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I think I killed it :-(
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 2194
Location: Somerset, UK

PostPosted: Thu Apr 01, 2021 6:28 pm    Post subject: Reply with quote

Layers on MLS is thickness dependant. Cannot remember the layers for 0.050. Mine is still wrapped up and unopened. I have 0.080 installed and that was 5 layers

Cometic not really needed on stock or motors running way less than 1bar. Recommended if the boost will be turned up and driven hard. I blew two stock HG's after my engine rebuild and boosting over 1bar. That was partly due to head build issues too. Since the latest rebuilt head and the Cometic was installed its been working fine for 6yrs......and its been driven real hard .....
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1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
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Mike9311  



Joined: 14 Dec 2004
Posts: 1102
Location: Chicago-ish

PostPosted: Thu Apr 01, 2021 11:01 pm    Post subject: Reply with quote

bureau13 wrote:
UPDATE: Used head from running car acquired and taken to the shop. They showed me my old head, it's so clean now I wanted to lick it.

I see the Cometic site has the 924 head gasket from the Ideola group buy a few years back. I believe 0.050" is the correct compressed thickness, right? One thing that's odd, their web site says that is a 5-layer gasket, but discussion on that old group buy thread was that that was 3 layers. Anyone know the story there? I do want to make sure I'm getting the correct thickness (I am guessing I should stick to stock? Or should I find out how much if any was taken off the head mating surface, and add that to the 0.050"?)


That is the simple most straight forward way or else you will have higher compression. Also Cometic adds layers as the thickness increases. The layers are 'active' and adjust to subtle head to block movement.

You could 'cc the chamber to know your chamber size exactly which should be 19.5 to 20'ish cc or play it safe. Asking the shop is also a great idea and never hurts

.050 is slightly less that stock compressed.
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1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA M650 Herausnehmbares Dach
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car
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Mike9311  



Joined: 14 Dec 2004
Posts: 1102
Location: Chicago-ish

PostPosted: Thu Apr 01, 2021 11:36 pm    Post subject: Reply with quote

Also finally found my pic of my 1980 cylinder 1 piston. Keep in mind this engine still ran when I tore it half down. Only reason I dug into it was that the turbo was falling off. Screws would keep it tight and I was tired...

I bought the car this way and ran it in anger with boost as high as 15psi. Regularly between 10-13psi with HKS EVC1 (still the best in my opinion since its so easy to go up or down in boost with preset buttons)... I'm holding back as to how hard I ran this car

Piston was always like this because I simply had no idea. No signs of det anywhere. It always ran nice and strong. The dust bunnies you see is because the car is in storage with head off all these years. Longer than this forum's existence


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1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA M650 Herausnehmbares Dach
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car
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bureau13  



Joined: 07 Sep 2017
Posts: 357
Location: South Florida

PostPosted: Fri Apr 02, 2021 3:03 pm    Post subject: Reply with quote

Thanks guys. I will ask the shop and go from there.

Mike, what do you think caused that piston damage, detonation that you didn't hear? Mine showed nothing like this, just the pretty obvious marks from valve contact.

Piston: "You should see the other guy."
Valve: Breaks in half when I remove it...

Steve, any reason NOT to go with the Cometic? I'm not likely to be running the car super hard, it's just a street car. I was trying to run around 10psi, but of course more is better It's not really that much more expensive than the Victor Reinz, the most annoying thing is that the head seal kits all seem to come with the VR so I'm either buying everything piecemeal if I go with the Cometic head gasket, or I'm getting an extra one that I don't need. Still, not a huge price to pay. I'm planning on using those ARP head studs too. Do I need 'em? Probably not, but you never know...
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1982 931
1986.5 Silver 928S
2007 Hummer H3 (Daily Driver)

Past lives (I miss them all):
2004 RX-8 (Wrecked)
1993 RX-7 (Sold)
1987 RX-7 Turbo II (Sold)
1985 RX-7 GSL (Stolen)
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 2194
Location: Somerset, UK

PostPosted: Fri Apr 02, 2021 4:14 pm    Post subject: Reply with quote

You pay your money and you take your choice....

If you have no intention of wanting to push the boundary of the motor, stick with OEM.....it all works. Swapping to ARP, Cometic etc will cost more and add nothing to a stock motors performance or reliability. Assuming the rebuild is done correctly and all other elements of the motor are to spec and in good order.

If you have future aspirations on performance, then now is a good time to future proof
_________________
1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
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Mike9311  



Joined: 14 Dec 2004
Posts: 1102
Location: Chicago-ish

PostPosted: Fri Apr 02, 2021 11:10 pm    Post subject: Reply with quote



I always thought it had something to do with the valves in that cylinder. The PO had the head pulled and rebuilt. They might have actually replaced it though now that I think about it

Needless to say I was more than a bit surprised. Just shows these motors are tough little beasts
_________________
1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA M650 Herausnehmbares Dach
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car
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Rasta Monsta  



Joined: 12 Jul 2006
Posts: 11556
Location: PacNW

PostPosted: Sat Apr 03, 2021 12:37 am    Post subject: Reply with quote

Are there marks on the head? That almost looks mechanical, like something was bouncing around in there.
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  • WeiBe (1987 924S) - 931 S3
  • Red (1987 924S) - Pro44/Spec944
  • Shaggy (1980 931) - SOLD (unlucky, but tried hard )
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Mike9311  



Joined: 14 Dec 2004
Posts: 1102
Location: Chicago-ish

PostPosted: Mon Apr 05, 2021 11:18 pm    Post subject: Reply with quote

I'll dig around my shelf and see. I don't remember any and the head was pulled an awful long time ago. Its mechanical for sure

Just trying to show these cars can take a beating at times and keep going just fine
_________________
1980 931 since 1989
1981 Ideola 931 Club Sport
1982 931 Entwicklungsfahrzeug
1979 924 NA M650 Herausnehmbares Dach
1982 931 Red Resurrection - 951 IC
1982 931 parts car / resurrection?
1980 924 NA (R&D lightweight)
1982 931 wana-be GTR race car
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View user's profile Send private message
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