What's the difference between early and late cat delete pipes?
 

Are they different lengths because of different mounting locations on the two different style exhaust manifolds?

Or is it just that they have extra bungs for o2 sensors?

I have an 01 with some cheap ebay headers on it and the fitment of the flanges going to the secondary cats is less than desirable.

I've either got to pull them off and have them fitted and rewelded, take a gamble on another pair (probably cheaper than the customizing of the first set), or maybe switch to a cheap pair of used OEM 97-99 manifolds which will have perfect fitment but will require another set of test pipes (or bungs to be welded in?)

Both the early and the late secondary cats, as well as the early and late manifolds, are dimensionally the same (including their tubing diameters) and are interchangeable. The only difference between them are at the 3-bolt flange.

Early manifolds and secondary cat flanges have the bolt c/c distances at roughly 66 mm, as can be seen here:

http://986forum.com/forums/uploads02...1530730765.jpg

While the later flanges, for some unknown reason, have these c/c distances opened up to roughly 78 mm, shown here:

http://986forum.com/forums/uploads02...1530730892.jpg


I've had my fair share of aftermarket headers "not quite" fitting well, just as you seem to be going thru now.

That's why I am in the process of fitting an early non-cat manifold (cheap!) and secondary pipe system, so to replace the flow horrorshow of the OEM cat manifolds:

http://986forum.com/forums/uploads02...1530731091.jpg

Exhaust manifold outlet diameter is larger on 2000 up "S" maybe base engine also. Exhaust pipe diameter has a big effect on exhaust flow velocity at various RPM's.

Yeah, I'd heard that exact same size difference anecdote myself as well.

But the early used non-cat manifolds (bought from Woody), when compared to my 2000 S USA cat manifolds, measure -exactly- the same.

Measured at their cylinder head flange openings (3 pipes) as well as their outlet flange (pictures of which I previously posted above), there are no pipe size differences between these different variations (other than maybe 1 mm or so which I attribute to manufacturer's production tolerances and/or carbon build-up).

Which makes the flange bolting pattern change, as pictured above, all the more puzzling to me.

But, even so, if you might have any photos which show my measurements to somehow be a weird fluke, please post here!

Thanks - DM

So with "back dating" your exhaust to the 97-99 stuff does this mean you are going to use some sort of o2 sensor extension harnesses to relocate the sensors?

Yup!

http://986forum.com/forums/uploads02...1530889063.jpg

I tracked down the OEM male and female fittings for each end, such that it then becomes a plug and play deal. Wiring enclosed in that hot-rodder sort of heat jacket, often used by that crowd for fuel or brake lines located close to headers.

If any interest, I can post the Bosch male and female fitting part numbers that you will need to use.

Thanks - DM

Might as well post them up so they're preserved for people's future searches haha

You could try looking at the European part numbers. Those cat or cat delete pipes pictured are the same sort of thing as European cars with the lambdas and bungs in the same place.

OK, but it might take me a couple of days so to find the data.

Thanks - DM

Nice Dave. What length did you settle on with which set of mid pipes? What the make of your conduit.....I would think the tricky part is mounting the cable under there and getting the right length

Well, it's been a couple of years now, but as I recall these extensions were something around 18" or so long. I'd obviously recommend that you measure first so to see what length you might need, and then add a couple of inches for slack.

The 'conduit' is nothing more than some high temperature fuel line sleeving, sold readily at such hot rod supply places like Jegs and Summit. Note that I intentionally cut the sleeving to be a few inches longer than the wire itself - thus the 'bunchy' appearance in my pictures.

Several years on now, it's all been working a treat!

Found a couple of 99611110105 manifolds. I assume these are the ones you used on your 3.2 heads and fit the circuit werks on the back. Did the standard 3.2 tune work for you. If so where did you put your pre cat O2s? Would it not be too cold back there? I am assuming you extended all four sensor leads to get back to mid pipe cat......

I had ECU Doctors down in Florida do a ROW flash, which eliminated the need for the secondary O2 sensors. Then the remaining pair of primary sensors were fitted to the existing O2 bungs in my Circuit Werks secondary non-cat pipes, using the cable extensions which I've shown above.

Several years later, I've been very pleased with the results - No error codes, and a notable increase in power and rev-ability over stock.

I see, yes ROW would do it. Did you somehow remove the secondary leads such that they could be put back if needed?

Yes, of course - every time that I make a mod like this one, I always retain all OEM parts and pieces such that the mod is easily reversed should future circumstances change.

Oh okay I was under there and one could just plug the unused receptacles with an old plug with leads removed and expoy sealed for moisture.....cut it off of and old o2 sensor