Modifying stock DP?

Let me premise this post by saying that I come from a american V8 background of parts and cost. It seems to me that there is an extreme markup on the cost of a DP for our cars. The DP, especially in shorty form, is really and exhaust pipe about 2 ft long with a simple bend configuration to it. Yet, the cheapest DP's typically run $260+. This in turn has caused many to turn to modifying their stock DP (i.e. gutting the cat).

The one real problem with the stock DP seems to be the mounting flang, where there is no escape for the exhasut from the WG. Has anybody tried or thought to simply cut a 1/2" or 3/4" flang in the same shape as the stock but with a provision for WG opening?

You could cut the new flang with a belmouth design and add a small section to the stock pipe to accomodate the larger opening or you could cut the flang with a divorced opening and run a smaller pipe down a bit, similar to the crucial.

I even think if you cut new flangs for both ends of the DP, you could get a section of 3" SS pipe and have a competent exhaust shop bend you a new pipe and weld it on for less than a new one.

I kn ow there has to be a recoupe of lost R&D for a mass produced part but honestly, it seems like overkill right now. If I am way off base here, please let me know but I am just trying to think outside the box. PLease give some input,

Kyle

I don't know about shorty but i heard that MR's dp would be around $200 or less(when is comes outs). They are leading the market in price as far as i can see. Their headers are under 300 (uncoated) and their uppipe is $100. Most people have been happy with their quality too.

Everyday i debate gutting the dp, because i have an ap and been stage 1 for about 4 months. I just can't make myself do it.

Goodluck on your project, I am sure some people will provide you with some help.

IMHO, it would defeat the purpose to gut the stocker and then try to modify it in the manner you describe.

Yes $280.00 it seems like a lot for a pipe, but we're talking about very limited production runs. If it makes you feel any better, I've been told the profit margin on these downpipes is quite small.

Look at it this way, the vehicle is $28,000. The downpipe is $280.00. That's 1% of what you paid for the vehicle.

^True, spoken like a true consumer.

Always look for least expensive option that gives you what you want!

^True, spoken like a true consumer.

Always look for least expensive option that gives you what you want!

I'm not sure that being a called a "true consumer" is a good thing.

The original poster was asking about modifying the stock DP by fashioning a one-off flange to accommodate either a bell mouth or divorced wastegate design on the turbo end. Basically, he'd be fabricating the top half of the pipe from scratch. Maybe he could do it all himself, in which case we'd want to know the value of his own time (labor) and the cost of materials.

My point was, whether he's doing the job himself or paying someone else to do it, I seriously doubt he'd be better off than if he purchased an aftermarket DP. On the other hand, I have no problem with simply gutting the stocker as a means to save some cash and retain a stock appearance.

i got a stock gutted up, and then gutted my down, and the down was maddd easy. i took me (n00b) and my dad about 11 hrs to do the whole thing (n00b). so i didnt have a chance to really drive it yet.

DP walkthroughs are all over this forum, basically a hammer, long screwdriver and/or crowbar did me wonders. i would highly recommend goggles and a facemask(or alteast something to breathe through)

Has anybody tried or thought to simply cut a 1/2" or 3/4" flang in the same shape as the stock but with a provision for WG opening?

 

Kyle

pre-cut flanges are available for $20-30. I have a 1/2" thick one cut with openings for a divorced wastegate setup. I had originally planned to get a 15 degree expansion nozzle from burns stainless and rig up a DP with the skinny end of the nozzle sitting just inside the turbine outlet. then I got lazy and bought a cobb pipe. truth be told, I just didn't feel like welding on car to get the one-off fit necessary for the setup I wanted and the cost would have been pretty close once all the stainless mandrel bends were ordered + time.

I plan to Dyno my car soon I have a stock up-pipe, a stock gutted down pipe and a stock gutted mid pipe. I have an AP with a TDC STG2. Im guessing that Im not going to be more than 5-10whp off a full length catless down pipe (Cobb ect). I got my down and mid pipe from the "For Sale" forum on here and paid a total of $100, I wanted to keep my original so I could return the car back to stock.

 

I say just gut the stockers "IF" you are on a budget. Its the cheapest way to STG2 with very little left on the table compaired to a Full Catless "Cobb or other" downpipe.

That is what I have done right now, although I have not installed or modifyed anything yet. Honestly, after looking at the stock DP, it seems that it may be more hassle than it is worth. Let's be honest, the WG only bleeds off excess boost to help maintain boost levels. It is not necessarily that much of a flow restriction. The valve itself is already impeding the flow of the WG anyways. I'll look more into it as I get closer to teh install.

Kyle

I plan to Dyno my car soon I have a stock up-pipe, a stock gutted down pipe and a stock gutted mid pipe. I have an AP with a TDC STG2. Im guessing that Im not going to be more than 5-10whp off a full length catless down pipe (Cobb ect). I got my down and mid pipe from the "For Sale" forum on here and paid a total of $100, I wanted to keep my original so I could return the car back to stock.

 

I say just gut the stockers "IF" you are on a budget. Its the cheapest way to STG2 with very little left on the table compaired to a Full Catless "Cobb or other" downpipe.

Keep us posted for the dyno results.

Well the car goes on the Dyno Tues@3pm anyone care to guess what it will put down ?

My 03 STG2 WRX TurboXS Turbo Back, STi Up-pipe put down 227WHP / 225WTQ on the same Dyno. Here is the Dyno plot:

http://Nutter.smugmug.com/photos/91946051-L.jpg

John

So on P&L's DynoJet I put down 242WHP and 291WTQ

A stock STi on the same Dyno puts down 247WHP and 268WTQ

A STG2 MT LGT With an up-pipe and down pipe, filter and Perrin Topmount did 254WHP and 295WTQ

Dyno plot to follow

John

So on P&L's DynoJet I put down 242WHP and 291WTQ

A stock STi on the same Dyno puts down 247WHP and 268WTQ

A STG2 MT LGT With an up-pipe and down pipe, filter and Perrin Topmount did 254WHP and 295WTQ

 

Dyno plot to follow

 

 

John

Great info!! Thanks John..

I am looking to go the way of the gutted DP..I want to retain stock look and still be able to go Stg 2. I guess it will leave about 6-7 WHP on the table..not that bad.

So on P&L's DynoJet I put down 242WHP and 291WTQ

A stock STi on the same Dyno puts down 247WHP and 268WTQ

A STG2 MT LGT With an up-pipe and down pipe, filter and Perrin Topmount did 254WHP and 295WTQ

 

Dyno plot to follow

 

 

John

That helps. No need to save up for a shorty if gutting is this good. I forget, are dynojets generally high reading or low reading?

I bet with a gutted uppipe (or sti uppipe) you may free up a few more hp and tq.

GOOD NEWS

Best Run 242.62WHP@5388rpm and 291.83WTQ@3045rpm

All three runs together with a/f:

http://nutter.smugmug.com/photos/112056048-O.jpg

Best Run with a/f:

http://nutter.smugmug.com/photos/112056041-O.jpg

That helps. No need to save up for a shorty if gutting is this good. I forget, are dynojets generally high reading or low reading?

I bet with a gutted uppipe (or sti uppipe) you may free up a few more hp and tq.

 

GOOD NEWS

Dont get me wrong, Im not saying that gutting is better than a true up/down pipe but its not far off for a lot less $$.

Im not sure if its high low or right on, thats why I took a look at the other plots done recently on teh same Dyno.

The stock STi is interesting, lost out big time up to 5000rpm then both hp and tq took a slight lead but not by much.

At 3100rpm I had over 30WTQ on the stock STi

I saw a plot of a LGT without and with an up-pipe. Gained about 8hp & 5tq, it had a downpipe and Top mount also.

So I would say an STi up-pipe would gain you some, maybe 5hp and 3tq ? however it did spool a few 100rpm later with the STi up-pipe.

^^ Without EM you will likely trigger a CEL. Folks running the Cobb AP can clear those code and run CEL free.

I don;t know exactly why the CEL gets triggered when you gut the cat (or install an aftermarket catless DP)

ok so am i going to mess anything up gutting the stock dp and not having any EM?

You will cause a P0420 CEL (CAT System Efficiency Below Threshold) from your rear 02 sensor.

Also your a/f ratio will not be ideal, you will gain much more by having EM (ie COBB AP)

there are plenty of v1.0 COBB AP's for sale right now because of the new COBB AP v2.0

so save your cash and buy a v1.0 AP used.

+1 I just got my used v1.0 from another member on the board..

They could be had fairly cheap thanks to the release of V 2.0.