alexmcrobbie

alexmcrobbie

Member
Hello All!

After nearly 10 years and 100k miles with my Westminster Edition P38 I’ve become a bit tired of the lack of performance from the M51 diesel lump and have been considering a change. I’ve had P38s with the 4.6 in the past and loved the smooth, torquey and effortless character it brought to those cars.

My question is this, how hard is it to swap from the M51 to a 4.6 RV8, and have people done it before? A sensible person would probably say “just buy a nice V8 P38”, but I’m really attached to my car (and have sunk tens of thousands into maintenance and upgrades, so it’s basically perfect apart from the engine).

Asides from the obvious (engine ECU, 4HP24 gearbox, instrument cluster, in tank pump etc), are there any big ticket items that would make things difficult?

Sorry if this has been covered before, I’ve looked long and hard but can only see posts about people trying to go in the other direction lol.

Cheers,
Alex.
 
You'd need to find a good engine, which is a gamble any 2nd hand RV8 while out should have atleast a top end overhaul, just so you don't end up dropping an old tired engine in place of your current one......

Or you could buy a recon unit from the likes of V8developments but that is big money....

To be honest your best bet is to find a good V8 P38, yes I know you don't want to but the cost and headache of converting your current one would be dire.

You can get the M51 Chipped which improves performance..
 
You could get V8 power out of your M51 for the comparative work involved. Not the same though. Only a V8 will give the V8 experience. The burble the smiles per miles.

Do you have room for 2??
1 of each would keep your options open 😉 your gonna have to buy most of one anyhow for a conversion, may aswell get the whole thing.
 
Henry_b said:
You'd need to find a good engine, which is a gamble any 2nd hand RV8 while out should have atleast a top end overhaul, just so you don't end up dropping an old tired engine in place of your current one......
Click to expand...
Don't really agree with this. Sure, if you have the cash to burn, then a rebuild is nice. But then, if it ain't broke, don't fix it.

Lets face practically nobody buys a used car and then rebuilds the engine. So I don't really see that buying a used engine is all that different. And before you say it, no, not every car and buyer see, hears or drives a car before buying. 1000's sold every wheel at auction, online or in person and loads of online and distant selling these days.
 
RangeRoller dt said:
You could get V8 power out of your M51 for the comparative work involved.
Click to expand...
Can you? Don't think there are many 225hp M51's running about. And the power delivery would be quite different. And a lot less refined.

Not knocking the diesel. In some ways I wouldn't mind one. Would love to know what you'd need to do in order to match a good 4.6
 
300bhp/ton said:
Don't really agree with this. Sure, if you have the cash to burn, then a rebuild is nice. But then, if it ain't broke, don't fix it.

Lets face practically nobody buys a used car and then rebuilds the engine. So I don't really see that buying a used engine is all that different. And before you say it, no, not every car and buyer see, hears or drives a car before buying. 1000's sold every wheel at auction, online or in person and loads of online and distant selling these days.
Click to expand...
Don't see your point.

A top end overhaul would cost around £400 if you put a Torquemax cam in, no point going to town doing a diesel to V8 conversion and fitting a potentially flat and shagged engine, :)

Rover V8's commonly suffer Slack chain - worn cam - headgasket failure, oil leaks etc if you're very unlucky worst case a sludge filled shítbox, it would be stupid to not rectify these issues when it's out of the car.. :)

it's your money at the end of the day, but i'd be inclined to invest a few quid and give myself a known fresh motor.

Simple really.
 
Last edited:
RangeRoller dt said:
You could get V8 power out of your M51 for the comparative work involved. Not the same though. Only a V8 will give the V8 experience. The burble the smiles per miles.

Do you have room for 2??
1 of each would keep your options open 😉 your gonna have to buy most of one anyhow for a conversion, may aswell get the whole thing.
Click to expand...
Nail on the head. My M51 is mapped nowadays and puts out a noticeable amount more power than stock, but it still doesn’t deliver power in a “nice” way. The V8s always feel like they burble along happily with just a tickle of throttle, whereas the M51 is screaming away on the turbo just to join motorway traffic.

The extra 10mpg made a big difference when I was a poor student and the car was a daily driver, but now I’d prefer more smiles per miles :p
 
The list of stuff to change is quite long radiator oil coolers, engine ecu , fuse box cluster, mounts, exhausts, wiring harness, throttle pedal, gearbox and transferbox, props and god knows what else.
 
pwood999 said:
Well some do !! I bought a project P38 with engine misfire issues, and had to rebuild the engine !!
Click to expand...
That is a little different. Thousands of used cars must be sold every day I should think. The vast majority are bought to be driven. Buying a project vehicle that you know before purchase needs an engine strip down is something else.

I have no problem with someone wanting to rebuild an engine. Only those that portray it as a must!
 
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300bhp/ton said:
That is a little different. Thousands of used cars must be sold every day I should think. The vast majority are bought to be driven. Buying a project vehicle that you know before purchase needs an engine strip down is something else.

I have no problem with someone wanting to rebuild an engine. Only those that portray it as a must!
Click to expand...
What part of "top end overhaul" do you not understand?

The RV8 is prone to several faults even when well maintained, such faults are easily rectified with the engine out of the car,
 
I have done the opposite conversion v8 out m51 in, it was quite straightforward, the engine mounting points on the chassis are the same, bell housing changed for diesel type and also the stator shaft and turbine shaft as the v8 ones are to long for the diesel torque converter, I purchased a case damaged hp22 box and swapped the front clutch pack which included the stator and turbine shafts, enabling me to keep my hp24 gearbox and I purchased a low stall converter for better performance

Pedal box had to be changed as the diesel has a throttle potentiometer instead of a cable.

My nano com allowed me to match the diesel eco to the becm with no issues

Exhaust was straight forward having to only change the down pipe,

Power steering pipes had to be changed due to different pump location between the v8 and Diesel engines.

Air con pipes were changed for the diesel version

Engine bay fuse box changed ( still have an issue regarding this im thinking maybe wrong fuse box I believe there are different ones used on the diesel version p38)

Wiring was a bit more complicated the loom that came with the diesel has a round connector and my car had 2 square connectors under the header tank, I didn't want to go to the trouble of changing all the loom going to these two connectors so cut a round connector from a donor car and with the use of workshop wiring diagrams removed the 2 square connectors and spliced in the donor round connector,

Cruise control wiring had to be altered as the diesel cruise control is via the engine eco. and I have to make up a loom from the throttle potentiometer, the wiring for the a/c had to be modified due to different location of the pump,

Radiator pack was changed for diesel type which was straightforward fitment, as were the coolant pipework feeding the heater matrix.

Gearbox oil cooler is a work in progress, as I want to mount a universal 9 row cooler I could have used the standard cooler mounted behind the bumper but I want to keep the driving lights .

Fuel filler pipe had to be changed as the petrol one has a smaller diameter hole which won't let you insert the diesel fuel filler nozzle when at the pumps. The in tank pump had to be changed and the fuel supply and return pipes were modified.

I had to fabricate a new exhaust manifold heat shield which I did in two layers of stainless steel with an air gap between which looks much better than the original fibre type

All in all I am pleased with the result, I have replaced the exhaust for a custom made stainless system, which looks and sounds good.

As the car has stood in the corner of me garage for the last 14 years all the steering joints and ball joints have been changed I used lemforder, all suspension rubbers changed for pollybushes, discs pads and callipers replaced and brake pipes replaced with kunifer
 
steveshone said:
I have done the opposite conversion v8 out m51 in, it was quite straightforward, the engine mounting points on the chassis are the same, bell housing changed for diesel type and also the stator shaft and turbine shaft as the v8 ones are to long for the diesel torque converter, I purchased a case damaged hp22 box and swapped the front clutch pack which included the stator and turbine shafts, enabling me to keep my hp24 gearbox and I purchased a low stall converter for better performance

Pedal box had to be changed as the diesel has a throttle potentiometer instead of a cable.

My nano com allowed me to match the diesel eco to the becm with no issues

Exhaust was straight forward having to only change the down pipe,

Power steering pipes had to be changed due to different pump location between the v8 and Diesel engines.

Air con pipes were changed for the diesel version

Engine bay fuse box changed ( still have an issue regarding this im thinking maybe wrong fuse box I believe there are different ones used on the diesel version p38)

Wiring was a bit more complicated the loom that came with the diesel has a round connector and my car had 2 square connectors under the header tank, I didn't want to go to the trouble of changing all the loom going to these two connectors so cut a round connector from a donor car and with the use of workshop wiring diagrams removed the 2 square connectors and spliced in the donor round connector,

Cruise control wiring had to be altered as the diesel cruise control is via the engine eco. and I have to make up a loom from the throttle potentiometer, the wiring for the a/c had to be modified due to different location of the pump,

Radiator pack was changed for diesel type which was straightforward fitment, as were the coolant pipework feeding the heater matrix.

Gearbox oil cooler is a work in progress, as I want to mount a universal 9 row cooler I could have used the standard cooler mounted behind the bumper but I want to keep the driving lights .

Fuel filler pipe had to be changed as the petrol one has a smaller diameter hole which won't let you insert the diesel fuel filler nozzle when at the pumps. The in tank pump had to be changed and the fuel supply and return pipes were modified.

I had to fabricate a new exhaust manifold heat shield which I did in two layers of stainless steel with an air gap between which looks much better than the original fibre type

All in all I am pleased with the result, I have replaced the exhaust for a custom made stainless system, which looks and sounds good.

As the car has stood in the corner of me garage for the last 14 years all the steering joints and ball joints have been changed I used lemforder, all suspension rubbers changed for pollybushes, discs pads and callipers replaced and brake pipes replaced with kunifer
Click to expand...
Apart from the bell housing and torque converter, the HP 24 from a V8 is a straight swap for an HP 22 on the diesel with the possible exception of the oil pump. There should be no need change any internals, many diesel owners have made the change
 
It wasn't in my case when it was v8 the turbine and stator shaft were to long and the turbine shaft was bottoming against the rear of the 2.5 converter
 
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