KY_BOB

iTrader: (2)

I have a '02 5.3 Avalanche with a Vortech blower. It originally came with a 3.33" pulley on it and was listed by Vortech as a 7# supercharger kit. With that set up I was seeing 6.5-7# of boost at my 5800 shift point.

I changed to a 3.25" pulley, which I know isn't much of a drop but I wanted to take it one step at a time. With the 3.25" pulley I would see a solid 7 to 7.5psi of boost at peak rpm.

I then went to a 3.12" pulley and am now seeing about 9.5 psi at 5800 in first gear and only about 9 psi at 5800 just prior to the 2-3 shift. I don't know why I see more in 1st gear than 2nd

Most everyone that I see with this pulley on a 5.3 is seeing about 11-11.5# of boost. I have a stock cam and shorty headers so I know that I'm not just running less restriction that others. I called Vortech yesterday and their tech said that that sounded about right but I wonder.

What do you guys think? Do I have a problem or not?

Could my gauge be off or slow reacting? I do have the line that runs to the gauge T'd to run the line to my meth injection. Am I loosing boost somewhere? I've looked everywhere that I could think of. I don't think I'm having any belt slip because I can hear the belt chirp when it shifts or if I get off of the throttle quickly just before the blow off valve dumps the pressure.

Any thoughts are appreciated.

BlownChevy

iTrader: (20)

Might want to look into possible belt slippage. Depending on the shift points, if the RPM is higher in 1st than second then you would be experianceing higher boost in first than second gear.

KY_BOB

iTrader: (2)

Belt slippage was my first though and is still on my mind but wouldn't I hear it? I definitely hear it for a split second when I lift just before I hear the pfffff of the blow off valve. The belt is the one that came with the kit and has less than 1000 miles on it. It's tight and the tensioner is about 75% compressed. With the 3.33" pulley the tensioner was maxed out an it was almost impossible to get the belt on. I don't think that I could go to any shorter of a belt and get it on.

Both shift points are set at exactly 5800 but it could be that it's revving quicker in first and running past that a little before the shift actually occurs. That sounds very possible.

Bad_Apple

iTrader: (1)

Man I would say your gauge could be off a lil....

greentahoe

iTrader: (2)

I saw 11-12 on cold nights with the 3.12 non intercooled. I saw a max of 10-11 when I added the FMIC and 2.87. I had a 113" belt with the 2.87 and that was perfect, but when the belt shredded I just replaced it with what was available (114.5) since I was going turbo shortly. I have thrown the belt twice and it slips terribly as evidenced by the dust and low boost. I think the kit comes with a 114 so you should look into a 113.5 gatorback
BTW I was shifting at 6000-6200 so that accounts for a little higher boost

KY_BOB

iTrader: (2)

The kit came with both a 113" and a 114" belt depending on the alternator that was on the truck and I am using the 113".

I wouldn't mind turning it a little higher rpm as boost is climbing pretty quickly at 5800 but I have a stock valvetrain and am leary of turning it more. Do you think I can go to 6000 with my stock springs? That would probably give me another # of boost.

KY_BOB

iTrader: (2)

One more thing. Are you saying that you don't hear any belt slip and the only way that you know that you have it is dust and low boost?

greentahoe

iTrader: (2)

yes.
Thats strange the 113 took me an hour of fighting to get it on when I went to the 2.87.
Im not sure on the shift rpm, I have 918's, hardened pushrods etc, and had no problems raising shift points.
Clean everything up in the engine bay and give it a few days and some wot passes and go back and run your fingers around and see if you have any black dust. I have a ton with this longer belt. slip usually looks like the boost is rocketing up and then just stays around a certain number as rpms rise, you should be able to tell by your gauge, I could

KY_BOB

iTrader: (2)

Thanks for the input. The last time I drove it I was pretty rough on it so I'll check it for dust when I get home tonight. I don't know that this is the problem, as my boost seems to climb all the way to the shift but it's worth looking at.

Can anyone tell me what auto part chain carries Goodyear Gatorback belts? I just checked with my local NAPA and they can't get one.

Bad_Apple

iTrader: (1)

I got my from AutoZone.....