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3.9 V8 exhaust downpipe variations


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I'm going to be fitting RRC downpipes to my 3.9 engined Ninety.

I'm just about to order the downpipes and Y piece, and have discovered there are different items for auto and manual gearbox versions. These will be non-cat pipes BTW.

Who can tell me what the physical differences are, and why?


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I'm not aware of any difference on the 3.9 whether it's auto or manual, so that's a new one on me!

The 3.5EFi (manual) had a smaller diameter and was routed above a square section gearbox crossmember, this is straight at either end and protects the exhaust. The exhaust is straighter here but dips down behind the crossmemeber. The end of the downpipe and Y peice are different.

On the 3.9 the pipe is bigger and is routed below a round tubular cross member that cranks up above the exhaust at either end. The cross member sits a bit higher but the exhaust is a bit more exposed. After I flattened mine I refitted the 3.5 crossmember and a sports exhaust (I found these are the same diameter on 3.5 & 3.9).

AFAIK the 3.5 auto had the same arrangement, I'm not aware of any reason it wouldn't fit.

Later 3.9 had cats in the downpipes but other than that they were the same as best I can tell.

If you do learn there's a difference I'd love to know.

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According to MCAT:

NTC7320 - Non cat auto transmission

NTC7321 - Non cat manual transmission

Gawd knows what the actual difference is :unsure::unsure:

Most of the parts suppliers seem to stock both numbers, so I guess I'll have to ring and ask.

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