I bought both drive and driven Pro 4 clutches from mark. 4 tower primary and standard dia. secondary. I went with Pro 4 for a couple of reasons 1st he makes both primary and secondary clutches and 2nd he is state side.
I have a 17 cross county 137 with stock gearing a 270 TD tune, cold air intake,exhaust 2 1/2",turbo smart BOV and before I went with these clutches I was running 180 to 190 belt temps and now run on the average 135 to 140 and with easy throttle I 115 to 120.
I had one problem right from the get go and contacted mark and he had me send back to him and he paid for shipping both ways and was always communicating with me.
I love the clutches and the customer service I feel is second to none.
FYI, Mark is a racer by heart and also sponsors the asphalt racing circuit here in Michigan. I have talked to him several times and he has always been polite, informative, and stands behind his work. We use his secondary on our PS1000 sled and have always gotten better ET's with his secondary VS the stock cat reverse cam and we have yet to wear out the bushings in the secondary in 5 years of racing and testing in the grass/dirt. When we were using the stock secondary we had to replace the bushings yearly.