Hi guys, I posted a thread earlier about my poor 1/4 mile and ET times at the strip, I think I may have a reason that explains at least part of it. I have the 11psi pulley installed (I just double checked today against the 7psi on...the one I have on now is considerable smaller, which would mean it should make more boost), but when I was romping around the highway today, I did some wot runs in 2nd and 3rd gear. I was able to only muster 7psi on the boost gauge. I brought the rpms up to about 6k in each gear. Now, I also noticed that my filter was very dirty (which i cleaned using the K&N recharge kit today) as well as the oil leak from the blower casing was getting kinda bad.
Here are the options:
1. I know nothing about blowers (somewhat true) and the smaller pulley I have on is actually making less boost that the larger one
2. The dirty filter was not allowing in enough air to make enough boost
3. My boost gague is reading incorrectly
4. The oil leak has something to do with it
5. I'm just not getting on the gas enough (not likely)
6. I'm missing something completely...
Any suggestions of likely possbilities?
-Adam

 

see if you can find a trail of belt dust under the hood. with a smaller pulley you are trying to spin the impeller faster with less belt contact. my guess is your belt is slipping. also check the belt for oil if you have a leak.

 

BMWKillR, I am in no way an expert on SC's, as I am in the process of building my first blower car. However, I have done an extensive amount of research on the subject. A few things that I can say is that I am sure the oil leak is not good, and your filter must be clean, especially at 11#'s. The stock "dryer hose" on the intake side of the SC does not flow very well at higher boost pressures, and at 10#'s and above you should be running something to cool the charge, whether it be methanol/water injection, or an intercooler (more boost = more heat). Keep in mind that the pulley size is not the only thing that determines boost, it also has to do with your internal motor components (i.e. piston dish size, head chamber size, porting, and so on.). You may also have belt slippage which is more common with the higher pressures. More boost requires more fuel, possibly bigger injectors, and definately a better fuel pump/fueling system. Your forged internals are good, but they still won't stand up to detination very long. At higher boost you also need to upgrade your bypass valve or you are going to get blower surge. When increasing boost above what Vortech designed the "kit" for it is necessary to upgrade the whole package as well.
If I am incorrect on any of these fact I welcome someone to correct me, but I'm pretty sure I am not.

 

You could be leaking boost out of one of the pressure tubes. Sounds more like belt slippage to me. A smaller pulley will make more boost but is more difficult to spin. This can lead to the belt slipping and making substantially less boost than the pulley is capable of. If the car accelerated like it was making 11psi then I'd check the vacuum lines for the boost gauge for a crack, kink, or bad connection to the gauge itself.

-Pete-

 

I checked the belt quickly yesterday when I was under the car. The Belt seemed like it was clean at the spot I was looking and it was relatively tightened up. Idk if there would be a sound associated with a slipping supercharger belt so I could hear it? As for the oil leak, the leak is not a fast leak, it has built up over time. I can see somewhat new oil every time I get under the car, b/c the leak is exascerbated by the heavy pressure load of the blower. I had to add about 1/2 quart after my last drag run due at least the blower.

 

The only other things I can say is that the filter is 4'' filter, which is over a foot long. Also, I have all the necessary fuel systems to ensure the car can handle the boost. One last thing, I beleive I have recorded 9psi at one point out of the blower, can't say exactly which pulley I had on, but that would indicate its not up to full strength as well.

 

you need a boost gauge if you ont have one...then watch it as you run it, the boost should keep climbing, if it hitsa point where it stops increasing, but you keep increasing rpms, then its slipping

 

I would also check the tubing/hose connections on the pressure side of the blower to be sure you don't have an leak. Also, have you verified the by-pass valve is fully closing under boost conditions and does not leak???

 

I have a boost gauge and it does as you say, stop at 7psi despite revs to work with. Now, I was told a theory contradictory to what I though. I was told that the larger pulley, which has more circumferance would make more boost, b/c the smaller pulley would spin faster, yes but would have to spin more to make the same boost as the larger pulley. Idk how else to describe it, I was a little confused. But he swears by it, and it could explain why I'm hitting 7 only. That could be maxing out the pulley b/c I do have one 7 and one 11 psi one. Anyone back up that theory?
-Adam

 

Depends which pulley you are referring to.

For the sake of comprehension, here's a generic explanation:

If you increase the diameter of the Crank Pulley, this will raise boost. If you decrease the diameter of the Crank Pulley, this will lower boost. If you increase the diameter of the Head Unit Pulley (on the blower itself) this will lower boost. If you decrease the diameter of the Head Unit Pulley, this will increase boost. (Assuming no belt slippage)

My recommendation...measure the diameter of the pulleys that are on the car, and figure out for sure what you should be seeing pressure wise. If you don't think you're seeing proper pressure...look for boost leaks and belt slippage.

 

Hey Adam, I just saw this post. Drop me a PM and I will give you my cell number. I would be glad to give you a hand.

Jason

 

I would agree with what most have said:

-Belt slippage
-Boost leak (possibly a bad bypass?)
-Bad gauge (like someone said - does the car feel like it making more power?)
-Wrong pulley (did you verify circumference? or is it verbally a different pulley?)
What is your crank pulley diameter? What are your old and new blower pulley diameters?

 

i dont like when old posts get dug up, but im interested to see what the result was.

did you confirm the pulley sizes?

im going to put a 2.95 blower pulley on and im looking at potential problems....

Jeremy

 

Adam is probably not on the board anymore. I built the car and bought it back from him last year. There really was no issue....he just wasn't reving the engine high enough to see the higher boost. He was shifting at 5700 and the car was making 10-11psi at 6400.

Jason

 

what size pulley was it?

if it is a pulley set up that was supposed to give 10-11psi, it shouldnt take 6400rpm to get that. the stock redline is 5600 right? i mean if vortech claim a certain psi range, it shouldnt take over-revving to get it...

and it seemed like he was getting less psi with the pulley change...or did he not have any experience with the bigger blower pulley? he also stated that he has poor et and trap speeds.....