Why not to run 15%OD with a stock outlet

Hock

Registered User
First let me say that it was not and is not my intention to run a stock outlet with this much overdrive. I'm currently in the process of making a custom outlet which will more then handle the amount of volume required for that much OD.

But anyways, I am running 15%OD on a fully ported 94 blower with a stock outlet. I just got the car back on the road and have been driving it hard and doing some shake down blast to try to reveal any issues that I may have.

Well this past week up in Williamsport I was smelling "burnt" oil like there was a valve cover leak. After doing some looking it turned out not to be a vc leak but instead it was blowing some oil vapor from between the S/C and the outlet. Now the only reason that I can think that it is doing this is that with the amount of air the S/C is moving that outlet cannot handle it which is causing excessive pressure in the outlet, which has to go somewhere. So with that the excess pressure is leaking out between the outlet and the S/C.

Now I know the question is going to be asked as to what I am using to seal the outlet. Well I am using Permatex Anaerobic Sealer which is the same sealer that is used by the factory. I used this before with the previous S/C, ported 92 w/5%OD, and I didn't have any issues with it so I don't see the sealer as being an issue.

Now the only thing I have to wonder is how much power is being lost because of this bottle neck in the system?
 
If the half pipe section of the outlet tube isn't flowing what the sc pushes, it will recompress the air. Every time its compressed it adds heat. Are you sure its leaking? Maybe when its getting hotter its just burning what it couldnt before? Just a theory. As far as it building excessive pressure under the top, i dont think so. Its only gonna build as much pressure as it can. Think about an air compressor that maxes at 120 psi. If you bypass the shutoff, the compressor will run nonstop but will only build 120 psi. Eventually it keeps compressing the same air because it cant pump new air in and evacuate it with more force than whats in the tank. So it compresses it over and over again. That creates a lot of heat.
 
Positive its leaking. There is oil residue all over the S/C and some "mist" on the surrounding areas.

Here is a test that Fraser did for an intercooler and it shows the pressure results before and after the intercooler.

http://www.sccoa.com/forums/showthread.php?t=116973

Obviously the IC that he was using could not flow enough air and ended up becoming a restriction causing increased pressure on the blower. So I would think that if this can happen with an IC the same will happen with an under sized outlet.
 
I am sure there is some restriction ... but I think the leak is just because of a bad seal. There are other people running big boost with stock blower outlets, and I haven't heard of anyone else having this problem.

Have you heli-coiled the blower bolt holes? The case is really soft. If you aren't getting great torque, perhaps the pressure opened up a leak path.
 
I wonder if your IC is stopped up with debris or something. I would think that the IC is usually much more restrictive than the sc outlet top.

I can't picture the pressure drop across the SC top (from the actual supercharger outlet V port to the collar for the IC tube) being very high as compared to the pressure drop across about any IC.

How much sealer did you use this time - maybe you need more? :confused: I know it doesn't take much...
 
Are you sure it's not the snout seal leaking and blowing the oil mist back onto the SC top ? If top is leaking it's not because the stock outlet is too small, it's just not sealed well enough. Suggest using a thin coat of Permatex high temp RTV to seal it instead of the anerobic stuff.

David
 
Are you sure it's not the snout seal leaking and blowing the oil mist back onto the SC top ?

David

I thought that first that at first but there is no moisture around or on the pulley. I then noticed oil near the outlet and thought that the rotor pack was blowing oil out between it and the snout, which I have seen before on my last SC when I bought it. I can take my finger the whole way around the outlet and feel the oil on the case.

I will be taking the outlet off to reseal it. I'm going to check it for straightness and put a little more sealer on it this time. I would you Copper RTV like I used to do but I hate the mess with it and its always a pain to pull the outlet off once it cures so I'm trying to avoid using it again on any part of the S/C that can be seen.

If I could acquire another outlet I would be willing to get a fitting put on it so I could measure the pressures there as well as other places in the intake tract to see what the actual pressure drop is. Anyone want to donate? I'll pay shipping!:D
 
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