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Old 11-27-2008, 11:56 AM   #1
Odyknuck
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Default 2000 N/A 25RS Head Gaskets

I have done a lot of reading in this forum on using head gaskets to lower the compression on the RS N/A motor. I ran across a post about the thicker head gaskets changing the timing from one side of the motor to the other. This would be a concern however I also read a lot of posts that use a thicker gasket without issue. I also read that head gasket changes the compression in the range of .3 to .8 ratio. So my real world questions are 1) does it actually change the timimg? 2) How much does the thicker gasket really drop the compression ratio. 3) what is the optimal thickness to use along with what ratio it gives you? 4) What is the best gasket to use?

BTW I will be installing a T3 Turbo and innercooler on the motor and would like to run 8PSI max with a lower compression.
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Last edited by Odyknuck; 11-29-2008 at 10:47 AM. Reason: Added Turbo info
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Old 11-27-2008, 03:24 PM   #2
ballitch
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Yes the thicker DOHC (96-99) HG changes the timing, advances one head, retards the other.

The calc. I just used said the stock CR for that motor was 11.0:1, although thats a lie, we all know it is 10.0:1. So when I plugged in the thicker gasket, it dropped it a full point.

So if you drop a full point (making it 9.0:1) it is in turbo territory, but since it's AFI, I would try to go a little lower. Or just swap in a EJ22 block and HG under your heads, and be done with it.


~Josh~
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Old 11-27-2008, 08:44 PM   #3
VIsubi
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I here something like 9.3..good if its 9.0 the nright on...I've been thinking bout just buying the kit for my 2.5i but from what I hear its more of a hassle than just a swap...and can take just as long so for about the same price I can have the same thing and later a bigger turbo and EGM and bring up the boost.....don't get me wrong if I new a turbo could be reliable then I'd buy the kit and spank cars all day but...for my money to show good investing I feel this route is gona be costly in the end.
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Old 11-28-2008, 11:31 AM   #4
Matt Monson
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Don't waste your time or money on this approach. With takeout STi pistons and rods so cheap and readily available there really isn't any reason to drop your compression any other way than the "right" way.

Otherwise, just boost your engine how it sits and be dead sure you tune is right. That extra compression point isn't going to give you all that much more of a margin of safety with respect to detonation and preignition. It's still going to be very dependent on your tune, in particular good timing and plenty of fuel. There are plenty of guys running around on 8-10psi of boost on stock RS motors.

Or, as ballitch said, get an Ej22 block, bolt it up and boost it hard. They're cheap, they're reliable, and mated to your heads they are in the low 8's for compression.
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Old 11-28-2008, 06:28 PM   #5
Odyknuck
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Well, I figured I was going to replace the Head gaskets anyways so while I am doing it why not reduce the compresion. My concern is the effect on cam timing. It is not something you can electronically tune.
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Old 11-28-2008, 10:44 PM   #6
Matt Monson
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If you do a search for a thread titled "my dyno results" you will see that I ran the thick head gaskets for about a year on my NA RS. It wasn't on purpose as they were installed by a dealer tech during a warranty head gasket job. I didn't discover it until about a year later when I removed the heads to replace them with a ported set. The car ran fine with no issues whatsoever. IIRC, the timing is moved about 1 degree on each head. The trick is that it's advanced on one and retarded on the other. My concern would be that there would be a risk of preignition on one side because of the turbo and higher effective compression.
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Old 11-29-2008, 07:12 PM   #7
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sorry but they are not that much thicker, doesn't make sense it will move the heads out a few thouandths so i dont see how a few thousandths are going to change the timing enough to effect anything.

also when you line up the belt they NEVER line up perfectally with the marks they are always slightly off, that on its own shows that its not going to effect it at all.
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Old 11-29-2008, 08:08 PM   #8
VIsubi
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still pointless to run a turbo...for that main fact of something going wrong..cause if that was the case you'd hear more people cheering the fact on about N/A with an AVO kit. The ratio to those that have blown to those that are still running is very slim and you don't hear to much of those people with those kits still talking bout it. They've moved on to engine swaps or custom swaps. Either way do your thing...bringing the compression ratio down might aid in boost spikes compared to the stock gap of the OEM gaskets but be careful. Hope this isn't a DD of yours.
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Old 11-30-2008, 09:39 AM   #9
Odyknuck
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Quote:
Originally Posted by VIsubi View Post
still pointless to run a turbo...for that main fact of something going wrong..cause if that was the case you'd hear more people cheering the fact on about N/A with an AVO kit. The ratio to those that have blown to those that are still running is very slim and you don't hear to much of those people with those kits still talking bout it. They've moved on to engine swaps or custom swaps. Either way do your thing...bringing the compression ratio down might aid in boost spikes compared to the stock gap of the OEM gaskets but be careful. Hope this isn't a DD of yours.
My Daily driver is a 2006 Impreza RS N/A. In the future I plan on doing an STI swap on it. The motor I am refering to is for my offroad Woodsbuggy car. I am currently running a Turbo VW motor in it and I want to replace it with the more reliable 2.5. I allready have the Turbo, wastegate,BOV and innercooler so my costs will not be that high to do this. The cost to rebuild a VW motor is higher than it is to buy JDM 2.5s Off of Ebay everyday at 800 bucks. So If I blow a motor I would just replace it. I really dont need more than 5 to 8 PSI and can get away with 5 for offroad.
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Old 11-30-2008, 07:46 PM   #10
VIsubi
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well in that case do your thing bro sounds good to me...I think you'll have that low torque already with the subbie but if its just a engine on hand do it.. I plan on swapping in my 2.5i into a VW dune buggy shell after I get the EJ255 come january I think that think is gona haul azz with out a turbo being fiberglass and looking like a tub lol...do some research on the EJ257...I know the engines will bolt up to the tranny but I hear alot of broken tranny's after..thats why I haven't gone that route but if I hear good ewnough reviews come before january I might shell out the extra 1500 for an STI motor and cross my fingers nothing breaks on the 2.5i..but I really think it might but owell its cool though things are ment to be replaced.
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Old 11-30-2008, 10:24 PM   #11
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I actually wa sorginally going to put an STI in the buggy however because of all the parts I allready had and the price difference between an STI and a N/A 2.5 I choose this route. I also agreee baout the trans and other drive train parts possiably not being stong enough to handel the abuse. 200 HP is plenty for what I do. Kennady enginnering makes the Subie to VW trans adapter plate and flywheel to bolt a Subie right up to the 6 Rib VW Bus trans. Good luck on your transplant and keep us posted. BTW ISeveral of my friends are allready running 2.2s and 2.5s in there buggys and will never go back to the VW power plant.
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