Strange problem with 6-71

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Coyote Jack

Coyote Jack

Member #55, I'm old
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Over the winter I changed out the top pulley to get a little more boost. I had 6 lbs last year and was looking for 7 to 8 lbs. The strange thing is that I have 0 lbs boost now and the car drives like 0 lbs of boost Still has lots of power but it doesn't have that wild punch when I put my foot down. I also changed my carbs to 600 dbl pumpers from 750 dbl pumpers. The blower is a Dyers with stripped rotors. I also hear a noise from the blower itself. Could my strips have worn out on me?

Jack
 
First install a boost gauge and get a correct reading go from there.
 
I'm definitely no expert on blowers. (I don't even play one on TV) We've had a blown 512 project that still hasn't been fired. I always thought that the Teflon stripped blowers were more for race applications. I'd heard that they produce too much heat for the street. I would think that it should be easy enough to pull your carbs again and see the rotors and tell if those strips look worn. It does seem strange that the performance changed dramatically at the same time that you did the carb swap. Maybe you're under-carbed now. Did the exhaust temp rise? I think I'd check to make sure your pop off valve isn't hanging up.
 
I do have a boost gauge. The needle barely moves from zero under any conditions. If I had a leak somewhere I think that is the reaction I would get from the gauge as under a no boost situation it should read good vacuum. I will start looking in that direction.

Jack
 
Change the pulley back and see what you get.
 
Did you go to a smaller or larger pulley. Top pulley, less coogs=more boost, more coogs= less boost.
 
The pulley is only 2 teeth different, (smaller),than the other one and it can't slip on the shaft as it has 4 bolts holding it in place.

Jack
 
Jack I agree with 67 cuda, little work but may be worth the effort. Did you by any chance drop your belt and roll your pulley by hand to see if you could find any hint of binding or anything. You said it was making a strange noise, can you kinda describe the noise.
 
My 1071 has the strips also, after they "wear in" they don't wear any more. Might loose a few lbs but not ALL. Does the vacume side still read the same???:coffee2:
 
HEMI-ITIS said:
My 1071 has the strips also, after they "wear in" they don't wear any more. Might loose a few lbs but not ALL. Does the vacume side still read the same???:coffee2:
Click to expand...

That is what has me perplexed right now. The Vac/Boost gauge is not showing any vac either. The gauge does move a little when I step on it, but not much.

Jack
 
You may have ruptured your intake gasket . What kinda blowby in the crankcase. Pull your oil cap. If your spraying oily mist , it robably has bad gaskets. Also , question. What will propane show? You have positive manifold pressure. It won't draw the propane in. Correct? I'd be more inclined to find a tech with a smoke check tool. Very useful in finding evaporative emission testing. Just my 2cents
 
funwithfuel said:
You may have ruptured your intake gasket . What kinda blowby in the crankcase. Pull your oil cap. If your spraying oily mist , it robably has bad gaskets. Also , question. What will propane show? You have positive manifold pressure. It won't draw the propane in. Correct? I'd be more inclined to find a tech with a smoke check tool. Very useful in finding evaporative emission testing. Just my 2cents
Click to expand...

At idle the blower does not produce boost and there is vacuum in a perfect world. If there is a leak in any of the gaskets then the propane will raise the idle. I have done this before to find a bad gasket at the blower base.

Jack
 
I did not know that. I was applying diesel theory. Positive displacement per revolution. now that I think about it , how can you have negative pressure @ idle and positive off idle. You are have a fixed displacement per rev. If you are over or under driven the displacement would still be fixed. Yes? I don't mean to hi-jack your thread for an education. Just trying to understand in effort to help contribute to a potential cause.
Good luck.
 
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