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Old 11-21-2004, 03:27 AM   #51
Wylde Horses
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I don't think it's possible to prove at the level of power we're dealing with. With only 2 litres of displacement, there's not a whole lot of exhaust. If one design is better then the other, the difference will be marginal at best, maybe one or two horsepower. Combine that with all the other factors that change between different cars, different exhaust components (mid-pipe/catback/etc.) and the fact that you will most likely get 5 different HP numbers with 5 different dyno pulls that can span 5 to 10hp, and any seeming design deficiencies become merely subjective - 100% opinion. In the real world, it's almost impossible to even feel anything less then a 10 horsepower difference at the wheels, so it's not even worth worrying about.
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Old 11-21-2004, 01:32 PM   #52
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I think you Wylde Horses should win the concise, common sense post of the year award!
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Old 11-27-2004, 10:22 PM   #53
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nice job
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Old 11-28-2004, 04:21 PM   #54
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never understood why someone would pay money for a DP with a flat flange when you already have one. got gut=got free money.
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Old 11-28-2004, 05:34 PM   #55
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So the way in which the air ENTERS somethingis the sole factor in determining its effectiveness?

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Old 11-28-2004, 05:44 PM   #56
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Quote:
Originally Posted by J-Rex2004
never understood why someone would pay money for a DP with a flat flange when you already have one. got gut=got free money.
Gutting the DP, while an option, is a MAJOR pain in the patootie. You have to gut it, drill it our, and reweld it. Even in doing so, you only gain the catless power. Other power is to be gained by going with a larger diameter pipe.

And as a polite reminder, this thread is about downpipe in general. If you have a review, please post it in the Car Parts Forum where it will be accessable via the search engine.
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Old 11-28-2004, 10:27 PM   #57
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Quote:
Originally Posted by Unabomber
You have to gut it, drill it our, and reweld it.
Sorry Unabomber but that's not true. The downpipe does not need to be cut up to be gutted. Mine has been gutted but not cut or welded. I bought it off of ebay so I didn't do it myself. I've been told that it can be done with rebar that has been bent a little. My guess is that it's a 2 hour job..... I gutted a 3rd cat and that took me less than an hour.
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Old 11-28-2004, 10:29 PM   #58
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That's news to me. Sounds like a major pain in any event.
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Old 12-20-2004, 09:27 PM   #59
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always like to bump this excellent thread. finally took the plunge and installed a stealthback system. General criticism to this thread: time involved/simplicity: to the avg noob reading this forum that hasn't had their hands in the engine bay of a WRX on a regular basis, I think the times are a bit understated. (i proudly fall into this category, BTW) My buddy and I, with good tools, and not even counting heatshield removal/replacement (did this a few days earlier) took over 2 hours. And we DIDN't remove the innercooler, since we had lots of goodies (flex sockets, breaker bars, etc) Had we removed the IC per TXS instructions, and done the heatshield work, would have easily been 3.

The reality is, if you've never done the job before, and get into "careful instruction-following mode", it takes twice as long as someone like yourself who has the plan in the brain, and is constantly turning a wrench.

my two cents.
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Old 12-20-2004, 10:22 PM   #60
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You are right, I changed the time to 1-2 hours. I keep forgetting what it was like to do it for the first time. I have some fast install times and some horror stories under my belt though.
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Old 02-22-2005, 03:44 PM   #61
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Maybe I'm wrong but I didn't see any gasket part #'s in this FAQ? I just bought a used downpipe and need to replace my worn ones
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Old 02-22-2005, 09:25 PM   #62
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No gasket #s sorry. The reason for this is there are 99,000 gasket combinations with different exhausts and I'm not about to look them all up.
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Old 02-22-2005, 09:27 PM   #63
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You need to replace the one from the DP to the turbo, or the DP to the cat-back?

At any rate, http://www.kastleskorner.com

They'll have them. If not, go to the dealer, shouldn't be too much.

Aaron
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Old 03-08-2005, 02:10 PM   #64
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What, if any, are the differences between the 04-05 Sti DP as opposed to the 02 WRX?
I assume it's not a bellmouth but just wondering. I heard the cats may flow a little better and the pipe diameter may be a little larger.
Pls shed some light....Thanks
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Old 03-26-2005, 02:27 PM   #65
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unabomber, i could not find the info about aftermarket compared to stock gutted downpipe. where as in the uppipe faq i found the info under the "cheapest uppipe"
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Old 03-27-2005, 01:21 AM   #66
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The STi downpipe has a bigger cat than the WRX and is either the same size or slightly (1/4") bigger. They are pretty much equal for all intents and purposes.

As all aftermarket downpipes are bigger in diameter, an aftermarket unit will always provide more power than a gutted stock downpipe.
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Old 04-30-2005, 03:01 AM   #67
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Has any one realeased an MIL fix for the 2005 WRX? The pony express site says the 2004 model won't work on the 2005.
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Old 04-30-2005, 03:45 PM   #68
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That's news to me. Go with the mechanical fix then.
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Old 07-19-2005, 01:33 PM   #69
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Thread resurrection-

Just wanted to compliment Unabomber on an intriguing and informative thread. Thanks for the intro into DP's!

-Mike
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Old 11-11-2005, 06:14 AM   #70
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If it's okay, I thought I would make a post detailing the reasons why we chose to create a divorced wastegate design downpipe and why we thermal coat our pipes. It's just a post about what we decided based on our research and why, so we're not saying it is the best, we're just saying we feel that it is and hopefully it's somewhat interesting food for thought ...most of this is from another post, btw, so I apologize if a couple sentences are slightly out of context ...


*** The Crucial downpipe is a full divorced wastegate design. We brought the wastegate pipe as far down the main pipe as possible and merged it at as shallow of an angle possible, to both minimize the turbulence caused by the merge as well as get that turbulence as far as we could from the turbine outlet. This is the absolute ideal situation while still using an internal wastegate turbo.

*** We choose to make a divorced pipe because of the benefits [in our opinion and testing] over a bellmouth or any other design. Giving the wastegate a consistent and efficient atmosphere in which to vent allows for extremely good boost response and control, and makes boost tuning a breeze. A well-known Bay Area tuner stated that, while tuning one of our customers' cars, the boost response felt like the car had an MBC on it, but it was stock ECU and stock solenoid. The huge reduction in turbulence behind the turbine outlet means smoother and more efficient exhaust flow, which means more power.

How much less turbulence? As a decent visual of how our divorced design works, here's a picture of a VF39 exhaust housing with a mock-up of our downpipe attached (gross looking mild steel flange [cut identically to our stainless ones, of course] w/ diver plate affixed, but no downpipe obvioulsy):



Our divorced design is the smoothest possible transition from the exhaust outlet to the downpipe that you can make with an internal wastegate! No wastegate gasses slamming right into the main stream causing huge amounts of turbulence, and no empty space to fill up and cause turbulence/eddies!

*** Crucial's thermal coating completely negates the need for pipe-destroying exhaust wrap or a big aftermarket heat shields in order to keep your top mount intercooler from getting heat soaked, which is a very pronounced problem with a bare stainless downpipe. How effective is it?.... here's a test conducted by Comp Cams of the coating we used to use on our pipes. We have since switched to an even better, more effective coating (but there are no 3rd party tests yet)!!!



Other not-trivial benefits of coating the pipes are: () the coating protects the metal from the corrosive elements in exhaust gasses, as well as from the weather and anything that may be spilled on it under the hood () the coating actually protects the metal itself from the exhaust heat, since it is applied inside and out. It also takes much longer for the heat to get to the metal. Both of these things add up to less stresses on the metal that are usually caused by the heat and the constant heat cycles. Less fatigue = longer life. () The heat is retained in the exhaust gas where it belongs. This means higher exhaust gas velocity as it does not lose energy, which translates to more power and more exhaust scavenging.

....and it's stealthy & sexy ...

Okay I think I've rambled enough! We're pretty proud of it though.

Jeremy Siwek
Crucial Racing Systems, Inc
CrucialRacing@gmail.com
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Old 11-27-2005, 12:50 AM   #71
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thanks helped a lot
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Old 01-07-2006, 09:35 PM   #72
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Will an aftermarket downpipe fit my oem exhaust with no problem/leaks?
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Old 01-07-2006, 09:45 PM   #73
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Quote:
Originally Posted by NoCalSubie
Will an aftermarket downpipe fit my oem exhaust with no problem/leaks?

If you get one that uses the factory donut gasket ie COBB, then yes.
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Old 06-24-2006, 01:45 AM   #74
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Default gutted oem vs aftermarket downpipe?

gutted oem downpipe vs aftermarket downpipe

can anyone show what the hp difference is?
I know there is some I just wonder how much?

If anyone has some head to head dyno stats , please let it be known.


thanks!
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Old 06-24-2006, 01:56 AM   #75
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No dyno stats and probably never will be. A full downpipe will give best results as a bigger pipe is the key. If I had to guess, I'd say a gutted OEM downpipe will net 50% of the results vs. a 3" aftermarket catless unit.
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