Quench clearance, a little help here?

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Post  AUDIOADDICT02 on October 24th 2013, 3:06 am

What's up guys, here I go with more questions about my engine build.

So as some of you may know, my engine is so close to being done & fired up, but before I do that I want to get some things cleared up since I'm losing sleep trying to decide what to do....now I know that "quench" is as
essential as it gets on an n/a motor..

So my engine is "zero decked", & my combo puts me at 9.83:1 scr & 8.6 dcr with .038 thickness gaskets.
BUT, I currently have a pair of Cometic mls gaskets .051 thickness which put me at 9.6scr & 8.4dcr..

So my question to you guys would basically be: should Igo with a more extreme dcr with tighter quench, or a lower dcr & more quench clearance? I know 35-45 quench clearance is ideal, so how much difference would .006" make?

Which option would you guys go with? It will be run on 91 octane at all times...


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Post  dfree383 on October 24th 2013, 4:13 am

.038 is a little tight on anything with a large bore, the lower side of the range you have given is for typical small blocks IMO. I'd get some .042 Felpros and run it.
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Post  AUDIOADDICT02 on October 24th 2013, 4:24 am

Ok, good to know, I was kinda skeptical since I have actually seen cases where the piston "kissed" the head.
I guess I'll go with some .041"s since they're readily available.
Thanks for the help!

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Post  LivermoreDave on October 24th 2013, 9:25 am

Dave offers a good point as to the bigger bore issues and piston rock. I too believe if the deck/piston measurement is done correctly the distance between the piston and cylinder head will be satisfied. Another check should be performed of the valve (depth & radial) clearance as well. I suppose if a piston is exposed to long service intervals and/or numerous high engine speeds the piston skirt/cylinder wall dimension can increase with wear. Also a piston with less integrity may deform and add to the piston/cylinder head problem. One area I do believe in is the tighter quench will assist with detonation control. Switching from (I assume) a steel shim gasket to a composite or visa versa, the cylinder head and block mating surface may require different textures for quality gasket sealing.

Just another opinion,
Dave.

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Post  Super Snake Steve on October 25th 2013, 9:12 am

Reading this has got me thinking where would one start measuring at to figure out what thickness gasket to use to get quench at its best

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Post  IDT-572 on October 25th 2013, 4:11 pm

Always measure on the center line of the wrist pin. As Dave and Dave have said your .041 Felpro is hard to beat.
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Post  Super Snake Steve on October 25th 2013, 4:49 pm

Can you do that with the pistons in you would have to know center of worst pin to top of piston witch I think the pistons have a number stamped on top maybe look that up and see what the specs are

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Post  Super Snake Steve on October 25th 2013, 4:52 pm

Thanks for all the info I just got this thing apart and I have a lot of irons in the fire on info. But I'm going to get it together right this time

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