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MG MGB GT V8 Factory Originals Technical - 3.9 mods

I have a '95 3.9 just as it was pulled from the Range Rover. Will I need to change the front cover to an SD1 type? Can the OEM starter be used with RV8 type headers? I'll probably ditch the injection for a 215 4 bbl intake and Edelbrock 500. Does anyone have the specs on jets, rods that need to be changed for the 3.9? Will I need to swap cams if I use the carb?

I have an SD1 and a Skylark distributor. Which is best to convert to pertronix or Crane? I have both.

Thanks for any comments.

What you really need to do to get any appreciable increase in HP is raise the compression ratio to at least 9.5:1

The Range Rover 3.5l V8 I bought (out of a 1988) was the standard low compression 8.13:1. Look at the stamping on your block, it probably says the cr on it.

Yes on the cover, at least I had too. The Rover waterpump sticks up really high.

On the manifold, I went with the Offenhauser 5165, along with a Holley 390 4 bbl. I built my engine to peak in HP in the 6500 rpm range. I used an Isky 270 cam and the 9 pound flywheel.

You will need to use a starter made for the Range Rover. I used one of the small ones. The diameter of the hole it goes through (the one that sortof centers it to the block) is apparently different on the Range Rover vs Buick.

You will find that the Buick distributor will not clear the Range Rover waterpump. (Thereby forcing a different front cover). I didn't know Crane made distributors or ignition products.

Make sure you get a timing cover with the long oil pump gears.

And most importantly, buy the books that tell you what to do on the Rover V8's (from eBay is the easiest).
Richard Morris


The 3.9 will possibly be 9.35:1, it is stamped by the engine number, or let us know the engine number and we can at least confirm what the CR was when the engine was built. You could increase the CR by changing the composite head gaskets to tin, but the composite gaskets are better.

Canít help with a change to a carb; from a simple and reasonably good fuel injection to a carb and less power seems the wrong way to go to me.

The Range Rover starter motor wonít fit. Well, it will fit the engine of course but the solenoid will foul the chassis rail. A SD1 starter motor has the solenoid on the bottom and will fit. Or use one of the aftermarket starters.

Does the engine have a distributor? If it does why do you want to change it? But by í95 it should have a crank driven oil pump and no distributor. The crank and cam may need some modification to convert to cam driven oil pump and distributor. Or you could have an earlier engine with an intermediate cover that has a distributor and a crank driven oil pump.

A SD1 cover has the longer oil pump gears.

Geoff King


I've re-jetted my Edelbrock 500 for my '80 SD1 3.5. Should be pretty close for your 3.9 or at least a good starting point.

Check in the archives for all the info you'll need. IIRC, I've got .080" primaries, .086" secondaries and .062" x .052" needles comes to mind. Quite a few stages leaner than the stock 500.

I'm running a Pertronix with an MSD ignitor box in a Buick distributor.

Not sure about the Range Rover starter but if it helps, I have an OEM Rover starter with RV8 headers. Lots of room to play with.
Simon Austin

I have a 3.9 like yours.
The cheapest option is to get an '80's cover. You can mod' the later front to take oil hoses & to have a remote oil filter, but it'll probably cost heaps. It can be either rangerover or rover front. I used a range rover front and a standard pump, but I did set the motor back a little further. The MGB RV8 used a range rover front but also a slightly shorter water pump (which are quite expensive) If you are get the choice use a rover one.
Modifying the fuel injection plenum to fit is very cheap and easy to do. Costs about $100 australian.
Use a Rover SD1 or P5 or P6 starter. These have the solinoid on the bottom, and fit in MGB's.
The rangerover solinoid is on the side and the one you have will not fit, by about 5mm. There is no way you will get it to fit either, I tried!

check with Mark at D&D ( or 810-798-2491. He can supply the correct parts and has the answers.

David, send me a ph. # were I can call you, it will take me to long to type this out! (hunt & peck) type hear.
Glenn Towery

David, I recommend the Pertronix unit in either distributor. The Skylark unit may be easier (cheaper)to find replacement parts for if needed.
With the Pertronix unit, you can later add a Muliple spark discharge system such as the MSD-6AL as a performance upgrade. The optical trigger in the Crane system is much more difficult to properly install and has a higher failure rate than the simple magnetic trigger in the Pertronix system.
Jeff Schlemmer

This thread was discussed between 07/12/2006 and 14/12/2006

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