V8 4.6 Gems conversion to automatic

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cmryan

cmryan

Member
Posts
41
Location
Lytchett Matravers, Dorset
Hi all,
I'm considering converting my Defender 90 (1993) to automatic. It's already a mongrel, with a P38 4.6V8 GEMS engine mated to a LT85 gearbox. The drive shafts rubn down the right side to Disco 1 axles.
I'm thinking of putting in an 4hp22 autobox but want to make sure the bellhousing and input shaft are correct to mate to the engine.
Which box should I look for (ie from which vehicle)
Do I need one with an ECU or manual kickdown?
Will my transfer case with outputs to right side mate to a P38 automatic box (4HP24) where the outputs are to the left?
It's all twisting my 🍈 man!
Thanks
 
The 22 wont put up with the 4.6 for long.
The bell housing will mount to the V8 no issue but you will need all the flex plate as well.
Transfer case will go on a 22 if its from a disco.
It wont go on a box from a P38 without some bits being changed.

look on Ashcroft site they will help, with 24 internals in a 22 without the need for ECU.

Oh and dont forget there is lots of fiddly bits as well. The 22 has a 3 bolt flex plate the 24 has a 4 bolt, I wonder why ;) . (I think)

J
 
Last edited:
marjon said:
The 22 wont put up with the 4.6 for long.
The bell housing will mount to the V8 no issue but you will need all the flex plate as well.
Transfer case will go on a 22 if its from a disco.
It wont go on a box from a P38 without some bits being changed.

look on Ashcroft site they will help, with 24 internals in a 22 without the need for ECU.

Oh and dont forget there is lots of fiddly bits as well. The 22 has a 3 bolt flex plate the 24 has a 4 bolt, I wonder why ;) . (I think)

J
Click to expand...
Hi J thanks for the info. I've reached out to Ashcroft but Dave is on holiday till next week.
Best, Chris
 
Not saying you shouldn't go for an auto, but is there a reason? I'd figure the manual would be more fun. Although an LT-85 is a bit agricultural, even by Land Rover standards. A nice built R380 might be a better option.
 
300bhp/ton said:
Not saying you shouldn't go for an auto, but is there a reason? I'd figure the manual would be more fun. Although an LT-85 is a bit agricultural, even by Land Rover standards. A nice built R380 might be a better option.
Click to expand...

The auto in our p38 can be fun enough, why would it not be more funner in a 90?
maybe he has bad knees?
plus V8 380 bellhousings are difficult to source cheap.

J
 
marjon said:
The auto in our p38 can be fun enough, why would it not be more funner in a 90?
maybe he has bad knees?
plus V8 380 bellhousings are difficult to source cheap.

J
Click to expand...
I have a 4.6 p38 too. It would be WAY more fun with a manual.....
 
And if you want me to justify it.

The 4.6 has a Sports mode on the gearbox, you'd not have this with a HP22 in a 90. But even this aside the 4 speed just has flat spots in the gearing. Meaning you have to really welly it to make it shift.

The RV8 does its best work at mid and high rpm, not low down. The auto box just makes the engine more lazy than it already is. Plus you don't have the physical interaction of changing gears.

I'm not saying the auto would be slower real world, although you are at a gearing deficit with the auto. I suspect some 4.10 diffs in a p38 would really help wake the motor and gearbox combo up. But that'd be true with a manual.

If you want fun an acceleration I'd go 1.6 transfer box (or 4.10 diffs and 1.4) with an overdrive on an R380 with a decent cam and supporting mods on the RV8.

We have a 3.9 EFI RV8 in a factory 90, so LT-85 and the very tall 1:192 transfer box. It actually goes really well and is quicker than my highly modded 200Tdi hybrid. But it too feels lazy due to the gearing.

I also have an RV8 in a Triumph TR7 with a 5 speed LT-77. It is a 4 brl carb setup but runs very short final drive gearing. It rips through the gears and is a complete riot. But could do with a 6th or over drive for cruising.

On the auto/manual comparison. I also have a LS1 Camaro. I owned a 4 speed auto and a 6 speed manual at the same time. The auto was probably easier to drive quickly on UK roads. But the 6 speed is masses more fun to drive. I no longer own the automatic one.
 
300bhp/ton said:
And if you want me to justify it.

The 4.6 has a Sports mode on the gearbox, you'd not have this with a HP22 in a 90. But even this aside the 4 speed just has flat spots in the gearing. Meaning you have to really welly it to make it shift.

The RV8 does its best work at mid and high rpm, not low down. The auto box just makes the engine more lazy than it already is. Plus you don't have the physical interaction of changing gears.

I'm not saying the auto would be slower real world, although you are at a gearing deficit with the auto. I suspect some 4.10 diffs in a p38 would really help wake the motor and gearbox combo up. But that'd be true with a manual.

If you want fun an acceleration I'd go 1.6 transfer box (or 4.10 diffs and 1.4) with an overdrive on an R380 with a decent cam and supporting mods on the RV8.

We have a 3.9 EFI RV8 in a factory 90, so LT-85 and the very tall 1:192 transfer box. It actually goes really well and is quicker than my highly modded 200Tdi hybrid. But it too feels lazy due to the gearing.

I also have an RV8 in a Triumph TR7 with a 5 speed LT-77. It is a 4 brl carb setup but runs very short final drive gearing. It rips through the gears and is a complete riot. But could do with a 6th or over drive for cruising.

On the auto/manual comparison. I also have a LS1 Camaro. I owned a 4 speed auto and a 6 speed manual at the same time. The auto was probably easier to drive quickly on UK roads. But the 6 speed is masses more fun to drive. I no longer own the automatic one.
Click to expand...

That’s all a pretty fair argument.
But then they are not sports cars are they? That said my RR is 6.3.

The bigger question is why do you want an autobox? Which you did ask in all fairness. I don’t care, the question was is it possible what do I need, was what I answered to. Now if he had asked about upgrading to a better manual box I would not have had an opinion.

J
 
Really interesting replies, so I'll add my thoughts. The LT85 is a slow gearbox that demands you work the engine hard to get a decent drive. Having driven it for 5 years it's not fun, you have to drive slow and lazy. The engine is OK, lacks power compared to more modern V8s but also needs to be revved to get the best out of it. At the end of the day it's a Defender, not a Triumph or Morgan.
I decided to go with the auto because driving convenience is more important than dynamics for what I use it for. For speed and fun I have an XKR V8.
Thanks all for your input.
 
So the conversion is done and I'm very happy with the result. Its a well matched engine a box, far better than the LT85. As before I don't want a sports car, mainly a good off-roader and general runabout. Note that I'm not doing trialling or serious mud-plugging so I'm aiming for a good all round setup, which I think I've got.
However, one snag: there's no connection for the kickdown cable on the Gems throttle linkage so how do I sort this? Change to a Thor linkage or is there an aftermarket/other Rover option?
 
So what route did you go in the end?
I take it a non electronic 22?

To answer your question I dont really know but would look at how they did it on the disco with the V8 4.0, but not sure if that was a mech or elec box.

Would it be possible to use the cruise control cam on your Gems ?

Or again speak to ashcroft as they do box conversions so may have the parts you need.

J
 
marjon said:
So what route did you go in the end?
I take it a non electronic 22?

To answer your question I dont really know but would look at how they did it on the disco with the V8 4.0, but not sure if that was a mech or elec box.

Would it be possible to use the cruise control cam on your Gems ?

Or again speak to ashcroft as they do box conversions so may have the parts you need.

J
Click to expand...
Hi J yes the non electronic 22 from a V8 D1. I'll email Dave Ashcroft again. What I've learned is that the kickdown connects close to the throttle shaft from below on a short pull. I might be able to rig the cruise but it pulls in the same direction as throttle cable. On a dry day I'll pull it apart and take a close look.
I'll also drop Dave Ashcroft another email.
Cheers
 
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