Thread: Quench Questions

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Hey guys, I did a search of quench and still have questions. I am assemblying a 40 over 5.7L sbc for my daily driven '86 shortbed GMC pickup. My Speed Pro flat top forged pistons are .028 down in the cylinder. With 64cc Alum heads, 6.10 dish, and a .040 head gasket my compression ratio is a street friendly 9.65. I'm worried about the .068" quench factor. My machinist says I have nothing to worry about. My search reveals you guys say anything over 040 is asking for trouble. Doing a spec. search for a '78 5.7L shows a deck height of 9.0315" and piston protusion of .025" below deck. Am I reading this as a stock quench of.065"? Should I go with .015" steel head shim in a street truck?
Thanks

I would be more concerned with brinelling (fretting) the aluminum heads using a thin steel gasket. Airflow Research recommends the Fel-Pro 1003 with their heads on a 350, so that's what I would use on AFR heads. They're 4.166" X 0.041" and you're correct, the squish won't be ideal until you cut the decks for zero piston deck height. Will you get by with it? Yeah, with aluminum heads and 9.65:1 SCR. Will it be as good as it could be? No.

David Vizard runs his motors at 0.035" and has said that he picked up power all the way down to that point. I suspect he would go tighter yet, but might be concerned about experiencing a piston/head collision.

You didn't say the manufacturer of your heads, but bottom line, use the gasket recommended by your cylinder head manufacturer and tailor other engine parameters around that (like cutting the decks for better squish).

Hey Tech, thanks for the reply. The heads are Patriots. They reccomend using FelPro #1004 that have a compressed thickness of .041". When reading about quench it seemed that high quench (.069") is considered distructive i.e. major detonation. I really don't want to zero deck the block for this build unless I need to. It has already been squared/leveled.

"It has already been squared/leveled."

Apparently it hasn't been squared/leveled enough to get a good squish. You are the owner of the parts. You can do with them as you wish, but if they were mine, I'd make certain everything was right before I began screwing bolts and nuts together. What's the compression height on your pistons? A good 350 piston should be at 1.560+. If the pistons are at that, I'd cut the block decks to zero. If the pistons are short, getting the correct pistons would put you a little closer. I personally wouldn't mind so much being at 0.050" with aluminum heads, but that's where I'd draw the line. All top builders will tell you the same thing.....0.035" to 0.045". David Vizard currently uses 0.035" and I don't think there is anyone on the planet who has more dyno time on small block Chevies than he does.

if you used a BHJ tru deck you have to cut more then 010 off the decks to true them up some of the hyper and stock pistons seem to have a lower ch some of the last sbc i was cutting the decks to 9.010

Hey guys, the compresson height of the piston is 1.563" according to the manufacturer. I'm at fault for not telling them specificly to zero deck the block. I did tell him that I wanted 10:1 CR though. Regardless it looks like I will now have my block decked AGAIN. Oh well, at least we caught it before assembly. Until I started reading these forums I would have just put it together and then start searching for the reason it didn't run right.
Thanks for being here for guys like me.