29 November 2006, 09:14
Hi.
All but one of the 90+ exhaust manifolds that I have examined had cracks in the back: around the goilet. I believe that the main reason those manifolds crack is because the outlet is so small; and because the Mitsu turbo is also very small on the turbine side. [the small outlet is a restriction to flow; and that leads to a lot of heat being retained in the manifold. That heat makes the manifold glow cherry red after a hard pull. And that heat can put a lot of stress on the manifold and cause it to want to twist and warp and crack.]
The picture showing the T3 flange gasket sitting there on the outlet shows just how small the opening is on the 90+ manifold. I use that gasket to scribe the outline of the standard size opening onto the 90+ outlet so that I know just how much iron to grind away with my air powered die grinder and carbide burrs.
I think that trying to use a Dremel tool to grind away that much iron would take you about a week to do the job. With the tool I have, it takes me about 6-8 hours to open up the outlet and blend the ports. [a lot of work; but worth it]
The other main reason the manifolds crack is because the four flanges...where the manifold bolts up to the head...warp. The four runners are tied together so that they cannot spread apart, but the high heat causes the runners to bend like a bow. This bending action puts enough stress on the manifold that cracks will form on the backside.
If you can find a 90+ manifold that has one, or two, or even three cracks on the backside, around the goilet, it IS possible to still use that manifold.
What is NOT usable is a manifold that has cracks on any of the four runners.
The 90+ that I have on my 245T has two cracks in the goilet. The 90+ that I installed on my son's 242T has three cracks back there. Mine has been on for three years, and is still fine. Ted's has been on for two years, and is also still okay. The cracks have not grown.
Besides porting the outlet to improve the flow, I also had to make sure that the four flanges were flat. EVERY 90+ manifold that I have examined has warped flanges. Every one that I installed had to have the four flanges restored to true flatness.
If the manifold you find has a crack or two in the goilet, but the cracks are not so large as to be close to letting a piece of the manifold fall out, then you could save it and re-use it:
...port the outlet to improve the flow: very good for power; and VERY good at reducing the amount of heat that stays in the manifold.
...restore the four flanges to true flatness. That will reduce the stress that can cause cracking; and it will also help to prevent any of the manifold studs from either breaking off or pulling out of the head.
Evaluating the cracks that you will see in the backside of a 90+ manifold to determine if the manifold is salvageable or not is not ends up being a judgement call. You might want to use the pictures of the manifolds I show in my pbase galleries as a guide: they can show you what to look for; and what is still usable. The picture that show the manifold with the three cracks is the one that I installed on my son's car.
If you find a 90+ manifold that has a crack or two, you might be able to buy it cheaper....because it has some cracks. Just don't tell them that you can salvage it by porting it. [no need to give away secrets]
If you cannot locate a 90+ manifold over there, then you might look on turbobricks classifieds: sometimes a 90+ comes up for sale. Or, post a 90+ wanted ad.
I don't have any spare 90+ manifolds right now. But if I come across one or two, I'll post that here.
TF
All but one of the 90+ exhaust manifolds that I have examined had cracks in the back: around the goilet. I believe that the main reason those manifolds crack is because the outlet is so small; and because the Mitsu turbo is also very small on the turbine side. [the small outlet is a restriction to flow; and that leads to a lot of heat being retained in the manifold. That heat makes the manifold glow cherry red after a hard pull. And that heat can put a lot of stress on the manifold and cause it to want to twist and warp and crack.]
The picture showing the T3 flange gasket sitting there on the outlet shows just how small the opening is on the 90+ manifold. I use that gasket to scribe the outline of the standard size opening onto the 90+ outlet so that I know just how much iron to grind away with my air powered die grinder and carbide burrs.
I think that trying to use a Dremel tool to grind away that much iron would take you about a week to do the job. With the tool I have, it takes me about 6-8 hours to open up the outlet and blend the ports. [a lot of work; but worth it]
The other main reason the manifolds crack is because the four flanges...where the manifold bolts up to the head...warp. The four runners are tied together so that they cannot spread apart, but the high heat causes the runners to bend like a bow. This bending action puts enough stress on the manifold that cracks will form on the backside.
If you can find a 90+ manifold that has one, or two, or even three cracks on the backside, around the goilet, it IS possible to still use that manifold.
What is NOT usable is a manifold that has cracks on any of the four runners.
The 90+ that I have on my 245T has two cracks in the goilet. The 90+ that I installed on my son's 242T has three cracks back there. Mine has been on for three years, and is still fine. Ted's has been on for two years, and is also still okay. The cracks have not grown.
Besides porting the outlet to improve the flow, I also had to make sure that the four flanges were flat. EVERY 90+ manifold that I have examined has warped flanges. Every one that I installed had to have the four flanges restored to true flatness.
If the manifold you find has a crack or two in the goilet, but the cracks are not so large as to be close to letting a piece of the manifold fall out, then you could save it and re-use it:
...port the outlet to improve the flow: very good for power; and VERY good at reducing the amount of heat that stays in the manifold.
...restore the four flanges to true flatness. That will reduce the stress that can cause cracking; and it will also help to prevent any of the manifold studs from either breaking off or pulling out of the head.
Evaluating the cracks that you will see in the backside of a 90+ manifold to determine if the manifold is salvageable or not is not ends up being a judgement call. You might want to use the pictures of the manifolds I show in my pbase galleries as a guide: they can show you what to look for; and what is still usable. The picture that show the manifold with the three cracks is the one that I installed on my son's car.
If you find a 90+ manifold that has a crack or two, you might be able to buy it cheaper....because it has some cracks. Just don't tell them that you can salvage it by porting it. [no need to give away secrets]
If you cannot locate a 90+ manifold over there, then you might look on turbobricks classifieds: sometimes a 90+ comes up for sale. Or, post a 90+ wanted ad.
I don't have any spare 90+ manifolds right now. But if I come across one or two, I'll post that here.
TF