Will 3.8L Stang downtubes fit my 89 SC?

phils89sc

Registered User
Is there a difference in pipe size between the SC, and 3.8L Stang (94-up)? I am talking about from the collectors to the cats.

I ask this because I was just wondering when I get my new cats put on this weekend, if they (the exhaust shop) may have a problem creating 2.25" downpipes on my stock manifolds to replace the POS restrictive 2" stock downtubes. Is it that hard for them to make new ones with flanges (2.25")

The setup I wish to have is 2.25" custom downtubes to my high flow 2.25" convertors (to be installed). From the convertors, 2.25" to the Flowmaster dual inlet (2.25") single outlet (3") big-block truck muffler (will be my "resonator"). I already have the Flowmaster cat-back setup (changed my fuel tank to 92-up style already) on the car now.

I was thinking about installing the Stang 3.8L downtubes (cut off from the factory y-pipe), that is if the exhaust shop says they cannot make my 2.25" down tubes.

What should I do?

Thanks

Phil
 
The exhaust shop I went to had no problem making my 2.25" downtubes, along with the rest of the exhaust (they did a great job). Any good shop should be able to do it. I can't answer your question about the Mustang downtubes, as I do not know the answer.

-Rod
 
Phil, It is funny that you ask about this. I too am looking to bolt up some 3.8 stang downtubes. But I also have the 95 mustang tubular headders that fit to the downtubes that you describe. I am looking to get a fully built exhaust from the manifolds back, but I wanted this part (downtubes) so I could drive it to the shop without running open headders. I have just finished a full rebuild on the motor and I dont even want to fire it up without having something more than the headders.
As for your application I suggest you have the shop do the flanges and downtubes, like racecougar said, the shops Ive talked with said they can make the whole exhaust.
Good luck
Brandon
 
The restrictions with the stock exhaust though is at the collector. So unless you are going to open up the collector, there is likely no need to change the down pipes at this time.

Your exhaust shop might be willing to open the collector up a bit for you, but otherwise it would be excess work if you plan on redoing the exhaust later down the road and are simply just changing out the cats right now.
 
I appreciate the tip, but...

I think the largest restriction in the factory exhaust is not the collector on the stock manifolds, but the POS resonator which, internally is a mess, and necks down on the outlet to almost less than 2" diameter. I agree the manifolds are restrictive, but nowhere near as bad as the resonator.

Phil
 
no..no.. you misunderstand me. I understand and agree the most restrictive part is the resonator. But now you are getting into other things.

If you are doing a full blown new exhaust to support your future efforts at 350hp, but don't have the money or time for the manifold porting right now, then bigger down tubes now is great.

But if you are scraping by and doing the cats because you need to, but the remainder of the exhaust is fairly stock, then doing the down tubes really isn't necessary. As bigger downtubes won't really gain you anything as long as the necked down collector is still left in place.

It's not necked down bad, but it is down to ,I think someone said, 1-7/8" which is less than 2" of the current down pipe, and much less than 2.25" or 2.5" that many people replace. Thus in the manifold-downpipe area, the collector on the stock manifold is the restriction, and until it's fixed up, you won't see a benefit to the bigger down pipes.
 
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