Omni
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| posted on 26/7/07 at 02:08 PM |
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Gear Ratios and What Diff is needed?
Hi All,
I just picked up an Injected Fireblade 929 RRY engine kit. I need a bit of help working out the above if poss. I will be running 185/60/R13's so
what diff will I need to get the best out of this combo?
It is for general raod use and the odd track day.
Cheers,
O
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worX
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| posted on 26/7/07 at 02:11 PM |
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I think you'd be fine with a 3.62 ratio diff with that engine.
Up to you whether you go LSD or not.
hth
Steve
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Omni
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| posted on 26/7/07 at 02:13 PM |
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quote:
Originally posted by worX
I think you'd be fine with a 3.62 ratio diff with that engine.
Up to you whether you go LSD or not.
hth
Steve
Cheers worX. Any idea of what RPM it will be doing at 70 mph? Also what the top speed might be?
Ta'
O
P.S. I just can't get my head around those calcs. lol.
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Kev99
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| posted on 26/7/07 at 02:54 PM |
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I beleve it will be around 7500 to 8000rpm with a 3.62
Kev.................
[Edited on 26/7/07 by Kev99]
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worX
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| posted on 26/7/07 at 03:27 PM |
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I'm not very good with the calcs either, but to be honest, you can't get it perfect with certain details...
To get a better approximation if you were to measure the rolling circumference of your wheel tyre package then you can work it out more
accurately.
I am on toyo 888's 195.50/15's with a 919 blade and a 3.62 diff, and I am doing virtually spot 7000 at 70 in top and 8000 at 80 and so
on...
hth
Steve
quote:
Originally posted by Omni
quote:
Originally posted by worX
I think you'd be fine with a 3.62 ratio diff with that engine.
Up to you whether you go LSD or not.
hth
Steve
Cheers worX. Any idea of what RPM it will be doing at 70 mph? Also what the top speed might be?
Ta'
O
P.S. I just can't get my head around those calcs. lol.
[Edited on 26/7/07 by worX]
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worX
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| posted on 26/7/07 at 03:30 PM |
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the top speed on most of the (slightly) lowered powered BEC's is limited by lack of horsepower being able to push a relativley UNaerodynamic
shape through the air!!!
I should expect to see in the region of 120-125mph!
Steve
quote:
Originally posted by Omni
Cheers worX. Also what the top speed might be?
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THE BEAR
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| posted on 26/7/07 at 08:34 PM |
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2lt zetec
here is one for you all i have a 2lt focus zetec engine a type 9 box ?? or is it t5 ??
and i do have a 3.62 lsd what box do i need and will this work and as iam thinking wheels next 15 what speedo will i need many thanks
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Ratters
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| posted on 26/7/07 at 08:45 PM |
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Do a search for the GearCalc program, very easy to use.
T5 is all alloy, type 9 5 speed has iron maincase & alloy tailshaft. Both have same input shafts.
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tomblyth
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| posted on 26/7/07 at 08:49 PM |
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put your info in this spread sheet and choose your own...
[Edited on 26/7/07 by tomblyth]
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THE BEAR
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| posted on 27/7/07 at 05:54 PM |
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tryed to do that down load but i cant seem to get it to work it out where am i going wrong  help will this set up work
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tomblyth
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| posted on 28/7/07 at 07:09 PM |
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detail for your wheels an engine
 
Rescued attachment 3.62 diff with 185 60 R13 wheels.gif
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Omni
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| posted on 28/7/07 at 07:13 PM |
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Cheers for that
What program is that????? My engine is the 2001 Blade Injected Engine
O
[Edited on 28/7/07 by Omni]
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Omni
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| posted on 29/7/07 at 09:20 AM |
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I found that spreadsheet and the exact gear ratio's for the Fireblade Injection Engine.
I need a 3.14 ratio diff by the looks
Knowing my luck I bet this is the hardest diff to get hold of! lol.
O
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ChrisGamlin
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| posted on 29/7/07 at 04:10 PM |
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The above spreadsheet is in my avatar below, originally written by a chap on the Yahoo List about 6 years ago. It doesnt have RRY ratios in it by
default but you can edit the entries to suit whatever bike engine you want.
Are you sure you have your peak RPM correct Omni because a 3.14 sounds rather extreme unless they significantly lowered the gearing on the RRY
compared to the last of the carbed engine which will hit 125mph with 185/60-13" with a 3.54 diff! If thats true though it will also be expensive
due to the 3.14's hens teeth nature!
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Omni
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| posted on 29/7/07 at 08:37 PM |
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Hey Chris,
These are the the figures I got for the 929 RRY:
Primary 1.521
1st 2.692
2nd 1.933
3rd 1.600
4th 1.400
5th 1.286
6th 1.190
Final 2.625
I figured that the RRY would peak at 11500 RPM. Do you get different figures than me then?
Cheers,
O
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Omni
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| posted on 29/7/07 at 08:52 PM |
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The other option on playing with the figures is to go for a 3.38 diff with 185/70/R13's.
O
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ChrisGamlin
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| posted on 29/7/07 at 09:10 PM |
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Id think the peak RPM will be higher than that, the older 893/919 engines hit their limiter at 11750, so Id expect the 929 to be 12k minimum but might
be wrong.
Those figures if correct are a bit lower than the older engines (same reduction ratio, lower top gear), but personally Id go with a 3.38 and put
205/60-13's on the back instead if gearing was an issue, rather than go for 185/70's, but if the rev limit is ~12k, even with 185/60s
you're going to get gearing to 125mph which is plenty.
[Edited on 29/7/07 by ChrisGamlin]
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Omni
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| posted on 29/7/07 at 10:13 PM |
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Hey Chris,
Cheers foe that. According to Fireblades.org one 929 owners rev limiter did not kick in until 12650 RPM. When putting 12500 RPM into the spreadsheet
is shows running the 205/60/R13's as coming out at about 135 MPH (Which is my overall goal)
Slight change of subject here but I am confused about how changing the width of the tire from 185 to 205, but not changing the profile helps. Can you
shed light on this?
Cheers,
O
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Omni
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| posted on 29/7/07 at 10:32 PM |
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Doh! I have just remembered I have picked up my wheels already. They are 6J x 13's so I can only get 185's on them! Oh well 130 mph will
have to do. lol.
A 3.14 does put me at 140 though with these wheels 
I have found a 3.14 diff for £188.
O
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ChrisGamlin
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| posted on 30/7/07 at 02:00 PM |
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You can put 205/60's on 6" rims, the RGB Class C race guys all run them like that (as they are restricted to 6" wheel width in the
regs but can pick tyre widths), and Ive also run them on mine with 6" rims. They werent so good on my car though being a live axle due to the
tyre not being quite as stable as it would be on a wider rim, meaning it rolls its outside edge a little bit on a live axle car (where you can't
put negative camber on the rear wheels), but on an IRS car it shouldnt be an issue.
As to the other question, the 205/60 bit of the tyre size relates to the tyre wall height as a percentage of the width, and 60% of 205mm
is obviously higher than 60% of 185mm hence overall bigger rolling circumference.
Chris
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ChrisGamlin
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| posted on 30/7/07 at 02:03 PM |
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Out of interest, why do you want to hit 130+, is it simply for lower cruising RPM on the motorway etc? I ask because with a seven style body (ie not
enclosed) you'll struggle to get over 125mph in it unless downhill and/or with a big trailing wind due to the appaling aerodynamics.
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Omni
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| posted on 30/7/07 at 02:34 PM |
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quote:
Originally posted by ChrisGamlin
Out of interest, why do you want to hit 130+, is it simply for lower cruising RPM on the motorway etc? I ask because with a seven style body (ie not
enclosed) you'll struggle to get over 125mph in it unless downhill and/or with a big trailing wind due to the appaling aerodynamics.
Hi Chris,
Many thanks for your help and info. Now you have explained about the % of the width it makes more sense. I didn't think of it like that. lol.
Looks like I will be putting 205/60/R13's on my rear Minilights then 
As for the wanting to achieve 130+ mph is it as you said for lower cruising speed but also to allow me to get some decent speed along the straights on
track days
Many thanks again for all your help.
Omni
[Edited on 30/7/07 by Omni]
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ChrisGamlin
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| posted on 30/7/07 at 03:56 PM |
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No probs, fair plays if its for road driving but if its mainly for trackdays you're doing it, don't chase the high top speed too much. Ive
got a 2003 R1 in mine with a 3.54 rear diff and 205/60-13 tyres so is geared for about 125mph, and Ive only twice maxed it out on the limiter in top,
at Rockingham having taken the banking at about 115mph on a couple of occasions, and at Spa when I got a tow up the Kemmel straight behind a
mate's Megabusa.
On 99% of circuits though (Ive driven Cadwell, Anglesey, Llandow, Oulton Park, Donington, Rockingham, Hethel, Brands Indy, Mallory and Spa off the top
of my head) and especially when you're still learning the car, you won't get above 115-120mph even on what appear to be fairly decent
straights.
cheers
Chris
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Omni
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| posted on 31/7/07 at 08:24 PM |
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Cheers again Chris. I am greatful for all your help
Omni
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