what ex gaskets to buy

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Do cast iron manifolds even need gaskets? If both surfaces are flat, smear a THIN layer a high temp rtv on them and send it. I've done that with great success before converting to header guy.
 
Manfolds, I think these are B/E body SB manifolds
"SB" doesn't help much. 318? 340/360?
Okay, the reason I'm asking is because of port size. Manifolds made for early 340/360 heads (X, J, O, etc.) have larger exhaust ports than later LA 360 heads/manifolds (587, 594, 308, 408, 409, etc.- anything with a smog-style exhaust port), which are actually closer to 318 sized... Since the port size on a Magnum is also closer to a 318 port size/shape, an early port 340/360 manifold can actually overlap the manifold mounting surface on many Magnum heads, causing chronic exhaust leaks no matter what gasket you use.
More detail and pics here, as well as some solutions:
Magnum Heads On 340
If you have later 360 or even 318 manifolds, it should be no problem. As was already said, Ma Mopar didn't even use exhaust gaskets- in some cases (but not all) they had thin steel shims that served as plug wire shields, yes- but no gaskets. Even on Magnums. So if your manifold and head surfaces are true and flat, you don't need them. Run 'em if you insist, but save the fancy and expensive gaskets for headers.
 
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EQ magnum exhaust port design is different than LA.The center ports are spaced farther apart and squarish shaped. They are also a little different than factory magnum. The center ports have more of a squarish shape. I Sent a rub of the ports to cosmetic and had gaskets made. They fit perfect. I think your problem will be finding manifolds that fit the ports.
You will be giving up a lot of power running manifolds. On a chevy hobby stock motor with the best ported vortecs or LT1 exhaust manifolds swapping to the shorty headers that IMCA allows is worth about an extra 25 hp. Nobody is running manifolds in that class anymore.
 
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If you have later 360 or even 318 manifolds, it should be no problem.
Never thought about this. I figured I needed gaskets to get 318 manifolds to seal on my magnum…now I might take them out and see

Always better to run without when you can, no gasket to blow out
 
Never thought about this. I figured I needed gaskets to get 318 manifolds to seal on my magnum…now I might take them out and see

Always better to run without when you can, no gasket to blow out
If they're already on there, I'd leave 'em. No harm, no foul (the old "if it ain't broke, don't fix it" thing).
If one blows out in the future, then yank 'em and try 'em bare. Same work, just different timing; and may not have to do it.
I have run gaskets on manifolds (one had an ever-so-slight warp to it and I didn't have time to get it surfaced), but all I used was a cheapie Mr. Gasket that I had left over and hanging on the wall. Cut away the excess to the shape of the manifold (I DETEST the look of full-length gaskets spreading exposed across the head), used a dab of copper sealer and it's been fine for 3 years now... But yeah, I won't use gaskets whenever possible.
 
very comprehensive info and very much appreciated guys. the manifold is still at the welders but I have an identical one & I will measure its & the EQ's ports for a start
 
Here is the cosmetic gasket I had them make.

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good additional info & very much appreciated for your time/effort. they changed the rules to allow headers, a specific one which was not too pricey but it requires a $390 robbmcperf starter plus the block needs to be ground & I think it might interfere with the kickdown linkage on the side of the trans. I wanted to wire it back but people said a reverse manual VB would be a better way to go plus the ex pipes are limited to 2". all of this had me hold back on a header decision. can I get those cometic gaskets in the pic with just the info on the pkg in the pic?
 
good additional info & very much appreciated for your time/effort. they changed the rules to allow headers, a specific one which was not too pricey but it requires a $390 robbmcperf starter plus the block needs to be ground & I think it might interfere with the kickdown linkage on the side of the trans. I wanted to wire it back but people said a reverse manual VB would be a better way to go plus the ex pipes are limited to 2". all of this had me hold back on a header decision. can I get those cometic gaskets in the pic with just the info on the pkg in the pic?
Should be able to order by part number. That's how I order them.

What does a Robmcperf starter look like? What starter are you using now? Where does the block need to be ground? I don't know much about auto transmissions but I don’t see why you would want less than max pressure for circle track.

The 25 hp difference is comparing manifolds with 2" vs headers with 2" pipes.
 
I run Flatout graphite with a steel core. Have reused them multiple times with no leaks. 340 manifold on X head massage as much as possible. Remflex for head pipe. They are weird and I tighten them much more than spec, but the don’t leak. Can reuse if careful disassembly.
 
the robbmcperformance starter is what looks like a direct drive which would have more space than the mini that is in their now which looks smaller than a regular starter. the tech sounded like a small amount of block deburring would suffice. I think I would be OK with wiring the kickdown all the way back if I have to eliminate the current kickdown linkage. I'm still considering the headers. the welder said wed for the welded ex manifold. excellent gasket info. RR
 
Too bad there wasn't a way to know for sure they would fit without buying a bunch of parts first.
 
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