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Gear Ratios and What Diff is needed?
Omni - 26/7/07 at 02:08 PM

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


worX - 26/7/07 at 02:11 PM

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


Omni - 26/7/07 at 02:13 PM

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.


Kev99 - 26/7/07 at 02:54 PM

I beleve it will be around 7500 to 8000rpm with a 3.62

Kev.................

[Edited on 26/7/07 by Kev99]


worX - 26/7/07 at 03:27 PM

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]


worX - 26/7/07 at 03:30 PM

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?


THE BEAR - 26/7/07 at 08:34 PM

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


Ratters - 26/7/07 at 08:45 PM

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.


tomblyth - 26/7/07 at 08:49 PM

put your info in this spread sheet and choose your own...

[Edited on 26/7/07 by tomblyth]


THE BEAR - 27/7/07 at 05:54 PM

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


tomblyth - 28/7/07 at 07:09 PM

detail for your wheels an engine Rescued attachment 3.62 diff with 185 60 R13 wheels.gif
Rescued attachment 3.62 diff with 185 60 R13 wheels.gif


Omni - 28/7/07 at 07:13 PM

Cheers for that

What program is that????? My engine is the 2001 Blade Injected Engine

O

[Edited on 28/7/07 by Omni]


Omni - 29/7/07 at 09:20 AM

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


ChrisGamlin - 29/7/07 at 04:10 PM

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!


Omni - 29/7/07 at 08:37 PM

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


Omni - 29/7/07 at 08:52 PM

The other option on playing with the figures is to go for a 3.38 diff with 185/70/R13's.

O


ChrisGamlin - 29/7/07 at 09:10 PM

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]


Omni - 29/7/07 at 10:13 PM

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


Omni - 29/7/07 at 10:32 PM

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


ChrisGamlin - 30/7/07 at 02:00 PM

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


ChrisGamlin - 30/7/07 at 02:03 PM

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.


Omni - 30/7/07 at 02:34 PM

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]


ChrisGamlin - 30/7/07 at 03:56 PM

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


Omni - 31/7/07 at 08:24 PM

Cheers again Chris. I am greatful for all your help

Omni