Minimum quench in BBC?

[Old School]

I am assembling a 454 BBC that will be a street engine and raced on grudge night at the local strip. With the piston rocked so the quench side is at the highest the outer most edge of the piston deck is .007 out of the cylinder. With the piston rocked so the quench is at its lowest the piston deck is .005 in the cylinder.

I was wanting to use a .039 gasket but now I am not so sure. The max rpm's will be 6500. The car has an excellent cooling system. Rods are Scat H beams. Rod clearance is .0028. Piston to wall clearance is .008. I know that is too much but you use what you have in some cases.

I was wanting the increased benefits of a tight quench. I do not want the problems of a piston hitting the head. Should I just put a .051 gasket on and play it safe. Compression will be 10.5 with the .039 and roughly 10.25 with the .051? The pistons have been coated so that rules out milling a few thousands off the quench.

Thanks for any help.

[af2]

I am assembling a 454 BBC that will be a street engine and raced on grudge night at the local strip. With the piston rocked so the quench side is at the highest the outer most edge of the piston deck is .007 out of the cylinder. With the piston rocked so the quench is at its lowest the piston deck is .005 in the cylinder.

I was wanting to use a .039 gasket but now I am not so sure. The max rpm's will be 6500. The car has an excellent cooling system. Rods are Scat H beams. Rod clearance is .0028. Piston to wall clearance is .008. I know that is too much but you use what you have in some cases.

I was wanting the increased benefits of a tight quench. I do not want the problems of a piston hitting the head. Should I just put a .051 gasket on and play it safe. Compression will be 10.5 with the .039 and roughly 10.25 with the .051? The pistons have been coated so that rules out milling a few thousands off the quench.

Thanks for any help.

My rule of thumb is .010 per inch and has never let me down N/A. I would definitely use the .051 gasket for the minimum. If you use NO2 you have to give it more IMO.

[540 RAT]

A buddy of mine runs his 540 at .028 quench and the pistons just ever so barely kiss the heads, but no noise from it, so it is just exactly there. And he turns 7,000 plus and runs 9.90 at 141 or so. In other words, he is getting max benefit, with nothing left on the table. I seem to recall his piston clearance is around .0045, so they don't rock maybe as much as yours, but you may still be OK.

If you look at your measurements, per Reher Morrison Racing Engines' method, you have a calculated piston deck clearance of .001 out of the hole. This is from simply averaging your measurements. So with an .039 gasket, that leaves you with .038 quench. And the generally accepted guideline is .035-.045 with steel rods, so you should be good to go as is with the .039 gasket. Using the .051 gasket will put you out of the sweet spot of tight quench benefits. Just let it warm up fully before you redline it, and you should be fine. Initially work your way up the rpm range, and if it hits, it will just be a rattle, and won't kill anything. And you can always go back and change the gaskets if you really need to.

My 540 runs .006 piston clearance and I set it up for .037 quench. It isn't running yet, but I want to get all the quench benefits I can. Even at that, it is rather conservative compared to my buddy's motor.

[bsfc9]

Check your piston rock measurements on the other side of the piston(plug side) also, it is not too uncommon for one side to be different than the other. Now check all your pistons in their respective holes. Make sure everyone is safe. Running this tight of quench requires everything to be exactly correct. I have pulled apart many BBC from a wide variety of builders(some good, others not so much) and it is not too unusual to find engines with really tight quench(under .045) to have pistons "kissing" the head. This is not good and can be quite serious. It can and will kill things. How tight can you run the quench on a BBC? IMO it depends on RPM, piston weight, rod design, and stroke length to name a few. Now I am not claiming this is gospel truth, just relating what MY hands on experience with competitve(super comp, super gas) big inch BBC's have been. I have had great luck running SBC's really tight(<.035) over 8000rpm with no problems. BBC's seem to be a slightly different animal. I have had the best luck with .045-.051.

[bigjoe1]

I have never seen any majic in the super tight quinch.The differance from 040 to 050 does not make anymore power. Why bother ?? The only time this stuff is really important is when you only have 9 to compression ( or whatever )When you have enough compression, the last 010 does not do anything.
JOE SHERMAN RACING

[Wolfplace]

I am assembling a 454 BBC that will be a street engine and raced on grudge night at the local strip. With the piston rocked so the quench side is at the highest the outer most edge of the piston deck is .007 out of the cylinder. With the piston rocked so the quench is at its lowest the piston deck is .005 in the cylinder.

I was wanting to use a .039 gasket but now I am not so sure. The max rpm's will be 6500. The car has an excellent cooling system. Rods are Scat H beams. Rod clearance is .0028. Piston to wall clearance is .008. I know that is too much but you use what you have in some cases.

I was wanting the increased benefits of a tight quench. I do not want the problems of a piston hitting the head. Should I just put a .051 gasket on and play it safe. Compression will be 10.5 with the .039 and roughly 10.25 with the .051? The pistons have been coated so that rules out milling a few thousands off the quench.

Thanks for any help.

=
To answer your question directly
In my opinion if this is the highest piston you should be fine with the .039 gasket but you are pretty close.
I have run less but not with .008 piston clearance
Many moons ago I ran a 482 to about 8500 with .039 gaskets & the pistons .005 out & I typically run 540's at -005 to zero with the .039 gasket with no issues & .0045-.0055 piston to wall clearance.

Yes in the 482 there were sometimes marks on the heads & no it never hurt a thing,
I ran this engine in three different cars & ended up selling it to a boat guy

Not recommending that you try this but I do know for a fact just touching the head did not hurt a thing.

Keeps the rods from stretching,,,

[63 Nitrous Ratt Vette]

Keeps the rods from stretching....... very funny Mike !!

[Ed-vancedEngines]

I will definetly tellyou that a .010 above deck and a .038 head gasket w/ 7/16 rod bolt LS-7 Rods TRW L-2307AF pistons with .008 piston to wall, will almost work. If you turn any high rpm it will give a little head gasket leak because of the pistons hitting the heads.

I agree with Joe. Be safe and use the .051 gaskets.

Ed

[Cris]

Joe:

I thought the reason people ran tighter quenches was to suppress detonation, allowing higher compression ratios and therefore more power. I know this is street stuff where you are octane limited, but does this make any sense?

Cris

[bigjoe1]

My experience is that you still get all the same bennifits of the tight quinch with up to 050 or 055. There is NO reason to take a chance with hitting the head because it will work just as well with 005 or 010 more room.
JOE SHERMAN RACING

[Cris]

Thanks Joe!

[1bossnova]

Chris

I respect Joe's advice but I would have to disagree with him on this one. In all of my testing a tighter quench (I.E. .030 to .035) is always worth more power. On a street engine with a small cam shaft (236 to 244 @.050)is where you will see the most power gains. On the typical 383 SBC a tight quench is good for 25 to 30 ft lbs and 10-15hp.

My 2 cents

[af2]

My experience is that you still get all the same bennifits of the tight quinch with up to 050 or 055. There is NO reason to take a chance with hitting the head because it will work just as well with 005 or 010 more room.
JOE SHERMAN RACING

Bossnova. Would you rather have a piston touching the head or sleeping at night because it won't?
You are correct on the #'s but what happens when the skirt decides not to not like the .008" and becomes one with the head?
Just a thought and no more.

[Ed-vancedEngines]

Ok guys,
This can be a littloe sticky, becuase all engine combinations and components are not shaped the same or made the same or assembled the same with the smae exact combinations.

What a bunch of worthless words. lol.

Some engines can better benefit from more enhanced quench/squich charastics than others need. Joe is correct that a .051 quench will still be plenty for what most of us will see any benefit from. I have seen benefits in certain combinations using a very tight quench and no benefit in other combinations doing the same thing.

In the listed combination in discusssion, I see no benefit to a severely tight quench at all. The disadvantages are piston hitting head and you lose head gasket seal or damage parts. . I do know for a fact that an exact accurately measured quench with a BB Chevy and big dome TRW Pistons will result in piston coliding with head at upper rpms when set-up at a .028 quench. IT will not work. .040 to .051 would be much better.

Maybe some of us do in certain applications with certain combinations do set things up for a very tight quench. WE who do have learned the hard way about what we can and can not do by over-pushing the limits. We know the limits becuase we learned the limits in an expensive learning process. All most of you should be doing is learning from our learning experiences and you not repeat those catastrophes we experienced in our learning curves.

For what it is worth, Mr Joe Sherman owned and drove the first barely streetable heavy Chevelle with a 468 cu in BB Chevy into the 9 second range in a 1970 Chevelle. Calculate the power needed to do that and know that he did that with old school heads and parts. So he does know several things about getting the 454 to run.

Ed

[MileHighMan]

Thanks guys. I've had this same question. [ so many different opinions ]. Since I see some agreement on this thread, I'm gonna take you guys advice. My new quench will be .045 plus. Again. I thank you all. Good Luck. Dan.