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MG MGB Technical - MGB v8s

Chaps

Driven over from the midget forum seeking a little advice, and apologies if I have parked incorrectly...

Seeking a little advice on MGBs - GT or convertibles - which have been fitted with a V8 - but not the factory originals.

There is an excellent article by Roger Parker - which I have digested - but I am looking for a ready made car.

I am an engineer, so I can have a good poke around armed with some degree of knowledge, and of course, I guess most aspects relating to standard MGB buying guide apply.

However, I am keen to understand any particular tips as regards buying one, and what experience others may have of driving one.
Mark Ogden

Mark
As far as driving the BV8 goes, it is the car that MG should have built from the off. With the appropriate air dam and nyloc suspension bushes, the car is steady on the road at 100mph with a lot to spare. The original 137BHP engine on SUs is thirsty and doesnt cut the ice with modern traffic - the 3.9 with 14CUX injection and a cut down plenum is a good compromise - there are a number of bigger beasts around but keep an eye on crankshaft length - The B has limited space. The OE gearbox has a tendency to split with increased torque and the Gentrag 5speed with a RV8/TR8 bellhousing is stronger - you need a different propshaft and a V8 crownwheel and pinion - all straightforward. Positioning the HP fuel pump for fuel injection is interesting - one needs to remember it is a pumper and not a sucker - the RV8 solution works but the pumps wear out regularly (and costs !). There are a number of independent rearwheel drive solutions for those who go round blind bends at stupid speeds but the nyloc bushes will help with normal cornering. The V8 brakes are adequate for road use.
Roger P gave me a hand with my conversion when he was still a policeman. I think you can still raise him through the MGOC. It is very useful to be able to call on someone who knows the ropes!

Finally there will be as many views on conversion as people who offer advice. You will need to plough your own furrow!
Good luck

Roger Walker

You are looking for a ready made car. There are many ways it can be built. In my experience, the majority of conversions will have either a 3.5 or 3.9 litre motor and will use a 4- barrel carb, either Holley or Weber/Edelbrock. They will probably use RV8 exhausts, a Rover 5 speed gearbox (either LT77 or R380) and should have a high ratio differential. This last is important as the V8 is not a revving engine, but has armfuls of torque. The ideal is the 3.07 that MG used, but a 3.3 from an MGC is better than nothing.

What else do you want to know?
Mike Howlett

The MGC 3.3 is the best solution IMHO - it gears the car for a realistic 137mph at peak power whereas the factory 3.07 gears it for around 170mph!

My V8 has a 3.5 bored out to 3.6 with the high compression pistons, twin SUs on the original MG manifold and block hugger exhausts coupled to a LT77 box.

As for buying one then pay attention to the quality of the body mods in the tunnel area, the presence of the V8 thicker front discs and clearance of the exhaust manifolds to the steering column.
Chris at Octarine Services

Mike

I guess a bit of a buyer's guide particular to a ready made V8.. Chris has offered a few tips for which I am grateful.

Mark Ogden

Mark
Having had the odd V8 B I would suggest the later the body shell the better
Rubber bumper models with the radiator mounted further forward and were ready to go as V8's where the earlier cars needed modifications
One very worthwhile mod to do that won't have been done is to re-enforce the shell if it's a roadster
I fit a 75mmX50mm box section along the top of the inner sill section from down at the toeboard right through to the rear wheeltub, and then brace off it up to the upper part of the firewall and up the rear inner guard -- The difference this makes to the feel and handling of the car is unbelievable- I did it to one just to find out what it would do and was blown away with the resulting rigidity of the car--Well worth the effort
On diffs
I've tried every diff ratio known to man, and my personal preference is a 3.08 and a four speed direct top non overdrive box for a good all round setup
But if you go overdrive around 3.2-3.3 as Chris suggests and for the reasons he suggests
Don't go 3.5:1 or lower, it just wrecks it all, you spend all your time changing gears and going nowhere

willy
William Revit

Mark, I got cut short in my message of last night so I'll add what I had intended to say. It would be worth getting a copy of Roger Williams' book "How to give your MGB V8 Power". He gives a comprehensive guide to what needs to be done to make a good conversion.

I'm sure Willy's mod to the chassis of the roadster makes sense, but you are not likely to find such a car in your search. As he says, the rubber bumper cars were already altered to accept the V8, whereas modifying a pre-1974 car involves quite a lot of work. That's what I did to my 1969 GT. I had to raise the height of the tunnel to fit the R380 gearbox, chop open the bulkhead corners and reweld them at a backwards angle to clear the rocker covers, cut out the radiator diaphragm and move it right forward, cutting back the lower duct at the same time, alter the gearbox cross member, and change the engine mounts. I also lowered slightly the cone where the steering column exits the bulkhead so the UJ wouldn't foul the exhaust manifold. This necessitated fitting a second UJ at the rack end of the lower shaft, but it all works well.

Since others have given their preference, I will tell you about my car. I used a 1991 3.9 Range Rover engine with the hot-wire fuel injection. In my opinion this is the best option as it is simple to fit, needs no special tuning and works every time I turn the key, whether the engine is boiling hot or freezing. I used an RV8 bonnet to clear the plenum, but it is possible with heroic machining to get it under the standard bonnet. My second choice would be SUs on the factory style manifold. I don't like 4-barrel carbs - unnecessarily complicated and prone to hot starting problems. Others will tell you different, I'm sure.

My exhausts are RV8 style through the wings, the complete system from Clive Wheatley. This takes a lot of heat from the engine bay, and you need to get rid of heat as the engine makes plenty. The V8 radiator is deeper than the usual one but is still only just adequate.

The Rover gearboxes are strong units but not desperately sporting in nature. Gear changes are not especially slick, especially not from 1st to 2nd, and the lower ratios are a bit too low, leaving a gap between 2nd and 3rd. Fortunately, because of the torque, gear changing is not something you need to do lots of. I often pull away from rest in second, which you can easily do, and so avoid the clunky change from 1st. The earlier LT77 box has reverse up beside 1st gear, whereas the later R380 is a more conventional pattern with reverse below 5th gear.

I'm interested to see folk advocating the 3.3 diff. I have Hoyle independent suspension front and rear, and this uses a Ford diff with a ratio of 3.14. To me this is still too low and I would love to try a 3.0 if such a thing was available. The theoretical maximum speed of the car is of no consequence as you are never going to get anywhere near it, but the ability to bowl along at 70 mph with the engine lightly stressed at lowish revs is worth lots. Using 15" wheels is a good thing as there are better tyre choices.

As for brakes, the car doesn't weigh much more with an alloy V8 than it did with the iron 1800, so in theory the ordinary brakes ought to be good enough. But I suppose you might be stopping from higher speeds so an upgrade of some sort is a good idea. Standard V8 discs are perfectly OK. I have 4-pot calipers and ventilated discs on the front, also from Hoyle, and the IRS uses Ford rear discs, but really this system is overkill.

So to sum up, look carefully at all body mods that have been done, including crawling under to see the gearbox mounting. Have a look at any compromises that have been made. On my car the front ant-roll bar wanted to occupy the same position as the front engine pulley. I tried moving the anti-roll bar forward, but that wasn't very satisfactory, so I now have an RV8 ARB which dips in the middle to clear the pulley. Problem solved. The oil filter can't stay in it's original position down at the front of the engine and most use the remote filter on the driver's side wing. Make sure this has been done well without pipework rubbing anywhere.

Lastly, when trying a conversion don't be mesmerised by the sheer power under your foot, listen carefully for creaks and knocks which might indicate that something isn't well fitted.
Mike Howlett

My V8 roadster has a SD1 Vitesse engine, originally flap valve fuel injection, converted to hotwire ,hotwire is much more fuel efficient, twice the power of the old B engine with better fuel consumption.

I have a cut down Sd1 axle, i tried the auto-transmission diff, which I think is 2.84, but went back to the Vitesse one, 3.08, as it would not pull below 35 on the flat in top.
Mike Barnfather

Mark,
I have two B V8's, one an early factory GT and the other is a roadster I built 12 years ago on a Heritage shell. The roadster has a 3.5 Viesse engine, LT77 gearbox and 3.07 dif, The GT now has a 3.9 Discovery engine. If you want to talk I'd be more than happy to. 07773909141
Allan
Allan Reeling

Hi Mike Barnfather - haven't heard from you in years. You must have rebuilt your car after the disastrous fire in your garage. I used your knowledge a lot when I built my GT, your ideas and Geoff King's too. Hope you are well.
Mike Howlett

Hi Mike,

Yes ...still around ! Nice to hear from you.

I presume Geoff retired to France ? He was a big help when I did the conversion.b

Car now restored ( for the third time ).....took about 3 years before I could face it....

Just about finished...putting in EPAS from a Corsa...then off for MOT...40 years old in July, so exempt from car tax from next April.

No pics on this PC, but will post a couple tomorrow from my archives.
Mike Barnfather

Mike, I still have photos of your car from when I was building mine between 2003 and 2009. I have the EPAS from the Dutch EZ company and wouldn't like to be without it now. Email me your pics on mikehpersonalATgmailDOTcom. I have kept in touch with Geoff and Claudine and Catherine and I have been to visit them in the hills west of Lyon three times now, once in the MGB GTV8.
Mike Howlett

Sorry Mark,

Didn't mean to hi-jack your post.

MikeH and I differ on the route we took, I basically stripped an SD1 Vitesse, and took :-

4 pot front calipers ( combined with Peugeot 405 gti vented disks they give good stopping power)

5 speed box (some mods needed to transmission tunel, but the grear lever comes out in approximately the same place )

engine (3.5 but high compression, bigger valves than 3.9)

Propshaft ( shortened by Hardy Spicer and fitted with grease nipples )

Rear axle and brakes ( shortened and fitted with uprated half shafts)

Suspension is pretty standard , uprated MGB, 600lb front springs,30% uprated lever arms 3/4" roll bar, at the rear uprated lower springs and Spax shocks.

Everyone seems to have their own idea of the perfect V8 conversion, so they all turn out individual, jury's out on the Bermuda hardtop, but it is off most of the time ! .


Mike Barnfather

Mark
As you can see-no two V8 conversions are going to be the same and as mentioned by Mike everyone has their own idea of what makes a good conversion
As an engineer you will be able to pick out a dodgey conversion I'm sure-- If it basically looks like a quality conversion and drives ok you can always change a few things like exhaust, induction, oil pump adapter etc
As long as the basic conversion is a quality job you can adjust accessories to suit your tastes
OR- get a factory car and do the originality thing

willy
William Revit

"OR- get a factory car and do the originality thing"

Easier said than done. The ones that do come onto the market aren't that original anymore, and the prices have gone crazy!
Dave O'Neill 2

You see what I meant ! If you want some fun for a couple of years find a car that works and enjoy yourself. If you want a keepers' car find one that is basically MG or Landrover/Buick throughout - you will always be able to source the bits you will need.
Roger Walker

what i would like to know is about mpg. is a 3.9 EFI more frugal than a 3.5 carb due to it's on-tap power and precision?

i just feel that a 3.9 engine is HUGE and i would not want to be thinking of the cost every time i drive it. sounds more like a USA big block.

i realise that it depends on how you drive it but personally i would not want to be less than high 20's on a run. is that achievable with a V8?

i have installed a supercharger out of a BMW Mini unit. Still tuning it. It's easy to get loads of oomph out of it if you don't care about mpg (20) but i am profiling needles to try and get a good balance. i am at 26 now (that's overall spirited driving) and tink i can get a couple more - which would put me back to where i was with the stock engine.

Thing is, when you get a taste for power, you want more.

one thing i would recommend for any major engine mods is an AFR sensor. I know there are a lot of folks who have installed the Moss supercharger (& i expect a V8) and are throwing fuel down the pipe. Many folks find with the Moss charger kit stock needle that whilst it gives a great fun drive, when on the RR, or when they install a sensor - cruise AFRs are down in the 12/13 region.

it's the best £100 i spent (& of course the vernier gears and ARP bolts from Octarine) it's a good diagnostic tool too.

G


Graham Moore

Graham, the MGB with a Rover 3.9 is not a fire breathing monster. Mine with hot-wire injection produces near to 200 bhp yet is docile and easy to drive. Ok if you have a heavy right foot it goes like stink, but that's not what is enjoyable. It's the amazing flexibility of the engine, the lack of the need to change gear often, and the tireless cruising at motorway speeds.

As for fuel consumption, I get about 27-28 mpg overall, including quite a few short journeys. I rarely got better than that with my 1800 MGB, and the V8 is SO much nicer. Also, because it was a Range Rover engine, designed to be used the world over, it isn't the least bit fussy about fuel, and will run smoothly on the cheapest stuff.

There's no substitute for cubes!
Mike Howlett

My V8 roadster, heritage build, started life with a 3.5 Vitesse engine, running on an Edelbrock. On runs it would do 32mpg. I have recently swapped out the Edelbrock for a pair of HIF 6's and now have smooth power, no flat spots and still returning over 30mpg. My V8GT is a 3.9, on twin HIF6's, that too will return over 30mpg. As Mike said they are a delight to drive with power on tap when needed. The 3.9 has more low down grunt, the 3.5 is probably the "sweeter" engine.
Allan Reeling

My 3.5 Vitesse with hotwire injection will give me over 30 mpg on a run, my brother in law lives 320 mile further south than me, and I can do it (just) on a tank of fuel.

Injected engines should significantly more mpg than carbs, my engine is mildly tuned 45mm short trumpets and 65mm throttle from V8 Developments, RV8 manifolds, it pulled 152 wheel Hp and 199lb/ft torque, so bags of power.
Mike Barnfather

if you drive in town and spend time in queues or at lights, the injection is relatively frugal. The 3.5 twin SUs gave me 23 overall with lots of London driving and 27 on a long run. The 3.9 gives me 25 mpg overall and 29 on a run. Not very different from our 1800 roadster.
Roger Walker

Hi
Just had a look around the cars for sale here

What price do you have to pay for a V8 converted B over there

The best two I could find here were $28-29000
Both really good cars, one black 3.5inj -4wheel discs et
The other red 4.4stroker 4wheel discs etc

The only factory v8 I could see was a full resto car at $70000

Man, the prices of these cars have spiraled up in the last 12mnths since I looked before

So what's the going price in the UK

willy
William Revit

There was a rubber bumper model at the Stoneleigh MG show, which wasn't original, wasn't that good and the seller was looking for £20000+
Dave O'Neill 2

Willy, have a look at the ads on here http://www.v8register.net/subpages/MGV8forsalerevised.htm

And a price guide for factory cars here http://www.v8register.net/v8/profileprices.htm
Mike Howlett

Thanks Mike
William Revit

Might get you doing another Willy. Have the engine and T5 box in my GT, front and rear ends. Got it into undercoat and stopped up yesterday. Still a way to go as this was a bare shell and no parts or glass. Gets expensive and time consuming chasing all the trims, door parts, instruments etc, although I am really enjoying it as I thought I had done my last rebuild.

Denis
Denis4

Hello Denis
I'll nick Mark's thread here for a bit- he won't mind
Sounds like you're getting on with it then
I'm just blown away by the prices they are asking for the v8 cars now- I didn't realise they had exploded like that- I've been a bit quiet the last couple of years for a few reasons and it looks like I've slid into the dark a bit there
That spare engine of yours had my thoughts wandering for a bit but I'm trying to be strong
Building from a bare shell is a major project, looking for all them little bits
You almost need a donor car for parts
What rear end did you use
A mate just bought an A coupe basket case in boxes, mate, it put a shudder through me the amount of work that's going to be involved in that
Later on if you really got stuck (last resort) for some hard to find little bits let me know and I'll have a looksee
Also-have you got an alloy sump on your s/charged car
If so, what do you think of it-baffles etc and what brand is it
Cheers
willy
William Revit

Hi Willy. Standard sump on the SC car. The V8 to start with will be the stock MK2 but the falcon T5 box has a .72 5th gear for 2.8:1 over all. Do for now, if its OK I will add a limited slip if not something else,?? ford 8", centura. I have chased up most of the "unobtainable" bits, and the more common stuff will be as needed. Door locks gave me a fright like several hundreds of dollars and left ones even more but EBAY came to the rescue. Be lost without ebay. Tossing up wether to do the final paint as its been a long time, so I thought I might practice on the guards doors etc while there off. If I dont stuff them up there's only the roof and back guards to go. Denis
Denis4

Sounds good
2.8 will be fine, she'll cruise nicely at that
The last car I did ,a 4.4ltr had a 1:1 top gear 4speed and a 3.08 and it was fine on 225/60/14 wheels- didn't feel undergeared at all , My next move was going to be a 3.23 for a try , had tried a 2.77 but it took too much grunt out of it compared to the 3.08-------I like grunt
We can't drive around at 100mph all day like we used to so as long as it will cruse nicely at 110ks-she's good
Your 2.8 will do that easily
IF you happen to go B/Warner as in Ford-Centura etc, I've found the easiest- best one to do is a Nissan Pintara/early Skyline The Skyline one has disc brakes already The bolt pattern for the wheels is the same as MG- All the ratios from the Falcons Commodores Chryslers etc will fit from 4.1 through to 2.77 and LSD centres
With a bit of carefull measuring and a little slice off the end of the short axle you can use the short axle as the long one on the other side and then you only need to have the old long axle shortened right up for the short side - it all works out nicely
Be aware though, there are two different axle splines and two different crownwheel carrier offsets to watch out for-The Skyline runs the larger axles already
And a Watts linkage cap off a Falcon will fit as well
willy
William Revit

This thread was discussed between 25/02/2017 and 04/03/2017

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