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Killer B holy header - manifold gasket?


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So I received my Killer B holy headers yesterday.  I had purchased new manifold gaskets from Subaru and when I lined them up to ensure correct fitment, the opening for the headers is only 1.5" but the opening in the gasket is 1.875".  Noticeable difference.  I checked Grimmspeed and their gaskets are the same size as the OEM ones (and GS put the OEM part number on their site for cross reference, which is the exact ones I have from Subaru).  Killer B offers a gasket kit, and they look just like the GS and Subaru gaskets.

With the gasket opening being larger, there isn't an issue with airflow being blocked but will the fire ring crush down to avoid leaks?  Or is there a gasket with 1.5" opening for use with these headers?

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I installed my Holy header maybe a month or so ago, using GS gaskets. Maybe I should have, but I didn't hold them up to the headers before doing so. However, I did hold them up to the exhaust outlets on the heads, and they were certainly bigger than that... So, maybe the headers are sized to be big enough in the event you have your head ported, or at least not to create any spots for reversion right at the head.

I also hit them with a couple coats of Copper Spray a Gasket and let that dry up as much as it does before installing, on advice from JMP. Makes it all easier to take apart in futures, should you need to...

I personally really dig the sound of the ELH, hopefully it works for you. I still kind of appreciate the Subaru Rumble, but now when I pass by another UEL Subaru it just kinda sounds, I dunno... lumpy?

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The GS gaskets seem to be the same size as the OEM, especially as GS references the OEM part number as being similar.  I wonder if the GS gaskets are just not layered?  I'll give them another look.  

The problem I'm wondering about is the header opening is 3/8" smaller than the gasket itself.  I can't see that being an issue except the ring in the middle of the gasket usually fits inside the opening.  

Either way, I will check out the GS gaskets again.  Maybe just order a set to be sure, they aren't a lot of $$.

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So… I stole this from Max Capacity in another thread:


This is what the GS gaskets looked like on the heads…. Correct size, fire rings slightly larger than the exhaust ports.

I suspect that unless you are gasket matching the ports, they’ll alL be similar to that. The header tube size us more a function of total  and laminar flow, as well as matching it to the output of the engine. Hence not need ‘big tube’ headers in all but the most extreme cases. There is probably nothing to be gained but additional cost from necking down the headers to match the ports.

This has been my experience in other engine applications anyway. Exhaust gasses should be expanding so rapidly as they leave the chamber anyway small (not smoothed) increase in diameter, or gaskets that aren’t perfectly matches won’t cause you any measurable power loss. In a high performance N/A application there may be a bigger difference, but even there…. You’ve got to be running a lot of power for gasket matching the ports to make much of a difference.


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  • 2 weeks later...

Yeah, I seem to recall talk over on NASIOC years ago about keep the velocity up on the exhaust gases to spool the turbo. That's why when porting the heads, you don't increase the size of the port to match headers.  My heads were ported, by thinning the divider and cleaning up in the valve pocket and exit area. 



305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.


Engine Build - Click Here

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My only concern was whether the gaskets would seal properly given the large difference in diameters between the gasket and the headers.  I grabbed some GrimmSpeed gaskets and had the headers installed.  All is good.

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