Difference between camshafts 4.0 and 4.6

9329 Views 19 Replies 7 Participants Last post by David Laird, Feb 13, 2021

Reinhoud

Discussion Starter · Jan 18, 2019

Gents,

The cams of the 4.0 and 4.6 are different, anyone who knows wich one has more lift and/or duration? If yes, how much?

I've got a Kent 180 cam in my P38 GEMS 4.6, and I miss the low end power the 4.6 in my Disco 1 has (3.9 camshaft) The 4.6 in my Disco is out of breath at about 3500rpm, the P38 with the Kent comes to live at about 3500rpm.
It's not that it's completely gutless in the lower revs, but more would be nice.

I was wondering if the cam from a 4.0 or 4.6 would be a good choice.
I've never driven a stock 4.6..

So if you drive a 4.0 or 4.6, would you be so kind to tell me at what revs you have power?

Thanks

1 - 20 of 20 Posts

95classiclwb

· #2 · Jan 18, 2019

2k, hse, 4.6, hp24auto, 212,000 miles, nas. although worn out due to high mileage it does come alive at about 3000k rpm, using the sport mode on the autobox keeps the power band available at any rpm up to 5500 shift point.
I am contemplating an engine overhaul and one of the plans is to replace cam, about a year ago I begun my search and found very little info on 4.6 cam specs.
places I visited were "crower cams", "the wedge shop", "rpi", "piper cam", "v8 developments", "ta performance". all of them have something to contribute.
this engine behaves totally different than the 4.6 in my classic which is mated to a hp22 auto box, the classic is a bit slow at take off, the power band is picked at about 2,000 rpm and remains constant until 6,000 rpm.
both trucks run completely stock gearing and tire set ups.
my 01 disco 2 4.0 with 120,000 miles runs strong and smooth from start up but fails on highway passing.
hope it helps.

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Reinhoud

Discussion Starter · #3 · Jan 18, 2019

Thanks.

Sounds like the 4.0 cam is close to the 3.9.

Does your RRC have a distributor ignition on the 4.6?

95classiclwb

· #4 · Jan 19, 2019

Reinhoud said:
Thanks.

Sounds like the 4.0 cam is close to the 3.9.

Does your RRC have a distributor ignition on the 4.6?

yes it does have a distributor and runs the 4.2 cam, I have acquired the complete distributor less kit from "trigger wheels". became extremely busy over the summer, thus it sits on my living room waiting on seasons to change and subsequent install, another planned upgrade is a stage 4 cam from RPI and ported heads, parts are sitting in living room closet as well.
I seem to be over scheduling my 2019 already, lol.

Reinhoud

Discussion Starter · #5 · Jan 19, 2019

Aha, so the 4.2 cam is different again?

I'll see what I do..

Richard_G

· #6 · Jan 19, 2019

From RAVE

4.0 litre P38
Valve timing Inlet Exhaust
Opens 28°BTDC .......... 66°BBDC
Closes 77°ABDC .......... 39°ATDC

4.6 litre P38
Valve Timing Inlet Exhaust
Up to 99MY
Opens 14°BTDC ........... 64°BBDC
Closes 70°ABDC ........... 20°ATDC
From 99MY
Opens 28°BTDC ........... 72°BBDC
Closes 64°ABDC ........... 20°ATDC

3.9 Classic
Valve Timing Inlet Exhaust
Opens 32°BTDC ........... 70°BBDC
Closes 73°ABDC ........... 35°ATDC
Duration 285° ................. 285°
Valve peak 104°ATDC .......... 114°BTDC

4.2 Classic
Valve Timing Inlet Exhaust
Opens 28°BTDC .......... 72°BBDC
Closes 64°ABDC .......... 20°ATDC
Duration 272° ................ 272°
Valve peak 108°ATDC ........ 116°BTDC

So they are all slightly different........

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95classiclwb

· #7 · Jan 19, 2019

Reinhoud said:
Aha, so the 4.2 cam is different again?

I'll see what I do..

once I complete the coil conversion on the classic and remove distributor, I could run any cam. the reason for sticking with the current 4.2 cam is because of the distributor drive.
I got a little ahead of my self and purchased the stage 4 before the coil conversion kit, the reason for the coil kit is because the dizzy has nearly 300,000 miles and it is worn out, thus it keep on loosing gap between reluctor star and pick up plate. it was much more beneficial (in my rationale) on the long term to eliminate the dizzy.

Richard_G

· #8 · Jan 19, 2019

Actually, looking at the figures I posted, the 4.2 cam is the same as a 4.6 Thor although it appears that the 4.0 litre P38 can has the longest durations. The lift will be the same on them all as the valve max opening is the same for all engines. The only thing the figures don't show is the cam slope so no idea which would open the valves fully for longest.

Alan Lindsay

· #9 · Jan 19, 2019

Hi all,
So, to distill this thread to it's essence, looking at the timing figures provided by Richard G, the early 4.6 cam looks the 'softest' to my inexpert eyes. Is this correct?
What is the ideal cam or cam grind for me, for my upcoming rebuild. Solid towing performance is my primary objectives?
What would be the preferred cam for someone looking for a sparkling highway performance?
Would the high torque towing cam also be the best in serious off road work and most economical?
regards
al

95classiclwb

· #10 · Jan 19, 2019

Richard_G said:
Actually, looking at the figures I posted, the 4.2 cam is the same as a 4.6 Thor although it appears that the 4.0 litre P38 can has the longest durations. The lift will be the same on them all as the valve max opening is the same for all engines. The only thing the figures don't show is the cam slope so no idea which would open the valves fully for longest.

thus my original comments and finding of being unable to locate specs.

Escape

· #11 · Jan 19, 2019

Reinhoud, is you Disco also a GEMS or a Thor/Bosch? The latter have a significantly lower power band due to the banana manifold.

Personally I'm a fan of the hi torque cams (Kent or Piper). They perform well when towing and offroad and don't run out of steam in higher rev ranges.

Filip

Richard_G

· #12 · Jan 19, 2019

Disco only ever got the Thor, albeit only the 4.0 litre, they went from the 14CUX motor as in the Classic straight to Thor and missed the GEMS completely.

95classiclwb

· #13 · Jan 20, 2019

Richard_G said:
Disco only ever got the Thor, albeit only the 4.0 litre, they went from the 14CUX motor as in the Classic straight to Thor and missed the GEMS completely.

correction, disco 1 in the US, 94-95 used 14 cux with 3.9, 96 to 98 gems 4.0... disco2 99 to 03 4.0 thor and 04 thor 4.6. 14 cux and gems saw 5 speed manual variants along with 22hp auto, d2 saw auto box only and we did not get diesel variants of any rover model.
as far as I can remember range rovers be classic or p38 never saw manual boxes in the US market.

Reinhoud

Discussion Starter · #14 · Jan 21, 2019

Escape said:
Reinhoud, is you Disco also a GEMS or a Thor/Bosch? The latter have a significantly lower power band due to the banana manifold.

Personally I'm a fan of the hi torque cams (Kent or Piper). They perform well when towing and offroad and don't run out of steam in higher rev ranges.

Filip

I've got a Discovery 1 which has a 3.9 from factory, I put a 4.6 GEMS in it, with all the 3.9 gear, so it has the 3.9 cam which has about 0.6mm less lift at the cam.
This engine with the 3.9 cam feels actually better than the 4.6 GEMS with Kent 180 cam in my P38.
The Disco has imidiate throttle response in the lower revs, but is out of breath above 3500 rpm, the P38 is sort of, gutless below 3500rpm, but she does sort of alright off road.
I was just curious about experiences from others regarding cams, I've never driven a stock 4.6, and I think I regret a little bit I got myself a Kent 180 cam, but I actually realized that when I got that 4.6 in my Disco..

Thanks for your rplies guys, much appriciated!

Reinhoud

Discussion Starter · #15 · Jan 21, 2019

Richard_G said:
Disco only ever got the Thor, albeit only the 4.0 litre, they went from the 14CUX motor as in the Classic straight to Thor and missed the GEMS completely.

So, the 4.6 only has been in the P38, from factory?

JohnnoK

· #16 · Jan 21, 2019

Reinhoud said:
So, the 4.6 only has been in the P38, from factory?

I believe the US market got the 4.6 in the Disco2, but I won't swear to it.

95classiclwb

· #17 · Jan 21, 2019

Reinhoud said:
So, the 4.6 only has been in the P38, from factory?

0n the p38 from mid 95 up to 2000 you had choice of SE trim with 4.0 and HSE trim with 4.6. 2001, 2002 p38 only had 4.6 with trim levels. only in 2004 did the disco2 receive the 4.6 standard as part of trim, in 2003 the disco2 had the option of 4.0 or 4.6. 2003. disco 2 with 4.6 option is very rare to find as it's cost and trim level rivaled that of the p38 thus buyers opted for the p38, unless they needed the 7 seat capacity of the disco 2. this was for the US market, cannot speak of other markets. any disco be 1 or 2 below 2002 had a 4.0 standard and no 4.6 factory option.

Richard_G

· #18 · Jan 21, 2019

In the UK the trim level and engine size were both available so you had a choice of 2.5 diesel, 4.0 litre petrol or 4.6 litre petrol in base (possibly only offered with the diesel, the 2.5DT), SE or HSE. The diesel engined versions were designated DSE and DHSE to denote trim level. But then there were the various limited editions that could have had any engine and yet another different trim level.

Escape

· #19 · Jan 22, 2019

As far as I know, the manual option for the V8 was only offered on the 4.0SE GEMS. Quite rare, I've had 2 and am now converting an automatic to manual because I can't find another.

I've also seen a RHD DiscoII with a 4.6 (and Bosch), so they must have been available in UK as well.

David Laird

· #20 · Feb 13, 2021

Richard_G said:
From RAVE

4.0 litre P38
Valve timing Inlet Exhaust
Opens 28°BTDC .......... 66°BBDC
Closes 77°ABDC .......... 39°ATDC

4.6 litre P38
Valve Timing Inlet Exhaust
Up to 99MY
Opens 14°BTDC ........... 64°BBDC
Closes 70°ABDC ........... 20°ATDC
From 99MY
Opens 28°BTDC ........... 72°BBDC
Closes 64°ABDC ........... 20°ATDC

3.9 Classic
Valve Timing Inlet Exhaust
Opens 32°BTDC ........... 70°BBDC
Closes 73°ABDC ........... 35°ATDC
Duration 285° ................. 285°
Valve peak 104°ATDC .......... 114°BTDC

4.2 Classic
Valve Timing Inlet Exhaust
Opens 28°BTDC .......... 72°BBDC
Closes 64°ABDC .......... 20°ATDC
Duration 272° ................ 272°
Valve peak 108°ATDC ........ 116°BTDC

So they are all slightly different........

Hi There, Ihave just purchased a rebuilt 4.6 for fitment into my Triumph Stag. I have been told that it is fitted with a 4.2 camshaft. Have you any idea how this will affect the performance?
Thanks

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