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MG MGB GT V8 Factory Originals Technical - The darkside

Well I've finally done it. The darkside has won.

I own a 1973 MG-BGT, i always said i'd not do a v8 and i'd just leave it standard... maybe tune the standard engine etc.. but never a v8 ... no ... nay... never...

Saturady happily minding my own business a *geaser down the pub* said "anyone wanna take a engine off me, its all over the garage and need to get the car in before the snow". I just causally enquired what it was more out of politness than interest.


Then the it came "3.5 V8 out of a Range Rover"... the imperial march started in the backgorund.


Hmmm isn't that the rover/buick v8 same as SD1


Thats means it'd fit in an MGB

I'd deliberatly not swapped accross to these forum pages becuase of the temptation. I knew it'd be too great. No never a v8... not even a engine swap if i could help it... definately not a v8...and now i own a MGB and v8. Even i've got to admit its only a matter of time.

In truth i've not actually decided whether I'm gonna do it to the 73. I've seen a fair number of tidy looking RB - GTs going cheap in the area and i believe this is the easier swap than my 73.

There's no major rush anyway i intend to do as much as i can myself on the engine. Being that i've never done one before its gonna take a while.

But i think i've officially joined the darkside. Someone tell my family I'm gonna be gone a while....
simon crozier


Welcome to the Clan of Non-Comformity!

Make sure to visit


rick ingram
"So many projects, so little time!"
rick ingram

Why the darkside, only of pleasure.
SD1 engine "slightly" tuned, dumdum-da-dum...

Yes Simon, that's how we all start.

A 73's perhaps a little early for an easy conversion, the later shell is already set up for the V8.... have you bought Roger's book 'how to give your MGb V8 power'....a new edition is out soon, but second hand ones turn up on E bay for chips.

Scrounge a drive in one , you will be converted, I promise.

M Barnfather

You will not BELIEVE what a fabulous car you are going to make. Every time I get into mine it is a thrill. The effortless surge of accelleration. In what gear?, why any gear you want of course, your choice. Blinding accelleration or effortless crusing.The power of the dark side is truely awsome, you will never go back. The alliance never had a chance young jedi !!

Of course now begins your long soujourne in the temple of enlightenment (the garage). Where you will meet many challenges, both mental and physical, to make you worthy of your new power. The sith of the MG BBS will surely guide your quest.

(I've realy REALY got to drink alot less red wine)

Jezzz !!!

They weren't kidding when they made all that fuss about the darkside praying on the weak were they... ?

So far I've owned one V8 for about a day never even heard it run and I'm already reading articles on how to convert the GT and potential power.

Not only that but it gets worse - I've been dicussing the purchase of a holley 390 carb. I orignally refused with a sensible "na mate my engine is still in about 1000 pieces" but then some B******d pointed out the air filters that go with them - the big circular jobs and I'd ALWAYS wanted one of them... what they called "lowrider". So now i'm seriously considering that too...

I think i'm gonna have to pull my neck pretty sharpish soon else gonna get myself in trouble. Just last week i was wondering if a weber on 1800 was OTT for my needs - now i'm eyeing up 4.2s.

Seriously thou :- current plan (using that term losely) is - over the next year or so rebuild the engine into it's standard spec. Just to sort of get it going again on a bench not actually installed in anything. Be worth is just to get some decent experience with the engine.

If that goes smoothly and I've still got the motivation, then I'll look at doing the min to get it safely into the GT. At the min that would appear to be front suspension, front brakes, steering column, engine bay mods and a new gearbox. I know the 73 isnt the ideal car but I'm not getting rid of her and have already got another car - 3 just seems obscene.

Again if i've still got the motivation, I can look at more exciting modifications to take more power. Than either putting in a better V8 or sorting the current one. Once it can accept a V8 dropping another in wouldn't be that bad. The experience of rebuilding one first should give me an good idea of what the perfect engine for would be.

I figure this plan gives me a few get out points with a usable car and no "unfinished project" advert going in the local rag. Albeit that the car could still be 1800 i'd rather this than halfway between the two. Although the timescale is probably going to be more geopyhsical than "a few months."

Does this sound reasonable from you experiences ?

From what i've read the 3.5L Range Rover engine is the runt of liter ? Is this true ? I'm sort of counting on around 125bhp to minimise the number of *absolutely necessary* thing to change in the first phase. Is this about right ?
Simon Crozier

Power corrupts - welcome to the Darkside

Minimum 135hp, the higher compression Vitesse 3.5 engine puts out 190hp on flap valve injection....not a lot more HP from larger engines really, the real strength of the Rover engine lies in its Vitesse screwed the half-shafts within 12 months , and even now I seldom have to use serious revs to out-drag most stuff.

M Barnfather

Quote: "I know the 73 isn't the ideal car..."

Sure it is - if it's the car you have!

The conversion is totally doable with earlier cars than yours... As for rubber-bumper MGBs, you couldn't give me one! Even if it's been lowered, an MGB just isn't right with huge black rubber bumpers. When you decide to put a different engine design in your car, you automatically become a hot-rodder. Any real hot-rodder knows that the FUN part is doing things that are original and creative... so my advice to you is to do your own thing wherever you can.

As for your timescale... you do have another mode of transportation don't you? I converted a junk heap, so it took about two years to be really driveable (under Buick 215 power), but that was nearly fifteen years ago. I've usually tried to do one major improvement every winter since. (Example: new paint, new rear axle, panhard rod, etc.)

Coitus- FWIW, I really love the look of a 1975-1980 RB mgb roadster, lowered, with LE wheels,decal, and a 3.8 EFI V6 unnoticeable under the hood! . Having been weanied on my beloved 1971 splittail ( bought new off the showroom floor in Sept 1970), for years I coveted those neat looking rubber bumpers on the later models.Now I have 2, but confess to lowering and converting one to chrome bumps in the interest of weight redux. Hey to each their own. Cheers. Vic
vem myers

Vern- Yeah, to each their own... IMHO anyone who's up for the task of lowering an MGB (with steering rack changes) and the body mods for swapping bumpers shouldn't be put off by mods inside the chrome-bumper engine bay.

I still say it's a pity MG didn't design and produce a whole new model for the 1970s and 80s. They missed an opportunity to grow in sales and status. TR7 was a disaster... What if that development money had gone into a new MG product, instead of band-aid "fixes" to MGB to meet US bumper and smog laws?

I did mine over the winter. If you get "through the guards" extractors/headers (like every one else nowdays) you just might be able to fit the steering joint into the gap between the tubes, if you place your engine mounts carefully. That way you can keep your steering set up, bulhead mods will be reduced to lopping off those small corners, which will save time and $.
The biggest delays you'll find are various suppliers not actualy supplying anywhere like the date they promised. The flywheel guy took about two weeks longer than promised, The bell housing and gear box people were three weeks late and then sent the wrong box and bell housing, so two weeks after that etc.. etc...

Thanks for all the comments guys really appreciate them !!! Even if it is drawing me further and further in.

I'm not so bothered about the timescale being a bit protracted I do have a Jaguar XJ12 that is running okay. I imagine she'll interupt the V8 every now and again with some sort of gripe but thats to be expected.

Peter I'm very interested in you comment regarding the steering. Am i reading it right that if you have the RV8 style exhuast that exits through the inner wing (i assume this is what you mean by guards), and position the engine in *exactly* the right place - then you can get away without modifing the steering at all ? That would be wicked to my mind this sounded like by far the most involved part of the process. Could someone confirm this for me...



Peter may have a point there, when I had block huggers the steering column clearance was very tight.. and I was using the recommended rubber bumper cross-member and column.

Fitting RV8 style headers gives rather more room, but bear in mind that the column has to pass through the O/S engine mounting, and run close to the rear lower manifold bolt, this probably determines the route and position.

Ken Costello used a double-jointed column originally to get around this problem.

M Barnfather

It can be done, though I think that rear manifold bolt may be more the issue than the header tube. I switched to stainless button head capscrews several years ago and I'm seeing them become more common. Before that clearance was so tight that occasionally engine torque would tighten up the steering a bit.

Did that engine have the EFI setup by chance? If the later one you'd want to keep that. Even if not you might want to keep an ear open for one.

The CB makes a wonderful V8 car. You will certainly not regret it.


Jim Blackwood

hi simon,
The steering knuckle clearance is just a guess. My car is a rubber bumper (coverted back to chrome now).
By comparing the rubber bumper to chrome cars it seems very likely that you would get away with this. The chrome steering knuckle is placed further forward than the rubber bumper one, and it looks like it's forward enough to fit into the space between the tubes. You might even be able to fit the rubberbumper knuckle if it gets too tight, not sure of the splines though. A try it and see deal. Anyway since you are going to get RV8 headers any way it's worth giving it a go first and not rushing out to get a whole new steering set up.
The advantages to the though the guards , RV8 set up are;
About 10-13 more BHP
Vastly improved cooling of the engine compartment and radiator (block hugger type usually have over heating problems in summer).
Easier fitting engine removal.
No problems with the starter motor over heating and failing.
It also looks very cool.

There are no problems with splashing from the wheels. I've driven over many muddy roads, not a single splash got in. This is because the wheel arches are a low pressure zone when the car is in motion so any air is moving out, not into the engine compartment.

The rubber bumper knuckle is smaller than the chrome one.

I built my own steering column with two small u-joints (Triumph TR7 provenance) for give some clearance at my in-board exhaust manifold (built by me). The difficult consist to build the steering rack shaft pinion. Flaming River has a modified steering rack. The steering column in the car is a collapsible type.

Simon, I have a photo of an empty engine bay from a converted chrome bumper which I own - if it would be of any use to you let me have your email address and I'll send it down the wires.


That would be most useful i'm sure !!!

Address is as above many thanks

Simon Crozier

I'll send it from my virgin account - broadband - big photo.

A thought,
I would be good if V8 headers were made so that the rearmost pipe goes wide around the steering knuckel. There would be a little bit of cheating, but not enought to significantly effect performance, and the benefits of not altering the steering would make such headers a sort after item.
Oportunity to slay the competition Glenn.

This thread was discussed between 03/12/2005 and 07/12/2005

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