Differential ratio choice

[dal2.0litrefrogeye]

Hi all , I've just ordered my 5 speed gear box from Elite , so this will be a T5 with 2.95 1st gear and I've gone for 0.08 5th gear so the revs don't drop off to much when I cog up from 4th to 5th , my car is a 69 USA car and I assume it's a 3.54 diff it does have a LSD (I've turned the wheels with them in the air and they both go the same way ) I've been offered a 3.3 diff , my reason for thinking about this ratio is it to make the intermediate gears slightly longer but without going for all out cruiser mode , I will be using the car for sprints and hill climbs , so my question is with the 3.54 diff and the T5 does 1st gear fill to short has anyone gone from a 3.54 to a 3.3 ? Any thoughts / ideas , cheers

[abowie]

I'd leave it with the 3.54 and see if you like it. I suspect you will.

[jag68]

I've had three different E Types over the years that I've autocrossed, raced, hillclimbed etc. One car is depicted here:

I've got a couple of observations that may be helpful, when you compete on short courses. First it's best not to have to shift while on course. Shifting up or down results in a markedly slower time, as unless you are very very smooth and can heel and toe, (difficult on a left hand drive E) you will unbalance the car - in particular when you downshift - say into first gear. Secondly driving the course in first gear is much more difficult than in second simply because the higher gearing makes the car more difficult to control, in particular when you are not on the throttle (too much rear wheel braking), and induces greater stress into the transmission.

I run a Medatronics 5 speed with a first gear that is the same ratio as stock, along with a 3:73 diff from a automatic S Type (the car came with a 3:31). This allows me to run these short courses in second gear. Sometimes I will start in second, using a bit of wheel spin to keep the rpm up if there's a problem in the course that doesn't supply a good opportunity to shift into second (and stay there) without loss of time.

First gear in this setup is a short gear, and is mildly annoying in heavy traffic but it's worth it while competing, as second covers virtually every situation that I encounter on the courses that I compete on - that is I don't have to shift out of it. Finally fifth gear gives a relaxed engine speed on the highway even with the 3:73. (2900 at 80 mph), although to be truthful I don't really notice engine speed over the wind noise. If I didn't compete I'd go back to the 3:31 diff. and get a more useable first gear.

[PeterCrespin]

Any thoughts / ideas , cheers

The diff is a way of multiplying torque to the wheels, which is usually what you want when competing on short courses. A gearing change reduces or increases torque to the wheels by the same proportion as the gearing change -give or take. So a 3:1 first gear puts three times the torque to the wheels as a 1:1 top. Subject to tyre adhesion and speeds etc more torque is always better when racing.

As mentioned, gearing is also a way of suiting the power and to the track and on short courses the number of changes and places on the track where you have to make them can greatly affect times. You aren't putting power down when you change gear in a single-clutch manual.

The JCNA slalom course is usually first gear but other autocrosses can be second. UK hill limbs can be pretty quick and do usually have a hairpin or two so you might gain/lose depending on specific course.

Race circuits can vary from 'pocket handkerchief' like Three Sisters in Wigan to the wide open spaces of Silverstone or Snetterton. Cadwell/Brands/Oulton etc are usually a bit of everything.

Pat attention to your engine mounts.

Have fun and if your gearing is borderline low fit a rev limiter to give you one less thing to concentrate on. Go for a 'soft' cut-off to avoid sudden lack of power and stress on the trans.

[JEP41]

Hi All,

I have a 3:31 in my E-Type with a T5 and I find this setup perfect for track days at Goodwood and Snetterton. Went to a track day at Mallory just once and it was just about ok, I had a problem getting good drive out of the hairpin with the 3:31

[dal2.0litrefrogeye]

Hi thanks for the replies . I think for the time being I'll stick with the 3.54 , , I've been looking at a few gear calculator apps and my 1st will be something like 46 mph theoretical 168 5th . With the tyre size I'll be using so 1st gear shouldn't be too short , that s one thing I cant stand is a light car with a fair bit of toque and power but with a1 St gear that barely takes you over 30 mph

[Steve Marshall]

My early 1969 US OTS came with 3.31 as standard anyway.

I am swapping it to 2.88 and retaining the 4 speed gearbox. Gives me a slightly lower top gear than you, and a higher 1st gear, which I think I will be OK with.

Before laying out any cash I suggest checking the actual tag on the diff or turning the diff input flange manually to check how many times the wheels rotate.

Or I believe that there is a code on the speedo face which reveals what ratios it matches.

[dal2.0litrefrogeye]

Hi Steve , thanks for the advice yes I think I will wait until I drop the rear axle , 1 to check ratios , even though I think if it's a 3.5:1 I'll be happy with it , and 2 just to check the condition , but with the low mileage the cars done , it should be (fingers crossed) be ok

[dal2.0litrefrogeye]

Hi Steve , thanks for the advice yes I think I will wait until I drop the rear axle , 1 to check ratios , even though I think if it's a 3.5:1 I'll be happy with it , and 2 just to check the condition , but with the low mileage the cars done , it should be (fingers crossed) be ok