Head Gasket for 83.5 BT build?

[zeeke069]

So I thought this would be an easy find but keep going in circles so looking for some feedback.

Need a head gasket for my b7 running mahle 83.5mm 9.0 power pack pistons. Will be running 2867R turbo. Will be running pretty high boost, using tuscan rods etc.

I want to stay as close to stock thickness as possible so was looking at cometic 0.036 or 0.040 but you have to order them.

There is also a mahle 83.5 thats much cheaper that I think will probably work out but wanted some thoughts from you guys.


Thoughts?


Thanks for any feedback.

[EvolutionArmory]

Have Cometic make you a gasket.

[zeeke069]

Yeah I can order the 0.036 from them it takes a month or so they say. Think thats the best route? That was my original plan then found the mahle and all kinds of other stuff. I think the cometic is safest option. 0.36 is .9mm which is the stock thickness.

For some reason ecs only sells the 0.86 which is WAYYY too thick I guess its for people trying to drop compression with stock pistons.

[zeeke069]

There are the cometic you can order:

https://www.cometic.com/applications...e/audi/a4/2007

[EvolutionArmory]

The sku numbers for the gaskets on their site come with a 83.5 bore. Don’t know if you’d want to order a 84mm bore to be a little over what your new bore will be. And don’t order a gasket until you know how much will be skimmed from your block or head if you’re having them decked.

I run a Cometic gasket in my car but it’s only been in the car for a few days so I can’t comment on the quality yet.

[EvolutionArmory]

And Cometic thickness numbers are compressed numbers so factor that in as well.

[zeeke069]

Hmm my post vanished when I replied so here goes again.

Thanks a ton, you win my best internet friend today. I totally didnt account for the head decking. Block is done and didnt need decking but I just dropped the head off today and have no idea if it needs decking or not. I would have ordered the wrong one for sure.

I have done so much researching building this and never even considered the head gasket would be so difficult until I sat down today to order one.

Also, thanks again didnt realize that was compressed for cometic so I am guessing thats what has been throwing me off when comparing them to other gaskets.


Thanks!

[EvolutionArmory]

When in doubt, call the manufacturer.

Since you’re shooting for such a low CR from stock, if you miscalculate by a couple thou I doubt it would hurt you too bad or at all.

Talk to someone at Cometic once you get your head deck specs.


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[aluthman]

Stock HG has an 84mm bore. Just run that. FYI, the stock HG is .8 mm compressed if you’re doing CR calculations. I’m using a $30 Elring stock HG in my car and have never had issues.

[EvolutionArmory]

Stock HG has an 84mm bore. Just run that. FYI, the stock HG is .8 mm compressed if you’re doing CR calculations. I’m using a $30 Elring stock HG in my car and have never had issues.

Running the stock gasket will have a bore big enough for the pistons but he won’t be able to add thickness that decking the surfaces will remove. His CR will go over the stated CR with a stock gasket.

Being such a low CR I don’t think it will matter much but the safer bet is probably a custom gasket.

My 2 cents.


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[EvolutionArmory]

OP, you also need to see what headgasket thickness your CR was calculated at and also account for any decking the head got.

Hopefully your pistons are application specific and an OEM gasket spec was used to calculate final CR. If they aren’t application specific, you should find out what spec was used and make your final gasket thickness decision with the calculated CR gasket spec and any decking needed factored in.


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[aluthman]

I’m running the same pistons, just in an 83mm size. Stock head gasket works fine for me.

[EvolutionArmory]

His CR is so low that it probably won’t matter much if they decked the head a couple thou. I can see where you’re coming from.




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[zeeke069]

Yeah if Aluthman is using the same pistons they are 9.0 as well. So now it just depends on if they have to deck the head and if so how much. So I just have to wait for the head to come back.

Thanks for the compression number at .8mm that helps as well.

I threw my stock gasket away when I tore down the engine and didnt measure it. I didnt realize it was 84mm, I thought it was smaller.

Thanks for all the help, its for sure appreciated.