E-Type differential ratios
What the best differential ratio is for a straight six engined E-Type (Series 1 and Series 2) is one of those topics that generates plenty of opinions. So much so that my car has had two changes over its life. US delivered E-Type started life with a 3.54 ratio, which my car now has. This is the same ratio it had when new (being delivered in South Carolina). When restored it was changed to 3.07, which was the standard ratio for cars sold in Europe. Later on, the owner before me changed it back to 3.54. This article covers the different E-Type differential ratio options and what that means for road speeds.
When these cars were new, in America it was important to show good 0-60 times even if this impacted overall drivability. What the US ratio means is that doing even the slow freeway speeds we have in Australia, the engine is turning at 3500 RPM. I would like to reduce the RPMs at freeway speed, but there are two ways. Either a 5 Speed transmission, or a rear end change. The table below shows some of the theoretical options (e.g. The E-Type is not going to hit 274km/h irrespective of gearing):
E-Type Differential Ratios
| Diff | 4th Gear @ 2800 RPM | 4th Gear @ 3500 RPM | 4th Gear @ 5000 RPM | 5th Gear (0.8) @ 2800 RPM | 5th Gear (0.8) @ 3500 RPM | 5th Gear (0.8) @ 5000 RPM |
|---|---|---|---|---|---|---|
| 3.54 | 97 | 121 | 177 | 121 | 150 | 221 |
| 3.31 | 104 | 130 | 192 | 130 | 163 | 240 |
| 3.07 | 112 | 140 | 206 | 140 | 175 | 258 |
| 2.88 | 119 | 149 | 219 | 149 | 186 | 274 |
The most common E-Type differential ratios were 3.54 (USA), 3.31, 3.07, and 2.88. 0.8 or 0.73 5th gears are the most common in the popular transmission kits.
The 2.88 I feel would reduce acceleration too much, and coupled with a 5 speed would be too tall gearing. 3.31 and 3.07 all provide good options. Without a 5 speed, 3.07 is probably better – with this ratio alone you get much more reasonable drive ratios. Translating to a more reasonable 2800 RPM at highway speed. With a 5 speed, the 3.31 is probably more suitable. Once you have a 5 speed, even the 3.54 can work, although you ‘run out’ of the other gears quite quickly.
From the chart, I would say that if you’re going to use the stock gearbox, 3.07 seems the way to go. If you consider a 5 speed as well, I would probably go with 3.31. 3.07 as a good option too. With a 3.31 option, you could also consider the 0.73 5th gear, that would not be as good with the 3.07 and a 0.8 5th gear would be preferable.
I don’t have immediate plans to change my E-Type. If the transmission failed on me, I would probably install a 5 speed. I may consider a rear end change in the meantime to make the car more useful on the open road.
It should also be noted that tyre size is another factor in determining road speed. This article assumes the tyre/wheel size staying the same as the differential ratio is changed or a 5 speed installed. My car does not have standard size tyres fitted so this made the RPM even higher.
Update, November 2016:
My E-Type has now been changed to a 3.07 ratio which I see as a big improvement. Even around town you can hold the gears longer and use 3rd more as a cruising gear on smaller streets. I have also fitted a ratio box to correct the speedometer.
well done for putting that up
Yes a good article. The one problem I have with driving my E type S2 is the noise from the 3.54 diff. My 4 speed is crying out for a 5th gear. Being a purist at heart I’d rather keep the original gearbox and change the diff. Which I understand is quite costly anyway.
Hi Interesting article I notice that you referred to Australian freeway speed so I assume you are in Australia I had several new E types back in the sixties in Australia the first was a 64 Mk I 4.2 I can remember it having a very tall diff as it would do 30 mph at 1000 rpm in top so this would have probably have been at the most a 3.07 or a 2.88 it seemed to me at the time to have plenty of acceleration the tall diff made the car very economical I heavily modified this car with three Webers extractors bored out with special high comp pistons and super race cams ported polished larger valves and fully blue printed, and a modifided advance curve on the distributor high performance coil etc etc and obviously 100 octane which was available the tall diff came in very handy as it would red line in top gear that is it would wind the speedo off the clock in top[ gear pretty scary on aqua jets but great fun I returned the car to standard except for the larger bore size when I sold it not too sure were it went to but it was registered E00 007 when I owned it my advice would be to get the tallest diff you can
Thanks Thom. I am very happy with my Diff change and going to a taller ratio. Even around town you can hold the gears for longer before having to change up. I don’t see much difference in driving the car either. I am located in Australia although my car was delivered new to the USA and remained there until 2011 when I brought it back to Australia with me.
Great article. I am currently in the midst of restoring 860206 3.8 FHC Coupe here in Australia. My Crown Wheel and Pinion was worn and thought this an opportunity to change ratios from 3:31 to 3:07. The challenge I had was finding quality parts not made in China. I eventually bought from a reputable supplier in the UK who assured me their parts are top quality but I guess I will will find out just how good it is once the car is on the road. I am using a standard Moss Box with suffix JS.
Good luck with the restoration! I am very happy with my diff ratio change. I think my crown wheel and pinion came from an XJ6.
Heck I’ll play along!!! Here in Texas, we go everywhere at 80mph! I’ve got a 4.2 E with a 4speed and had the original 3:54 rear end. The noise was almost deafening.. It did make it easier to tell the wife I didn’t hear her, but I digress. Jag originally said the cars would do almost 150mph. Fact is they lied! I pulled my diff and gave it to CW in Georgia to make the swap. Sadly, 3.07 gear sets are next to impossible to find. So I ended up with a 2:88. Tomorrow it goes in the car and I’m hoping I made the right choice. I have to say, with the 3:54 set, the car was an absolute riot to drive around town. But as I get older, I’d rather not drive the car around town like an a-hole sliding around corners. I won’t miss having to shift into 2nd gear half way through an intersection.
Jason good luck with the change. Would be interested to see how you feel about it once done
Well Jason, Whats the verdict?
Hi Jason yes what is the verdict i’m pretty sure you will be pleased with the taller diff as the engine with that diff makes full use of the engines torque curve much more economical and much quiter as well
especially at highway speeds and plenty of power in third for a quick overtake