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Post by stevew on Aug 18, 2011 20:15:47 GMT
Hi all , I have been in contact with a differential supplier over a period and things look as though something may be developing. Here is a copy of an email( not to sure about the figures of cars on the road though) I'm wondering if other p5 members would be interested in this to help with fuel consumption figures? Please post up your thoughts and comments Thanks Steve.
Hi, thanks for the reply. For your information there are over 3000 p4 models 2600 p5 models that all suffer from over revving engines at speed due to these cars being produced with cross-ply tyres,and nearly all owners now fit radials that have a 20% smaller rolling radius making matters much worse, and I don't know how many classic range rovers that use this CWP set. If you estimate 5% are interested that's 280 units alone. I have been in discussion with our p5 rep and the p5 club is adding spares to their list, I'm sure there would be a lot of interest once folks know what is available. Some members are changing to Jensen interceptor axles as they fit the dimensions of the rover model, these are now like "hens teeth", this modification is very expensive and may be not welcomed in the p5 fraternity as it's not an original axle. I personally know of a local p4 owner that has a V8 fitted and a 2.8:1 ratio diff that increases his MPG by over 30% This figure alone should sell it with the price of fuel, everyone he tells wants one , but you can't buy one, anywhere. Other owners have increasing the performance of there engines but are constrained by there existing ratio. Should you persuade your supplier to manufacture, I'm sure there is a ready market for supply as CWP set, or for you to supply service exchange differential units as most owners probably wouldn't tackle the shimming set up but could change a diff unit. Good luck with the talks with your supplier, please keep me posted. Many thanks.
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Post by johnwp5bcoupe on Aug 18, 2011 20:41:49 GMT
I will watch and wait with interest
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Post by redsunbeam on Aug 19, 2011 15:22:22 GMT
Have you tried talking to KAMDIFFS ? I looked for an lsd for the rover axle from them. I think they also do different crown wheels and pinions. Swapping to the jensen rear axle is going to be much cheaper than uprating the rover axle.
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Post by stevew on Aug 19, 2011 18:13:33 GMT
Well redsunbeam, £250 for a CWP is not to bad when you reflect the cost of a second hand Interceptor axle recently on ebay ( probably i was outbid by your good self at over £200) and the condition is unknown. P5 rear brakes are massive and up to the job, so what advantage is it trying to buy and intercepter axle at that price? I know you would gain a LSD but in the real world when will it be used, a lot of horse power required to shift around 2000Kg and spin the wheels. Any way there are probably not enough interceptor axles left to go around the p5 group. I have spoken to Kamm Diffs , minimum order of 600 units but was informed they threw the tooling away recently for 2.8:1 CWP and they are not interested. What a shame, seems like easy money making these again, guess they are too busy doing routine stuff. I'm very interested in your mods especially the steering , how are you fixed with current new regulations SVA etc.I think it only considers monocoque mods so would you not qualify for inspection? I am interested as I plan body mods myself.As you guess I am not to clued up on this, Your comments would be very welcome.
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Post by Baldrick on Aug 19, 2011 21:07:57 GMT
Steve, was the p5b originally high revving in top gear with the original tyres? Also as I am not sure where the speedo is driven from, would the 2.8 diff and original size tyres mean the speedo would read wrong?
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Post by stevew on Aug 19, 2011 21:46:14 GMT
Steve, was the p5b originally high revving in top gear with the original tyres? Also as I am not sure where the speedo is driven from, would the 2.8 diff and original size tyres mean the speedo would read wrong? Yes absolutely, but we have "sat nav" now. Having such a powerful engine in your car, I'm sure it feels like another gear change is required in top gear ( by the way you have a 3.5:1 ratio diff)235-75-15 tyres would help but that's a lot of excess tyre width on a 5 inch rim, that would lower engine RPM and save you fuel.
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Post by Phil Nottingham on Aug 20, 2011 8:54:53 GMT
The P5B/P5 was designed to give just over 3000rpm at 70 mph which is low these days anyway
It depends on which radials are used but lower profile ones will increase revs and cause the speedo to overrecord - the V8 in standard tune could get away with a lower ratio diff but accerleration would suffer a bit and more on a P4 although no P4's used the 3.54 diff as later ones as did P5 6's had overdrives.
Most P4/P5/P5B owners do not drive their cars in a way to make this worthwhile anyway and few use their existing performance potential anywhere near to its limit
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Post by Deleted on Aug 20, 2011 11:58:10 GMT
I agree with Phil's posting on this topic.
I haven't noticed much difference in engine speed since changing from Xplies 670x15 but I am using the highest profile tyre I could obtain which is 195x80x15. For our cars, I think profile is more important than width.
I surprised more owners don't go for higher profiles as the higher profile looks better in the wheelarches.
Mess about with new diffs....not for me thanks!
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Post by stevew on Aug 20, 2011 11:59:15 GMT
Hi Phil, changing the CWP is really for economy cruising at speed. Acceleration times might take a bit longer, but probably the result would be the gearbox would take a little longer to change up, not really a problem I feel. Our old Volvo 940 would cruise at 70 @ 2200 RPM When you accelerated the gearbox changed down a gear. That used the ZF ph 22 with a 3.5:1 CWP The very same gearbox used in some Rover conversions . I think the CWP route is a quicker cheaper alternative way forward. Steve
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Post by stevew on Aug 20, 2011 12:06:55 GMT
I agree with Phil's posting on this topic. I haven't noticed much difference in engine speed since changing from Xplies 670x15 but I am using the highest profile tyre I could obtain which is 195x80x15. For our cars, I think profile is more important than width. I surprised more owners don't go for higher profiles as the higher profile looks better in the wheelarches. Mess about with new diffs....not for me thanks! Nice to know where you stand on this? To retain the same rolling circumference the only radial tyre I know you can get is 235x 75x 15 This width is too wide for a 6 inch wide rim, but does look good as it fills the arches and looks as it should when the car had crossplies. Not sure about the handling though. 185 x80x 15 are 20mm smaller on the radius than 235x75x15
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Post by Deleted on Aug 20, 2011 14:29:27 GMT
As it was back in 1968 when I got my "O" level maths could you break down your calcs so that I can try and understand a bit better?
If a tyre has a higher profile doesn't that increase the radius and how do you compare the new tyres with the old crossplies as far as dimensions are concerned?
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Post by stevew on Aug 20, 2011 18:28:58 GMT
235x75x15 The first dimension is the tread width in mm The second dimension is the percentage of the first, this is the tyre wall profile The third dimension is the wheel diameter You can find the tyre sizes if you search around. Have a play on this site www.northhantstyres.com/radial-tyre-search.html I remember pounds shillings and pence, your never too old to learn math. Hope this helps
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Post by Deleted on Aug 20, 2011 19:24:12 GMT
I know what the markings on a radial tyre mean!!!! What I wanted you to explain was this statement....... To retain the same rolling circumference the only radial tyre I know you can get is 235x 75x 15 This width is too wide for a 6 inch wide rim, but does look good as it fills the arches and looks as it should when the car had crossplies. Not sure about the handling though. 185 x80x 15 are 20mm smaller on the radius than 235x75x15
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Post by Phil Nottingham on Aug 20, 2011 19:41:17 GMT
Quire right X plies I got my O level maths too in 1971! Still use it as well
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Post by stevew on Aug 21, 2011 1:41:44 GMT
I know what the markings on a radial tyre mean!!!! What I wanted you to explain was this statement....... To retain the same rolling circumference the only radial tyre I know you can get is 235x 75x 15 This width is too wide for a 6 inch wide rim, but does look good as it fills the arches and looks as it should when the car had crossplies. Not sure about the handling though. 185 x80x 15 are 20mm smaller on the radius than 235x75x15 Do the maths
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Post by stevew on Aug 21, 2011 1:53:10 GMT
The whole point of this post was to see if p5 owners would be interested in being able to buy a CWP for their car to help them save fuel etc. not to keep" banging on" about tyre sizes. Using "google" to search for what you're not to sure of is easy, I guess some folk can't help them selfs, never mind.
Would the moderators on here set a pole to see if the manufacturers of CWP could see if it's worth there while to set up the required tooling to make these again?
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Post by Deleted on Aug 21, 2011 10:01:34 GMT
Stevew, I was genuinely asking for help to explain your calcs because I didn't understand the figures. No need for a sarcastic response.
With regard to the diff, totally uninterested thanks and I'd be surprised if many others were either.
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Post by johnwp5bcoupe on Aug 21, 2011 15:16:57 GMT
Just done a service took the car up the road 3000rpm = 63mph, 3500 rpm = 70 mph on Satnav speedo 6mph too fast
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Post by Deleted on Aug 21, 2011 17:37:06 GMT
Stevew, I was genuinely asking for help to explain your calcs because I didn't understand the figures. No need for a sarcastic response. With regard to the diff, totally uninterested thanks and I'd be surprised if many others were either. i would be interested steve
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Post by harvey on Aug 21, 2011 18:14:53 GMT
I don't think you're going to get the increases in economy that you think that diff is going to give you. It's not the same as having another extra overdriven gear, all you're doing is raising the three gears you already have, which is going to mean higher throttle openings to get things moving in the first place.
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Post by stevew on Aug 21, 2011 20:43:29 GMT
I don't think you're going to get the increases in economy that you think that diff is going to give you. It's not the same as having another extra overdriven gear, all you're doing is raising the three gears you already have, which is going to mean higher throttle openings to get things moving in the first place. Check out the first post, It's been done and its proven
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Post by harvey on Aug 21, 2011 20:47:40 GMT
It may have been done, but i doubt that's with the 35 box as in a P5B. It's a 20% increase in the ratio, and I think pulling that is going to be hard work if everything else is standard.
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Post by stevew on Aug 21, 2011 22:42:17 GMT
yes p4 car v8 and bw 35
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Post by Baldrick on Aug 21, 2011 22:47:50 GMT
Steve,
I'd be interested. You could do a bundle offer - zf 4 speed, 4.6 engine, set of 16 x 7 American wheels for the back and a set of tyres that have the same circumference as the originals. Now that would look good and move nicely!
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Post by enigmas on Aug 22, 2011 0:21:30 GMT
I run a 2.9:1 differential in my modified P5Mk3. The final drive unit has been heavily modified incorporating a salisbury centre (from a Ford) and modified P5 axles. There are very comprehensive range of ratios that I can choose from. As I believe crossplies or Harvey were inferring all the ratios become taller. The P76 engine in my car is nearly a litre greater in capacity (4.4) and the gearbox internals (are from a late model Aussie Ford EA which incorporated part throttle shifts into both 2nd & 1st). This shift allows the box to change up & down the range significantly earlier (under load) than does anything in a P5B. The engine is also of a longer stroke and has significantly more torque low down (it doesn't rev as a high a a 3.5. The P76 sedan ran these same ratios. On a P5B with the standard 3.5 engine acceleration would be down considerably in the lower gears and you would definitely notice it. I calculated all the ratios when I first considered this option and given the cost was about $2500 18 or so years ago I needed to be sure. Fuel mileage won't improve with the 3.5 as you will need to use larger throttle openings. The highway may be a different story. Towing with a taller ratio would probably also be torturous.
If you going to fit a big inch engine go for...otherwise an AOD gearbox is the way to go as these boxes incorporate very low first gear (to get moving quickly) and and a tall overdrive for economical cruising.
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