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MG MGB GT V8 Factory Originals Technical - Rover 4.9


I have the specs for the Rover engines from the 4.6 down to the 3.5. But I am wondering if any one can tell me what the Bore,Stroke, Cylinder Capacity, Compression Ratio, BHP and Torque are for the 4.9.

I have located a 4.6 and wonder if I should wait to find a 4.9 or go with the 4.6. I will probably run it as a carburated engine. Hopefully all my external stuff from my 3.5, headers, intake, oil filter conversion from D&D, etc will just bolt on.

Would it mate up to the tranny bell housing?

Thanks for any information


Bruce Mills


4.9 was not a standard factory size. 4.6 was the largest version made by Rover. However, TVR and others built modified engines of larger sizes. It is inevitable that these are much rarer. You could spend all your life waiting for one to come up for sale.

If you use standard 3.5 manifolding etc on a larger engine you may restrict its power output at higher revs.

David Witham


As David said there were no factory V8's bigger than the 4.6 (4554cc) The TVR Griffith had a 5.0 engine that was based on the earlier intermediate block, similar to the 3.5/3.9 engines but with the ability to cross bolt the mains like the 4.0 and 4.6 and they used their own stroker kit to achieve the 5.0 capacity.

Any thing is possible with lots of cash and capacitys of 5.2 and above are available but work is needed to the block to stop things hitting each other.

The 4.9 figure could be the buick 300 engine which was that size 4.922cc.

If you intend re-building the 4.6 do have the block pressure tested,as they are notorious for cracking behind the liners and the liner itself sinking in the block due to these engines being run leaner and at higher temperatures for emission reasons.

If you just want a decent engine for a road car a 4.6 can be mildly modified to give approx 260+ BHP whilst still retaining some nice bottom end grunt without having to spend a fortune, just a fast road cam and a good pair of heads with valve sizes of 1.63" Inlet and 1.4" exhaust. and a decent inlet and exhast system.

If you intend using the original ECU a chip upgrade is recommended. but it is expensive and its alot cheaper to go megasquirt to controll fuelling and ignition. Of course a Edelbrock 500 and performer manifold is even cheaper if you don't fancy setting up an EFI system.


Kevin Jackson

Thanks for the info guys.

I would want to use my Edelbrock 2198 intake and Edelbrock 500 carb as well as the existing headers and upgrade the exhaust to 2".

Perhasp in the future I would use the EFI System



Bruce Mills

Hello Kevin,
I'm right now looking at swapping out my 4.0/3.9 for a 4.6 and would appreciate your advice.
These guys
Seem to be the best value locally.
I was thinking of their stage two heads, $2000
and the high comp 4.6 that they will build for you for around $5000.
You mentioned a mild road cam, I don't know much about cams, lift etc.
7000 does however seem allot of money. Worth it for 260bhp, not for 225 (the standard 4.6)

I'll be keeping my 3,9 efi setup, I'm told I need to use and adjustable fuel line pressure valve.
Peter Sherman

Hi Peter,

Still haven't managed a trip down to Melbourne where I have family but still hoping to get there.

Firstly before I make any suggestions is your current engine a 4.0 ie. late type engine or the earlier 3.9 and also what is the intended use of the car?

I have just built a new engine for my car based on a 3.9 block with a 4.2 crank, chevy rods and Keith Black Hypereutectic pistons, Crower 50232 cam topped off with a pair of big valve Buick 300 alloy heads which are roughly the equivalent of stage 3.

There was a lot of machining involved and although I aquired all the parts at very reasonable prices it still cost me about 3250 to have it built, should produce approx 260BHP.



Kevin Jackson

I bought the motor from a fellow who had got a 20000K, replacement short motor, off a friend. That is, his friend had put a new short motor under an old set of heads etc. The efi is the 3.9 gear. The Motor is a 3.9/4.0. It has the longer crank, stiffer block and provision for crossbolting, but not bolts.
It is not a race track car, every day use. I need reliability, a good drivable acr , with a bit of go to it :) .
The motor is now up to 120,000 and the heads 190,000 . This is approximate, given the history, it might be more.
The engine is still very good, a little bit of oil in the exhaust when warming up, the occasional tappet noise. It's essential approaching post middle age (I know the feeling well !). Another 50000 and I think it will need replacement. However mostly I would like to gain extra 60 bhp. That would make the gearbox diff' combination perfect. I have the standard Salisbury diff' and toyota supra gearbox. I don't want more than 260 bhp, I'd have to change out the diff'. Not really worth it anyway in a street car.
I'm looking for a straight, and quick swap. I can't have the car off the road too long.


Thats a stroke of luck. your current engine is a rare intermediate, and the blocks are quite sought after because of the fact that they can be cross bolted, and have the better oil pump drive system, so will have some value. These are only normally found in TVR's and possibly a few late range Rovers.

You can also use your existing front cover on the 4.6 because it will match the oil pump drive and you still have the distributor so can also utilise the 3.9's Hotwire EFI with a chip upgrade for the 4.6 engine.

If you intend running with the hotwire system it will limit you a bit on the cam as the airflow meter does not like a cam with too much overlap but the guys you mentioned should be able to advise you.

Price wise they would seem to be very competitive, we would have to pay more in the uk for similar specs.

Head wise it would be nice to see a picture of the work behind the valve seats,the throats should be opened up and blended to to valve seat size, with a three angle valve job.The guides shoud be bulleted in the port and the guide tops should machined down approx 100thou to allow for a high lift cam. The valve sizes 1.63" Inlet and 1.4" Exhaust will be fine for a road car.

Just a thought, if they have a 3.9 intermediate block would they rebuild it with one of their 4.8 stroker kits cross bolt the bottom end, and you part exchsnge your existing engine you could then just do a straight swop over with little off road time, might not be more expensive than using a 4.6 engine which will need top hat liners fitting to prevent the inherent problem with 4.6 blocks.


Kevin Jackson

Thanks Kevin,
Useful information

I was just re-reading this thread.

David "3.5 manifolding etc on a larger engine you may restrict its power output at higher revs."

Do you think the Edelbrock 2198 would be ok as an intake?

Do you know of anyone who makes a larger header for these engine?


Bruce Mills

David, I think you are right,
I would do far better, value for money wise, to buy their stroker kit and their top end heads, and fit it to my current motor.
I would imagine that the cylinder bore/sleave would have a bit of a lip which would have to be removed. The short motor would have around 100,000km on it. I've not done this before, so please bear with what might be a silly question. Does this need a machine shop, or can I just buy a cylinder honing widget and do it myself?
Often with these things it is a case of due care and diligence, rather than expensive equipment.
Also cross bolting. Same question basicly. I've never seen a 4.6 block taken apart, but drilling some holes in the existing pads on the block and tapping a thread into the caps doesn't strike me as too hard, what do you think?.

Been reading around the subject,
honing is machine shop.


You need to get a quote from the engine builder for reboring the block 20 thou and cross hatch honing and having the block and caps drilled and threads tapped for the cross bolts. The stroker Kit will almost certainly come with 20 Thou+ pistons.

This all precision machine shop work which you can't really do at home unless you have all the equipment and know how to use it.

Please realise you are going to end up with an engine with around 280 BHP and you will definitely need to do something to keep the rear axle in place.

Have you seen the 4 link kit with coil overs that Bill Guzman at Classic Conversions in California is producing, it's very good value at around a $1150.00 US.

Don't go too mad on the heads Stage 2 with big valves and standard size port runners would be fine for the street and still retain good bottom end torque.

Have fun,

Kevin Jackson


The Edelbrock performe and 500 carb will work fine on an engine up to 5.0L/300CI.

On the exhaust side the block huggers are very restrictive but the RV8 style with 1.5/8" primaries will work fine.

They are available in the UK from in stainless steel who supplied my complete system for approx 400.00 but Simon Austin who is quite close to you and I believe he has them on his car may have sourced them more locally.

Kevin Jackson

Thanks Kevin,
There is a fellow nearby who does good work.
For the back I'm using Doug's composite springs, antitramp bars (and panhard).


Have you already got the springs and panhard rod?

Kevin Jackson

Yes I have Kevin,
Your implication is correct, Bill's set up is very good, mechanically and weight wise, the best, however it involves welding to the axle and legally (here) you then need to get your axle X-rayed by a NATA certified agency, or get a registered Blacksmith to do the job. Then get an engineer to certify it. ie not worth it. It's not just the money, it's all the stripping down and time and transporting about. Bolt on is the way to go. I do wish Bill make up a bolt on bracket for the upper arms.
I did design a bolt on trailing three link, putting a bracket on top RHS of the diff', running the the top right hand diff' cage bolt all the way though, as a front purchase point for the bracket. This plus Diff' cover bolts at the back would have tied the bracket into the toughest part of the diff housing. Even bought Gaz coil overs and the taps ad drills. however this would still have involved an engineers certificate, which you don't need with Doug's set up.
I did read about issues with de-laminating the composite springs. However, diligent net searching did not bring up one case where body mounted (as opposed to front of the spring loading) antitramp bars caused de-lamination.
If I do get problems, i can still adopt the diff' bolt approach, however, six months so far, and Doug's set up works just great! Roughly two Kg a spring.
Peter Sherman


I too had heard rumours about delamination of the composites when used in conjunction with anti tramp bars so was a little concerned but your research would seems to counter that.

Keep us up to date as to what you decide to do re the engine.


Kevin Jackson

One of those unfortunate half true rumors that get started.
I have really tested them out over the last 6 months, at least 10 to 20 thousand km's of 'spirited' driving on them. They are designed to be super light and flex up and down, not push the car around. I've also fitted a panhard rod for much the same reason, plus of course the cornering gets better with one of those locking the back axle in place. I sail catamarans and we use fiber glass sail battens (and masts and boats) that really take a flogging (lit' flogging sail). However, you must feed forces into fiber glass in the right way and not have point stresses.
I found that people who used the composites without any sort of anti tramp bar could have problems. If these springs reverse (tramp), they are almost certainly history. All the force gets concentrated on the edge of the spring eye metal bracket, crunch! With anti tramps bars this can't happen. Plus of course, anti tramp bars really feed the power onto the road. Without them the car was much harder to drive, bit of a handfull and not as quick because I had to go easy on the accelerator.
People who used the wrong sort of antitramp bar could have problems. This is the sort of bar that loads the front of the spring with those triangular bolt on bit. Popular with steel spring folks because its so very easy to set up and with steel springs works fine.
No one who used the right bar set up had anything bad to say, quite the reverse.
If they do ever fail (something I doubt) I won't be all that sorry because I'm looking for an excuse to try the 3 link trailing arm idea. I spent heaps of time working out every detail and it'd be quite easy to set up, It's just that Dougs set up is a little bit lighter, cheaper (no engineers fees etc.), easy to install, already street legal etc. It's hard to let go a cherished idea or plan, but reason must rule.

This thread was discussed between 08/09/2008 and 23/09/2008

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