MrPoseidon Posted August 8, 2017 Posted August 8, 2017 Hi all. After a trackday, my 3k mile brand new alternator decided to die me. Looking for a racing one that an handle a few revs...... Cheers.
Dave Eastwood (Gadgetman) - Club Chairman Posted August 8, 2017 Posted August 8, 2017 Generally speaking, racing alternator = ordinary alternator + big price. Some "racing alternators" may have a different sized pulley on, so that they don't rev as high, but by no means all do. Pulleys are normally interchangeable on the small type alternators anyway. 1
John Loudon - Sponsorship Liaison Posted August 8, 2017 Posted August 8, 2017 4 hours ago, Dave Eastwood (Gadgetman) - Club Secretary said: Generally speaking, racing alternator = ordinary alternator + big price. Some "racing alternators" may have a different sized pulley on, so that they don't rev as high, but by no means all do. Pulleys are normally interchangeable on the small type alternators anyway. Agreed. I kept killing alternators and then discovered that the pulley size on them was wrong for my max engine revs. The small Nippon Denso alternators don't like more than 18k rpm (most standard road car one are 15k max rpm) Measure your engine front pulley and then the alternator one to work out the ratio and multiply it by your max engine rpm. If it exceeds the recommended rpm for the alternator, change the of alternator pulley to bring it within the recommended maximum 2
Dave Eastwood (Gadgetman) - Club Chairman Posted August 8, 2017 Posted August 8, 2017 What John said. BTW, especially with some modern higher reving engines, its much simpler to change the alternator pulley than the crank pulley. Changing the crank pulley can achieve the same speed reduction, and will do the same for the water pump, BUT, often times you can only get a simple billet aluminum version of the crank pulley - good for looks, but loosing the harmonic damper that many modern cars build in to it, can cause long term issues with some engines. 1
MrPoseidon Posted August 8, 2017 Author Posted August 8, 2017 The car has a Zetec 2L and revs to 7,250. Crank pulley is 13cm and alternator pulley is 6 cm so on the face of it, the sizes appear correct. So by my calculations 7250rpm at the crank will equate to 15,700 rpm at the alternator....... Maybe I just got unlucky.....
the stoat Posted August 9, 2017 Posted August 9, 2017 Nope you did not get unlucky, I had the same issue. A swift change of pulley size and no more issues. Although I do now run a small Denso one, ex GadgetMan , you can avoid the motorsport tax on these by buying one for a Kubota tractor. I have stated this many times only to receive feedback there is no way a diesel alternator could cope with the revs, check the part numbers is all I have to say...... 1
the stoat Posted August 9, 2017 Posted August 9, 2017 I forgot to add I found a local motorfactor had a bucket of pulleys and a quick rummage and a few pounds was all that was required as opposed to trying to work out the pulley required from specs and pictures on the Internet.
MrPoseidon Posted August 9, 2017 Author Posted August 9, 2017 Great info, thank you . Any link as to the exact one I need mate?
the stoat Posted August 12, 2017 Posted August 12, 2017 I unfortunately do not have a part number I, although will be taking mine off soon so will double check. Although I may have to eat humble pie as online the Kubota ones seem to have rocketed in price. It could be worth trying a local agricultural equipment supplier.
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