Possible solution for mating 2.5" to 3" exhaust parts?
 

I e-mailed grimmspeed to ask them but am awaiting a response. However I may order it anyways just to see.

I have a PLM header which as a 3" flange mating to the 2.5" flange of the stock and aftermarket overpipe I just bought. Now with this I had to sort of rig it up using a 3" and 2.5" exhaust gasket. Not exactly ideal or efficient.

Short of taking out my header and finding a place that can adapt it to the 2.5" I decided to google around and see if people had soloutions to doing such a thing for those of us without the tools/know how to do such a thing or want to pay a shop to do so..

I came across this...

http://www.maperformance.com/grimmsp...ck-subaru.html

It's meant to mate a 3" downpipe, however I'd imagine it would also work for this application as well and may help me also when I change out my front pipe to my TRD exhaust which uses a donut gasket..

Was not sure if anyone else has seen this before, but figured id share and keep this thread updated as I do plan on ordering it regardless.

I hadn't seen this before, but looks like it would work.

I don't know if you could do that at the header without moving the overpipe too much (clearance seems right on OPs sometimes...) but it should work anywhere after that I expect.

As mentioned above, this part is exactly what you are looking at, but I would want to confirm fitment since there is tight fitment between the header and overpipe. What overpipe are you running?

That part is to join a 3" fp to a 2.5" midpipe with the oem dougnut gasket... I have this on my car.

Best solution is to buy a 3" overpipe, fiebruz, my local tuner sells 3" overpipes, as well as they can custome make a 3" to 2.5" op or 2.5 to 3" op.

Just bought this. I'll try to include pictures of the install when I get it. I had like 2 days where I didn't smell exhaust after I installed my PLM header with 2 gaskets to make it seal to a 2 7/16" aftermarket overpipe, then it started to leak. My aftermarket overpipe says it's 2 1/2", but that's the outer diameter. It's probably only 2 7/16" inside.
This is worth it just to be able to breath fresh air again. I should have enough play in the mounts to account for an extra 1/4" of flange. Like I said, I'll post here after I install it with my impressions and whether or not it rubs or causes any other problems.

Lots of the guys here (including who you emailed) were gone for Wicked Big Meet. I stayed here designing parts like a good boy :P

So this is certainly an interesting use of our downpipe adapter. I think it'll probably work for you, but after some modification. Subaru has "interesting" bolt spacing on their flanges. So I bet the 3in side will bolt up to the adapter fine, but the overpipe will not I don't believe.

I just grabbed an adapter, and the gasket that would go between the header and overpipe, and the gasket doesn't fit over the section of tube intended for the donut gasket. No big deal, you could cut that off. BUT, the bolt holes just barely don't line up either. They might, and they might not. I'd remedy that by just cutting a slot for the hole. But you'll probably have to do that in your overpipe flange too. Of course, I'm probably wrong as your set up already allows you to bolt that 3 in flange to the overpipe.

So we'll see. But with such an unorthodox setup that we personally can't test we won't know for sure until you try. Since I can't see whatever question you emailed in, is there any specific question you want to ask me?

Chase
Engineering

You pretty much just answered what my question was. If you think it could possibly work.

I understand there is very limited spacing available between the header and the overripe. Right now I have the stock Overripe however I also bought a DC one. There is some room to move the overpipe and hopefully sandwich this in there, however the question is if that will cause any rubbing issues as far as clearence with the overpipe once that is intalled.

Also @Cartman you are right however per-grimmspeeds own description it is slightly less than 3" and slightly less than 2.5 where it is flared out to be able to also fit inside if no donut gasket is used and to provide a smoother air pathway.

@KoolBRZ i have a feeling you will have yours before mine. Interested to see your results as well. Do you have an aftermarket overpipe or the stock one?

I have the cheap Ebay Top Speed Pro 1 2.5" overpipe. I've used Top Speed Pro 1 from front to back and it sounds just fine. I also have concerns about the thickness of the flange causing rubbing against the car. I have lots of clearance now though. I plan on leaving the header bolted up and loosening up both the front pipe and the overpipe to line everything up. This will also alter the resonance wave coming back from the overpipe flange, hopefully for the better, so I'll need to dial in my AVCS tables again. I'll try and get a before and after dyno as well, since I'm doing dyno pulls next Monday.
P.S. I won't be installing it this weekend, since I'm getting dyno pulls this Monday.

Buy the adapter, it works, sorta, after modification
 

I got my dyno's done and am underwhelmed again. Today I determined I'm going to install this adapter flange and stop the leaks for good. I got pics before the removal. I have lots of overpipe clearance, but just one thing won't clear, the flange pipe into the 2.5" overpipe.

See pics below, I had to cut the pipe flush with the flange, then grind down to make the pipe lip flush, then sand and sand to get rid of the gouges I made in the flange while cutting the pipe. Notice how shiny the flange is now? There is about 1/4" of play in the flanges once the bolts are through all three plus the 2 gaskets. The bolt holes will not line up with a stock overpipe, but only an idiot would mate a 3" header to a 2.25" stock overpipe. I used a shorter bolt on the inside of the header curve, and a longer bolt on the top, outside of the curve.

I didn't have an assistant, so there isn't any video, but I got some good pics. If anything my overpipe has even more clearance then it did before. I have before and after clearance pics if you're interested. It really only applies if you also have an inexpensive, Top Speed Pro 1 Overpipe. How does it work? Great, now the only time I smell my exhaust is when I open a door or a window. I'm sure it flows a lot better too.

I apologize for not taking any pictures however much like @KoolBRZ i was able to use the adapter with some modification. The smaller diameter pipe which is meant to take the exhaust donut had to be cut off and then the flange sanded/smoothed.

Once that piece was gone however the tapered side fit into the 3" flange of the header with room to spare. No more exhaust leak and there was plenty of room still even with it shifting the overpipe a bit.

so there's some trimming needed for this conversion? thanks

Yes, it requires cutting the non-flared side of the flange, you can see it from the photos above.

Mine fit without any modification... PLM header to Motive Concepts OP. I chose to try one of these even though its not technically the intended application, and I've been having good luck with it.