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MG MGB Technical - Best engine option?

I can't seem to come to deal with way engine i'd prefer to put in my GT.
Options is to stick with the stock B-enigne, choose a solid fuel-injection engine as a mazda mx5 or k-series, or the more commonly trailed road choose a Rover v8..?

I've got two OD gearboxes so fitting one of them to a V8 might be an easier build than than k or mx5.

The availability of all the options vary but right now there is a 4,6 v8 listed for sale, thinking that might be a good option and swapping the frontplate and mount carbs as the injection builds to high i presume.

I'm really keen on keeping the stock bonnet and outward appearances as original as possible.

There is a vast variety of info on google and forums but hard to narrow it down, so someone please tell me what to do as I can't be trusted with such important decisions.

/Alex
Alexander Sorby Wigstrom

You can get the Rover efi under a standard bonnet(hood) but it does involve some quite drastic machining of the plenum components. As you know, MG-Rover took the option of a bump in the bonnet for the RV8, and that's what I have on my V8 conversion.

The only thing I would say is that an MGB overdrive gearbox is not really up to the task of transmitting the torque of a V8. On the factory MGB GTV8 the engine was in a very low state of tune producing only 137 bhp from 3500cc, which is ridiculous really, but even then the gearboxes have to be treated with respect if they aren't to fail.
Mike Howlett

Valid point, the appeal with the stock gearbox is that in Sweden it's different rules to register a car with a non stock engine if you stick with the cars original gearbox. Then it's a "light mod" but if you sway engine and box then it's a "larger mod" witch is more expensive and a lager amount of work to register.
Alexander Sorby Wigstrom

Look at costs of an exchange. Then look at what it would cost to do a B with head, cam and supercharger.
Bruce Cunha

Bore Bseries engine 1950. Have the head port polished, skimmed to run 98 octane petrol, Weber carby, 123 Tune distributor and stick with 4 syncro overdrive gearbox, good tyres, alloy minilites, four pot calipers. Then you have a classic that will keep up with today’s traffic.
Mike
Mike Ellsmore

It's a bit like asking what paint colour you should choose :o) You need to decide what your objective is in terms of reliability, originality, performance and ultimately the depth of your pocket.
paulh4

Put a snail on the B series and then when you get sick of paying the speeding fines just take it off and it's back to original
lol
willy
William Revit

I've got two B V8's, a 3.5 and a 3.9. They both use 1 3/4" Su's and are wonderful cars, but the power goes through LT77 boxes with 3.09 dif. These are both necessary, in my opinion, unless you are happy with the original, low tune, small valve P5 engine. Depending on the year of your GT you will also have to carry out body modifications and finding an inlet manifold and plenum for the rear mounted SU's is getting more difficult.
I've also, on a previous GT, bored out a standard B engine plus 0.060", flowed the head and skimmed it to raise CP, fitted a better free flow exhaust, K & N's and balanced it, this produced an engine, still working on standard SU's, which gave 105 bhp and 131 ft/lbs at the flywheel. It had a better mid range, reved freely and the extra torque made it beautifully flexible.
I've also read some pretty good reviews of "O" series installations. Significantly this was a road BL were going down before production folded.
Allan Reeling

Snail? Supercharger? Not heard it called that before but it's a good'un.

paulh4

You mentioned the Mazda engine, and this is what Frontline are putting in their special MGB. Certainly its an excellent engine mated to a brilliant 5 or 6 speed gearbox. You don't need to go all out as Frontline have done with a 2.5 litre 289 bhp engine. Even a bog standard 1800 MX-5 engine will give you 130 bhp, a useful increase on the MGB unit. Later MX-5 engines will give a reliable 150 bhp and will really make an MGB go. The Mazda gear change is one of the best you can find.

The V8 option also makes a satisfactory car. The bucket loads of torque make the V8 MGB very easy to drive and frequent gear changing becomes unnecessary, which is a good thing as the Rover LT77 and R380 gearboxes aren't the nicest boxes to use. Because the engine doesn't care to rev in its ordinary form, you do need a high ratio final drive, as Allan has stated. Mine has a 3.14 Ford differential.
Mike Howlett

Snail=turbo
William Revit

The most simple boost in power and still remaining 95% stock is a Moss supercharger. An afternoons work will put a smile on your face. You can then over time if you feel like it, modify the engine to supercharger spec for even more performance. The SC will give you a lot more Torque or pulling power even on a stock engine. Extra SC spec mods will add HP and top end.
I have not long done a V8 GT Rover 3.9 and T5 BW box.
Goes well with heaps of power and handles good but I also have a B roadster that has been supercharged since 2004. It was stock/SC for 10 years with gradual
small mods then about 4 years ago I built an engine around the SC. There would not be a lot between the two cars in performance, different and both fun but the little SC roadster is more sporty snappy and fun to drive and still 95% MGB. The SC if installed correctly will give many years of trouble free service. My SC B engine is not radical, idles like a watch and when built was 148WHP. I built my GT from a bare shell and I wont say what it cost as my wife might read this. Superchargers are a lot of fun and you can still close the lid. Denis



D M Hill

I fitted a tuned 5-brg engine to my MGA, it is sleeved out to 1950cc, has a stage 1 Newman PH1 cam, tubular manifolds and runs on a Weber 45 DCOE.
It gives 140 bhp with similar torque, pulls incredibly strongly but smoothly from 1000 rpm and yet will rev to 6000 rpm. It is amazing.
Cameron Gilmour in Perth built it for me.

It drives like a stock motor until you floor the pedal and then the big smile appears😊.

I was going down the S/C route but realised that I needed a new engine anyway and so this was the less complicated and more economic route.

Colyn
Colyn Firth

I am eagerly waiting on Chris Betson to deliver a 1950cc engine built to supercharger spec - add supercharger - should be an absolute ripper!
Dominic Clancy

Alexander
What do you use your car for ? The Rover options are thirsty over short distances but no more so than the B series at speed over long distances.

One has to consider fuel consumption and petrol prices if you intend to keep your converted car for a long time.

If you do want to create a car to keep for years,there are advantages from choosing a large lazy engine over a smaller hard-working alternative - the Rover engine can last for ever and because of the large numbers of Landrovers with versions of the Buick design, will be supportable for years to come.

With all these considerations in mind, I drive a fuel injected 3.9 - my son drives a cleaned up 1800. I ran with the GTV8 gearbox until the casing split - now a LT77S. We both have fun - both cars are comfortable on the motorway - with poly suspension bushes both cars go round corners at speeds which allow us to stop within the distance we can see.

Roger
Roger Walker

Having had several V8's and modified fours, I tend to lean towards a good modified 4cyl if you are after fun driving it- Don't get me wrong I like the v8's my last one being a monster bored and stroked 5.4litre job
The problem with a good v8 is that if you go out for a good blast ,it's getting hard to stay out of jail but with a four cyl you can actually have some serious fun without upsetting too many others
A std v8 conversion would probably best suit an everyday use car for cruising etc,
Maybe if you're not a purist, a 2.0 Zetec might be a choice-put a set of sidedraughts on it and an Edis and they're good for 180-190hp like that and you could still run the MG box
It all depends on what YOU want, and what you use your car for
But I 100% agree it has to have a flat bonnet
When I sold one of my v8s the first thing the bloke did was put a scoop on the bonnet-grrrr
willy
William Revit

Roger and Willy make a good point when they question what you want out of your car, as the 4-cylinder and 8-cylinder cars are very different in character. The 4-cylinder car feels more sporty as you have to rev the engine and swap the gears to get the best out of it, whereas the V8 is all about lazy power. The engine doesn't rev very high and gear changing is minimal, so it can be a quite relaxing drive.

As for fuel consumption, I have found with my 3.9 injected car that it uses virtually the same amount of fuel as the standard 1800cc car, around 27 miles per UK gallon, or 9.6 Km/L.

Willy says the car must have a flat bonnet, but I rather like the RV8 bonnet on mine. The bump certainly looks good from behind the wheel (rather like an E-type Jag), and it makes fitting the Efi much easier. I certainly wouldn't fit a scoop!
Mike Howlett

This thread was discussed between 17/03/2018 and 07/04/2018

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