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MikeJinCO · Posted: Thu Mar 19, 2015 11:18 pm Post subject: Fire Rings

I'm working on modifying a 931 head for NA use. The head ha s grooves for Fire Rings. I have some exhaust gaskets that fit. Do I need to buy(make) some fire rings? Or will the gaskets do? If I need some where do I get them? If I make some will steel do or do I need stainless? It looks like 1.5" tubing would fit.

The exhaust header tube size almost perfectly matches the exhaust port. In both size and location. I might need a fire ring that is slightly thicker as the stock 931 port flows significantly better than a polished NA port(larger valve) and a reversion dam might be necessary. That's a strange thought considering how poorly these heads flow. I'll let my final testing determine the need for reversion dams as I want the exhaust flow to be about 80% of the intake flow..
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Mike

'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild)

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

On my setup, I used stock 931 fire rings and cut them down so they would fit. I have many spare sets of fire rings that I collected over the years, but alas, they are all in MI so getting a set to you couldn't happen any time soon.

Regarding the reversion dam, I acquired a strange setup from a guy on the east coast a few years back, it was a crank, 931 head, and some custom NA exhaust header I'd never seen before. It was pretty well-made, but no identifying marks. It had anti reversion built into it. I traded it to Fifty50Plus for something, I think he still has it, he might be able to make some photos so you can compare notes.
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erstwhile owner of just about every 924 variant ever made

Fifty50Plus · Posted: Fri Mar 20, 2015 8:18 am Post subject:

Yep I still have it and am getting ready to ship it off for Jet Hot coating. I'm building the second 924 and the anti-reversion header will be going on it in the next month or so. Lemme take a couple pics and see if I can remember how to post them here.

Dan, I sent you an e-mail on your gmail account. Need and answer......
Chuck
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1979 924 NA race car H-Prod SCCA
1982 924 NA race car - Sold
1981 924 Turbo sold
1982 924 Turbo sold
1972 911 E race car - traded for Cayenne Diesel
1975 914 1.8 Building for H-Prod SCCA

leadfoot · Posted: Sun Mar 22, 2015 1:06 pm Post subject:

Both Simsport and I offset blended the ports in our SC conversions...
The N/A header bolts up with a little grinding to the bolt holes on 1 & 4 IIRC,
In my case the approach was to...
get the bolt holes spaced correctly so the manifold was evenly spaced, line up 931 gaskets to the manifold and offset blend, then smooth out the head runners leaving a small lip as a reversion dam...
main difference is the n/a is oval port whereas the 931 stuff is round...
I think you'll have adequate sealing with just a gasket...
Stu
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

MikeJinCO · Posted: Sun Mar 22, 2015 1:48 pm Post subject:

Leadfoot- Thanks for the adviice. I measured and drew up a flange from the head, then cut one in wood on my cnc router. Three tries as I didn't use bridges between the cutout sections and loose pieces started flying around and destroyed the firstcouple. I then placed it on the header and found it fit the ports perfectly, just the bolt holes not matching. The perfect fit allowed space for the fire ring or possibly could operate like an anti reversion expansion in a minor way. I' have got to get my porting and valves done done, then measure the flows and figure out if I want either reversion or anti reversion. This will probably take another month at the rate I'm proceeding. I can't work on getting pistons until I get all this and the finished combustion chamber volume figured out.
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Mike

'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild)

emoore924 · Joined: 13 Apr 2004 Posts: 2822

Anti-Reversion header pics courtesy Fifty50Plus:

Oh, hey, how'd that last one get in there ...

Fifty50Plus · Posted: Tue Mar 24, 2015 11:50 am Post subject:

Okay, now I see wat you meant in your PM.
_________________
1979 924 NA race car H-Prod SCCA
1982 924 NA race car - Sold
1981 924 Turbo sold
1982 924 Turbo sold
1972 911 E race car - traded for Cayenne Diesel
1975 914 1.8 Building for H-Prod SCCA

emoore924 · Joined: 13 Apr 2004 Posts: 2822

Har, devious old farts at work