How not to make your own Downpipe.
 

So today I took my downpipe off to weld in a bung for my AEM Wideband. I had no idea how crappy it is. First of all the bends suck, they aren't welded very well though and look like crap. The final bend is crush bent, making my 2.5" DP more like 1.5" so my entire exhaust system is bottlenecked at that point. To top the cake my external wastegate system is also complete crap. I'll post some more pictures of that after a bit when I take them. I also spent 5 minutes today drilling a hole in the pipe and welding the bung in it. I didn't care what the weld looked like so don't let that be a example of my welding ability.
Again:
HOW NOT TO BUILD YOUR DOWNPIPE!

Hahaha that's sweet.

wow that is one ugly bend but i don't know if it gets any smaller than stock

The rest of my exhuast system looks good, all 2.5" going back after that flange. That is definitely the bottleneck of the system for sure. That's what I get for buying a car with the DIY turbo setup already on it. Always better to do it right yourself.

WOW!

That has to be the fugliest D/P ive seen! I hope you didnt make that..If you did then think of it as a learning experience!! that thing will be killing so much power from your system. I bet when you get a proper 2.5"DP youll spool at least 300 rpm earlier and make 10-15 more RWHP without any other changes!

Have a look at the bottom of page 6 on my Cardomain site for a real DP!
http://www.cardomain.com/ride/264041/6

Yeah i definitely didn't make that downpipe. The sad thing is the guy i bought the car from in Kentucky had the entire kit put together by a performance shop. They must have been smoking rocks to think they were building a good product. Mine would look far better. I might end up rolling out my own product early '07 we'll see.

that looks pretty bad, you'll pick up some power if you get a nicer downpipe 3" would be nice.

Check out my old vs. new downpipe, that sure made a huge difference in spoolup/response/power on my car.
Attachment 217204

Man, do you have pics of your manifold as well. because that downpipe is pretty badass.
Who made it up for you?

holy shit that thing is beefy

No way...Not possible ;)

Thats a gorgeous piece RusMan.

Very quality looking piece. 3"? Gotta love some real craftsmanship.
-Michael-

Holy crap rus....
How do you stop your transmission tunnel from melting with a 3" dump pipe?? i have enough trouble with a 2.5"!:eek:

SS would be better at it than Mild Steel.

anybody who has made one can appreciate all those cuts and welds

cjernigan, what's up with the wastegate port, it looks like it comes back around the front?


ohhh, wait, were you the dude who bought that used kit off ebay? So your external wastegate was actually a port off the exhaust, not the manifold?

No, SS would be worse.

Doesn't stainless steel have greater insulating properities. Mild Steel on the other hand radiates like a champ.

No 304 SS will conduct heat better than 409 MS.

I'm still sticking with more heat stays inside the stainless tubes and does not get passed into the surrounding air. Mild steel tubes will give off heat rather then insulatling it. It's exactly why SS downpies do better for underhood temps then MS, and why you need to get them thermal coated.

matweb says otherwise (16.2 W/m-K vs. 24.9 W/m-K). A mild steel like 1018 is 51.9 W/m-K, chrome-moly 4130 is 42.7. As a reference, 6061-T6 aluminum is 167!

Generally speaking, stainless steels conduct less heat but expand more than mild steels. I think this expansion problem is why you don't want to ceramic coat stainless pipes.

Thanks for the awesome site, Tim. Looks like both materials have about the same specific heat capacity, but steel is a *little* better thermal conductor. So, why do all the Viper and Mustang guys report higher under hood temps when they switch from mild steel to stainless headers?

Below is the equation for thermal conductivity (k). The factor L is the thickness of the material used. Tim, since you're a fabricator (and I obviously am not), what is a typical wall thickness for a mild steel exhaust pipe? How does that compare to the typical wall thickness of a stainless pipe?

Is it possible the difference isn't material but thickness of the tubing used?

anyone know where i can get the flange that connects to the cat?

Yes, that's what I asked in the post above. The specific heat and conductivity properties are *very* close on both of the raw materials, so I'm thinking the diffence is in volume.

Isn't it the metal's inability to cope with it's expansion? IOW mild steel is way softer and can manage the expansion and contraction without cracking/tearing. Whereas stainless being harder will tear/crack sooner. I think that's why you don't see any super thick SS manifolds like you see thick mild steel.

I got mine here (https://www.headersbyed.com/), nice folks and the cheapest prices I could find. They do have a minimum order requirement though so you migh want to get a few other people together.

it's just a standard 2-bolt flange correct? you should be able to find tons of sources. call some muffler shops.


BTW i responded to your FMU post with pictures as requested....

Yeah my downpipe is 3", I didn't notice any difference in temperatures, I did when I took the cat out. The downpipe, as well as my exhaust, were fabricated by a local one man shop Garage Auto Hero, very nice guy and does awesome custom fabrication stuff, they specialize in datsun510's/ae86's, one interesting car in the shop is a bmw z3roadster with sr20det running 470rwhp. The best part is I only paid $240 for that downpipe, I think it's a steal!

Here's a pic of my new exhaust, just finished last week. 3" turbo back with just one muffler.
Attachment 217203

ok and when are you ready to get me a copy of that exhaust?!

I didn't buy a used kit off ebay. I did however find my car on ebay and it just happened to come with this shitty kit already installed. If you look at the link in my signature you can see how the WG piping is routed in a engine bay photo. It is in the exhaust instead of the manifold though. I'm running a HKS manifold right now, but not for long. This crappy setup is killing me.

yeah thats the ride. i can't believe how nice the rest of the car was done compared to the creative turbo setup.....

Yeah it's kind of funny really. That awesome stereo system that was in it. It was complete garbage, didn't work half the time. So i tore all of it out. Saved about 25lbs in stereo crap including the subwoofer enclosure in the floorboard. Replaced the deck, trashed the DVD player replacing it with a gauge face plate. So that is much better now. It's been running a Narrowband 02 gauge and sensor so I got an AEM controller w/gauge. Replacing that this week. The indiglo gauge faces have some wiring problem and don't work half the time. The IC piping is all powdercoated mild steel and is a terrible fit. Seriously took me like an hour and a half to reinstall all of it again because i had to bend the couplers so much. The oil lines were all high temp silicone with like five brass fittings coming off the turbo. Really i could keep going on. The built motor is good with the wisecos and pauter rods. The powdercoating is nice. The wheels are cool but heavy and the BFG KDWs are really nice. The body is nice with like 2 small door dings in it that I'll have fixed within the year. The alarm that is in it needs some major adjustment because it goes off whenever i start up my truck so it's way too sensitive(or my truck's too loud.)
So yeah, i'm pretty much redoing the car slowly but surely because someone didn't know what the hell they were doing. What blows me away is the invoice for the turbo kit.
T25- 620.00
HKS manifold- 424.99
Spearco IC- 524.99
Tial WG- 239.00
Tial BOV- 239.00
IC piping Powdercoated- 350.00
Oil lines- 75.00
Labor for Turbo kit- 400.00
Apillar guage pod- 35.99
T25 DP flange- 35.99
Autometer boost gauge- 52.95
Autometer A/F gauge- 58.98
Total For the crappies turbo kit ever- $3056.89


WTF was he thinking. Either way i got the car for less than dealer black book with less than 20,000 miles on the rebuilt solid motor. Clean body with one wreck in it's history, but that's non big deal. It wasn't the best deal ever but it was alright.

The car itself looks very nice! There are certainly a lot of high quality parts there, maybe the fabrication man was sick that week...real sick... If you want any of it refab'd let me know if I can help.
-Michael-

This thread is how NOT to build a down pipe, how about a HOW TO build a down pipe forum, for those of us that are about to??

Sexy looking downpipe Rus!

Very nice DIY stuff.

MarkP's setup might be ghetto, but I bet it kicks the Sh*t out of my setup.

How about a DIY manifold and DP sticky. Get everyone to post pictures of what they are running together on their car. Give some people ideas that want to venture making their own or having one fabbed up for them. A good visual archive so people know what a "megan racing" or "ETD" manifold really is and how it can be used.