Rover 3.9 to 4.6 is it worth the swop, Discuss.........!

Goughie · Post by **Goughie** » Tue Apr 22, 2008 5:24 pm

I have a 3.9 (on a Holley 390) in my Capri at the moment, was running fine, gone really tappety now and is seriously down on power, i was thinking of fitting a new cam kit as it has been recently rebuilt.
But to throw a spanner in the works i have been told of a localish scrap yard that has a 4.6 engine with starter/dizzy/alternator but is missing the ecu/airflow sensor and engine wiring loom.
Unfortunately i know nothing of this type of engine, does it run a standard dizzy, would it run with my existing Holley and manifold (although would look to upgrade to Weber 500 when funds allow) will my 3.9 flywheel bolt on and what do you think i should be paying for it?
Or i have been told with a new chip in a 3.9 ecu it would run on the hotwire sytem?
I know this is personal choice really but i would like to hear your thoughts before trekking over there.
Thanks in anticipation,
Paul
P.S. The white Capri in my avatar is going, i am in the process of stripping it, and the bodyshell will be offered really cheap to a fellow enthusiast, PM me if genuinely interested

Post by **katanaman** » Tue Apr 22, 2008 5:28 pm

4.6 doesnt run a dizzy as standard, it can be converted to run one or it might not be a 4.6 at all. Give the engine numbers a good check before you go into any deals. Apart from that the usual scrap yard 4.6 pit falls apply.

ChrisJC · Post by **ChrisJC** » Tue Apr 22, 2008 7:28 pm

All the various Rover V8's are interchangeable in terms of fuel system, igntion system etc etc.
For example I've got a 4.6 with all 3.5 ancillaries including distributor.

If I compare driving my 3.5litre van vs the 4.6litre Land Rover, the 4.6 is far more powerful. I'm sure the difference between the 3.9 & 4.6 would be less, but still significant.

I'll have it if you don't want it!!

Chris.

mgbv8 · Post by **mgbv8** » Tue Apr 22, 2008 8:05 pm

Same here.
I'm running a late Rangie 4.6 in the MGB. But I've fitted all the pre SD1 stuff to it.
Front cover, dissy and oil pump.
The only niggle I had was one of the crossbolts by the oil pump casing.
Had to grind a bit off the head of one of the cross bolts to make it fit.

I also run a Weber 500 on it with a 351 manifold.

Goughie · Post by **Goughie** » Tue Apr 22, 2008 9:07 pm

Bugger! Its looking like i am going to have to look at this engine

Thanks for the advice so far, the question is, whats it worth assuming it is a HC engine? done searches on ebay and cannot see any listings for a complete engine, finished or not, another how long is a piece of string question i know but guestimates would be appreciated.

Chris, will let you know if i decide not to go for it

Thanks again,
Paul

RoverP6B · Post by **RoverP6B** » Tue Apr 22, 2008 10:49 pm

The biggest difference is in the torque. The 4.6 has tons of it.

Torque gives you acceleration, hill climbing ability, overtaking ability, that shove in the back of the seat when you plant your foot.

I went from a 3.5 to a 4.6, and wow.......totally awesome

Ron.

ChrisJC · Post by **ChrisJC** » Wed Apr 23, 2008 7:19 am

You need to be wary of unknown 4.6's. It may well have a cracked block (most of them seem to go that way), and that's why it's in the scrapyard!

I'd offer £250 I think and see what they said. And tell them the block is likely to be cracked!

Chris.

Goughie · Post by **Goughie** » Wed Apr 23, 2008 5:23 pm

Cracked block

got me worried now! i guess there is no way of testing out of a vehicle? and if it is cracked are they repairable?
(excuse my ignorance if that is a silly question)
Wonder if they will give me a 60,000 mile/6 year warranty

ChrisJC · Post by **ChrisJC** » Wed Apr 23, 2008 6:59 pm

You can pressure test the block, but sometimes they only leak when warm!!

They can be fixed by relinering with top-hat liners.

Chris.

yorkshire-spam · Post by **yorkshire-spam** » Thu May 15, 2008 10:29 am

My 3.9 had a cracked block and it only showed when it was warmed up.
But once the heads were off it was obvious - no. 5 piston completely steam cleaned.

In the scrap yard, if you can, get the spark plugs out and see if any look unusually clean... once you have the engine at home get the heads off and check it.

Goughie · Post by **Goughie** » Sat May 24, 2008 11:33 pm

Finally took delivery of two 4.6s, Yes two

Thought it would be a case of swopping the front cover for an SD1 type so i could use a dizzy but the cam is to short, do i have to buy a new cam (if so what would you recommend for a street 4.6 with a Holley 390) and will an SD1 sump and pickup go on without the crank catching?
Do i have to modify a dizzy for decent running? If not, which would be a good starting point, 3.5 or 3.9, i have a choice?
Thanks in advance,
Paul

RoverP6B · Post by **RoverP6B** » Sun May 25, 2008 3:29 am

Hello Paul,

Because the 4.6 litre engines were designed without a distributor, the 4.6 camshaft has a short nose with no provision for being used with such.

In order to use a distributor, you have a choice, of either a 3.9 or 4.2 camshaft, both of which were fitted with a distributor.

Second choice which is what I have, a custom grind, an enhanced 4.6 profile ground onto a 3.9 billet, so I have the best of both worlds

A Lucas distributor designed for the Rover V8 can be used on any Rover V8 engine in any state of tune, but you will need to have it regraphed so that the rate of and total advance suites the 4.6. If you don't do this, your engine will not be at its best, and if the advance to too great you could cause permanent and costly engine damage

You will use the oil pickup from your SD1, and if using the sump it may have to be relieved depending on its shape in order to make room for the throw of the 4.6 crank.

If you have 'Tempest' 4.6 engines, you can fit a windage tray directly, as the block is drilled to accept one. If you have a 'Thor' engine, the block is not drilled, although the casting is there, so to fit a windage tray you will need to drill and tap the block.

You will also need to close off the access hole on the near side flange where the the electronic sensors normally reside for reading the rotation of the flywheel.

You will most likely need the spacer for your cranksahft pulley too.

Best of luck,
Ron.

Post by **Coops** » Sun May 25, 2008 10:47 am

you jammy bu@@er,
two 4.6's theres me just trying to find one,

mgbv8 · Post by **mgbv8** » Sun May 25, 2008 7:17 pm

You will deffo need the crank spacer if you intend to re-use the old 3500 crank pulley.

Goughie · Post by **Goughie** » Tue Jun 03, 2008 5:43 pm

Thanks for all the advice and sorry for the late reply, having serious computer issues here

Ok, it looks like i have to splash out on a new cam, what do you reckon to this:-
http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... :IT&ih=020
or is there something better/cheaper available?
Looks like the sump will be fine although the drive gear off the old SD1 cam is knackered, about 6 of the teeth missing

how it ever ran i will never know.

Spacer for the crank? i take it is to line it back up to the water pump? I suppose that will become obvious when i start to put it back together.

Ron:- Cheers for the reply, Rover P6 with a 4.6 sounds great, have fond memories of my Dads old chocolate brown V8 with full leather, went to the big scrappy in the sky before i had chance to drive it