To gut or Not to gut?

[SallySpeed3]

Funds are short after my recent purchases and I can't rationalize more money on a DP since it's something I was trying to stay away from anyway. So I thought maybe gutting it would be a good way to achieve the last bolt on mod I have left to do without spending too much money. Would it need to be removed in order to do so? and if yes, how much do you think a shop would charge? I know its a vague question, I'm just looking for estimates to give me an idea.

 

[blackdragon0731]

I wouldn't gut the stockers personally. How much are you limited to fundwise? The ATP full downpipe is less than $400, but it's catless. You can get either the midpipe or short downpipe for cheaper than that too, and they bolt right up, the only issue I have had was the flange to the CBE not mating up correctly when both hangers are used with the long DP, so I have one hanger on the DP and the other just hangs off, but the hangers on the CBE portion are so close it makes no difference.

 

[MSMS3]

I'd say save up and do it right. Besides, you might need to go back to stock if/when you decide to sell the car or trade it in.

A gutted stock dp would eliminate that low flow primary cat which would free up some power. I see you already have a test pipe. But there are several disadvantages to gutting the stock downpipe (beside not being able to go back stock).

First, the stock downpipe has a very sharp right angle pancake design, probably optimized to help the primary cat heat up and to please the emission nannies.

A good aftermarket downipipe is going to have a large CAST stainless bellmouth shape leading into a smooth transition 3 inch stainless section. The bellmouth part will have a much greater inside diameter front chamber than the stock one. That shape and design really helps with flow and reduces turbulence as the super hot gasses from both the turbo exhaust and the wastegate first expand into that bellmouth and then cool down entering the pipe. Some downpipes have a "divorced" wastegate pathway that also cuts down on turbulence.

Second, the stock downpipe remains a flow restriction because you have a 3 inch test pipe and CBE, but still have the smaller stock diameter in the downpipe, which is going to reduce flow. Pipe diameter needs to be larger first coming out of the turbo and can be smaller once the gasses cool down some.

Third, gutting the cat (which you can do yourself, if you are really interested in this) increases flow but may actually induce some more turbulence because of the hollow cat shell creating some disruption in smooth flow. You really want a smooth pipe with as few changes in direction of flow as possible.

You might want to go over to the MSF board and read some of the "Nator" threads there for guys who have done the DYI downpipe gutting. Maybe that will provide some better info. A quick check there shows one guy who did get impressive dyno gains by gutting. He is running Cobb AP tuning.

I'd just save up and get the matching downpipe for your test pipe and do it right. I love the TXS downipipe because of that big cast bellmouth, its flex joint, and its high quality construction. Priced different places between $250 and $300 shipped. The Corksport that would match your test pipe has the divorced wastegate, a very elegant design and very high quality construction, around $300 also. There are others out there, as you know. There's even a single long tube e-Bay one for only $170 I think, but I'm not impressed with the thin walls and the design (no cast bellmouth).

 

[SallySpeed3]

Thanks for your thoughtout response. I guess it's just going to come down to whether or not I have the nerve to go for it. I know I'm probably looking at anywhere between $250-$400 to have a shop properly do the install, plus the $300 for the downpipe. But that doesn't include the possible added costs of stripped o2 sensors, seized studs, and then there's my big worry that once they get the DP off I'll find out my turbo seals are shot to s*** or some other problem. Ah worry worry

 

[blackdragon0731]

I personally installed my downpipe in my driveway with a group of buds I trust working on my car. We used a lot of PB blaster and took our sweet time and it came out great! The biggest thing was being careful with the o2 sensors but luckily we had no issues and used anti-seize on the threads of everything when we put them back in. Take it to someone you trust and it should be nowhere near $400 for an install, it took us a few hours but we were working in my driveway... with a lift and some better tools (more specialty tools than I have) the stock DP could be out in a relatively short amount of time.

 

[Darth Vader]

I'd rate the DP install on this car maximum 7 out of 10 on the difficulty scale. As has been stated, a patient person with a few hand tools can do this relatively easily in the driveway. I did it solo, taking my time, in under 6 hours, including breaks for lunch, etc. That said, I am in no hurry to do it again.

If you want to punch the cat out of the DP, you could do it with the DP in the car. A small piece of rebar up the outlet, bash the media out and, that's that. You could do the same with the mid-pipe. I wouldn't be surprised if you got most of the gain of an aftermarket DP doing this.

 

[saxmanbrad]

the rebar suggestion seems really cool! Tempting as well!

 

[Darth Vader]

Yeah just mark off your depth with a bit of masking tape so you don't punch too far and hit the upper O2. You'll want to pull the lower one before going at this, I'm sure. It's cheap but, why bust it if you don't have to?

 

[saxmanbrad]

Darth, just seemed like any easy way to get the advantages of a gutted cat without the pain on the DP install. I am still considering a catless upper DP, as I have a testpipe currently. The pain of install and possibility of smoke make me hesitant though. (I have been on the fence about the DP for quite a bit). If I go with the catless DP, is it worth it to upgrade the intercooler and fuel pump? I don't think my mods plus a DP would put me in dangerous territory for low fuel pressure. The increased drone is also an issue I would have to address as well. Man, I have too much time think about all this stuff!

 

[SallySpeed3]

After reading some threads on the other forum I feel better about gutting the DP. I might look into a shop doing it for me because I also want to have a high flow cat welded in my exhaust somewhere for backpressure and I don't have a welder. If it's possible to do it with it still on the car that would be fantastic but I read that the angle of the DP makes it impossible to get to part of the cat, don't know if that's true or not.

 

[MSMS3]

Good decision, Sallyspeed, IMHO. I have a complete shop with all the pneumatic tools and hand tools anyone could ask for, and a nice lift. Still after reading some of the threads, I realized that unless you do exhaust work every day, you can spend a lot of time and still mess up no matter how careful you are. So I did farm out the dp install to a local performance exhaust shop that we do business with and that does a lot of work on race cars, mostly circle track sprint and stock cars that now have to have some kind of muffler on them.

Two guys, four hours total, one up top in the engine bay another under the car. $200 and that included the labor for changing out my stock exhaust tip to a slightly smaller 3 1/2 inch Magnaflow stainless single wall. Extra charge for the part, of course, but not much.

When I discovered the severe drone this setup had at 2,500 rpm when decelerating I ended up adding a big 3 inch Vibrant UltraQuiet reso in the middle of the test pipe. I did that myself up to the point of making the cuts and clamping the reso in place, road testing it, adjusting it just right, locking the clamps down and then removing it. Took it back to them and got it permanently welded in place - $30.

Yeah, I could have done it and like Darth and spent 6 hours (or more, because I'd be very, very slow). I just felt more comfortable letting "do it every day" pros work with easily stripped out studs and O2 sensors. Besides, I'm 60 years old now and busted knuckles ain't as much fun as they have been in the past, either. lol.