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Manifold Crack Prevention

 
Old 12-02-2007, 10:38 PM
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Default Manifold Crack Prevention

So far, I've read that cracks w/ the Greddy manifold can be reduced by:

1) Large relief cuts.

2) Making sure that the mating surface on the exhaust manifold is flat.

3) Not using the hard bracket to tranny

4) Don't wrap the manifold

5) I read on m.net that someone put some sort of extra rubber bushing on the exhaust hangers to prevent them from flexing?

Is there anything else anyone can think of? Thanks.
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Old 12-03-2007, 10:08 AM
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Personal Opinion:

Making the three reflief cuts between the runner is probably the big-ticket item. When I removed the turbo and manifold a couple of months ago (for some unrelated work) I found that the cut between #2 and #3 had essentially closed up completely, so theres definitely some expansion taking place. I re-opened that cut by running the hacksaw blade down through it again- we'll see how it looks in another year or so.

In my case, I found it necessary to fabricate a hard bracket to the bellhosing bolts, since otherwise my 2.5" DP tended to bang into the frame. As it is I've only got about 1/4" clearance, but with the Mazdacomp mounts that seems to be enough.

It's been running like this for about a year and a half, and no cracks thus far.

YMMV.
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Old 12-03-2007, 01:20 PM
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hey i always thought if you put a flex pipe on the downpipe you can relief some of the movement. that way when the engine moves it doesn't move the whole exhaust system putting more pressure on the mani
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Old 12-03-2007, 01:34 PM
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What I found that really works are polyurethane exhaust hanger bushings.They pretty much eliminated all the movement of the exhaust and seem to hold it in place better than the rubber ones.
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Old 12-03-2007, 02:53 PM
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Originally Posted by Joe Perez View Post
Personal Opinion:

In my case, I found it necessary to fabricate a hard bracket to the bellhosing bolts, since otherwise my 2.5" DP tended to bang into the frame. As it is I've only got about 1/4" clearance, but with the Mazdacomp mounts that seems to be enough.

It's been running like this for about a year and a half, and no cracks thus far.

YMMV.
I've read on m.net that Corky Bell recommends exhaust manifold support only if it's given some flex. He stated it can help prevent manifold cracking quite a bit. I believe Braineack's manifold cracked b/c of his hard mount to tranny.

Joe, does your bracket flex or move at all?
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Old 12-03-2007, 02:58 PM
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Originally Posted by mx03tb View Post
hey i always thought if you put a flex pipe on the downpipe you can relief some of the movement. that way when the engine moves it doesn't move the whole exhaust system putting more pressure on the mani

I've read this too. Sounds like a good idea.

I wonder if a spring plate is adequate or does a flex pipe give you more room to work with?
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Old 12-03-2007, 03:06 PM
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Originally Posted by kenzo42 View Post
Joe, does your bracket flex or move at all?
The first two flexed until they broke. The one that's on there now is made from 3/16" steel, and flexes less than not at all.

However, my DP is a two-piece unit, with a slip-coupling in the center. The rigid bracket is attached to a U-clamp that is installed after the coupling, so the upper section can move about a bit if it needs to. Between that and the catalytic converter is a flex section.

In this picture you can see the general design. That particular bracket is one that broke, but the current design is the same idea, just much thicker.

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