Melted exhaust housing

97singlecab

97singlecab

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Mar 12, 2008
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Need some help tuning my truck. Truck is a 97 12v, 215 pump no plate stock afc with star wheel set really tight. Timing at 23 degrees. DDP delivery valves with 5x18 injectors 145 degree spray pattern. With .093 haisley lines. Truck has twin turbos with a super b special on top and an ht60 on bottom. Also has two stages of nitrous with .78 jet first then a .110 jet run on seperate bottles and solenoids. Everything on the fuel side has only been in for three days. This last weekend at the nhrda race I made one pass to the tune of 12.20 at 113mph. In that one pass it melted the divider for the scroll on the top turbo completely out of the housing, melted the pucks for the wastegates and opened the holes for the gates up to about 2 inches long by an inch wide. It also melted the 71mm exhaust wheel down to about a 42mm wheel.

My question is why? To much fuel, to much nitrous not enough nitrous? When testing the setup before the race I only ever hit the first stage. It smoked like a freight train and pulled hard egts were only around 1250. On the pass down the track it cleared most of the smoke but not sure where egts went didn't pay attention. I was wanting to get some of your guys insight on what I should change so I don't do this again once I get my turbo back.
 
I've heard of guys with big fuel that start running nitrous having issues. Maybe thats what it is. Weird part is the exhaust manifold and pyro probe are fine and so is the bottom turbo.
 
Yeah I got pics before I sent the turbo off today, but I left my camera at work. I'll try to upload em tomorrow. I just would like to know roughly what caused it. Can't really afford to keep fixing turbos.
 
So melted two of them so far. Second time had smaller injectors and different nitrous but same results.
RunninBroke007.jpg

RunninBroke006.jpg

RunninBroke005.jpg
 
Use those pics the next time someone says nitrous cools off the EGt's.
IAT's yes, EGT's ughhhh no.
 
How much boost was the truck making with the nitrous on? Without the nitrous?

On my brothers truck we run a very similar setup on the fuel side. In the past we have also had similar problems when running nitrous, melted the pucks out of a housing and some melting to the exhaust wheel but no where near as bad as yours.

How quick does the truck run the 1/4 without nitrous?
 
I never ran the twins down the quarter with out nitrous so not sure. Boost was around65. Thing I don't get is the head and exhaust manifold and the pyrometer probe are all fine. You would think if the egts were that hot the soft metal of the pyro would of melted to. The highest the egt gauge read was only 1550 to.
 
Only time that happens is when the drive psi is way high, properly done, nitrous engines will put in cooler air and egt's about 14-1500*, sometimes lower.

But you cant bottle neck the exhaust, when you do that, you increase psi in the turbine area, and psi makes more heat.

another thing is timing, depending on where your egt guage is, if it's way hot before the turbine you need more timing.


what was you wastgate set at?
 
Timing is what I was wondering to. I have it set at 23 degrees. I had the internal gates set to open at 20 psi since I didn't have an external gate at the time. How high should I run the timing? Also since going to a single gt42 turbo I haven't had any issues so far with melting.
 
My thoughts on this is that it is different and safer to run nitrous on a CR then at 12 valve. On a CR the combustion is more complete in the cylinder because of the atomization of the fuel so you can get away with it more. But on a 12 valve you have a ton of unburned fuel and when you add all that oxygen to it, it is going to burn like a cutting torch whether in the cylinder or in the pipe until there is no more fuel to burn. A few years ago there were allot of pro street 12 valve guys running nitrous and they were melting down turbos right and left. Maybe if you were going to run nitrous in a 12/24 valve you would want to chose your injectors to atomize the fuel the best so you have a more complete burn and not so much going out the pipe. Just my thoughts
 
Toolman said:
My thoughts on this is that it is different and safer to run nitrous on a CR then at 12 valve. On a CR the combustion is more complete in the cylinder because of the atomization of the fuel so you can get away with it more. But on a 12 valve you have a ton of unburned fuel and when you add all that oxygen to it, it is going to burn like a cutting torch whether in the cylinder or in the pipe until there is no more fuel to burn. A few years ago there were allot of pro street 12 valve guys running nitrous and they were melting down turbos right and left. Maybe if you were going to run nitrous in a 12/24 valve you would want to chose your injectors to atomize the fuel the best so you have a more complete burn and not so much going out the pipe. Just my thoughts
Click to expand...


Very good point!
 
97singlecab said:
Timing is what I was wondering to. I have it set at 23 degrees. I had the internal gates set to open at 20 psi since I didn't have an external gate at the time. How high should I run the timing? Also since going to a single gt42 turbo I haven't had any issues so far with melting.
Click to expand...

i would start at 25 and gate the turbo were you have it, but watch your BP and DP, you want DP to be less than or equal to BP.
 
Toolman said:
My thoughts on this is that it is different and safer to run nitrous on a CR then at 12 valve. On a CR the combustion is more complete in the cylinder because of the atomization of the fuel so you can get away with it more. But on a 12 valve you have a ton of unburned fuel and when you add all that oxygen to it, it is going to burn like a cutting torch whether in the cylinder or in the pipe until there is no more fuel to burn. A few years ago there were allot of pro street 12 valve guys running nitrous and they were melting down turbos right and left. Maybe if you were going to run nitrous in a 12/24 valve you would want to chose your injectors to atomize the fuel the best so you have a more complete burn and not so much going out the pipe. Just my thoughts
Click to expand...


If its doing what toolman is describing I would thrown another egt probe behind the exhaust housing just to see whats going on.

Makes me think twice about nitrous :badidea:
 
Toolman said:
My thoughts on this is that it is different and safer to run nitrous on a CR then at 12 valve. On a CR the combustion is more complete in the cylinder because of the atomization of the fuel so you can get away with it more. But on a 12 valve you have a ton of unburned fuel and when you add all that oxygen to it, it is going to burn like a cutting torch whether in the cylinder or in the pipe until there is no more fuel to burn. A few years ago there were allot of pro street 12 valve guys running nitrous and they were melting down turbos right and left. Maybe if you were going to run nitrous in a 12/24 valve you would want to chose your injectors to atomize the fuel the best so you have a more complete burn and not so much going out the pipe. Just my thoughts
Click to expand...

Spot on.
 
YOUNG GUNS15 said:
If its doing what toolman is describing I would thrown another egt probe behind the exhaust housing just to see whats going on.

Makes me think twice about nitrous :badidea:
Click to expand...

It might really surprise you with what you find. Another thing to think about is the timing . When we are running the CR's on nitrous we try to go to a low timing tune but on a 12 valve you may actually want to add timing to help keep the combustion in the cylinder.
 
Thanks for all the insight on this, its been an expensive summer due to this. I'm gonna try setting the timing higher and see how that helps. I'm running a big single with an external gate now so hopefully that helps with the back pressure to.
 
Toolman said:
My thoughts on this is that it is different and safer to run nitrous on a CR then at 12 valve. On a CR the combustion is more complete in the cylinder because of the atomization of the fuel so you can get away with it more. But on a 12 valve you have a ton of unburned fuel and when you add all that oxygen to it, it is going to burn like a cutting torch whether in the cylinder or in the pipe until there is no more fuel to burn. A few years ago there were allot of pro street 12 valve guys running nitrous and they were melting down turbos right and left. Maybe if you were going to run nitrous in a 12/24 valve you would want to chose your injectors to atomize the fuel the best so you have a more complete burn and not so much going out the pipe. Just my thoughts
Click to expand...

Kind of what im leaning towards. Ive heard this numerous times for a 12/24v running big fuel and a healthy shot of nitrous. Timing and Injection Pressure/Pop pressure are a huge factor when running nitrous on these motors.
 
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