Problem with excessive quench dimension.

[fdicrasto]

Been curious as to what issues I am going to have with this excessive head to piston quench area dimension. .065" clearance and can't change until pistons are flycut at next teardown. Sbc, 421" w/ 18 degree Chevy heads. 15:1 static C.R. 3.80" stroke w/ 4.185" bore. Going to dyno soon and looking at 8-8200 max rpm. Never had to deal with this on NA application before. Will be using VP C14+ fuel.

[Frankshaft]

Honestly, nothing. It may want a bit more total timing. To be honest, it's quite possible at 15:1, it may be an advantage. I have had engines where I went from .041 thick to .051 thick head gaskets. It actually worked better. With high efficient chamber, and the high compression, it just may surprise you. I know that may be a contradiction to the norm, but it will run just fine. I would probably use a better fuel for 15:1 though. Why not some q and pick up 15-20 extra hp. Sorry, just saw your using c14, I had c12 on my brain. Still, I would use the q.

This should get interesting though, I am sure we will have another20+ pages of replys. Ranging from OH MY GOD, it will rattle the pistons out of itself idling, to, it won't even run, to, it will be down at least 50hp. Dang it, I can't find the imogi eating popcorn.

[joespanova]

I wouldn't worry about it either. But if you're asking this question NOW , why wasn't it addressed at assy?

[statsystems]

Honestly, nothing. It may want a bit more total timing. To be honest, it's quite possible at 15:1, it may be an advantage. I have had engines where I went from .041 thick to .051 thick head gaskets. It actually worked better. With high efficient chamber, and the high compression, it just may surprise you. I know that may be a contradiction to the norm, but it will run just fine. I would probably use a better fuel for 15:1 though. Why not some q and pick up 15-20 extra hp. Sorry, just saw your using c14, I had c12 on my brain. Still, I would use the q.

This should get interesting though, I am sure we will have another20+ pages of replys. Ranging from OH MY GOD, it will rattle the pistons out of itself idling, to, it won't even run, to, it will be down at least 50hp. Dang it, I can't find the imogi eating popcorn.

I agree. Quench gets way too much love. The OP will not have issues.

[Carnut1]

Many of the Mopars has horrendous quench clearance and they ran pretty well. I always considered a tight quench good for low rpm torque, reduced timing at low rpm, increased detonation resistance at low rpm and throttle responsiveness. After the rpms get going the chamber turbulence is high enough that turbulence from the tight quench is less effective. JMO

[mag2555]

If that 15 to 1 level of compression is had without restricting flame travel then you will have more mixture turbulence taking place then if you had a flat top piston with .035" quench, so I would not bat another eye at it as it's a non issue, and as posted start off with 2 degrees more timing than you normally would and run a timing loop!

If we where talking about looking for max torque below 3K out of a motor then that .065" would be a possible detractor , but not with a power band of 6500 to 8000!

[fdicrasto]

Appreciate the feedback and definitely feel at ease about it. The other 18 degree heads went on another engine and these(46cc) were a last minute replacement with the PTV clearance a problem so the .020" thicker head gasket. Thanks again.

[Tuner]

Anybody who thinks tight quench is irrelevant must have never spent time tuning the same engine before and after the quench clearance was qualified.

[ptuomov]

Anybody who thinks tight quench is irrelevant must have never spent time tuning the same engine before and after the quench clearance was qualified.

Where does it make a difference?

I haven't experimented on it, really, but have a squish band on the motors because of my belief (not a fact) that it makes low rpm, part throttle, and off boost combustion better. I believe (don't know) that at full load and high rpms, especially when turbocharged, squish band isn't really needed. But again these are not facts, these are beliefs based on theories and whatnot. And the engines I'm thinking about are four-valve pentroof heads.

I think this is separate issue from making the combustion chamber more compact and the plug as close to the center of it as possible. If doing that results in squish or squish-like shapes, that's not really squish that's doing the work. Right?

[lance flake]

I took and engine apart once that was suppose to be a 393 Windsor. When we pulled the head off the piston looked to be down below the deck 1/8 inch or so. Upon further disassembly found it was a stock stroke Windsor crank and rod length with a 302 piston! Suprizingly the thing ran pretty well. It was kinda sluggish on the low end. I think it ran like a 7.00-7.20 1/8 mile in a fox body mustang.

[statsystems]

Anybody who thinks tight quench is irrelevant must have never spent time tuning the same engine before and after the quench clearance was qualified.

Actually I have. Both on SBC's and small block Chrysler's. I found zero. Nada. As long as the actual CR stayed the same there wasn't any difference in power.

If you are talking about emissions, that I do not know. What I do know is guys (especially the Chrysler guys) were squealing for quench to be like the Chevy guys. So they paid the price for nothing.

[gottago]

On a 12.5:1 sbc approx. 60 thou quench I pinged under low rpm load. Street driven. No other changes except head gasket, now 38thou quench, no pinging even have vacuum advance operating. No difference at upper rpm on either..

[statsystems]

On a 12.5:1 sbc approx. 60 thou quench I pinged under low rpm load. Street driven. No other changes except head gasket, now 38thou quench, no pinging even have vacuum advance operating. No difference at upper rpm on either..

You changed the CR with the thinner gasket if you didn't do anything else.

[gottago]

True, but it was then with the higher compression when it became more ping resistant. If compression alone was the determining factor that should not result.

[af2]

True, but it was then with the higher compression when it became more ping resistant. If compression alone was the determining factor that should not result.

That is a proven...