Doug Thorley Header and Pre-cat Fitment

Hello,


The background...

This past weekend I replaced my cracked head. Because it was off, I went ahead and replaced the exhaust manifold with Doug Thorley Header setup. My pre-cats were also bad, so I bought replacement Catco dual pre-cat setup.



Now the issue...

I doubted the way the pre-cat and Headers mated. It didn't seem like a strong connection. Although the stock exhaust manifold and Pre-cat flanges don't actually touch and mate together, the Doug Thorley and Catco pre-cats were spaced even a bit further far apart. I went with it and installed the rest of the exhaust system.
After installing late last night, I took for a test drive. As FYI, I've had my front DS out for some time and didn't have the intention of putting back in last night anyway.

This is what happened when I first applied the brakes and front suspension compressed...
The differential yoke took a chunk out of bank one pre-cat.
When installing the pre-cats it never occurred to me that the pre-cats were in the way of front DS.





So my question is this....

Does anyone have any experience with installing Doug Thorley headers, and if so, what pre-cat setup did you use?

I'm hoping it's just a faulty pre-cat design (too long, wrong routing of collector and flange, wrong flange design etc.) and that removing Catco and installing Walker or other may resolve. But I'm curious what others have experienced so I can make the correct action to resolve.


Thanks in advance for those who can offer advice.

That can not be the proper header for your application. That exhaust looks like ass. Just get a stock replacement and call it done. There isnt alot of room around the pinion. Especially if you are not lifted high.

The header (Doug Thorley) is correct, for my MY (2001, California emissions).
But I agree, the pre-cat fabrication quality isn't the greatest.
And I do remember that the stock exhaust was very close also to the yoke, but it never hit (I have a 3" lift).
Perhaps a Walker is my best bet then for resolving.


Does this type of exhaust manifold require any gasket to mate with the pre-cat flanges?

Looking at the original OEM manifold and pre-cat set-up, I would say no. But I have a hard time imagining how a good seal is made without some donut gasket etc.

I can't tell from the photo, but is that still the low pinion D30?

Ian Christiansen said:

I can't tell from the photo, but is that still the low pinion D30?

Click to expand...

It is.

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As FYI, in the meantime I've ordered a walker 52304 pre-cat which should be here by Friday. I have the Walker mid-pipe, perhaps this will provide better fitment than the Catco. I'll have to judge on Friday.

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The biggest issue I see is the non-mandrel bent pipe! It will cost you more in benefits than the header investment will ever produce!

RCP Phx said:

The biggest issue I see is the non-mandrel bent pipe! It will cost you more in benefits than the header investment will ever produce!

Click to expand...

A valid point as well.

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