JakeFusion

iTrader: (7)

If you are running dynamic compression in excess of 8.5:1 on 93, what's the ideal quench?

I know lots of the highest dynoing setups have flirted with 9.0:1 DCR but they run Cometic .040" gaskets for quench in the 0.033-.030" range. Stock MLS gaskets are .051" and provide quench in the 0.043-.040" range.

Just wondering if I try to aim for a DCR in the 8.7:1 to 8.9:1 range, should I go ahead and invest in the Cometics too? Or is the cost/prep time unnecessary?

Grr

iTrader: (2)

when pushing compression, the tighter the quench the better. go with the cometics and a couple more cc's in the head

A.R. Shale Targa

iTrader: (2)

The closer the piston comes to the head without touching the more snap the combustion process has by virtue of atomized compression. This is why direct
injection has soooo many positives. When the piston approaches the head it
causes the air/fuel mixture to violently turbulate and effectively reducing the
BSFC(brake specific fuel consumption)...the number of pounds per hour of fuel
needed to support each horsepower the engine makes. Efficiency.....WINNING

JakeFusion

iTrader: (7)

This is one of those things that's essentially free horsepower. Yeah, the GM MLS gaskets are like $40 and the Cometic .040" gaskets are closer to $170, but milling the heads more, going with the thinner gasket, and flycutting if needed will make for more power with all else being equal.

FlamingTA

iTrader: (8)

Or you could go with the Fel-Pro for just a little more then the GM. I think I got my set of Fel-Pro .041" gaskets for $100 shipped.

JakeFusion

iTrader: (7)

That's a good point. I forget about those. Are those the 4.135" bore ones?

I know some cylinder chambers require that bore size (like AFR) but wonder about TFS or ported LS6 heads? Wonder if they'd be okay with it?

chrisfrost

iTrader: (8)

The ideal quench for any application is going to be the smallest You can go without PTV contact . Generally .030" is accepted as the smallest You want to go and have a buffer in the case of spun rod bearing and shutting it down before the bearing gets really bad . Also stretch of the connecting rod and piston and crankshaft are factored . More quench allows more timing /less retard = more power .

SS10Tech

Personally i believe you are pushing it at 8.9:1 on 93 pump gas regardless of the ideal quench. Mixtures on pump are not consistent by shipment, store location, or by brand. 9:1 is considered race gas worthy. 8.5:1 has always been the absolute ideal maximum to account for your level of elevation and accounting for atmospheric pressure. If you go to high you will have severe detonation down low or when you cut the motor off which will be an absolute pain to remove without progressively pulling timing.

Aim for 8.5:1 DCR as an absolute max and aim for a quench of .035 to allow for rod stretch to be on the safe side.

JakeFusion

iTrader: (7)

I'm sea level and I can get straight 93 no ethanol mix. What about adding Torco?

SS10Tech

The 10% ethanol in gasoline really does nothing to detere detonation. It is added more as a cleaning agent and for pollution control than anything else.

Octane boosters do not work because people misjudge the amount you actually need to boost the octane rating efficiently - it is way more than the advertised amount on the bottles.

Torco is just lubricant additives and race gas if i am not mistaken. Same thing as cutting your own mixtures. The problem with this is that you still have the mix of 93 which can still cause detonation. Substituting one for another in a mixture does not work, you need to replace the fuel all together to gain the benefits of higher octane. That is why i said 9:1 is race gas. Not mixtures, additives, cut, etc.

Ill make sure we're clear here and i am assuming you're tuning for optimum performance. If you retard your timing then there wont be any need for it but you lose on overall HP and efficiency. It would be better to use a lower CR and add more timing to make more HP than to have too much and pull timing to keep from detonating. Get stuck in traffic on a hot day and you could be in trouble.