Minimum quench in BBC?

[Strange Magic]

I read through most of the posts above and I don't believe anyone has asked the question if this is a dome or a flat top style piston.

If it is a dome I would suggest that you bore scribe the chambers and fit each piston accordingly if you don't have the room. If it is a flat top style piston than a steel rod with what you described should work out just fine at that type of rpm as you mentioned. From my experience another .005-.008 in the hole (assuming the compression ratio is still the same) will not really make any difference what so ever as Joe mentioned, although if doing so nets out a loss of compression that is significant than it will show up as a torque output loss.

I have also seen in cases that when a piston touches the cylinder head and harmonics are created, the engine will be down 8-15 hp depending on how severe it is crashing. Harmonics show right up in power losses.

[Old School]

Thanks for all of the replies. I have checked all of the pistons/decks and I have one rocking about .010 out. I will put the .051 gasket on and play it safe.

The slight loss of compression will not hurt anything with today's gas. The engine has the 990 heads and the old Chevy LS7 pistons similar to the L2307's Ed mentioned. There are no clearance problems on the dome side.

Thanks again. Billy

[540 RAT]

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

Hmmm, .028 will not work, you say. Geez as I said above, 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 rpm and runs 9.90 at 141 with no issue, for I guess a couple of years or so now. He also is a member of this forum. I won't give out his name, he can do that if he cares too. Maybe he'll chime in on this.

[Ed-vancedEngines]

Hmmm, .028 will not work, you say. Geez as I said above, 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 rpm and runs 9.90 at 141 with no issue, for I guess a couple of years or so now. He also is a member of this forum. I won't give out his name, he can do that if he cares too. Maybe he'll chime in on this

Those words were written for the purpose of being instructional not confrontational.

Perhaps two people are not measuring dech ht the same. Perhaps two people are dealing with a different amount of piston rock. Perhaps two people are dealing with different weight pistons. Bottom line is I strongly suggest to not do it, and in your post by your words you are saying that his is showing marks of piston contact. In his examples you are saying he ran in excess of 7,000 rpm, amd in my example I was running in excess of 8,000 rpm. So it looks to me that we are both saying the same thing here.

Before Fel-Pro came on the scene we used the factory recommended head gaskets made for Gm by Victor. They were red in color and had two little holes punched in a certain palce on them to distinguish them from the other Vistor gaskets made for OEM & replacemet. The part number was VictorCore 3868VC. IT had a compressed thickness of .038 and In that engine to begin with I had an accurate deck ht of .010 out of the hole. Do the math.

Now when I say accurate deck ht, I mean accurate. Back in those days we wasted too much time in making the deck ht to be exact with each other, the head chamber cc to be exact, the blocks to be honed with 180 degree water running through them as they were honed, and a lot of other useless tricks we all went away from. Accurate deck ht was achieved by measuring the piston on each side and intentionally making it taller than wanted so we could then accurateloy mill down the piston top to achieve our perfect combinations of perfect deck ht and perfect chambers to give us perfect engines. It was mostloy all wasted time, for the good it did. lol

Ed

[540 RAT]

Hmmm, .028 will not work, you say. Geez as I said above, 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 rpm and runs 9.90 at 141 with no issue, for I guess a couple of years or so now. He also is a member of this forum. I won't give out his name, he can do that if he cares too. Maybe he'll chime in on this

Those words were written for the purpose of being instructional not confrontational.

Perhaps two people are not measuring dech ht the same. Perhaps two people are dealing with a different amount of piston rock. Perhaps two people are dealing with different weight pistons. Bottom line is I strongly suggest to not do it, and in your post by your words you are saying that his is showing marks of piston contact. In his examples you are saying he ran in excess of 7,000 rpm, amd in my example I was running in excess of 8,000 rpm. So it looks to me that we are both saying the same thing here.

Before Fel-Pro came on the scene we used the factory recommended head gaskets made for Gm by Victor. They were red in color and had two little holes punched in a certain palce on them to distinguish them from the other Vistor gaskets made for OEM & replacemet. The part number was VictorCore 3868VC. IT had a compressed thickness of .038 and In that engine to begin with I had an accurate deck ht of .010 out of the hole. Do the math.

Now when I say accurate deck ht, I mean accurate. Back in those days we wasted too much time in making the deck ht to be exact with each other, the head chamber cc to be exact, the blocks to be honed with 180 degree water running through them as they were honed, and a lot of other useless tricks we all went away from. Accurate deck ht was achieved by measuring the piston on each side and intentionally making it taller than wanted so we could then accurateloy mill down the piston top to achieve our perfect combinations of perfect deck ht and perfect chambers to give us perfect engines. It was mostloy all wasted time, for the good it did. lol

Ed

Ed, not trying to be confrontational, just a bit surprised when someone says something won't work when it does work. I was wondering though what your method is for "accurately" measuring piston deck clearance, in case you are doing something different than the rest of us. Personally I try to be as accurate as I can, so I use a deck bridge and a dial indicator. Zero it to the deck, then rock the piston up as far as it will go with finger pressure, then rock it down as far as it will go with finger pressure. I record both the "out the hole" and "in the hole" dimensions, average them, then that is my piston deck clearance. That also is the method that Reher-Morrison calls for in their Pro-Stock engine building book. I'm not sure how you can do it any more accurate than that. So what is your method?

[Ed-vancedEngines]

Ok guy,
You are being confrontational. In other words you are arguing and I refuse to argue. It serves no constructive purpose for anyone to read posts of members arguing.

Yes you are mesuring Deck Ht correct. What has that to do with your friend's engine at all. I guess it does, only if you are the person who measured it. That is not the proceedures though that everyone uses. I talk to many different people and not everyone is measuring the deck ht the same.

Did you not read where I said we used to then use a milling machine to cut the tops of the pistons so that all decks of each cylinder was exactly the same. All pistons at exactly the same Ht is accurate deck Ht, and is a waste of time to do.

I can sit here and write some things I have done, but that does not mean I would be suggesting for everyone to try the same things. I have done some things and gotten away with it that could bite someone else on the butt.

I am done with this thread. Posts have been made answering the questions by some very informed engine builders and the original poster's question is answered.

Ed

[af2]

For some reason I have to jump in this fire! The .010 is the max. The piston rock has to be part of the equation period!! This has never let me down ever!!!!!!!!!!!!! I have never in 30 years seen a piston go less and survived? Crazy you want to set it at .028?????? With rock about .020! crazy!!! I don't understand!!!!

[540 RAT]

Ed, in case you are reading this, truly no confrontation was intended, nothing is further from the truth. Please don't assume that someone is being confrontational just because they try to make sense of something you say. The mere fact that I was trying to consider your input, shows that I respect what you have to say. I was simply trying to clear up the discrepancy between what you said and what my buddy is running. That's why I asked what your methodology was, we can always learn from others, no matter how much we know or think we know. I don't know you or your background, but you seem to be quite knowledgeable and experienced. But then my buddy who is also from Texas, you may even know him, is a respected engine builder in his own right. So when he tells me he had .028 quench, I don't question him, I take what he says at face value as fact. That's why I was trying to get to the bottom of this .028 works vs .028 won't work deal. They can't both be correct at the same time regarding high performance BBC's, since we are comparing apples to apples. Since I have not finished my 540 yet, it could potentially be of tremendous value to me, if something new were to come out of all this discussion. Currently mine is setup at .037 quench (I have another buddy from New Hampshire with a 540 who has been running the same .037 without issue for a couple of years now, as well), with about .009 rock up and about .011 rock down as I recall, which I thought was fairly conservative since my Texas buddy does great with .028. But I'd be happy to learn something new if it is the real deal. It seemed to me that there could be good information come from all this discussion for others as well, who might have questions in this area. But since you are done with the discussion, I guess we'll never get to the bottom of it. That's a shame, and no one benefits. If you read through discussions on any of the Hotrod forums, you'll see that people most often have different viewpoints on things, just like we are here. That doesn't mean they are being confrontational, but simply expressing opposing ideas about things.

[af2]

540 I see what you are saying but I don't agree! you are going the extreme and no one wants to go there! That is what ED is talking about!
If you built a motor for someone else and it failed because the tolerance was held to tight and the real #'s came into play. You are going to buy the person another motor period!!!
Not a good thing unless you are in the R@D and everyone knows what is is involved?

[540Hotrod]

WOW...isn't this fun???

OK.....I'm the controversial one here I suppose.

My motor is nothing fancy.....Merlin block with .009 positive deck....measured just as you all say. Might be a hair more since it's been running for quite a few years and surely has some piston/wall wear going on. It has .0045 wall clearance with SRP pistons. I did have to clearance around the edge of dome and chamber a little though to clear with the positive deck height.

My deck is .0005 shorter on one side than the other...but hey....that's as close as we messed with it to make it *perfect*.

The head gaskets are Ferrea's that compress to .037. That's a measured .037....numerous times measured....not what's printed on the package.

The pistons just slightly polish the head and piston....can't really feel it...but you can see it. So far no issues with ring seal, bearings etc....but I know I'm pushing the edge. The reason I measure the head gaskets so much when assembling is that I know there is no tolerance to go tighter.

Last dyno session printed 825.1HP at 7400 rpm. I've since changed to a smaller cam that moved powerband downward some and car is faster with it that way. But it still routinely spins 7200-7400 rpm. It has a 4.40 final drive ratio now with 10x28's and traps over 141 mph. You can do the math. The newer gearing combo that has me in the low 7000's range would probably like the old cam better...but at the time it had a 4.08 final drive ratio and RPM's were a lot less....while still running 141 mph though the traps. The car has 3.07 rear gear with a G-Force 5 speed used a 4 speed at the track...and 5th is 1 to 1 for cruising.

It runs on 93 octane...race gas gives it no improvement at all with only 11.06 compression.


Now would it really matter if I had .037-.040 in it? I dunno...I doubt it...but it works well this way and I'll leave it alone. I agree....you build them to whatever comfort level you feel with them.


Thanks,

JIM

[af2]

540 every thing you said was from my motor, as in yours. Would you build the exact same motor for a customer is my question??
That is what I feel is the real question and not what you can get away with it's you're motor but what the average one will race day to day and can't check things that a builder will do and usually make them mad saying the clearance is too tight we have to address that!!
I am trying to give the difference between an owner builder and a builder non owner sense on things.

Why the name change!

[Ed-vancedEngines]

Ok guys you have drwn me back into this, but not to argue. I refuse to argue. Yes' I do read most if not all of the posts on this board or I try to. As one of the moderators it is also part my responsibility to keep the forum clean and git rid of the trash and to keep sure things go as they should on a professional board.

All of that said, I will do my best to come back tonight and hopefully be more descriptive of how something can work ok for your friend and not have worked well for me. I would love to know who the engine builder in Texas is you are talking about. I do know many of them and also their building traits. I can only think of but 5 including myself that like a tight quench and one of them does not do it with but his own personal engines.

It also looks like we picked up a new face using the nick of 540. That is ok too. We are all in this hot rod jungle together.

See ya later tonight I hope.

Ed

[af2]

Ok guys you have drwn me back into this, but not to argue. I refuse to argue. Yes' I do read most if not all of the posts on this board or I try to. As one of the moderators it is also part my responsibility to keep the forum clean and git rid of the trash and to keep sure things go as they should on a professional board.

All of that said, I will do my best to come back tonight and hopefully be more descriptive of how something can work ok for your friend and not have worked well for me. I would love to know who the engine builder in Texas is you are talking about. I do know many of them and also their building traits. I can only think of but 5 including myself that like a tight quench and one of them does not do it with but his own personal engines.

It also looks like we picked up a new face using the nick of 540. That is ok too. We are all in this hot rod jungle together.

I call it collective criticism and it is good! You have to read a couple of times to see what they said but when you realize it it is good!

See ya later tonight I hope.

Ed

[540 RAT]

:D 540 every thing you said was from my motor, as in yours. Would you build the exact same motor for a customer is my question??
That is what I feel is the real question and not what you can get away with it's you're motor but what the average one will race day to day and can't check things that a builder will do and usually make them mad saying the clearance is too tight we have to address that!!
I am trying to give the difference between an owner builder and a builder non owner sense on things.

Why the name change!

I guess at this point I should clear something up. I am 540 RAT from Southern California. My buddy Jim, from Texas, with the .028 quench 540, is 540HOTROD, two different people, not a name change.

[af2]

:D 540 every thing you said was from my motor, as in yours. Would you build the exact same motor for a customer is my question??
That is what I feel is the real question and not what you can get away with it's you're motor but what the average one will race day to day and can't check things that a builder will do and usually make them mad saying the clearance is too tight we have to address that!!
I am trying to give the difference between an owner builder and a builder non owner sense on things.

Why the name change!

I guess at this point I should clear something up. I am 540 RAT from Southern California. My buddy Jim, from Texas, with the .028 quench 540, is 540HOTROD, two different people, not a name change.

Good deal!