Boost Problems?

[REPCobra10]

A buddy of mine recently did an automatic transmission swap with non-lockup torque converter and had his motor built for high boost and a little nitrous like mine. Before the swap and the engine build he had a 2.76" upper pulley only with intake, catless x-pipe, cat-back, and a tune and was seeing 14.5 pounds of boost. Now he has put on a 2# lower along with the 2.76" upper pulley and is only seeing 12-13 ppunds of boost when he should be seeing around 16-17 pounds. He has a single idler pulley. Could this problem be vacuum related, belt slip related or something else? Any and all advice would be helpful for him so please give your input guys. Thanks. All, take it easy.

 

[REPCobra10]

One more thing. The idle at times kind of bounces up and down between 500 rpms and 1100 rpms. It doesn't do it all the time but when it does it gets rough and annoying.

 

[-Chip-]

Probably beltslippage. You may need to invest in a manual belt tensioner.

 

[REPCobra10]

If it was belt slippage, would it still hold a constant boost pressure? It holds like 12.5 pounds perfectly. I though boost pressure would be all over the place with belt slippage. What do you think about the idling issue though? The bouncing between 500 rpms and 1100 rpms?

 

[REPCobra10]

Anybody other than -CHIP- have any ideas, tips, or suggestions? To the top please.

 

[racebronco2]

something doesn't sound right, you should have some boost drop with the stock blower especially at those boost levels unless you are having belt slip, a true tell sign is belt dust. as far as your idling problem is sound like a maf/vacuum or tuning problem. did he change anything during the auto swap.
what belt are you using, i pulley combo is 2.80, old style snub idler, 2# lower and i am using a 4080760 belt.

 

[REPCobra10]

There is belt dust on the blower snout but if that is the cause of the boost issue, why is the belt slipping so damn bad. He has the Whipple belt tensioner pulley and the belt is as tight as he can get it. The belt size is the same as your's (4080760). He's never had that problem before when he had the upper only with the automatic. He was seeing 14.5 lbs of boost with that which was a 2.76". Now he put the 2# lower on as you have on your car but only see's 12.5 lbs of boost. All these problems started after he had his engine rebuilt with Diamond Racing Pistons. As for the idle at times, is really pissing him off because of how bad the rpms bounce. I guess we'll check for MAF/Vacuum problems as I doubt it's the tune but you never know. Thanks. Take it easy.