Topic: One for Dr Mike..... (Read 12496 times)

chrisjones · « **on:** April 03, 2006, 06:38:14 PM »

What's the diff ratio on a '98-'99 XJ 4.0L Limited?

Mik · « **Reply #1 on:** April 03, 2006, 06:47:47 PM »

3.55:1 (usually)

Mike Pavelin · « **Reply #2 on:** April 03, 2006, 07:02:40 PM »

He's right, but if you look at the aluminium tags on the rear cover, it states the ratio anyway.

chrisjones · « **Reply #3 on:** April 03, 2006, 08:07:28 PM »

I assume, that the tags SHOULD be under one of the bolt heads? :roll:

Anyway, all I need to know is if they are ever lower than 3.54:1

trent · « **Reply #4 on:** April 03, 2006, 08:12:12 PM »

Quote from: "chrisjones"

I assume, that the tags SHOULD be under one of the bolt heads?

Anyway, all I need to know is if they are ever lower than 3.54:1

Chris,
Are you looking into a re-gear?

Mik · « **Reply #5 on:** April 03, 2006, 08:23:33 PM »

Quote from: "chrisjones"

I assume, that the tags SHOULD be under one of the bolt heads?

Anyway, all I need to know is if they are ever lower than 3.54:1

2.5 TD - 3.73:1
2.5 Petrol - 4.11:1

chrisjones · « **Reply #6 on:** April 03, 2006, 08:38:15 PM »

Since mine's a 4.0L I guess the answer to that is no then. :lol:

Interseting though, an easy re-gear would be to fit 2.5 petrol axles.

Mike Pavelin · « **Reply #7 on:** April 03, 2006, 10:41:54 PM »

....and the UK spec 2.5s usually had the Chrysler 8.25 rearend which is supposed to be stronger than the 35

chrisjones · « **Reply #8 on:** April 03, 2006, 10:52:29 PM »

Cool. Worth thinking about. :wink:

Anonymous · « **Reply #9 on:** April 04, 2006, 09:17:15 AM »

Hmmmm, could be time to break a cpl of 4-bangers!!

hope you kept the spare u-bolts that came with yer lift kit chris...cos they were for a 8.25......

chrisjones · « **Reply #10 on:** April 04, 2006, 09:39:53 AM »

Doh!!

Anonymous · « **Reply #11 on:** May 04, 2006, 09:45:09 PM »

right, a techy one.......

if one were to fit the axles off a 2.5 petrol to a 4.0 auto, could one get away with 33's & how diiferent would that be to the existing stock setup with 31's........

cos i have NEVER been able to get my head round gear ratios.... :roll:

Anonymous · « **Reply #12 on:** May 04, 2006, 10:46:23 PM »

Piss about with R&P's here....

http://http://www.ring-pinion.com/content/calculators/RPM.asp (Cheers to Greggmo for the link

)

chrisjones · « **Reply #13 on:** May 04, 2006, 11:23:38 PM »

You could just do a bit of simple maths.

Percentage difference between 3.55 and 4.1 and the same for the difference between the circufrence of a standard tyre (about 28" I think) and a 33" tyre.

If the diff ratio % difference is higher you'll have lower gearing with 33s than stock and if t'other way round higher gearing.

You get the idea.

Anonymous · « **Reply #14 on:** May 04, 2006, 11:32:26 PM »

so if i got this right......

changing the diff to 4.10 gears & keeping 31's would slow it down even more than now...... :shock:

but changing to 4.10 gears & 33's would be very close to stock ratios therefore giving me back the stock performance/acceleration/top end??

does that sound right??

chrisjones · « **Reply #15 on:** May 04, 2006, 11:33:44 PM »

By my reckoning you've got about a 15% difference in gear ratios and about an 11% difference in tyre circumfrence, so the gearing with 4.10:1 diffs and 33" tyres would be slighty lower than stock diffs and tyres.

...........................I think! :?

Anonymous · « **Reply #16 on:** May 04, 2006, 11:35:24 PM »

Since when have 31s been stock

?

It means you would rev faster on 31's, not go slower, your 0-60 would improve. Your top end, would decrease and the revs you were doing at 70mph would be higher.

EE :twisted:

Mike Pavelin · « **Reply #17 on:** May 05, 2006, 07:30:44 AM »

I have 3.73 gears on 31s fitted to my (manual) XJ. Gearing is about right, feels stock on the road. It started out with 3.07s which was way too tall for 31s.

chrisjones · « **Reply #18 on:** May 05, 2006, 07:59:42 AM »

Quote from: "EvilEd"

Since when have 31s been stock ?

It means you would rev faster on 31's, not go slower, your 0-60 would improve. Your top end, would decrease and the revs you were doing at 70mph would be higher.

EE

Who said anything about 31s being stock? :?

chrisjones · « **Reply #19 on:** May 05, 2006, 08:50:17 AM »

Ok.

Now I'm awake. I've worked it out again, in an easier way! :roll:

You need to work out how far the truck travals for one revolution of the prop. Which is:-

1/G x pi x D

Where G = diff gear ratio. and D = Tyre diameter.

The answers are:

For a stock set up (taking the tyre to be 28") the truck will travel 24.78" for every turn of the prop.

For 4.10:1 gearing and 33" tyres the truck will travel 25.28"

A difference of........................0.5"!

If you take a stock tyre to be 29", the difference is 0.4" the other way.

For my money that's as close to stock gearing as you're going to get!

Anonymous · « **Reply #20 on:** May 05, 2006, 09:34:09 AM »

Quote from: "chrisjones"

For my money that's as close to stock gearing as you're going to get!

thats what i reckoned........

deffo time to look for a 2.5 petrol to break!!! :twisted:

Anonymous · « **Reply #21 on:** May 05, 2006, 10:01:19 AM »

Quote from: "The Kitchen Devil"

right, a techy one.......

if one were to fit the axles off a 2.5 petrol to a 4.0 auto, could one get away with 33's & how diiferent would that be to the existing stock setup with 31's........

cos i have NEVER been able to get my head round gear ratios....

Erm, KD said about it

Anonymous · « **Reply #22 on:** May 05, 2006, 10:17:14 AM »

i meant stock gearing....didnt say anything about the 31's being stock!!!as i am running stock gears with 31's now, thats what i wanted to use as a benchmark.......numpty!!! :roll:

Anonymous · « **Reply #23 on:** May 05, 2006, 10:34:20 AM »

It's there in bold Mr Plough... :twisted:

chrisjones · « **Reply #24 on:** May 05, 2006, 10:38:34 AM »

You're gonna need at least 4.5" of lift and cut away arches fo fit 33s.
I know you're sorting the lift (don't forget the skyjacker rear springs are only 2.5" lifts).
The rear arches will need cutting back as far as they'll go, which means plating and welding the uni-body like they do on rally cars. :wink:

Author Topic: One for Dr Mike..... (Read 12496 times)

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Mike Pavelin

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Mike Pavelin

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