I always hate to go against a manufacturers advice/recommendation but in the case of the Whipples, I guess I have a difference of opinion when it comes to their belt tension recommendation. Some Whipple owners have occasionally complained about an annoying belt-chirp that sometimes appears when the car is cold. I remember reading on here that a remedy is to slightly lessen the tension applied by the idler pulley. Eventually Sam's (HHGT) car developed the chirping sound and I recall writing or calling Whipple to see what they thought about slightly loosening the idler pulley tension. I received a stern recommendation that this SHOULD NOT be done and I passed the advice to HHGT. Several months later (and not so many miles for Sam's car), Sam still had the occasional chirp problem. At our next opportunity to service his car, we did the adjustment to back-off on the idler pulley tension. Happily this fixed the chirping probem. The downside is that with less tension (and fractionally less belt wrap), the opportunity for belt slipping occurs. My personal opinion is that we are not getting any belt slip although I don't have the data (on Sam's car) to prove it.
Fast forward to the past weekend when we installed a Whipple on FastFreddy's car. Hmmmm.... what to do about the belt tension. Too tight and he will likely have or develop the chirping. Too loose and we risk having belt slipping which will show up on the dyno. Mind you, FastFreddy has the 21lb pulley and many others have "only" the 19lb pulley. While assembling FF's car, we really paid close attension to what was going on with the OEM belt tensioner arm. What we found is that if we had the idler pulley adjusted as hard as we could, we had virtually no play left in the tension arm. Alternatively, if we had just a modest pressure with the idler pulley, we regained more of the OEM motion on the tensioner. We opted for this less-than-max tension in order to have more buffering with the OEM tensioner. Early results is that this is the right decision. There is no chirping AND there is absolutely no belt slip up through a maintained 21psi boost level.
I'm not sure how many of you have had an opportunity to see a GT engine run with the cockpit engine access plate off. We have. With both the blower belt and main accessory belt properly tensioned (with the OEM tensioners), you miht think that those tensioner arms don't move much with the car running. (This was my thought, anyway.) I was quite surprised to see the range of motion that the tensioners go through when you blip the car. The transition from acceleration to de-celereration, really makes these tensioners work. My thought is that if you severely limit their range of motion, then you take away one of the critical "shock absorbers" for the harmonic balancer. John, INDY, and many others here are much smarter than me on this whole engine dynamics topic, but I would advise everyone to be cautious of the tension you have in your Whipple belt. Our (LIMITED) experience would suggest that you may not need as much tension as perhaps Whipple thinks you do and, secondly, that extra tension may very well inhibit the built-in shock absorber for the harmonic balancer. Again, with my LIMITED experience - certainly if you are having the belt chirping problem, you may try to back-off on this idler pulley a bit. Just maybe your car is trying to tell you something. If you have access to a dyno, it's easy enough to confirm if you have any slipping or not. This is my LIMITED-Experience perspective and I let the experts comment if I'm full of crap or not.
