I went with GTT. wen it was being done it was noticed I had some problems their already with stripped threads so a helicooil needed to be inserted. I *think* that was with my crankpully. I suppose if the threads had fully stripped I would have had a very nasty failure. I also had the GTT pullystop installed, so if it did fail it would limit the amount of damage done.
I have read that if you replace the stock crank pulley with a lightweight pulley of the same same size, thus reducing the weight of the pulley by about 6lbs, it is equivalent to removing approx. 100lbs from the weight of the car in terms of performance. This is due to a reduced rotational mass.
If you change the stock crank pulley for for a lighter weight larger pulley, then you not only get the benefit of reduced rotational mass but you also increase the speed of the supercharger pulley, thus gaining performance from that as well. However, the larger crank pulley spins the alternator pulley too fast and so it was recommended to me that that pulley should be replaced with a larger one to compensate.
Last edited by MisterMINI; Sep 26th, 2006 at 07:41 PM.
Reason: Corrected size of alternator pulley from smaller to larger
Hi Guys, the pullers we use are made & designed by me, we only have one of each tool so we cannot lend /rent out (sorry). Although you see 2 different Idlers on our website the earlier (single bearing) type are no longer available, this was due to the introduction of the GTT Twin Bearing Idler which is even better and is the current design. GTT crank pulleys are available in stock size +1% and +3% sizes. IMO its not worth the effort changing from the early 7Ib stock unit to the later 5.5lb stock unit. If you dont want to go ' too mad' I'd suggest you do the GTT Crank pulley in +1% ,the GTT twin bearing Idler and new belt to start with. Allow around 3hrs to do all this. TBH its better to let us do the pulleys unless you have workshop facilitiys ,I for one couldn't do it without heat, air tools and special pullers. We can do all this for you in a morning if you wanted too,that way you dont have to worry about possible buckling of pulleys, getting pulleys stuck half on /off, threads stripping, pulley alignment,snapping or jamming lengths of stud in the end of the crank nose Just sit in the Gorge Cafe sipping coffee and munching a bacon sandwich
Best Regards Roland GTT
Roland. If you change the stock crank pulley for a +1% pulley and already have a 15% supercharger pulley, how much extra power would you expect to gain? Would I feel the difference in performance or is it marginal?
Do you recommend increasing the size of the alternator pulley to compensate for the larger crank pulley?
Don't do it! i have Had two light weight crank pulleys on my cooper s both have failed when they fail they spin on the end of the crank shaft, taking vital metal off your crank (new crank) The std one is put on with heat. hope this helps.
Gary what make were the crank pulleys? Were they oversize and if so what size? Also who fitted it?
reason I ask is I am booked in on Tuesday to have the GTT lightweight oversize crank pulley and GTT twin bearing idler pulley fitted by BMW. Have seen lots of varying opinions but none bad from folk who have had them professionally fitted so curious as to the above questions.
Roland I have no idea what size crank pulley I have. Above you mention they come in 1% or 3% yet your website says stock or +4mm. Very confusing The receipt doesnt say, just says oversize crank pulley. Would like to get my MTH map updated to the correct crank size. I have emailed you couple of days ago but no response yet.
2003 BRG/W JCW MCS - 2002 PS/PS JCW MC - 1970 BRG/W MK2 Morris Cooper S - 1964 Blk 850 (eaton supercharged 1293) - 1961 Morris Traveller - 1974 Ex Army Moke - 1978 1275 LS
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