Smaller SC pully, no more boost?

[wpurple]

Well I changed my Powerdyne SC pully from the stock 3.12 to 2.93 to gain some lower end psi and also to lift the higher end (6psi) to 7.5psi...
well I noticed no real change.
I don't think the belt is slipping as it is quite tight....

what I am wondering is whether the Torque monster headers and Gibson cat back is allowing a very good exhaust flow thus keeping the back pressure down to up the boost????

 

[boominXplorer]

Are you monitoring by a gauge? Any noticable differance in any driveability? Check ALL vaccum hoses for leaks. 9 PSI is where the stock tensioner usually starts to slip on the powerdynes.

 

[wpurple]

Not really any noticable difference really (I have been using a 4cyl as a dailey driver, so coming from that it is difficult to tell), although I just took it out today, I will check all vacuum connections. Yes, I am monitoring it by gauge.

I now have a bypass valve installed too, that may be leaking, will check.

 

[SploderXLT]

I had a blower on another car I had and putting on headers and a catless midpipe dropped me almost 2psi. You have to think of boost as a restriction... boost pressure is air built up in the intake that cant flow into/out of the combustion chamber. If air flows better, more air can move... thus less backpressure in the manifold(boost)

 

[Turdle]

Wait a minute
I am still trying to understand how headers will have any effect on intake manifold pressure----unless they allow a higher rpm. This I can understand. the intake manifold is a sealed unit until an intake valve opens.

I do understand though how a leak in the intake system could result in low, or limited boost. I suggest looking at the hoses, as suggested earlier, and intake gasket?? BTW what is the guage reading?

 

[boominXplorer]

The only way I can think backpressure would do anything against boost would be if you changed your cam to a very emission friendly cam.

 

[Fredness]

Are you running the factory valve springs? Chances are they have weakened to the point that they are now leaking with the increased pressure. Is there anyone else running this set up? What were their results?

I'd start by checking ht ebypass valve and other areas for leaks, then start looking at other things.

My 3.0L Whipplecharged Ranger lost boost with headers, and then lost some more with ported heads, its the restrictions in the engine/exhaust that give you "boost" since there is no where for the exhaust to go. This causes increased intake pressure.

Remember, the cam has about 110-115 degrees of overlap where the intake and exhaust valves are open at the same time. There is a direct correlation between increased CFM capacity for an engine and lower boost.

Now, increase the blower speed with a smaller snout pulley and you regain your previous boost levels and have even more HP than you did before. Boost is a strange and wonderful thing....

 

[wpurple]

Yes, factory valve springs....
I checked for vacuum leakes including the bypass valve and everything is in check.
The vacuum hose going to the HVAC has a very very slow leak, but not enough to cause any problems.

I am going to tighten the belt a few notches and see...right now I only getting 5.5psi at 5000rpm.....

Certainly may be due to the unrestrictions in the exhaust...