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Author: Subject: What ratio do i need for bec
madteg

posted on 19/8/08 at 07:51 PM Reply With Quote
What ratio do i need for bec

Will be running f/blade engine, got no idea what ratio to run, can anyone point me in the right direction.
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StevieB

posted on 19/8/08 at 07:55 PM Reply With Quote
I assume you mean for your diff?

I've got a 3.62, but no idea how it goes yet

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smart51

posted on 19/8/08 at 07:56 PM Reply With Quote
I don't know the fireblade well my self but people on here do. They'll want to know which size or year of engine plus what tyre size you're going to use.

I'd guess that a 3.38 would be ideal but a 3.62 would do. Are you mainly using it on the track or the road?

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madteg

posted on 19/8/08 at 08:04 PM Reply With Quote
ratio

I am starting of with a 893 1995 engine on to a chain diff, running 16/65/195s. Trying to build as light as possible.
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LBMEFM

posted on 19/8/08 at 08:25 PM Reply With Quote
Sierra 3.62 is perfect. Most replace the sprocket with a flange and attach a modified Sierra propshaft. How you are going to do it with a chain drive I am not sure.
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motorcycle_mayhem

posted on 19/8/08 at 08:25 PM Reply With Quote
With 205/60/13 you'll be happiest with a 3:36, or at least I was. Mainly used on a track, but nonetheless, it was awesomely good on the road.
Tried the 3.2 Freeloader with the engine, but way too much for the torque curve to handle.

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madteg

posted on 19/8/08 at 08:33 PM Reply With Quote
diff ratio

Building rear bike engine car, engine front facing with chain diff similar to a atom
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mark chandler

posted on 19/8/08 at 08:38 PM Reply With Quote
893 blade, 13" wheels and 3.62 diff for me.

It will pull 12,500 rpm in top, 13,000 going down a hill so perfect for power although a bit noisy at 70mph.

I recon its touching around 125mph flat out.

Regards Mark

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JoelP

posted on 19/8/08 at 09:04 PM Reply With Quote
quote:
Originally posted by madteg
I am starting of with a 893 1995 engine on to a chain diff, running 16/65/195s. Trying to build as light as possible.


what you want to do, is find out the top speed of the bike, then the final drive ratio of the bike, then work out what top speed you expect your power and body style to manage (guess 120), then compare your tyre circumference to that of the bikes standard back tyre, then merge it all together to pick a ratio for your set up, and shimmy it about to get two teeth numbers for front and back sprocket.

As an example, if the bike is geared to 180 with a 2.5 final drive ratio, and has a 1m circumference, and your car will aim for 120 with a 0.8m circ, then you need rato of 2.5/120*180*0.8, or 3. So maybe a 14 tooth front and 42 rear.

Simple, but bear in mind i totally made up the rolling radius.

And whilst you're buying cogs, get 3 back ones so you can change at will for different circuits. Its very annoying hitting the rev limiter on straights!

[Edited on 19/8/08 by JoelP]

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madteg

posted on 19/8/08 at 09:49 PM Reply With Quote
Thanks all.
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ChrisGamlin

posted on 21/8/08 at 05:39 PM Reply With Quote
quote:
Originally posted by mark chandler
893 blade, 13" wheels and 3.62 diff for me.

It will pull 12,500 rpm in top, 13,000 going down a hill so perfect for power although a bit noisy at 70mph.

I recon its touching around 125mph flat out.

Regards Mark


Hi Mark

Unless you've got a modded (or CBR600) ECU, a stock 893/919 blade hits the limiter at 11,750rpm so if you're showing 12.5-13k then either your clocks are over-reading or you don't have a stock ECU.

Madteg - download the spreadsheet in my sig then you can see what different ratios/tyres give you. I used to run a 919 blade in mine and with 205/60-13's, a 3.54 was about ideal for track work. You won't find one of those ratios in a Sierra so 3.38 or 3.62 would be the ones Id go with.






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asl

posted on 22/8/08 at 06:48 PM Reply With Quote
Chris, Thanks for the excel spreadsheet, but how should I use it?

I've got an 893 Fireblade with 195/50R15 and was at Brands and spent the whole of the straight on the rev limiter (11750) with a max speed of 107.

What diff do you think I have? I've checked the number against the sticky on the transmission forum but can't match the number (mine looks like 83BG 4033BA)

Thanks for your help

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ChrisGamlin

posted on 23/8/08 at 07:29 PM Reply With Quote
Id say you've got at least a 3.9 in there, if not a 4.1.

With the spreadsheet, you can if you want type in alternate diff ratios into the "Data" tab, and you can also edit the tyre sizes in that tab and it will calculate it all properly. Once youve done that, go to the Speed Chart tab, select the engine, tyres and diff ratio and it will give your top speeds in each gear on the chart (hover over the chart for the actual figures).

Chris






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asl

posted on 24/8/08 at 03:58 PM Reply With Quote
Thanks, I will have a look. Do you have any data how the 0-60 changes with different diffs?
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ChrisGamlin

posted on 24/8/08 at 08:34 PM Reply With Quote
Nope but its not a lot. A low diff will mean you'll need 3rd gear at least to hit 60 so the little you gain in acceleration you lose between gears.

I had a 3.5 and a 3.9 in my blade BEC, and side by side against my mate's Megablade there was naff all in it with either diff. The 3.9 feels faster because the revs are rising faster and you're changing gear more often, but actually it makes little difference.






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