Ok I have been reading old posts on this subject all day. So..........

Here is the set up. K27/6 with a gutted cat, 38mm Tial, Vitesse MAF and chipboard for the K27 along with 72 LB injectors. There is ABOUT to be a 3 inch stainless catback with a Spintech muffler installed to replace the back section.

The origianl muffler had rusted (of course) and been welded by the P.O. So the catback is going on just to replace the bad muffler section, plus I am hoping the Spintech will sound better.

My question is, (pause for effect) will I see much (if any) in the way of HP/TQ gains by going to a full 3 inch, front section over the stock 2.5 inch with a gutted cat? Will it be worth the cash to go ahead with full 3 inch at this level of mods to the system?

Oh yeah I am running 15psi of boost.

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I'd be willing to put money on it, you will see an improvement. Will the improvement be worth it? The only way to know is to try it. If you don't get what you want, sell it

 

Karl at Imagine Auto dyno'd a 3" Lindsey vs a 2.5" factory system with a gutted cat and got a whopping 3-4 hp difference. The car was running a stock AFM and K26/6 turbo tho, so it had some other restrictions that make it a bit harder to say what the effect would be with your mods. I doubt you will see as big a gain as you would expect, as I think the cat is the biggest obstacle and you have removed that already.

FWIW, I have a 3" Lindsey on my car as well, and I like it.

Regards,

 

when I went to a 3" exhaust I noticed a difference in spoolup time (quicker vs stock exhaust), of course replacing the 20 yr old cat with a new one may have been the real reason for the difference. Also, I like the sound alot better, that alone was almost worth the cost to me.

Another thing to think about is that while the 3" exhaust may not make a huge difference now, if you are planning on continuing to upgrade your car, eventually you'll get to a point where a bigger exhaust is needed, so might as well do it now

 

Muffler design and bends are the biggest losses in the exhaust system followed by overall flow volume restriction in the piping diameter.

I will say the standard for the rest of the 4-Cyl world is 3" even on N/A engines. You guys were blessed with a stock exhaust that isn't complete trash, but with an upgraded turbo you'd be crazy to think it isn't causing backpressure.

 

Plus whatever weight savings you will get. We noticed about half the weight of the stock one v's the full 3" system on the car now. Worth it in my book let alone the new sound which is worth it just for that!

 

I would say 80% of the gains are just getting the cat outr of there.

But, with a bigger turbo and MAF, then there is more use of the 3" beyond just the cat being out.

 

Because you have so many mods it will be noticable. I say just go ahead and go full 3"

 

I am really thinking about it at this point.

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Dyno it before and after. Do your P-car family a favor and let us all know once and for all.....is 3" really a gain or not.

 

Oh absolutely. If I do it that will be posted like it is cool.

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On my old car I put in a test pipe and noticed only a small difference. Because I didn't like the idea of getting a huge ticket for no cat I had a high flow racing cat installed with a new magnaflow muffler.

That's when I noticed a huge difference. I really think the stock cat and muffler combined are the biggest culprits. I've heard 3" exhausts before and for me they are too obnoxious for daily driving. 2.5" high flow was just right. for me anyway

 

don't forget the 3" downpipe!

 

Just do it......then smile as you look back at what tried to pull next to you.....I will say that more then once I have had people say they really liked the sound of mine....so ?

 

Jeeze, how much has been written about this already...

Did you happen to use the search function?