/forums/showth...fective+quench

That's a good thread about effective quench.

Bret

Frans96SS

well a sbc is 9.025 from the factory so if its 9.005 the its decked .0020...and if u have a .026 gasket then u will be at 31 quench which is alittle low i think....u would stay in the 37-42 range..

SStrokerAce

The LT1 block commonly measures out to a little higher than 9.025, usually in the 9.030-5 range.

BTW Stu, is the whole screename of yours related to the Disco Stu of the Simpsons? You know he doesn't advertise.

Bret

disco192

Yes, my SN is related to the simpsons. Disco Stu likes Disco music It goes back to high school.

On a serious note:

Would running Keith Black Hypereutectic pistons and total seal gapless rings made it any safer ?

He didnt say anything about zero decking the block... he just had it surfaced. What is a typical "surface"? If it is 9.03.. he could have had it surfaced 20 thousandths and it would still be fine. Is that more than average?

arnie

There isnt anyone (knowledgeable) here, that is gonna guess. Sounds as if you still intend to run it without actually checking/measuring the block. Typical? What is typical is to measure what ya got. Or better yet, have assembler's documented notes to verify clearances. All the guessing, thinking and calculating does mean squat. There is no point in patronizing you, by telling you what you want to hear. It may not be in your better interest, long term. Sure, more work, but what ya gonna do. You can gamble, or you can do the labor. Chances are, the assembler was aware it was ok to assemble. You wanna take that chance?

SStrokerAce

Arnie, thanks for that.

arnie

Bret, that wasn't meant to be derogatory, to you, or any of the others I consider knowledgeable. I was implying no one is gonna guess, or stick their necks out with assurances as to whether or not, what he's got, (bottom line) is adequate or not. Wasn't referring to the std. specs that are 'knowns', that were given. Anyway....

Stu, I've a suggestion, (seeing you'd rather no go thru any more labor than necessary - and it's hard to blame ya) that I would consider a compromise. If the engine can be put on, or is still on an engine stand, in lieu of removing a head, how 'bout removing the pan instead? Certainly not of the utmost precision, but should be close enuf to give you the insurance you are after. With the pan off, break loose one, or one on each side, or better of the lot, loosen one rod at each corner. Resnug up the rod nuts (or bolts) enuf not to be loose, and turn the crank over till a given piston is at TDC. Now give the nuts (or bolts) some slack and push the rod toward the head, while checking the amount of movement with an indicator. Oil and/or lube will influence the reading, but I believe this would still be reasonably close for what you are after, the quench clearance.

jdizzell

Didn't you get a blueprint sheet w/ your engine?

SStrokerAce

Arnie.... none taken. I was thanking you for telling it how it is.

Hell I would yank a head and check the dam thing if it was me.

Bret