aluminum downpipe?
The Bull
Joined: Jun 2002
Posts: 3,578
Likes: 2
From: Grand Rapids, MI
Simple math really when dealing with center lines. If it's a 5" pipe on a 7-1/2" radius the inside bend has a radius of 5" (7-1/2 - 2-1/2) and the outside radius has a 10" radius. There are limits to how much bend radius you can get vs the diameter of the pipe. For instance, a 7-1/2" radius bend will have a thinner wall thickness along the 10" radius than say something with a 10" radius bend. The thinner the wall on the long side is generally going to create a bad situation for a 90 degree bend out of a turbo.
You also have to be careful of how you position the radius, especially when you discharge almost 90 degrees immediately post turbo. All the exhaust gas is going to slam into that like a wall and force a lot of heat into a very concentrated area. If you look at a lot of the drag cars that run straight aluminum there generally are no 90 degree bends anywhere. And if there are the wall thickness on the tubing is going to be a lot thicker. Same goes for your waste gates and where / how you direct those back into your downpipe. The turbo will take some heat out of the exhaust but when your waste gate opens there will be very little temperature drop in comparison and that can really cause the fun stuff. You're not going to want to have your waste gate pipe into the downpipe pointing into any bends or 90 degrees to the pipe. The longer an approach you can give it, the better off.
The first aluminum downpipe we had for the Red Rocket ended in a mild disaster as we blew out a sizable hole the first pass out. A combination of both factors mentioned above. The new setup takes away some of the heat first by using steel off the turbo and then aluminum the rest of the way after the second bend then it's completely fine from there. You can get aluminum to steel v-band assemblies from several places.
You also have to be careful of how you position the radius, especially when you discharge almost 90 degrees immediately post turbo. All the exhaust gas is going to slam into that like a wall and force a lot of heat into a very concentrated area. If you look at a lot of the drag cars that run straight aluminum there generally are no 90 degree bends anywhere. And if there are the wall thickness on the tubing is going to be a lot thicker. Same goes for your waste gates and where / how you direct those back into your downpipe. The turbo will take some heat out of the exhaust but when your waste gate opens there will be very little temperature drop in comparison and that can really cause the fun stuff. You're not going to want to have your waste gate pipe into the downpipe pointing into any bends or 90 degrees to the pipe. The longer an approach you can give it, the better off.
The first aluminum downpipe we had for the Red Rocket ended in a mild disaster as we blew out a sizable hole the first pass out. A combination of both factors mentioned above. The new setup takes away some of the heat first by using steel off the turbo and then aluminum the rest of the way after the second bend then it's completely fine from there. You can get aluminum to steel v-band assemblies from several places.
LS1Tech Sponsor
Joined: Feb 2007
Posts: 101
Likes: 0
From: Houston, TX
Simple math really when dealing with center lines. If it's a 5" pipe on a 7-1/2" radius the inside bend has a radius of 5" (7-1/2 - 2-1/2) and the outside radius has a 10" radius. There are limits to how much bend radius you can get vs the diameter of the pipe. For instance, a 7-1/2" radius bend will have a thinner wall thickness along the 10" radius than say something with a 10" radius bend. The thinner the wall on the long side is generally going to create a bad situation for a 90 degree bend out of a turbo.
You also have to be careful of how you position the radius, especially when you discharge almost 90 degrees immediately post turbo. All the exhaust gas is going to slam into that like a wall and force a lot of heat into a very concentrated area. If you look at a lot of the drag cars that run straight aluminum there generally are no 90 degree bends anywhere. And if there are the wall thickness on the tubing is going to be a lot thicker. Same goes for your waste gates and where / how you direct those back into your downpipe. The turbo will take some heat out of the exhaust but when your waste gate opens there will be very little temperature drop in comparison and that can really cause the fun stuff. You're not going to want to have your waste gate pipe into the downpipe pointing into any bends or 90 degrees to the pipe. The longer an approach you can give it, the better off.
The first aluminum downpipe we had for the Red Rocket ended in a mild disaster as we blew out a sizable hole the first pass out. A combination of both factors mentioned above. The new setup takes away some of the heat first by using steel off the turbo and then aluminum the rest of the way after the second bend then it's completely fine from there. You can get aluminum to steel v-band assemblies from several places.
You also have to be careful of how you position the radius, especially when you discharge almost 90 degrees immediately post turbo. All the exhaust gas is going to slam into that like a wall and force a lot of heat into a very concentrated area. If you look at a lot of the drag cars that run straight aluminum there generally are no 90 degree bends anywhere. And if there are the wall thickness on the tubing is going to be a lot thicker. Same goes for your waste gates and where / how you direct those back into your downpipe. The turbo will take some heat out of the exhaust but when your waste gate opens there will be very little temperature drop in comparison and that can really cause the fun stuff. You're not going to want to have your waste gate pipe into the downpipe pointing into any bends or 90 degrees to the pipe. The longer an approach you can give it, the better off.
The first aluminum downpipe we had for the Red Rocket ended in a mild disaster as we blew out a sizable hole the first pass out. A combination of both factors mentioned above. The new setup takes away some of the heat first by using steel off the turbo and then aluminum the rest of the way after the second bend then it's completely fine from there. You can get aluminum to steel v-band assemblies from several places.
The Bull
Joined: Jun 2002
Posts: 3,578
Likes: 2
From: Grand Rapids, MI
It's not a straight 90, from the angle of your photo it also looks like it's on a pretty generous radius too. I can't tell, but it doesn't look like you dump your exhaust from the waste gate back into your down pipe either. The exhaust out of the waste gate by far is the hottest and most likely to cause the damage, as was our case. A tight radius 90 straight down off the back will be something to talk about. For instance, I bet you can put your arm in on the turbo flange side and reach down and touch the second bend from the inside. That's a hell of a lot straighter than what some people have. Especially compared to those where they have the turbo offset to the front of a wheel well with a tight radius 90 going straight down.
