Is belt slip due to psi alone?

[Sluggie24]

Currently my 04 GT is running the 3.33" 6 rib pulley with stock crank pulley on a Vortech V3 si. CX racing FMIC, PP, bolt ons and full exhaust on stock engine. No belt slip and getting 10-11psi at 6k rpm.

I'm planning a forged lower, porting the heads and blower cams. This should cause a boost loss as the engine breathes better. Once I do this I was thinking I should go to the 3.1" pulley or even the size below that to at least keep the boost at about the same level.

My question is if switch to a smaller pulley with the engine build will I develop belt slip? I'm not sure if slip is a factor of pulley size itself (surface area contact) or due to increased resistance turning the pulley due to higher boost pressure. I'd rather avoid having to upgrade to the 8 rib setup if I can.

Any insight or experience would be appreciated. Also curious what would be the best compression to use for a street car? Stock or a bit lower?

 

[MG0h3]

belt wrap and tension have more to do with it than anything. Typically slip does show up as you run smaller pulleys. Probably a combination of the increased rpm and reduced belt wrap.

Id say run what you plan to and deal with it then if you have slip. Not sure if you can get a slotted pulley like the RR pulleys we use.

 

[CobraBob]

I agree with MG0h3. Belt wrap and optimal tightness are key factors. If you're not seeing any slippage now with the 3.3, you'll probably be okay with the 3.1.

 

[Brutal Metal]

I have a Reichard Racing 3.1 6 rib on my Vortech with an ATI crank damper (factory size). I'm seeing 14lbs of boost with no slippage which is near the max without going to an overdrive crank pulley or 8 rib conversion.

 

[Sluggie24]

Thank you everyone. Good info. I guess once I do the build I'm gonna try the 3.1" pulley with a new belt and tensioner and see what happens.

 

[Blown_By_You]

Overdrive crank pulley..

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[Sluggie24]

If I use an overdrive crank pulley do I need to use under drive pulleys for the accessories so they operate within their specs and don't get damaged?

 

[Brutal Metal]

If I use an overdrive crank pulley do I need to use under drive pulleys for the accessories so they operate within their specs and don't get damaged?

no.

 

[OU812IC]

I have an oversize crank pulley and 3.6 pulley on my Paxton 1500. 11ish psi at 6500 on good air... no intercooler. When you do your build you are going to upgrade you balancer/crank pulley anyway right? Few dollars more...

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[DRK HRS]

no.

He'll likely be overspinning the shit out of the alternator at high RPMs actually. That would have been the case on mine, although I don't have a GT. Maybe they have a different pulley size and/or spin limit than the 4G on the Mach.