Jaguar speeds and diff ratios
Discussion
Sounds as though you are a bit low geared. I think either a 3.07 or possibly a 3.31 diff would probably be closest to your ideal, depending on how you intend to use the car.
A 3.31 diff will give you 137mph @ 5500 rpm and 75mph @ 300rpm.
A 3.07 diff will give you 147mph @ 5500 rpm and 80mph @ 3000 rpm.
I went through all of this when I was building/modifying my own cars and made up a calculator that allows you to input wheel size, tyre width and profile, top gear ratio, diff ratio and revs. I found it invaluable.
A 3.31 diff will give you 137mph @ 5500 rpm and 75mph @ 300rpm.
A 3.07 diff will give you 147mph @ 5500 rpm and 80mph @ 3000 rpm.
I went through all of this when I was building/modifying my own cars and made up a calculator that allows you to input wheel size, tyre width and profile, top gear ratio, diff ratio and revs. I found it invaluable.
lowdrag said:
A question for the cognoscenti. My E-type, on 15" wheels and 3.31 axle ratio records 70mph at 3000 rpm. On the XKSS, with 16" wheels, I still see 3000 rpm at 70 mph. This indicates to me that it is probably a 3.54, but if it was a 3.31 what speed would the car be doing at 3000 rpm?
From memory, the standard diff in an early E Type was 3.07:1. The 3.54 was the ratio mostly used in overdrive MK 11s.J
lowdrag said:
A question for the cognoscenti. My E-type, on 15" wheels and 3.31 axle ratio records 70mph at 3000 rpm. On the XKSS, with 16" wheels, I still see 3000 rpm at 70 mph. This indicates to me that it is probably a 3.54, but if it was a 3.31 what speed would the car be doing at 3000 rpm?
Try this http://www.boosttown.com/gearbox_differential/spee...lowdrag said:
A question for the cognoscenti. My E-type, on 15" wheels and 3.31 axle ratio records 70mph at 3000 rpm. On the XKSS, with 16" wheels, I still see 3000 rpm at 70 mph. This indicates to me that it is probably a 3.54, but if it was a 3.31 what speed would the car be doing at 3000 rpm?
3000RPM @ 70MPH on 16" x 6" tyres sounds very much like the 3.54 in the XK150 with direct drive top.I'd have thought the final drive on the D would have been more highly geared or you'd just run out of revs at about 130MPH, which would be about right for an XK150, where 130 would be in hope & a prayer range.
There is a reason behind all this, but I'll let you all know why later. This relates to the XKSS which supposedly is running on a 3.31 on 16" wheels with Blockley crossply tyres.
jith, the early E-types, like mine, had 3.31 axles but that changed - I think - in December 1962 to 3.07.
Ken - you have the same thoughts as I on this matter. It matters, but all will be revealed later.
So, my gut feeling is that I have a 3.54 ratio which is driven by a Jaguar (not Moss) box, and that in effect I am running a lower ratio than I thought originally. 3.54 +16" is roughly the same as 3.31 + 15" wheels.
Unless you say different of course.
jith, the early E-types, like mine, had 3.31 axles but that changed - I think - in December 1962 to 3.07.
Ken - you have the same thoughts as I on this matter. It matters, but all will be revealed later.
So, my gut feeling is that I have a 3.54 ratio which is driven by a Jaguar (not Moss) box, and that in effect I am running a lower ratio than I thought originally. 3.54 +16" is roughly the same as 3.31 + 15" wheels.
Unless you say different of course.
Tony, when you are quoting the wheel sizes, you also need to quote the tyre width.
My understanding is that these tyres have a height to width ratio of 1:1, where as low profile tyre's don't.
So if you've got 15" wheels with a 6.7" width tyre, the outer diameter actually larger than a 16" wheel with 6" tyres.
The numbers you quote sound like 16" x 6", where with a 3.54 ratio diff you should get 70.59MPH @ 3000RPM. A 3.31 diff would 75.5MPH.
A set of 15" x 6.7" tyres should give you 71.6MPH and 76.5.
If you are still running Blockley's then they do a 16x6.5, which would give you 73 & 78 respectively.
My understanding is that these tyres have a height to width ratio of 1:1, where as low profile tyre's don't.
So if you've got 15" wheels with a 6.7" width tyre, the outer diameter actually larger than a 16" wheel with 6" tyres.
The numbers you quote sound like 16" x 6", where with a 3.54 ratio diff you should get 70.59MPH @ 3000RPM. A 3.31 diff would 75.5MPH.
A set of 15" x 6.7" tyres should give you 71.6MPH and 76.5.
If you are still running Blockley's then they do a 16x6.5, which would give you 73 & 78 respectively.
lowdrag said:
Ken - you have the same thoughts as I on this matter. It matters, but all will be revealed later.
With my new box (The Guy Broad 5spd conversion which uses Ford MT75 internals in a custom casing) then top is an ideal lazy cruise, but the bottom gear is too low for my application. I wonder whether it is possible to swap ratios without taking the whole box back out again. With the new inlet cam the torque curve is much flatter so hopefully I won't notice the gap between the ratios so much.a8hex said:
With my new box (The Guy Broad 5spd conversion which uses Ford MT75 internals in a custom casing) then top is an ideal lazy cruise, but the bottom gear is too low for my application. I wonder whether it is possible to swap ratios without taking the whole box back out again. With the new inlet cam the torque curve is much flatter so hopefully I won't notice the gap between the ratios so much.
Some of the aftermarket five speed boxes have a large gap between fourth and fifth which doesn't always suit the car's characteristics.IMHO a replacement five speed should have the first four ratios at least somewhere close to the original box and the fifth gear not too far away i.e. not too big a ratio drop to fifth.
I ended up changing the five speed box in my E-type some years ago as the car felt like it wanted to be somewhere between fourth and fifth all the time.
If I recall the first box had a top gear of around 0.6? and I changed to one with a ratio of 0.8 something. The car was much more pleasant to drive.
mph said:
Sounds as though you are a bit low geared. I think either a 3.07 or possibly a 3.31 diff would probably be closest to your ideal, depending on how you intend to use the car.
A 3.31 diff will give you 137mph @ 5500 rpm and 75mph @ 300rpm.
A 3.07 diff will give you 147mph @ 5500 rpm and 80mph @ 3000 rpm.
I went through all of this when I was building/modifying my own cars and made up a calculator that allows you to input wheel size, tyre width and profile, top gear ratio, diff ratio and revs. I found it invaluable.
Hello,A 3.31 diff will give you 137mph @ 5500 rpm and 75mph @ 300rpm.
A 3.07 diff will give you 147mph @ 5500 rpm and 80mph @ 3000 rpm.
I went through all of this when I was building/modifying my own cars and made up a calculator that allows you to input wheel size, tyre width and profile, top gear ratio, diff ratio and revs. I found it invaluable.
I am about to change my car. Would you mind to sent me the calculatorvas above mentioned.
This would easy up my task and be very much appreciated.
My mail is hb03@gmx.com
Thanks
HB
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