Thread: Does a smaller s/c belt create more boost?

Ok so I have an mps with a 3.5, 3.4, and 3.3 pulley. I'm using a gates 653 belt. According to zzp the maximum pulley to use for this belt is a 3.5 and so I'v been using this belt for awhile on my 3.4 press on before I got my mps so it's probably a little stretched out from use. It fits snug on the 3.5 and actually has some belt squeak when the engine is cold. When I put it on my 3.4 I'm logging at most around 11.5 psi, now when I put it on my 3.3 pulley I maxed out around 11.2 psi. The belt goes on like butter on the 3.3 so I'm thinking since it's been taken off and on so many times on larger pulley's it might have stretched causing it to be looser on the 3.3. Driving conditions where the same when logging with both pulley's around 80-85* weather, car fully warmed up, no knocking. So I'm thinking since it's tighter on the 3.4 that it's spinning the s/c quicker then with the 3.3. I'm thinking of trying the 650 belt to just see if it increases my boost because it doesn't make sense to me that a 3.4 would make more boost. Do you guy's have an opinion?

11.5 with a 3.4 man your engine is restricted.

Ya, it's getting up there in miles and the weather has been humid here. Also a hai probably doesn't help and my blower isn't ported.

Originally Posted by ITHURTZ

11.5 with a 3.4 man your engine is restricted.

i had a solid 10 with around 12 at shift with a 3.4 w/ CAI homemade box, headers, self port and polish on supercharger/lower intake/ and tune. but prior to porting was only getting 8-9

Watch your boost on both pulleys. If the belt is slipping any, you'll be able to see the boost come on/off/on/off unless it's slipping really badly, in which case you should have telltale rubber on the underside of the hood.

Anything that increases out flow drops boost. The most I ever saw on a 3.4 setup with a HAI and headers was 8 psi with a ported Gen 3.

I'm now at 16psi on a 3.0/IC/Cammed/ all that good stuff.

The PLOG and DP help quite a bit, and without having any knock, that's a good thing. Headers would net you more flow and more room to pulley down or pull more timing.

Ya, I was thinking doing header's but I'm pretty content with a PLOG, dp set up right now. I guess it's not that low of boost then. Could of been weather related from humidity or something like that, or my car just likes a 3.4 better lol