[ColeBalster]

I have a fresh build SBC with 4.155 bore/1.125" CH Wiseco Quick 8 Pistons and 8.995 deck. The pistons are out of the hole by .020". The piston to wall is .006" and I have steel 6.00" I-beam rods.

Do you think an .051" gasket and .031" quench is too tight. I'll probably shift around 8000-8200 and cross the stripe around 8300.


Cole

 

[bigjoe1]

YES--- 031 is TOO CLOSE


JOE SHERMAN RACING

 

[ColeBalster]

YES--- 031 is TOO CLOSE


JOE SHERMAN RACING

Joe, thanks for the info. It's good to see you on here. We spoke years ago and I bought a Isky cam and springs for my previous 406 with iron Bowties. I've always admired your work since I saw the brown Nova run against a Pinto at Pomona. It ran in the 9's with a NA SBC if I remember correctly.

What would you recommend as the minimum to run? I hate to give up compression, but if I have to, then so be it.

 

[Graphic Man]

i ran a .041 at 8500 and it did not touch but IMO .031 may be a little tight

 

[CNC BLOCKS]

I have a fresh build SBC with 4.155 bore/1.125" CH Wiseco Quick 8 Pistons and 8.995 deck. The pistons are out of the hole by .020". The piston to wall is .006" and I have steel 6.00" I-beam rods.

Do you think an .051" gasket and .031" quench is too tight. I'll probably shift around 8000-8200 and cross the stripe around 8300.


Cole

Flat top cut the pistons or get a custom cometic gasket.

 

[cardo0]

I think u can find thick solid copper gaskets or possibly stack them. But from what ive seen the copper gaskets have a tiny amount of leakage. Not enough to really hurt the engine or combustion but u can watch tiny gas bubbles come out at the gasket. Best part is copper is reusable.

Heres some in different thichness: http://www.headgasket.com/gaskets.html

IMHO for 8300rpm u would want to be in wide end of the quench spec near 0.060".

 

[qtrpounder]

My 4.155 x 3.875 had .038-.040 and 2 pistons were touching the heads at 8400.

 

[Lobes]

I have a fresh build SBC with 4.155 bore/1.125" CH Wiseco Quick 8 Pistons and 8.995 deck. The pistons are out of the hole by .020". The piston to wall is .006" and I have steel 6.00" I-beam rods.

Do you think an .051" gasket and .031" quench is too tight. I'll probably shift around 8000-8200 and cross the stripe around 8300.


Cole

That's a little close. Probably, somewhere between .036 - .040 is going to be your magic number. Since you have to cut the quench area of the pistons anyway, start at .040 and work your way down.

 

[clevo]

If you have more than enough Piston to valve clearance take .020 of the pistons.

 

[ordinary builder]

I agree on at least .038" under the best piston / wall fit and proper everything else..
not much to be gained under .045" when relative compression is under 13 to begin with anyways...

 

[ordinary builder]

proper and accurate machine shop work should be able to hit the number within one / two thousandths.....

 

[Homespun91]

Keep in mind, the more piston to bore clearance, the more piston rock you have. Some skirt profiles rock more than others, too, IMHO.

 

[ordinary builder]

properly equipped shop should be able to cut the piston quench as others have said above...
and then u use the thin gasket....

 

[Lobes]

Rule of thumb. "Cold" piston to wall clearance should give you .001" piston to wall clearance with a "good" oil film at operating temperatures. Run the numbers.

 

[Mike Beck]

I am in a similar situation. Putting my wifes 383 together and after torquing down one head I fell the pistons hitting it when I turn it over. I took it apart to find all four pistons were kissing the head, but not at the quench, have plenty there. It is the side of the dome rubbing, close to the spark plug, about midway down the dome. I took a dremel tool with a small drum sanding wheel and started working on the chamber, especially near the spark plug, that area is far from flat across. Just removing a little bit at a time, reinstalling the head, no bolts, and I can see the head move as I turn it over. Got it to the point that with a gasket and half the bolts in it is all clear. I think I may want to do this without a gasket and see if it still clears. How much will the rods stretch? This is a 4.040 piston and steel rods, keeping it under 7200 rpm, mild Bracket Engine.

 

[bigblockmark]

It needs to clear with no gasket if gasket is at least .040" thick. You can use clay around the tight area to get a better look at what to work down. .060" clearance might be better.

 

[RCM Racing engines]

Just go to a cometic .060 and be done..............

I've run stuff at .027 already and the pistons just so slightly "Kiss" or "Polish".......
But you better have stuff right as far as clearances and such........

On higher rpm stuff I try to stay safe with .040 or so

I really like to run'em tight on low compression stuff...........

 

[HOT340]

Just go to a cometic .060 and be done..............

I've run stuff at .027 already and the pistons just so slightly "Kiss" or "Polish".......
But you better have stuff right as far as clearances and such........

On higher rpm stuff I try to stay safe with .040 or so

I really like to run'em tight on low compression stuff...........

The problem ive always had with measuring quench is actually measuring it accurately. If you measure above the pins its easy, but when you measure perpendicular to the pins, you have rock. Then you throw operating temps in, differnt piston material expansion rates, block expansion rates...how the heck can you say the quench is within a couple of thousanths on any combination. Seems almost impossible to measure with certainty.

 

[jbss71]

Summit shows a .06 4.200 gasket. I get mine from CV Products usually a few dollars cheaper than summit pro shop

 

[Lobes]

Just go to a cometic .060 and be done..............

Of course!