Lets talk Custom downpipes.

[1fastlaser]

So i have all my goods together to put on My ON-GREEN t4 cast manifold with a gt4294. Now ive been searching for mandrel piping. Its really expensive to get this done. I was looking into stainless but you have two different kinds 409 and 304 stainless. 409 is from the explaination what they use on factory exhaust systems for cars/trucks and ofcourse less expensive. 304 is typically what nice tubular manifolds like dnp etc, and way more expensive.

Talking to acouple friends that are fabricators i gained some information. I was told if money is tight, do a mild steel downpipe, have it ceramic coated. I was going to put another v-band to seperate the downpipe from the back part of the exhaust. The 2nd part of the exhaust is going to be aluminized. Found out i have to use a 309/312 mig wire, if i remember gas to be used is straight argon.

I planned on doing full 4" turboback, but now maybe for the sake of making it alittle easier i might do 3 1/2". I doubt ill see any or little loss, but if anyone thinks otherwise please let me know.

Now the question is for guys who fabricate exhaust, and maybe know were to go with things as ceramic coating, metal type please let me know. It comes down to this

If i was to do stainless would 409 be ok, and can it be coated? Or sould i just up for a 304 stainless downpipe (remember after the downpipe, there will be a v-band then aluminized steel the rest of the exhaust).

Or sould i just to a mild steel downpipe, get it ceramic coated (were is the best, i know jet hot, but other opinions count).

 

[Slippi84]

So i have all my goods together to put on My ON-GREEN t4 cast manifold with a gt4294. Now ive been searching for mandrel piping. Its really expensive to get this done. I was looking into stainless but you have two different kinds 409 and 304 stainless. 409 is from the explaination what they use on factory exhaust systems for cars/trucks and ofcourse less expensive. 304 is typically what nice tubular manifolds like dnp etc, and way more expensive.

Talking to acouple friends that are fabricators i gained some information. I was told if money is tight, do a mild steel downpipe, have it ceramic coated. I was going to put another v-band to seperate the downpipe from the back part of the exhaust. The 2nd part of the exhaust is going to be aluminized. Found out i have to use a 309/312 mig wire, if i remember gas to be used is straight argon.

I planned on doing full 4" turboback, but now maybe for the sake of making it alittle easier i might do 3 1/2". I doubt ill see any or little loss, but if anyone thinks otherwise please let me know.

Now the question is for guys who fabricate exhaust, and maybe know were to go with things as ceramic coating, metal type please let me know. It comes down to this

If i was to do stainless would 409 be ok, and can it be coated? Or sould i just up for a 304 stainless downpipe (remember after the downpipe, there will be a v-band then aluminized steel the rest of the exhaust).

Or sould i just to a mild steel downpipe, get it ceramic coated (were is the best, i know jet hot, but other opinions count).

DP's are for suckers

Well you could always make the dp out of one material use the vband to seperate the two sections and make from the vabdn back aluminized but the problem is finding someone who sells vband clamps individually and in both steel and in aluminum to weld to the rest of the given sections. What happend to the big ass s374 by the way when you pick up a gt4294?

 

[1fastlaser]

No you use a 309 mig wire to weld say a stainless steel v-band flange to a mild steel pipe. Then i would put a v-band in your typical downpipe ending spot, and do v-band back aluminized steel (typical exhaust shop metal). So again i would be welding stainless steel to aluminized steel. It would save in cost, and last plenty long. I have other stuff i can think of spending 1000 dollars on rather then a sewage pipe.

Just trying to get some opinions on exhaust size, and maybe metal that im using. Because i was still thinking of using the big bucks for a 304 stainless downpipe and doing aluminized the rest of the way, but mild steel with a ceramic coating will I hope yield cooler underhood temps, less expensive, and last as long or longer.

I picked up the 42 last month on a way sick deal i could never let go brand new (lets just say under 500). The other turbo got traded for my k-sport coilovers.

 

[andy4g63]

My advice is go with 4" DP and 3.5" the rest of the piping. If you want or have money to spend, go with 304/ is excellent material for DP and exhaust systems/. If it was me, I would go with mild aluminized steel. Wrap up the DP with black wrap and paint it black. Looks decent and it does its purpose and offers more insulation, than ceramic coated DP.
The more gains from any exhaust sysytem on TURBO CAR, is seen in the DP, the rest of the system has to be decent size and of course bigger than exducer of turbine wheel.
And last, look here:

http://www.dsmtuners.com/forums/newbie-forum/316211-shearer-3-5-v-band-exhaust-pics.html


P.S. I am sure you didn't forget the cost of alternator relocation kit, plus relocating the oil filter and installing oil cooler...
Good luck.

 

[1fastlaser]

Thanks for the reply. I already have the Jays racing relocation kit, and as for the oil filter, and local guy in pa setup his 4" downpipe to fit with the normal oil filter housing, so im going to shoot for that. I use evo oil filters so it should fit, and be able to come off when oil changes are needed it. Im sure ill end up relocating it eventually.

The only thing with aluminized is that im wondering if the joints will start rusting. The v-bands are going to be stainless so i have to put that into consideration. Im not a professional welder, so i like personal opinions of guys that have done it.

Ok why a 4 inch downpipe? I was thinking of doing a 4 inch downpipe, and 3 1/2 after the v-band.

 

[Slippi84]

No you use a 309 mig wire to weld say a stainless steel v-band flange to a mild steel pipe. Then i would put a v-band in your typical downpipe ending spot, and do v-band back aluminized steel (typical exhaust shop metal). So again i would be welding stainless steel to aluminized steel. It would save in cost, and last plenty long. I have other stuff i can think of spending 1000 dollars on rather then a sewage pipe.

Just trying to get some opinions on exhaust size, and maybe metal that im using. Because i was still thinking of using the big bucks for a 304 stainless downpipe and doing aluminized the rest of the way, but mild steel with a ceramic coating will I hope yield cooler underhood temps, less expensive, and last as long or longer.

I picked up the 42 last month on a way sick deal i could never let go brand new (lets just say under 500). The other turbo got traded for my k-sport coilovers.

Sounds like a good deal. Real close to what I got my hx52 for. I disagree with stepping down in exhaust size though if anything I would go from 3.5 or 3.75 to 4" back. It will help keep exhaust velocity up and backpressure down. Not to mention it will be a lot easier to slip a 3.5" dp threw the opening next to the oil filter vs a 4" one.

I take it you will be using all mandrel bent pipes for this? If so it shouldn't be that expensive for what you need. You gonna run a muffler on the end or just open pipe out the back? I knwo your trying to keep it "Street" friendly, or as much as you can with a non ball bearing gt4294

 

[andy4g63]

Why 4" and then to 3.5"??? As I said, that is my personal opinion, that DP is most important piece of exhaust system. This is from what i've read and seen over the years. Here is another confirmation of my theory. And I am pretty sure, he did on purpose and he knows. Ask him...


View Profile: twicks69 - DSMtuners.com

 

[Slippi84]

Why 4" and then to 3.5"??? As I said, that is my personal opinion, that DP is most important piece of exhaust system. This is from what i've read and seen over the years. Here is another confirmation of my theory. And I am pretty sure, he did on purpose and he knows. Ask him...


View Profile: twicks69 - DSMtuners.com

Twick also get's 740whp out of 1000cc injectors he is more the exception than the rule with some of his parts and performance. 99% of the people I have come across and any car I have ever built increases exhaust diameter from front to back not vis versa. The most comcon setup is 2.5" dp to 3" catback or just straight 3" turbo back.

 

[1fastlaser]

Why 4" and then to 3.5"??? As I said, that is my personal opinion, that DP is most important piece of exhaust system. This is from what i've read and seen over the years. Here is another confirmation of my theory. And I am pretty sure, he did on purpose and he knows. Ask him...


View Profile: twicks69 - DSMtuners.com

sorry didnt mean to say that, drank alittle to much last night. I would do eather a full 3 1/2" exhaust or 3 1/2 downpipe to 4 inch after the downpipe.

 

[T9S1i]

i was always under the impression that the hotter the exhaust gas (ie. closer to the combustion chamber) the more condensed the gas was. As it cools and exits the turbo and out the downpipe, it expands, so you would step up in size to keep velocity up.
Say your turbine exit is 3" i would have a 3" downpipe, and after the first bend or flex sextion, i would open it up a half inch or so and have a 3.5" exhaust the rest of the way.

 

[Slippi84]

Ok now I"m lost . Either you too are dislexic or you were both drinking. Andy in your first post you say to go from 4-3.5(bigger to smaller) then you say in your very next post why go 4-3.5? Steve you did the same thing but I think you just clarrified with your last post.

 

[Slippi84]

i was always under the impression that the hotter the exhaust gas (ie. closer to the combustion chamber) the more condensed the gas was. As it cools and exits the turbo and out the downpipe, it expands, so you would step up in size to keep velocity up.
Say your turbine exit is 3" i would have a 3" downpipe, and after the first bend or flex sextion, i would open it up a half inch or so and have a 3.5" exhaust the rest of the way.

RIght this is why I said 3.5" dp to 4" back which is what I think everyone is trying to say.

 

[1fastlaser]

Sounds like a good deal. Real close to what I got my hx52 for. I disagree with stepping down in exhaust size though if anything I would go from 3.5 or 3.75 to 4" back. It will help keep exhaust velocity up and backpressure down. Not to mention it will be a lot easier to slip a 3.5" dp threw the opening next to the oil filter vs a 4" one.

I take it you will be using all mandrel bent pipes for this? If so it shouldn't be that expensive for what you need. You gonna run a muffler on the end or just open pipe out the back? I knwo your trying to keep it "Street" friendly, or as much as you can with a non ball bearing gt4294

It will have a magnaflow race muffler hanging off of it. Yeah i was getting myself all crazy. Ive been researching exhaust pipes/v-band flanges, peoples opinions and what not. I would want to maybe do a 3.5" downpipe because of room...im sure it wont be an issue. The outlet on the 42 is 4", but ive seen hondas do 3.5" downpipes for room reasons also.

 

[romeen]

i was always under the impression that the hotter the exhaust gas (ie. closer to the combustion chamber) the more condensed the gas was. As it cools and exits the turbo and out the downpipe, it expands, so you would step up in size to keep velocity up.
Say your turbine exit is 3" i would have a 3" downpipe, and after the first bend or flex sextion, i would open it up a half inch or so and have a 3.5" exhaust the rest of the way.

Actually the opposite is true. When a gas is heated it expands, when it cools it contracts. It's the rapidly expanding gas coming out of the exhaust manifold that drives the turbine. Stepping up to a larger pipe diameter will cause the velocity of the exhaust to decrease although total flow volume may be increased. In a turbo car it's all about the pressure gradient/differential pre vs post turbo in order to get the turbo spooling as soon as possible. More pressure before turbine (to a point) and as little pressure as possible after the turbine.

Here is a very good read about exhaust principles:

Turbo Exhaust Theory

 

[1fastlaser]

Very good info in that. Im trying to keep it a street car as much as possible, it would be so much easier to run it out the bumper , but im not going to.

 

[Slippi84]

Actually the opposite is true. When a gas is heated it expands, when it cools it contracts. It's the rapidly expanding gas coming out of the exhaust manifold that drives the turbine. Stepping up to a larger pipe diameter will cause the velocity of the exhaust to decrease although total flow volume may be increased. In a turbo car it's all about the pressure gradient/differential pre vs post turbo in order to get the turbo spooling as soon as possible. More pressure before turbine (to a point) and as little pressure as possible after the turbine.

Here is a very good read about exhaust principles:

Turbo Exhaust Theory

Good thing you pointed it out his sizing supported the right info but I think he just said it wrong when he reffered to exhaust expanding. The hotter gas will expand further than the cooler gas so as exhaust flow travels to the rear of the car it gets cooler and contracts compared to the exhaust right after the turbine housing in the DP. The key like he said is to keep velocity without creating back pressure which is NEVER good on a turbo car. A lot of tuners mix up velcouty or backpressure.

 

[Slippi84]

Very good info in that. Im trying to keep it a street car as much as possible, it would be so much easier to run it out the bumper , but im not going to.

DO IT !!!!

 

[1fastlaser]

This is "blinkerfluids" on-green many/gt4202 setup. God its so much cutting and welding to make it work.

 

[Slippi84]

IC piping looks like it would have to come out below the corss member meaning under the bumper line which is a big no no. That or run crazy close to the dp meaning high pre-intercooler temps.

 

[1fastlaser]

Well that was test fitting. The compressor wasnt in position yet. I will be putting aluminum IC piping on regardless

 

[Slippi84]

Well that was test fitting. The compressor wasnt in position yet. I will be putting aluminum IC piping on regardless

What else would you be putting on

WHat you going with for IC piping size and IC setup to squeez in there?

 

[T9S1i]

Our DPs have a 2 1/2" stainless steel first bend with a 2 1/2" stainless steel flex section. They then expand to 3" right after the flex section right under the oil pan area. Why start out at 2 1/2"? If you are running on the stock O2 sensor housing, even ported it is 2 1/2" inside diameter. When the exhaust gasses are hot, they flow better, 2 1/2" is plenty for the first 12". As the gasses cool , bigger helps. By going to 3" after the flex section, we allow this expansion and also allow for better clearance at the front where room is tight.

Eclipse Exhaust System Upgrades


I used this downpipe from rre when i had my 16g setup... it worked fine then, maybe the theory that rre says here works for 16g sized turbos, with 42r's and other monsters, it might be different.

Since ive upgrade to a s258 with t3 housing, im running 3" mandrel bent piping from the turbo back.

 

[romeen]

Our DPs have a 2 1/2" stainless steel first bend with a 2 1/2" stainless steel flex section. They then expand to 3" right after the flex section right under the oil pan area. Why start out at 2 1/2"? If you are running on the stock O2 sensor housing, even ported it is 2 1/2" inside diameter. When the exhaust gasses are hot, they flow better, 2 1/2" is plenty for the first 12". As the gasses cool , bigger helps. By going to 3" after the flex section, we allow this expansion and also allow for better clearance at the front where room is tight.

Eclipse Exhaust System Upgrades


I used this downpipe from rre when i had my 16g setup... it worked fine then, maybe the theory that rre says here works for 16g sized turbos, with 42r's and other monsters, it might be different.

Since ive upgrade to a s258 with t3 housing, im running 3" mandrel bent piping from the turbo back.

The basic exhaust principles are the same regardless of turbo size. But I agree that the RRE DP is not big enough for optimal turbo performance with the really big turbos.

IMO, the description from RRE is not worded very well although I understand what they are trying to say. In large part it's the expansion of the gas itself that causes the gas to cool (probably not as much the other way around).

I have the RRE DP and it is a very nice piece.

 

[1fastlaser]

What else would you be putting on

WHat you going with for IC piping size and IC setup to squeez in there?

thats still up in the air, i gotta do one thing at a time. Once the exhaust is figured out, then ill worry about intercooler piping, and so forth.

 

[twicks69]

Ok, pretty much any 3.5" or 4" exhaust system is going to be a custom piece as the person's application will vary from car to car. There isn't going to be an off-the-shelf setup for you. Either way, no biggie.

Are you intending on running a relocated alternator? Power steering? If so, you will likely need to go with a 3.5" downpipe, so you will need to start with your 4" V-band off the turbo, then reduce it to a 3.5", make the bend and then continue.

A 3.5" exhaust will do just fine.

As for my exhaust, it is nothing special...It is just a 3.5" V-band off the turbo, then making the bend, then reduced to a 3" flex section and 3" pipe to my 3" Burns muffler; no biggie.

If you are intending on running a full-length exhaust, I would suggest a complete 3.5" turbo-back solution or larger. The downpipe is key, but you do not want to put a muffler on the end that is going to restrict exhaust flow, so keep it the same size or larger. With turbo cars of this level, you want as little back pressure as possible.

As for materials, I really would stick with a 304SS 3.5" setup vs. a mild steel one; for the weight savings and the corrosion resistance.

You can't just cheap out on an exhaust after building up a badass setup. If you don't have the money, then wait until you do and do it right.

Good luck,