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Old 07-29-2008, 06:58 AM
 
Location: Austin TX
1,565 posts, read 2,937,275 times
Reputation: 394
Default What headgasket to use?

Short story!!!

I have had this 5 cylinder 20 valve turbo charged Audi for 8 years and 110k. It is chipped and when dynoed it was putting about 28psi of presure through! So it broke at 190K after a number of track days etc....

I got a new head for it as well as a bigger turbo, injectors, exhaust, exhaust manifold, and an upgraded ECU (ecu is what we think failed in the first place) this is all done to Audi RS2 specs. Not cheap but I love the car!

The machine shop that cleaned up the head shaved 0.012 in off even though they were told NOT to!!! Like my 4.5 year old son they were not listening and used to work on big american V8's. When you are putting close to 300hp on the ground with a 2.2 liter motor things get a bit more dicy

MY question: Should I get a compression droping gasket or should I put a stock gasket back on there?

It is turbo charged and higher compression is not good but will -0.012 in matter or should I not risk it and go +0.005in. USING A THICKER GASKET?

I have both gaskets just debating which to use!!!!

Thank you for your thoughts!!
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Old 07-29-2008, 09:22 AM
 
Location: Oswego, IL
5,626 posts, read 6,567,693 times
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Use the thicker gasket unless you plan on using racing fuel. Extra compression is likely to cause detonation.
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Old 07-29-2008, 10:34 AM
 
Location: WA
4,027 posts, read 12,952,895 times
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I suggest you try some of the Audi forums to get experienced advice.

On many cars you would be OK and many others have a problem.
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Old 07-29-2008, 11:08 PM
 
Location: We_tside PNW / CO / SA TX / Thailand
10,907 posts, read 17,983,114 times
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I would use the thicker gasket, but you can do a volumetric calculation of reduction in compression chamber since you know the head cavity configuration. There may be some SS shim gaskets available. I can get them with a CDN part number for my VW's (diesel). If you can get a SS head gasket, they are typically laminated and you can pull off the stack height you need.

Do Check out the forums, there are some Audi groups on VW Vortex.
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Old 07-29-2008, 11:29 PM
 
Location: Chicago
36,072 posts, read 55,982,669 times
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I don't understand why you'd even want to take a chance when you're already cramming 28 pounds worth of boost.
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Old 07-30-2008, 09:42 PM
 
Location: Austin TX
1,565 posts, read 2,937,275 times
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Quote:
Originally Posted by Drover View Post
I don't understand why you'd even want to take a chance when you're already cramming 28 pounds worth of boost.
Yes I won't. A headgasket to new spec is on its way!

I had ask the question to several old school audi mechanics, but I wanted an unbiased more theoretical confirmation!

I am on vortex but find the noise to knowledge ratio on older Audi stuff to be rather high .
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Old 07-31-2008, 06:35 AM
 
Location: Incognito
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I would use the thicker one.
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Old 08-01-2008, 04:47 PM
 
Location: Eastern Washington
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You might want to cc the head as-milled, compare to stock. Without knowing the combustion chamber shape you can't say for certain how much milling a head will change compression. There are thumb rules out there for the most popular Detroit V-8's, IIRC, but a. I don't know them and b. they wouldn't apply to your Audi.

Once you know how many cc's you lost, you could approximate the added gasket volume of a cylinder (OK, a pancake-shaped cylinder but mathematically it's a cylinder) with diameter equal to bore size and height equal to the *difference* in thickness between the regular gasket and the thick one.

I'd at least check with a turbo-Audi guru and consider maybe getting an un-milled head. I do know that BMW's party line is you can't mill the head much at all or it's not usable.

You may want to think about valve clearance to the piston, although with turbo engines this is usually not an issue.

At 28# of boost (roughly 43 PSIA), your ideal charge density would be nearly 3X what a very good breathing NA engine makes. Due to charge heating it's not that high, but, you are getting pretty close to Jet Propulsion Lab's turf, if you know what I mean. (not that that's a bad thing)

Last edited by M3 Mitch; 08-01-2008 at 04:48 PM.. Reason: correct spelling error
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Old 08-01-2008, 09:39 PM
 
Location: Austin TX
1,565 posts, read 2,937,275 times
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Quote:
Originally Posted by M3 Mitch View Post

At 28# of boost (roughly 43 PSIA), your ideal charge density would be nearly 3X what a very good breathing NA engine makes. Due to charge heating it's not that high, but, you are getting pretty close to Jet Propulsion Lab's turf, if you know what I mean. (not that that's a bad thing)
Mitch thanks a bunch, I have spoken with several Audi techs and they all agree: put the thicker one on! Several had at first said that they thought it would not matter, but when I found someone that could make the proper gasket for a reasonable amount of money they all said to go for it!

As for the 28 lbs of boost, it had been running that for 130k so I am not that concerned with it, obviously it is not an american V8 where tolerances are a lot looser, so things in this motor need to be as close to specs to get the proper compression and everything needs to be clamped down pritty well! Getting a masive boost leak on TWS sounded like a bomb exploded out front . This old lady does put over 100hp per liter to the wheels so its got to be right the first time!

Thanks for your input!!! Now cross your fingers! rep points to all!
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