Board logo

swap 3.54 to 3.77 on 5jj R1
r1bob - 19/9/11 at 08:43 PM

as above, running 13" x 80 profile, car tops out approx 125 mph in 5 gear, no faster in 6 gear, i dont mind sacrifing my top end to 110 to 115, has any one had experience on switching to the 3.77 , cheers

r1bob - 19/9/11 at 08:52 PM

sorry should of said tyre size of 185 x 13 x 60 doh!,, not 80 ......

progers - 19/9/11 at 09:21 PM

You should be able to rev out in 6th with a 3.54 ratio. Regardless of what ratio you run, this would indicate to me that you are for some reason down on power with your installation. Has it been on a rolling road?

By all means drop the ratio if you want to limit your top speed, but I would keep it at where you are as it is an ideal ratio for reasonable cruising revs and being geared correctly for long straights on circuits (if you do trackdays).

Regards

Paul

ReMan - 19/9/11 at 09:28 PM

Hi are you sure of your current ratio
Most R1's run 3.62 successfully on 15's so why you should have a problem on 13's is odd?

big_l - 19/9/11 at 09:51 PM

my 5jj 7 tops out at 115mph in 6th 5 goes to just over 100 !!
im using 3.89 i would say as close to 3.6as poss would be perfect im on 15s

progers - 20/9/11 at 08:57 AM

I have just done some calculations on the expected top speed of you car with a 3.54 diff and 185/60 R13 tyres

Works out to around 121mph at 11,750 revs. Max is 112mph in 5th.

So I think your speedo is way out or you have a different diff in there than you think!!

- Paul

r1bob - 20/9/11 at 05:40 PM

quote:
Originally posted by progers
I have just done some calculations on the expected top speed of you car with a 3.54 diff and 185/60 R13 tyres

Works out to around 121mph at 11,750 revs. Max is 112mph in 5th.

So I think your speedo is way out or you have a different diff in there than you think!!

- Paul




You could be right about the diff,,,as was going on hear say from the previous owner. Did'nt really explain myself very well about the lowering of diff gearing . The car is road going hill climb and used on short sprints, don't use it on the road much so i could prob live with it . i know it will be more revvy on road cruising , my main aim is to increase acceleration over short sprints hill climbs, The engine is running very well producing good bhp and rev's right out ,run a 12 .2 quarter mile at shakespear county race way. The speedo i know is about right as it's the same as the speed traps on the track's when crossing over the line, so i could have a different diff to what i think. Hence lowering the gearing to 3.77 as im never going to hit my top speed on the tracks i go on so thought i would make use on the lower gearing to get there quicker.
I guess i will have to try it and find out for my self as the diff is lying on the garage floor grinning at me. thank's for your input Paul.

If anybody has tried this diff combination on this set up i would like to hear. Cheer's Bob