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Username Post: Stock deck height / quench of a chevy 350 ?        (Topic#13889)
Bob_T 
Senior Member
Posts: 469
Bob_T
Loc: Tucson, AZ, USA
Reg: 10-28-00
Re: Stock deck height / quench of a chevy 350 ?
02-15-02 11:21 AM - Post#92358    
    In response to

I don't think a deck height of .050" is unusual if the block hasn't been decked before. I'm in the same boat as you (maybe worse, I'm re-using the dished pistons that are currently in it), I have a 350 that has the same .050" deck height along with dished pistons, not exactly ideal from a quench standpoint. My intentions are to check all clearances and put it back together with new rings and bearings (so far so good). I'm trying to minimize the cost on mine so I'm putting it back together with a .020" gasket. This setup is against my better judgement but I'm using parts I have on hand as much as possible to minimize costs.

I don't think milling the block .050" will create any problems, I think (somebody correct me if I'm wrong) most of the SBC blocks out there with standard pin height pistons and zero deck height have probably been milled a total of about .050" somewhere along the line.

 
the_gman_69 
Senior Member
Posts: 445
the_gman_69
Loc: Artesia NM
Reg: 07-12-01
Re: Stock deck height / quench of a chevy 350 ?
02-15-02 11:32 AM - Post#92359    
    In response to Bob_T

Some rebuild flattop pistons come with a lower height. I think they say its to keep the compression from being too high. That is backwards for us hotrodders. If your talking about the pistons that came in that block from GM then that does go against the grain a little. Maybe they just don't come from the factory with the optimum quench.
1969 Camaro small block street car 11.37 @ 119 (no nitrous)


 
Anonymous 

Re: Stock deck height / quench of a chevy 350 ?
02-15-02 11:54 AM - Post#92360    
    In response to the_gman_69

Older stock engines used .020 compressed steel head gaskets, and combined with between .020 to .025 deck clearance, gave the proper .040 to .045 quench distances we seek. They knew the right way to do it even 45 years ago, it took others later, on to mess it all up.

Gasket manufacturers started the "thicker, pack type" gaskets to avoid problems with rebuilding leakages, and that led to the quench going right out the window of useability.

Silv-O-Lite started all this "destroked" piston bull, where the compression heighths were lowered .020 or so, and it just doesn't work. It is pheasable to get some really bizarre quench distances out of earlier engines when all the improper parts are compacted into one disaster package, like .020 "destroked" pistons, with a stock below deck of .025, rebuilt rods with .005 shorter overall length and a .051 compressed head gasket, ends up at a cool .101 quench, and nobody has the answer as to just why nothing will stop the detonation, no matter what the tune is done with.

They got away with it for a while, because the fuel was still relatively good, not like the mule urine we have to ateempt to burn now.

It isn't easy anymore getting the quench right. I prefer using the head gasket thickness to get the quench where I want it, but setting the deck to the piston top is OK as well, if done right.

Main thing is to get that quench between .039 and .045 on steel rod engines, and adding .010 to .014 for aluminum rod engines, so the whole disaster will come together and work right.

 
Bob_T 
Senior Member
Posts: 469
Bob_T
Loc: Tucson, AZ, USA
Reg: 10-28-00
Re: Stock deck height / quench of a chevy 350 ?
02-15-02 12:16 PM - Post#92361    
    In response to

quote:
Originally posted by IgnitionMan:
Silv-O-Lite started all this "destroked" piston bull, where the compression heighths were lowered .020 or so, and it just doesn't work.

I checked out a few piston websites and it looks like the two most common piston compression heights I see for a 350 with 5.7" rods are 1.560" and 1.540", or .020" difference as you indicate.

Check these sites out for examples:

http://www.kb-silvolite.com/slvpg29.htm

http://www.flatlanderracing.com/trwchevy350.html

(I should have done my homework before my first reply )

 
Anonymous 

Re: Stock deck height / quench of a chevy 350 ?
02-15-02 01:57 PM - Post#92362    
    In response to Bob_T

ttt
I think I know but just to be sure.
How do I measure compression height ?

Thanks for the help.

 
Anonymous 

Re: Stock deck height / quench of a chevy 350 ?
02-15-02 05:43 PM - Post#92363    
    In response to

From the center of the pin to the flat edge of the piston top. Since it's difficult to locate the exact center of the pin hole, measure from the top of the hole and add half the diameter of the hole.

I ran into the same thing, a crazy deck height. Turned out the engine had Silv-O-Lite cast pistons instead for the TRWs I was told it had. One piston even had "TRW" hand stamped on the top but they actually were Silv-O-Lite rebuilder pistons. I was rather pissed.

------------------
Pat Kelley
67 El Camino, 66 El Camino
Car specs, CR Calculator and DCR Calculator

[This message has been edited by Pat Kelley (edited 02-15-2002).]

 
Anonymous 

Re: Stock deck height / quench of a chevy 350 ?
02-15-02 08:33 PM - Post#92364    
    In response to

I use a lot of Silv-O-Lite and KB 305 pistons in my 215 Buick/Rover engines, both compression heights, to adjust for different stroke cranks used.

In my case, it works out, but for most, the "destroked" pistons are just a pain if you are unlucky enough to get the wrong ones.

 
Anonymous 

02-15-02 10:25 PM - Post#92356    

I under stand that I should try to get the quench height to about 0,040. But my 350 from 79 has a deck height of 0.050 + 0.040 gasket =0.09 quench. Maybe GM used thinner gaskets at factory but quench would still be around 0.07 did GM make it wrong ?
If I mill my block 0.050 to acheive 0.0 in deck height will my intake ports and intake bolt holes line up afterwards ?
If I use the 1094 felpro shim gasket do I need to retorqe it after a few miles ?



 
Anonymous 

Re: Stock deck height / quench of a chevy 350 ?
02-15-02 10:36 PM - Post#92357    
    In response to

That's wierd! Maybe when you measured the deck height the piston(s) weren't perfectly at TDC??? If you were going by the harmonic balancer to tell you exactly where TDC was, that could be your problem. The dampner is just pressed together with a rubber bushing in between, they can slip and give incaccurate readings.

------------------
1972 Chevrolet Nova 307 block 305 heads(9.6:1) Crane 272H single pattern cam Summit HEI Edelbrock S.P.2-P. intake Edelbrock 600 swirl torque carb. spacer aluminum H2O pump Flowtech headers dual exhaust w/ h-pipe ladder bars

 
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