im building a spire gtr with an 09 fireblade engine. After talking to spire, ive always planned on putting an elite reversing diff in it. The time has come to order it...and i need to pick a ratio; advice please! ! At present I do not have any wheels for it. I am not building it as a race car, more of a road toy with occasional track days.

Im thinking ill prob use something around a 15-195 wheel, and playing around with the calcs, looks like my ratio of choice would be around 3.2-3.3 ish. giving a top speed around 140. Its a lot of money to spend so i want to get it right (although I guess I can always buy other drop gears if i want to change it later).

Does that sound about right to you guys?

Think a 3.2 may be a bit tall for a blade engine, great for cruising but will take the fun away on acceleration.

Buddy of mine runs a blade motor in his live axle westy with a 3.54 Diff and its a good balance for road and track use. Another buddy uses a 3.62 in his blade engined Indy and is a wicked track toy tho a little rev happy in road use but very usable.

In my Busa I am putting a 3.38 due to the extra torque, end of the day its what type of road use you have planned, touring versus local back road hooligan.

Not sure how the 09 gearing is compoared with the older 'blades

My 95 one was on 3.62, but have recently dropped to 3.38
I like them both, in their own right but a 3.5 would be perfect

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Originally posted by ReMan
Not sure how the 09 gearing is compoared with the older 'blades

My 95 one was on 3.62, but have recently dropped to 3.38
I like them both, in their own right but a 3.5 would be perfect

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Keep in mind the 2 comments above relate to 7's where the poor aero limits the top speed anyway. The Spire aero will easily take it past 125 with that engine and the right gearing. The down side is a high first gear so setting off is trickier and all the gears are a bit longer and I doubt you'd max it out on track.

I've a 3.21 in my R1 Fury and that gears it to 149mph and on the limiter in first hits 72mph. Around 3.4-3.5 would be nice on track but the current gearing is fine on the road and really helps on a long run, where 70mph is 6500rpm so not reving too hard.

do the elite diffs not have drop in ratios so you can alter to suit?

I had this exact setup in my GTR, I've got all the ratios on a spreadsheet and graphs from Elite I can email you if you'd like. Mine was for the track rather than the road and was geared for 130mph.

thanks; elite have done me graphs and sent them through anyway so ive got them already!

Daniel, yes they do...but you gotta pay for em so itd be nice to get it right of the bat! Saying that they arent that expensive so its not the end of the world, but good to know others have gone similar and it works well.

It may not matter much for the road, but you do lose more power putting it through a prop and diff than if you were go use a chain diff setup. I've just sold my car and the new one will have a radical/quaife reversing chain diff setup.