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.

Injuneer

If your calculations were based on a 9.012" deck height, and he only cut it to 9.020", wouldn't the compression ratio drop, not increase. Piston is deeper in the hole. Or did I misunderstand what happened?

87Aerocoupe

Fred I was thinking the same thing, I will say you should be fine, .046 - .038=.008 not enough to cause any detonation issues.

97 6SPEED Z

Injuneer, you are right on two (2) counts, 1) both the SCR and DCR will decrease from what I designed on this engine, (because of the piston being .008 deeper in the hole), and 2) you did not misunderstand what happened. The question posed in the title though is what is the effect on that .008" increase in quench .... in causing detonation on 93 octane pump gas in this engine?

Fred, the prevailing theory here is that a 13.0 SCR/9.3DCR engine with .038" quench, will be less prone to detonation on pump gas, than say a 12.8SCR/9.2DCR engine with .046" quench. Got it?

And 87 Aerocoupe, where did you get your info about a .008/.038 = 21% increase in quench .... not affecting detonation on LT1 engines running 12.8SCR/9.2DCR and 93 octane pump gas?

Injuneer

Guess I should have given the simple answer to your actual question, which would be "no".

Might have better luck finding someone who could answer "yes" on ltxtech.com

97 6SPEED Z

Fred, your input is always appreciated!

I will give your suggestion a try.

Injuneer

Very few, if any, people here that have built what you built. My thought was that your goal was so close to the realistic limit, maybe even under what some people quote as the minimum (0.040) that the small difference would be offset by the compression change. Nothing scientific there, just a thought. Some of the literature suggests that the quench question is a single-digit HP consideration.

97 6SPEED Z

Fred, once again your input is truly appreciated!

As the HP vs quench literature you referenced suggests, I'm really not interested in whether this motor makes 550 or 559 FWHP, but ..... I do want it to run on 93 octane premium unleaded fuel.