87-93 stock cats fit 85?

[Dogster]

I was getting ready to buy the Magnaflow H Pipes w/CA legal cats but since I'm in CA the X and H are illegal until they release the new units. The release date keeps getting rolled back and I need to get something on the car so I can replace the rest of the system. I currently have the stock two pipes into one cat, going back out to two mufflers and tailpipes set up (which have large holes in them from the car sitting, cat pipes included). So Plan B was to buy the stock Ford dual cat w/dual pre cats setup. There are plenty of new ones on Ebay but the seller says the Ford part number listing was only for 87-93. Since I've read here the Ford H Pipe will bolt up to my 85 headers, why is the seller saying that? I asked him but he didn't know why, only assumes there must be some difference between 86 and 87. Were 86 H pipes different? Thanks for any info.

[grtskydog]

86-93 are the same. You would need '86-up headers, or a/m shorties to use the H-pipe...the heat riser mechanism on the '85 header makes it a funky size. Don't forget the double-hump transmission crossmember change too. With Kalifornia, there may be some requirements/restrictions I'm not aware of. Marz or Cook can chime in with that info. They're kinda the resident Emissions Experts.

[RedRS]

^Exactly, the headers would need to be swapped for '86+units, or just get some aftermarket shorties, they are cheap, can be had used for $50 or so.

[GTJerry]

The ends of the 85 headers are bigger than the 87-93 headers. I've heard that some folks have used the 85 headers, but I think there is a risk that they will not seal properly. The first picture shows the ends on the exhaust headers - 85 on the right. The second picture shows the 85 header next to the flange of the 87-93 H pipe.

I think most folks replace the 85 headers with 87-93 headers, but you will loose the heat tubes to the air filter and the heat riser at the end of the driver's side manifold. May not be a big deal depending on what you want to accomplish.

Like Ed says, you will also need the double hump transmission crossmember and a H pipe bracket. And you will have to do a little replumbing of the air tube from the air pump to the cats. You will need the H pipe bracket specific for the 87-93 exhaust - it's different than the one on the 85.

Hopefully the pics will help.

Jerry

[Marz]

From what I remember on previous discussions... with the heat riser on the drivers header it is the same length as the 86+ headers.

You can go with the 86+ stock headers and just have heat risers welded on so you look smog legal.

Just get a factory stock 86+ h-pipe (with air injection line) and double hump cross member and you'll be set.

My 85 GT has this set up. You're welcome to come to Culver City to take a look at it if you want.

Also, you'll want to keep that stock exhaust... just in case....

[JACook]

Near as I've been able to tell, it depends on which '85 headers you have. The
4-into-1 style '85 headers, with the heat riser on 'em, are longer than the '86-
up headers. From what I can gather, not having ever tried it myself, if you have
the headers that join two tubes ahead of the collector, and then merge three
tubes at the collector, you might can bolt up the later h-pipe.

The size difference is not a problem. The length difference is.

I don't know that the '86-'93 cat pipes were ever technically smog legal on an
'85, but I do know I've never had anyone even comment on them, either on my
'85, or the StaWag. The '85 was last smogged end of January.

IMO, this latest round of regs is aimed at people who modify Honduhs. I think
it'll eventually sort itself out. Worst case, I still have a complete stock '85
exhaust system...

[Marz]

Ok, at my mothers place and looking at my 85 parts in the garage. The one wher the #3 cylinder goes into the #1 cyl pipe 1985 header is indeed shorter than the 4 in to 1 collector 1985 headers. Possibly by a halft an inch or so.

I looked at the driverside header

[escogt]

Nice info Jerry Cool pics too bro.

[GTJerry]

Thanks, Mike.

When I tried to install the 87-93 H pipe on my 85, I could not get it to line up with the stock exhaust manifolds - if anything, the stock manifolds seemed to be a little too short. And maybe the H-pipe was tweaked a little - seemed that the spacing between the H-pipe ends where it connects to the manifolds was a little different that the Y-pipe I removed.

Anyway, after wrestling with it for a few hours (on my back under the car on jack stands), I decided that the original exhaust wasn't all that bad an idea and bolted it back in.

I've got my two other Mustangs with H-pipes, so I decided to keep the "stock" theme going on the 85 until something wears out or breaks.

But that's just me. Let us know how this goes and if you run into any problems. I still have the parts and may go back to trying this when the mufflers go.

[Marz]

Thanks, Mike.

When I tried to install the 87-93 H pipe on my 85, I could not get it to line up with the stock exhaust manifolds - if anything, the stock manifolds seemed to be a little too short. And maybe the H-pipe was tweaked a little - seemed that the spacing between the H-pipe ends where it connects to the manifolds was a little different that the Y-pipe I removed.

Anyway, after wrestling with it for a few hours (on my back under the car on jack stands), I decided that the original exhaust wasn't all that bad an idea and bolted it back in.

I've got my two other Mustangs with H-pipes, so I decided to keep the "stock" theme going on the 85 until something wears out or breaks.

But that's just me. Let us know how this goes and if you run into any problems. I still have the parts and may go back to trying this when the mufflers go.

Well, you can always do something similar to what my LTD LX has. Have the stock 85 tubular exhaust manifolds and stock 2.5" duals. But instead of the 2.5" Y collector do a 3". So it'd be 2.5" dual to 3" single (only difference is my LTD is 3" single all the way to the rear). Then have the rear Y redone to 2.5" dual with a new set of 2.5" Stainless steel tipped flowmaster tailpipes.

[Dogster]

Now I remember why I didn't change the system before... Thanks for the info. I'm going to check my headers tomorrow to see what style I have.