westy turbo Posted July 18, 2008 Share Posted July 18, 2008 As a newbie am kinda confused the 3.92 gives a higher speed than a 3.62? which will you recomend for track use,and also if the diff hasnt have that little label on in,how i can regognize which one is it...IF i can Quote Link to comment Share on other sites More sharing options...
cleowuss Posted July 18, 2008 Share Posted July 18, 2008 Hi Westy A 3.92 diff will give you a lower top speed but improve the acceleration of the car. If the part# tag is missing the only way to tell is to turn the input shaft and watch the outputs. I would mark one side on the case and output turn the input shaft and count how many revolutions are needed to turn the output around once. Or if the diff is stripped then you can count the teeth on the pinion and on the crown wheel and then divide the no of teeth on the crown wheel by the no of teeth on the pinion. Hope this makes it all clear Richard Quote Link to comment Share on other sites More sharing options...
westy turbo Posted July 18, 2008 Author Share Posted July 18, 2008 Thanks Richard! you know about how many turns will give the numbur for each(3.62-3.92) Quote Link to comment Share on other sites More sharing options...
wacomuk Posted July 18, 2008 Share Posted July 18, 2008 just over 3 and a half for the 3.62 and nearly 4 for the 3.92 Quote Link to comment Share on other sites More sharing options...
combatsapph Posted July 18, 2008 Share Posted July 18, 2008 Edit: Removed until I'm sure of my facts! Quote Link to comment Share on other sites More sharing options...
markboyce Posted July 18, 2008 Share Posted July 18, 2008 As a newbie am kinda confused the 3.92 gives a higher speed than a 3.62? which will you recomend for track use,and also if the diff hasnt have that little label on in,how i can regognize which one is it...IF i can Not sure if Ive just been lucky but Ive always found the ratio written in yellow pen in the crown wheel. Access is fairly easy by removing torx bolts on back of diff. You will need some RTV silicone to re-seal it however. Before you settle on a diff ratio I would work out what your peak rpm is likely to be along with what size wheels you will be running. If you are running 15" wheels you shouldn't have a problem but if you go for 13" wheels you may end up with a very low top speed compared to what the car is actually capable of. For example Ive got a 3.36 diff with 235x45x13" rears (i.e. small overall diameter) and a T5 gearbox which gives an attainable speed on the road of around 155mph @ 6600rpm. If I were to fit the 3.92 diff the top speed drops to a rather pathetic 135mph @6600rpm. The diff ratio has a big influence on top speed especially when a turbo motor is unlikely to be pulling as many revs as its gutless normally aspirated cousin. All of the above is utter tosh however if you have some fire breathing 500 bhp lump reving to 9000 rpm which I hope you do Gear Calc is an excellent program for working out what diff ratio will suit you better. Pre-programmed into it are all the gearboxes you are likely to see in a Westfield so it is easy to play with the numbers. Cheers Mark p.s. Best time with the car was when I converted it from NA throttle bodies to the Turbo XE. Diff ratio was 4.27 with a 4-speed dog box that was 1:1 in 4th. Top speed was 105mph but it did get there very quickly if you could keep the car in a straight line. Quote Link to comment Share on other sites More sharing options...
samcooke Posted July 18, 2008 Share Posted July 18, 2008 QUOTE a rather pathetic 135mph @6600rpm. Some of us can oly dream of such speeds. 129 @ max revs in top using a 3.54 for me If it only revved to 6600 I'd barely be able to break the speed limit What engine / box / wheels are you going for? Quote Link to comment Share on other sites More sharing options...
westy turbo Posted July 19, 2008 Author Share Posted July 19, 2008 Thank you all for your inputs!! Quote Link to comment Share on other sites More sharing options...
westy turbo Posted July 20, 2008 Author Share Posted July 20, 2008 a rather pathetic 135mph @6600rpm. Some of us can oly dream of such speeds. 129 @ max revs in top using a 3.54 for me If it only revved to 6600 I'd barely be able to break the speed limit What engine / box / wheels are you going for? sorry forgot to write...its gonna be a drysumped let with MBE 967,T5 box and 7x15 and rear 8x15 Quote Link to comment Share on other sites More sharing options...
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