Is .074 an abnormally large quench for a factory set up? That seems like an awfully large gap to me. What are some common quench numbers from other factory engines?
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1991 Coupe - 6 Speed - Black on black - 11.37 @ 122.88 -
If that is the total of the deck clearance and gasket thickness specs, then it is likely even worse. Blocks are often taller than the 9.025" blueprint number, and that results in a greater than the target .025" deck clearance. The "spec" quench on the '85 is (.025 + .021 =) .046", but I'll bet few are very close to that.
I once pulled the heads off an early 90s 350 to upgrade the heads and cam. We found .040" head gaskets with the pistons .031" down the hole. Since the engine had always run well, the owner didn't want to take it apart to deck it, so we reassembled using .028" gaskets.
I can tell you it has no detonation and runs like a scalded ape with ~9.3:1 compression, Dart Iron Eagle 180s, and a 208/221 ZZ4 cam.
When I reringed my 86 I found the pistons .030" below the deck and it had a .041" head casket. I reassembled it with FelPro 1094 .015" gaskets. It runs great and no knock counts on 87 Oct.
Location: So Cal- - Defend your ideas with facts. Not personal attacks.
You need to know both deck hieght and compressed hieght.
There's a critial number called compressed hieght of the piston. It tells u where the top of the piston is with respect to the center of piston pin. I was surpized to find mine lower than expected and instead of the .040" quench height i plan for i really have .060". I had installed the .015" FelPro gaskets thinking my stock deck was 9.025" and the stock flat-top pistons where only .025" down the hole - not. Well years later i found the correct piston part number and correct compressed height - my piston tops where really .045" down the hole. Only fix is to deck the block or replace the pistons. But heck my c.r. is only 8.8 and quench not really an issue. U have >9.2 c.r.? If not then not really that important. And really all quench really helps is prevent detonation. What i'm saying is good quench will allow you to run another .5 to 1.0 c.r. on pump gas. .045" quench height allows u to run 9.5 c.r. with iron heads and 10.5 c.r. with aluminum heads.
But ya know if your using NOx quench may not be as important. NOx accelerates the fuel burn much better than any squish from quench will. More important with NOx is to retard timing, maximize the exh port, reduce exh back press, increase exh vlv duration.
Hope this helps.
cardo0
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74 T-top, L-48, 4spd, A/C, narly blue. Goodwrench 350 underwent new heads (SR Torquers), Schneider solid cam and Thorley headers due to domino effect of broken motor mount >broken fan shroud>remove radiator & A/C package. Now runs a Performer Air Gap with a lars majic chokeless Qjet on top. Also Street dampner, MSD dist, 6AL and Baster II. http://members.cardomain.com/cardo0
Location: Mississauga, Ontario I know all the answers it's the questions I don't understand
I would not worry about qyench unless you are building a true blueprinted racing peice. FOr the street if it runs good on the octane you want to use, then fine leave it at that. The general built 100000000000000000000000 engines with over .060" quench and not one person returned his new car because the quench was not tight enough
Mt 11:1 cr 406ci runs perfect on 91 octane and makes 550HP with ~.060" quench. I measured everything and for my buildup it was very hard to get the quench any tighter. You start to run into piston to valve clearance problems with bigger lift cams. I talked to my machinist about it and he told me to just leave it at .060" and pretend I have .040" and I wouldn't know the difference
__________________ 1980 Corvette, 427ci Motown SBC 465RWHP N/A so far,500 is the goal, AFR 227 Eliminators
T&D Shaft Rockers,Vic Jr, XR286R solid roller,248/254 dur .640" lift 10.6:1 Mahle pistons
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Quote:
Originally Posted by C4Techie
You seem to be quite excitable, at the least. I have responded to Neat, and will do so again if he desires further discussion. Meanwhile, it is evident, that you had nothing worthwhile to contribute either in your text or your signature.
C4Techie, it's best just to ignore this guy. And CFI-EFI has forgotten more than this guy will ever know.
Neat, it's rare for factory set-ups to provide optimum quench. They just have too many other design factors, goals and of course the number crunchers to contend with, to be able to worry about it. But if you can easily design it into a build, do so. It limits detonation because it improves combustion efficiency. This also enhances power of course and increases fuel mileage. People think I'm full of it when I tell them what kind of mileage I'm getting with my 388 LT1. And it'll get better yet because there's still fine tuning to do. My quench is at .041"
C4Techie, it's best just to ignore this guy. And CFI-EFI has forgotten more than this guy will ever know.
What did I miss??? Things must have gotten interesting while I was away. Did CFI-EFI and/or I get a dose hostility? My my!
I am not familiar with the "critial number called compressed hieght of the piston". I can't imagine how one compresses a piston in order to measure it's "compressed hieght". The "compression height" of the piston is the distance from the centerline of the piston pin to the top of the flat (deck) of the piston. One little tidbit of uncommon information is that stock, replacement, pistons are "decked" .010" or more, so the catalog information for a stock piston does not accurately apply to what the factory installed. Just another good reason to MEASURE the piston to the top of the block dimension rather than read about it. Not all pistons are created equal, nor are blocks. Neat, you are smart to be measuring.
Corvette Store
Is the quench on my 91 L98 really .074?
Only fix is to deck the block or replace the pistons. But heck my c.r. is only 8.8 and quench not really an issue. U have >9.2 c.r.? If not then not really that important. And really all quench really helps is prevent detonation. What i'm saying is good quench will allow you to run another .5 to 1.0 c.r. on pump gas. .045" quench height allows u to run 9.5 c.r. with iron heads and 10.5 c.r. with aluminum heads.
My quench is at .041"
