Justin@VMP
August 16th, 2007, 12:20 PM
I've seen many posts on here where people insist the belt will slip if you run a 2.6" pulley without the auxillary idler bracket made by Metco (and now a few other companies as well). Some have even warned of damage. Based on the testing I've done this is untrue.
I datalog boost using my Dynojet, I just don't believe you can safely and accurately watch the boost gauge and RPM while accelerating a 500+RWHP car. Anyways, the boost gauge in our cars is based off inferred boost calculated by the computer, there is no sensor.
I've ran GT500s on my dyno several different ways with the 2.6" SC pulley. I've found that average boost is the same regardless of no idler, 90mm idler in place of stock 75mm idler, and with metco aux idler bracket.
http://www.vmptuning.com/dynographs/boostcompares.jpg
You can see that average boost is the same regardless of idler used. The car with LTs was down about .5psi over everyone else.
If you are running a KB with a 2.5" pulley then the extra wrap of the aux idler with bracket may be of benefit to you. However, with a stock blower and 2.6" pulley I don't see the need for it.
Some have claimed that belt stretch over time will result in slippage, but I believe there will be very little stretch due to the massive 10 rib belt (a design originating from the Ford GT).
Ford designs that belt to last 100,000 miles.
My car is coming up on 3,000 miles, each time I have it on the dyno I'll continually check for belt slip and boost loss. At this rate its usually up there every few weeks to try different parts and combinations.
I datalog boost using my Dynojet, I just don't believe you can safely and accurately watch the boost gauge and RPM while accelerating a 500+RWHP car. Anyways, the boost gauge in our cars is based off inferred boost calculated by the computer, there is no sensor.
I've ran GT500s on my dyno several different ways with the 2.6" SC pulley. I've found that average boost is the same regardless of no idler, 90mm idler in place of stock 75mm idler, and with metco aux idler bracket.
http://www.vmptuning.com/dynographs/boostcompares.jpg
You can see that average boost is the same regardless of idler used. The car with LTs was down about .5psi over everyone else.
If you are running a KB with a 2.5" pulley then the extra wrap of the aux idler with bracket may be of benefit to you. However, with a stock blower and 2.6" pulley I don't see the need for it.
Some have claimed that belt stretch over time will result in slippage, but I believe there will be very little stretch due to the massive 10 rib belt (a design originating from the Ford GT).
Ford designs that belt to last 100,000 miles.
My car is coming up on 3,000 miles, each time I have it on the dyno I'll continually check for belt slip and boost loss. At this rate its usually up there every few weeks to try different parts and combinations.