s2konroids

Hi guys,

I have just installed a second hand CT pulley and a brand new Dayco belt. I've upgraded from a 4.25" to a 4" pulley, previous to this I was using a gatorback 4060395 (toothed) and now I've fitted a ribbed 5060390 for the new 4" pulley.

Thing is I'm sure I've tightened it but come 4000 rpm its making the same amount of boost as the 4.25", and just after 4200rpm less where it only hits around 4.9psi at 8200, previous to this is was about 6psi at 8200 (6.5 at 8800rpm) - this according to logs I've done with the greddy emanage ultimate.

Am i right in thinking it should make more boost all the way through the rev range as opposed to the 4.25"? (should make roughly 1psi more throughout)

Is it simply belt slip as the belt is new?, i would have thought if i tightened it very tight it would just gradually slip NOT straight away?

Cheers

erikvanden

are you sure you were making more boost than that before? I am doubting the stock pulleys ability to make 6PSI, even if you didn't have an afercooler.it shouldn't be a huge boost increase going to that pulley. Honestly it is difficult to see how much boost you are making without going on a dyno when you are talking about a few PSI. those mechanical boost gauges aren't that good and you have to be at WOT to read it through the entire RPM range.

But. new belts will loosen and you need to keep tightening them until it stops stretching. you may need some kind of pry bar to get enough leverage on the pulley to tighten it. I did with my 11PSI pulley. people say you shouldn't be able to twist the belt more than 90* on the nontensioner side.

some tip:

I never noticed much if any difference between belts. the gatorbacks might grip a little better but with belt slip I found the issue with reasonable sized pulleys to always be related to the belt tension. switching belts will probably be more of a pain than a solution.

If you have belt slip the PSI will normally drop at a point when the RPMs are climbing. (example: makes boost up to 5PSI at 7K then boost drops to 0). If the RMPs don't drop there may not be an issue. As the engine revs up it makes more boost but the engine then also needs more air.

s2konroids

I'm an idiot!, I didn't tighten the nut to secure the tensioner arm .

I was AP1 running the AP2 pulley so should be around 6.5psi at redline - i get just over that, and today after installing the smaller pulley i now get 7.7psi at redline, so the GEMU logs are correct and showing what i thought i should have.