Compressed thickness of a stock head gasket?

[JeepSJ]

Shopping for head gaskets and I see that Cometic has a big selection of thicknesses. The only reference I can find on other gaskets is "stock" and "010 thicker". But 010 thicker than what? Anyone have the compressed thickness of a stock gasket? Cometic are available at .036 all the way up to .120.

[Robyn]

The .010 gasket is just .010 thicker than the standard one.

It's been a long time since I was involved with the gasket thicknesses but IIRC the stock gasket is .045" when compressed.

I strongly advise against the cometic gasket.

The 6.5 simply does not have enough bolts to clamp this type of gasket well.

I used a cometic on one side of a 6.5 I built up for the Dahoooooley and within a year it was leaking between the layers.

The composite gaskets (Felpro) with the stainless fire ring are the best you can hope for (Subjective)


The .010 thicker gasket is designed to allow the block to be decked ONCE and the thicker gasket will get the head back to where it needs to be to keep the compression correct and the alignment between the head and intake correct.

Actually a 10 thou difference is not going to bother the manifold, but the compression will change.

If your decks are in good shape and do not have any erosion at the fire rings
(Common near the front two cylinders where coolant sits against the deck)

If the decks are stock and good USE THE STANDARD FELPRO gaskets and the accompanying bolt sets.

These engines were designed to use the TTY bolts and they work well.

Exceptions are if one is boosting the thing beyond 15 psi and really these engines just do not do well when being stuffed real tight.

Mostly it's a longevity thing.

300 hp
12-15 psi max
1000 F exhaust temp at the ports MAXIMUM
220 F coolant temp MAX

Beyond these specs things just go downhill...

The 6.5 is not designed for extremes

A marine app is a horse of a different color, as the coolant temps can be dealt with easily (pond of cold water)

The tough thing is the heat.

The 6.5 carries most of the combustion heat in the head as opposed to a direct injected engine like the Cummins, Dmax or the P Stroke.

Hope this helps...

[JeepSJ]

I thought the cometic MLS were being touted as the new hotness for the 6.5? Hadn't heard about the leaking issues.

My decks need done. Heads too. Going to need a thicker gasket.

[ronniejoe]

The stock FelPro thickness is .039".

I completely disagree with Robyn (no offense intended).

I would highly recommend using the Cometic MLS gaskets if you plan to push performance boundaries. I'm running them now. They are the best gaskets available for the 6.5. Period.

[ronniejoe]

By the way, the real problem for high EGT with the 6.5 is the factory turbocharger. I've said this a hundred times and no one gets it. By my calculations (with some dyno data in them), I estimate that my engine is somewhere around 324 hp at the rear wheels with around 580 lb-ft of torque. This is real, not the fantasy 300 hp that Peninsular used to advertise.

The stock GM-X turbocharger is way too small, both on the turbine and compressor side. At higher engine speeds, above about 2800 rpm, the exhaust flow chokes in the turbine housing. This is an engineering term that means that the flow has reached sonic speed at the nozzle. Under these conditions, the downstream conditions of flow are independent of those upstream. No matter how much more pressure increases upstream of the choke, no increase in flow through the nozzle can occur. In 6.5 terms, this means that exhaust gas temperature increases rapidly -- out of control.

For comparison, in the early days of my Suburban, I struggled to tow my trailer at 65 mph with stock max fuel rate of 62 mm3 per stroke. EGT on level ground at these conditions would run steady at around 1350 F (pre turbine). Had to constantly watch the coolant temp because it often overheated. Today, I can tow much heavier at much higher speeds (80 mph is no problem) with current max DS4 fuel rate (79+ mm3), running in excess of 20 psi boost and EGT reading around 1100 F (pre turbine). ECT stays easily in control.

I have had three head gasket failures with FelPro gaskets since the first build of my engine. So far, the Cometics are doing quite well.

If you want to solve the heat problem with the 6.5, you need to address the turbocharger.

[Robyn]

Sounds good to me.

My 6.5 ran only a year on the cometics and then issues arose.

I agree with the tech on the turbo's

The GMX are sketchy at best.

[JeepSJ]

By the way, the real problem for high EGT with the 6.5 is the factory turbocharger. I've said this a hundred times and no one gets it. By my calculations (with some dyno data in them), I estimate that my engine is somewhere around 324 hp at the rear wheels with around 580 lb-ft of torque. This is real, not the fantasy 300 hp that Peninsular used to advertise.

The stock GM-X turbocharger is way too small, both on the turbine and compressor side. At higher engine speeds, above about 2800 rpm, the exhaust flow chokes in the turbine housing. This is an engineering term that means that the flow has reached sonic speed at the nozzle. Under these conditions, the downstream conditions of flow are independent of those upstream. No matter how much more pressure increases upstream of the choke, no increase in flow through the nozzle can occur. In 6.5 terms, this means that exhaust gas temperature increases rapidly -- out of control.

For comparison, in the early days of my Suburban, I struggled to tow my trailer at 65 mph with stock max fuel rate of 62 mm3 per stroke. EGT on level ground at these conditions would run steady at around 1350 F (pre turbine). Had to constantly watch the coolant temp because it often overheated. Today, I can tow much heavier at much higher speeds (80 mph is no problem) with current max DS4 fuel rate (79+ mm3), running in excess of 20 psi boost and EGT reading around 1100 F (pre turbine). ECT stays easily in control.

I have had three head gasket failures with FelPro gaskets since the first build of my engine. So far, the Cometics are doing quite well.

If you want to solve the heat problem with the 6.5, you need to address the turbocharger.

I want to give my TE06H a fair shot with an engine that isn't beating its valves against its pistons. Who knows...I might be calling you for one of your turbos in a few months if I can't get this thing to work as it is rumored to work on a 6.5. I still wish I could find a map for the dang thing.