kevmcdo
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| posted on 15/8/11 at 08:48 AM |
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diff ratio query
Morning Guys
Just recently changed the engine in the car from the 1600 cross flow to the 99 R1 engine and after a few attempts to get the fueling all is running
very well with the exception of the gearing which is really low.
As said the engine is an R1 (99 MODEL) and is running 13" wheels with 185/60's on and the the car is topping out at around 90, this has
been verified by another car. At this stage I still have plenty of throttle travel left to go but have to lift off as it would go into the red
otherwise.
It gets there at a rate of knots that you can barely keep up with gear changes and spins up at the slightest provocation of the right foot, great for
short sprints down the back roads and annoying the life out of the local sportsbike lads but a bit too frenetic everywhere else.
Question is what diff ratio do you think it may be running at the moment ( no id tag on / english axle ) and what difference would either fitting a
3.44 diff which I have or a new set of wheels say 15" with 196/50"s?
Thanks in advance........
Kev
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mcerd1
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| posted on 15/8/11 at 09:15 AM |
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[edited]
best way to find out what yo've got now it to jack it up and count the numer of turns of the prop it takes for one turn of the wheels (as long
as you make sure both wheels are turning together this will be the ratio)
on there own the 15" wheels with 195/60's will increase the gearing by about 4%
[Edited on 15/8/2011 by mcerd1]
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adithorp
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| posted on 15/8/11 at 09:38 AM |
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quote:
Originally posted by mcerd1
best way to find out what yo've got now it to jack it up and count the numer of turns of the wheels it takes for one turn of the prop (as long
as you make sure both wheels are turning together this will be the ratio)
on there own the 15" wheels with 195/60's will increase the gearing by about 4%
[Edited on 15/8/2011 by mcerd1]
Couple of things from that. It's the number of turns of the prop for one turn of the wheels (not the other way). Also because it can be
difficult to get both wheels to turn evenly and to accuratly count the complete and partial turns of the prop, it's more accurate to do multiple
turns and get an average. Jack up one wheel (now turns x2 as fast per prop rotation), turn it 10 turns counting the prop turns (tipp-ex is handy) then
divivd the result by 5.
So for a 3.8:1 diff. ten turns of one wheel gives 19 turns of the prop. 19/5=3.8
17.2 turns would be a 3.44:1
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
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JimSpencer
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| posted on 15/8/11 at 09:40 AM |
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Hi
Oddly was chatting to a bloke at Loton about this at the weekend, think the lowest diff available is a 3.54? Whatever you've got in must be
higher than that, so get one of them in and give it a go.
Try and leave it on 13" rims as anything bigger messes the handling up, and will compromise your tyre choice as you'll be wanting
something properly tacky to keep that in check, R888, A048's or ZZR's so staying on 13's will be a huge benefit, though perhaps
205's on the back?
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mcerd1
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| posted on 15/8/11 at 09:41 AM |
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quote:
Originally posted by adithorp
It's the number of turns of the prop for one turn of the wheels (not the other way)
opps, I'm not quite awake thismorning
(edited above)
[Edited on 15/8/2011 by mcerd1]
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pewe
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| posted on 15/8/11 at 10:16 AM |
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I've just been researching diff ratios.
There's a great article here www.rallyanarchy.com/EscortRallyPrep/Rear Axle.pdf which explains the effect of different ratios on speeds through
the gears (think it was on page 13 out of 17).
HTH
Cheers, Pewe 
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kevmcdo
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| posted on 15/8/11 at 10:18 AM |
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I have seen ratios of 4.1 and 4.44 advertised, suspecting that I may have the 4.44 fitted?!!?
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Minicooper
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| posted on 15/8/11 at 11:07 AM |
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I agree 4.4 if you put your information into the bike ratios.xls spreadsheet 185/60/13 tyres, R1 and 4.44 you get a top speed of 94, if you use a 4.1
it's 103 and using the 3.54 gives you about 120 much more useable
Cheers
David
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kevmcdo
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| posted on 15/8/11 at 01:20 PM |
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I have the 3.44 gears already, just need to wait to save a few quid to get them swapped over 
Biggest fear is losing too much of the acceleration, less time changing gear would be handy though I suppose 
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Minicooper
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| posted on 15/8/11 at 01:42 PM |
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A mate of mine had a Zcars R1 mini, it was properly timed at shakespear county over the quarter mile, first geared to 115, which gave a best of 13.2
and then geared to 130, which gave a best of 12.9. Your acceleration will be very similiar
Cheers
David
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Bigboystoys
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| posted on 25/8/11 at 10:24 AM |
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The main reason why the acceleration wont be a lot different it because you will get much longer gears meaning you can make the most of bike engines
big rev range. Mine is a gsxr powered car and I'm using a 3.44 which works well round town and on the a roads.
Cheers sam
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matt_gsxr
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| posted on 25/8/11 at 12:44 PM |
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You might want to make sure you can do a motorway cruise (i.e. 75mph) with reasonable RPM. Maybe 6-7k in top gear.
Above those sort of revs things get a bit aggressive and although this might not wear out the mechanicals it will certainly tire the driver.
Mine is 5.8k at 70mph, but I have a 1:3.1333... (aka 3.14)
Matt
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procomp
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| posted on 25/8/11 at 01:22 PM |
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Hi
As mentioned earlier by Jim. The best ratio you'll get is the 3.54 What would be the best compromise then would be to retain the 13" rims
but move to 205/ 50 or even 60 if available in your choice of tyre.
Cheers Matt
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ginger ninja
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| posted on 26/8/11 at 07:09 AM |
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We run a ZX9R with live axle on 205/60/13 R888 tyres. We had a 3.89 diff. - and found the same problem. We swapped tp a 3.54 and last time we had it
in the rollers it showed 115 mph at approx. 11000 rpm.
The gearing in your gearbox may be different so the top speed may be different, probably faster.
useful info. the 3.54 are prized by the mk1 and 2 escort enthusiasts and are not so common , so expect to pay a premium, ours was just over £100 on
the bay, whereas a 3.89 might be £40.
happy hunting
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