Effect Of Quench On Detonation Question

[97 6speed z]

Okay guys I’ll try to make this as “short and sweet” as possible, but, simply stated (?) …. here is my problem.

I’m building a 396 LT1 stroker motor and I designed this motor to have a .038” quench, (block decked to 9.012” using a .026” compressed head gasket), specifically ….. so that it would run on 93 octane premium unleaded fuel.

The problem is that something got “lost in translation” at the machine shop and they square decked the block to 9.020” instead of the requested 9.012” deck height. Soooooooooo …. after thoroughly washing and painting the block, installing all the freeze plugs, oil galley plugs, cam bearings, main and rod bearings, crank, rods, pistons, rings and torqueing everything to final specs …….. I finally “discovered” this deck height/quench error.

Furthermore, to complicate the problem, I’ve already got the cam, heads, throttle body, etc., etc., etc. to finish this motor, so changing cams to bleed off dynamic compression might be a more expensive solution to this, than just dis-assembling the short block, and sending it back to the machine shop to correct the deck height error.

So here’s the $64,000 question ….. have any of you built an LT1 stroker motor running 12.8 static and 9.2 dynamic compression ratio with a relatively “loose” .046” quench …… and have it run okay during the Summer months on 93 octane fuel ………. WITHOUT pulling timing or having detonation issues???

TIA for any experience, comments and/or suggestions you may have had in building LT1 stroker motors like this.

[Camaro96]

I want to make sure i understand your situation. The stock hight of a sbc is 9.025 and the shop removed 5 thousands and not the requested 13 thousands. So you need 8 thousands less to get your desired quench. If you have ptv clearance if you remove the 8 thousands need out of your head gasket? Ideal quench on sbc is 38 to 44 thousands for performance. You have deigned the engine that way. Changing your head gasket from the 26 to 18 thousand to get the desired quench. Running 46 quench. And that compression my cause you detonation.


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[Camaro96]

I wanted to post the information below


When the parts that make up the reciprocating assembly are selected, these parts have to fit into the deck height. For a Small Block Chevy (SBC) this value is ~9.025". When calculating the height of the parts that make up the reciprocating assembly, use 1/2 of the stroke, add the rod length, and piston compression height. For a stock 350 SBC, this would be 1.74" + 5.7" + 1.56" = 9.00". If the block is uncut, the decks will be about 9.025". Using a head gasket of 0.015" will give a quench figure of 0.040". If the decks are cut the thickness of the head gasket can be used to compensate as needed.
In a running engine, the oil clearance will create a slightly longer stack- a 0.003" rod bearing oil clearance will add something slightly less than 0.003". In this article, oil clearance will not be added to the stack height. If desired the oil clearance may be added; easiest way to do this would be to either add the oil clearance to the rod length, or simpler yet, just add the oil clearance after the stack height is calculated. The added height from the oil clearance would only be an issue if the engine is being built with a marginal amount of quench (<0.035" for steel rods); if built with the "ideal" 0.040" quench, the oil clearance can be basically ignored.
Another consideration is piston "rock". At TDC as the piston transitions from upward to downward movement, the piston will tip on its wrist pin. This causes one edge of the piston to be a small amount higher than the other edge. The exact amount will vary with how much piston to wall clearance there is; more clearance means more piston rock. Forged pistons generally have a looser piston to wall clearance than cast pistons, but newer design forged pistons have tighter clearances than was used in days gone by. This is another thing that's basically accounted for if a 0.040" quench distance is maintained. Only if less than 0.035" would this possible be an issue.
The bottom line to all this is it's best to maintain an adequate quench figure of 0.040". There's nothing to be gained by going tighter, and a 0.040" quench distance will avoid unseen problems for the most part. If the quench is less than 0.040", be sure to double check clearances to be sure there is no contact between the piston and head- for obvious reasons.

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[firebird_1995]

Have you measured to verify that the piston is .020 in the hole? Is the compression ratio you mentioned (12.8:1) at the .046 quench or .038?

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[97 6speed z]

Have you measured to verify that the piston is .020 in the hole? Is the compression ratio you mentioned (12.8:1) at the .046 quench or .038?

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Firebird_1995, yes indeed I have measured and confirmed that the piston is .020" in the hole, and, that 12.8 to 1 SCR is at .046" quench.

I want to make sure i understand your situation. The stock height of a sbc is 9.025 and the shop removed 5 thousands and not the requested 13 thousands. So you need 8 thousands less to get your desired quench. If you have ptv clearance if you remove the 8 thousands need out of your head gasket? Ideal quench on sbc is 38 to 44 thousands for performance. You have deigned the engine that way. Changing your head gasket from the 26 to 18 thousand to get the desired quench. Running 46 quench. And that compression my cause you detonation.
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Camaro96, yes, instead of cutting the deck to my requested 9.012" height (i.e. removing 13 thousands), they just cut the deck .005" to square it, and left me with a 9.020" deck height. Also, I already bought the Victor Reinz .026" head gaskets for this build, and, I wouldn't trust a steel shim .018" head gasket running both 1) an aluminum head on an iron block, and 2) 12.8:1 SCR on this build.

[firebird_1995]

Is this strictly going to be an N/A engine, or are you possibly going to be spraying in the future? I think you're ok on that quench either way, I don't see the extra quench at that compression ratio being any less safe than what you were shooting for at 13.1:1.
Either way you're going to have to sneak up on the tune if you're going to be leaning on it.
The Victor reinz .026 gasket is basiclly a graphite coated shim gasket. I run one on a sbe engine I have. It was hell getting it out of the package with the graphite intact.
If you did decide against running it as is and it's got to go back to the machine shop, I would personally consider having the block zero decked and running a Cometic .040" or a felpro 1074 @ .039"

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[97 6speed z]

Is this strictly going to be an N/A engine, or are you possibly going to be spraying in the future? I think you're ok on that quench either way, I don't see the extra quench at that compression ratio being any less safe than what you were shooting for at 13.1:1.
Either way you're going to have to sneak up on the tune if you're going to be leaning on it.
The Victor reinz .026 gasket is basiclly a graphite coated shim gasket. I run one on a sbe engine I have. It was hell getting it out of the package with the graphite intact.
If you did decide against running it as is and it's got to go back to the machine shop, I would personally consider having the block zero decked and running a Cometic .040" or a felpro 1074 @ .039"

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Chris, thanks for your vote of confidence!

[97 6speed z]

One last chance to get your comments!

"Engine A"
Bore: 4.030 Stroke: 3.875 Cylinder Head Volume:54.4
Effective Dome Volume: 5.8
Deck Clearance: .020 Quench: .046
Compressed Gasket Thickness: .026 Number of Cylinders: 8

Compression Ratio: 12.61 : 1 Total Displacement (in.3) : 395.42



"Engine B"
Bore: 4.030 Stroke: 3.875 Cylinder Head Volume: 54.4
Effective Dome Volume: 5.8
Deck Clearance: .012 Quench: .038
Compressed Gasket Thickness: .026 Number of Cylinders: 8

Compression Ratio: 12.9 : 1 Total Displacement (in.3) : 395.42


So what's the thinking here. What engine will be LESS prone to detonation on 93 octane premium unleaded fuel?

A) 12.61 SCR with a "looser" .046" quench or

B) 12.9 SCR with a "tighter" .038" quench?????

Your comments are always welcome!