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MG MGB GT V8 Factory Originals Technical - V8s V6s and all sorts of Conversions

Back in the late 1990s and early 2000s, this website was The place to get all your MG information. I post thousands of times in the threads here. I still wander by from time to time to see what has been post but mostly post elsewhere now. I'm very glad to see this site is still around.

How many still wander by this site, specifically the conversion thread and what engine are you running in your MGB?

Myself, 1980 MGB with the fuel injected 3.4L 1995 Camaro V6, the T5 five-speed behind that and four wheel disc brakes amongst other modifications.

BMC Brian McCullough

Hi Brian

The most common conversion down this end of the world would be the Leyland P76 engine and 4spd. box
The engine is a 4.4 litre version of the Rover v8 and comes with a semi close ratio (2.5 1st gear) B/W 4spd single rail gearbox
Your Chevy conversion sounds like a nice package
What, roughly is the output of that engine
William Revit

Hi William,

160 BHP and 200 foot pounds of torque. A bit more than the original factory 3.5L V8. My first gear is 3.76:1 with a 3.42:1 crown and pinion. If the 3.31 that we now offer would have been available at that time, I would have preferred that. 4th is 1:1 and 5th is 0.72. For an engine that has power between idle and 5,000 RPM without trying, the wide spaced gears works very well for a light car with this engine.

There are two guys in Australia that have a 3.4L V6 placing them in MGBs. I have yet to hear about either closing in on completion though.

BMC Brian McCullough

Your 0.72 5th gear would be a nice cruising gear
Some of the guys here use Toyota Supra 5 speeds which I think is about 0.8
Your 3.76 1st. with a 3.42 would be a revvy little thing at takeoff
A mate here runs a 2.78 diff with the B/W box's 2.54 low gear but is a tiddle tall in my opinion
The last car I converted ran the B/W box and a 3.08 final drive - Off the mark it just hooks in and being a fairly tall gear you really get going before needing 2nd
I agree fully that with a bigger engine in these light cars, they seem to like larger gear spacing to get away from that rev change rev change style of driving
Our 4.4 engines here are just a tiddle under 200 hp
They are a fair bit wider than the 3.5 Rover making exhaust manifolds an interesting adventure
A pic of my last car during the conversion process


William Revit

The 4.4L- is that an Australian version of the Rover or a bored and stroked 3.9/4.2?

Photos of a few of our conversions can be found here:

BMC Brian McCullough

G'day Brian
....Bit of a gap in the post
The 4.4 engine was available here in the Leyland P76
Which was built here to compete in the market against the might of Holden (GM) and Ford Falcon
It was a reasonable car but it copped some flak in the press which didn't do a lot for it's success
The engine was also in the Leyland Terrier truck

Basically (loosely speaking) it's similar to a Rover 3.5 but with 3.5" stroke---The block is taller making the engine wider with the heads further apart
Found this---

1973 Leyland P76 V8 data

maximum power output (SAE) 195 PS (192 bhp ) (143 kW ) at 4250 rpm
Specific output (SAE) 43.5 bhp/litre 0.71 bhp/cu in
maximum torque (SAE) 386 Nm (285 ft·lb ) (39.4 kgm ) at 2500 rpm

You can see in that pic I posted earlier how much taller and wider the block is compared to the Rover block--They are quite a torquey engine, specially in a B
William Revit

Gday Willy, doing a 3.9 v8 conversion at the moment, with the BW T5 box. Its also a bare shell rebuild so progress, although keeping it moving is a bit slow.
Huw is your supercharger project going?

Hi Dennis
Yeah------------slowly would cover it
It's all a big compromise really
I'm converting the 2.3 B series engine that I used to run in the midget hillclimber back into a more docile unit for a road/competition car
Removed the cranky cam and pulled the compression back and adding the s/charger, hoping to at least retain the same power output and maybe some extra---hopefully
Have got most of the mechanicals gathered up and about to start the body-----I hate bodywork--
What bellhousing are you using with the T5- I did one once using a P76 housing and the Ford version of the box(short shaft)-Had to spin a bit off the outside of the front bearing cover to suit the hole in the bell- and redrill bolt holes-I think there was some welding somewhere,around the bottom bolt holes--The Commodore box has a longer shaft which would allow room for an adapter in between but I would think the box would be too far back then
All the best for Christmas to you and your family-
William Revit

Back in the 70's, one of our neighbours worked at the Rover factory in Solihull and brought an orange P76 home on a couple of occasions.

It was like nothing we had seen before...or since, as they weren't available in the UK.
Dave O'Neill 2

Willy I am using a bell housing from Dellow in Sydney
They make one specifically for the Falcon/T5/Rover. Had to knock a lot off the rover flywheel to fit a 10" falcon clutch but it came up nice. Best wishers to you and your family. Denis

When they were selling them new here ,one of the adds boasting the size of the boot (trunk) featured a car with a 44 gallon (200lt) drum sitting comfortably in there--not many cars can do that----or want to
I've had a few of them, they're fairly big but were canned here by the press-There was a bit of a run on them catching fire at one stage if I remember corectly- Really though for a biggish family car they're not too bad---starting to be a bit of a collectors car now
I had a Targa Flourio version at one stage--they were dark blue with a largish silver side stripe and alloy wheels. It was a v8 4speed and was quite a quick car once you got used to the size of it and the slight delay in altering it's direction at speed--
I've got a bit of a grin on the face thinking about it
William Revit

Willy I see the MG V8 people, and others, in the states use the connecting rods from the P76 in their BPOR performance engines. I don't know if its a stroking or breathing thing. Denis

Interesting Denis
That would be a bit like a chicken climbing back in it's egg



William Revit

If anyone around here (OZ) is after a rover V8 and auto transmission I have one that's free to a good home.
Its complete with carbs, altinater and all the hangon bits but I imagine a rebuilder. Denis

I have a V8 roadster, built on a heritage shell. It started life with a 3.5 Rover Vitesse engine, running on an Edelbrock 4 barrel. I have recently swapped out the Edelbrock for a pair of HIF 6's and now have smooth power, no flat spots and will return over 30mpg. My factory V8GT has a 3.9 Discovery engine, on it's original manifold and twin HIF6's, that too will return over 30mpg. The 3.9 has more torque and therefore more low down grunt, the 3.5 is probably the "sweeter" engine. The 3.5 gives somewhere around 200bhp, the 3.9 220. Both have Viper Hurricane cams, electronic ignition, LT77 gear boxes, uprated brakes, much modified suspension and 15" wheels. They are a delight to drive with power on tap when needed and incredibly flexibility.
Allan Reeling

Allan did you use the Edelbrock manifold when fitting the SUs? I have an Edelbrock 4B on at the moment, still unrun, and the car is still a few months off. SUs may save bonnet mods and I do prefer them as a carb. When using the SUs in this application do you use one for each plane of the manifold or both into a common inlet. Thanks. Denis

You could knock up a couple of these tonight and have them ready for the morning

William Revit

G/day Willy, I do have a couple of OE manifolds but the Edelbrock is matched to the ports and already on. I think I will keep a look out for a couple of HS8s or similar. I have them on an old Jag I did a few years ago, about the same displacement, and really like SUs. Even HS6 or HIF6 might be big enough with a balance. Will stick the bonnet on today and measure the clearance over the 4B. Denis

I mentioned in a thread somewhere to you about fuel surge in the Edelbrock carby
i must clarify
The carby I had was actually a 500 Competition Carter which I am led to believe is the carb that the Edelbrock is a copy of.
They may well have changed the float setup compared to the Carter and fixed the problem
Thought I better mention it in case I had swayed your thoughts on changing out of a four barrel
There's a pic of it on the 4th posting on this thread
It fitted under an early B alloy bonnet"the flatter one" with a lowline big round aircleaner on it-but I had to rework the cross brace of the bonnet frame- the later steel bonnets have more curl in them-
This was with a taller P76 motor so you should have bucketloads of room with the Rover donk
William Revit


Any chance you could let me know how you went about using SU's.

I'm still in the body restoration phase but thinking ahead I would like to use SU's on a SD1 3.5 motor. I can source the MG style plenum but the manifold to suit doesn't appear to be available.

Any advice would be appreciated.

P B Booth

I'm nowhere near 100% sure but I think the bottom part of the manifold is a Rover 3500 manifold with the top piece milled off to take the adapter manifold

William Revit

Im new to this and planning what i need to buy for the V8 conversion whilst my block and crankshaft are in for machining. My V8 arrived with the SD1 carbs and manifold. Is there any reason these just cant be reused ?
Chris Silk

None at all if you are prepared to cut a big hole in the bonnet for them to poke through ....
Chris at Octarine Services

As already stated the MGB V8 inlet is a modification of the SD1 item. Also the SD1 HIF 6's can be modified to suit the "factory" installation, but you will need to either make, adapt or acquire the inter-carb linkages.
I have a spare V8 inlet manifold which requires a bit of TC but not there plenum.
The air box is a recent addition, I originally had a K & N panel filter but, despite K & N claiming it would flow sufficient air, on the rolling road it was found to be too restrictive.

Allan Reeling

I also have the JWR Offie dual plane inlet, plus the Edelbrock 4 barrel and Low Rider air filter with K & N if anyone is interested in my Mk 1 induction system.
Allan Reeling

Taken a bit over twelve months but now just about finished. Built from bare shell, 3.9 rover with high comp pistons, RV8 exhaust, light flywheel and Edelbrock intake, T5 Ford box and clutch. Only thing I shopped out was the upholstery. Test driven so far
but seems good. Looking forward to reg. Denis

D M Hill

Looking good.
Dave O'Neill 2

i have read speculation that a factory BW35 with a V8 bellhousing fitted will not fit in the engine bay with a rover V8.

now i am unsure if that comment was intended to mean "with the usual chrome bumper engine bay modifications for V8 installation" or not.

anyone with an opinion from your collective experience? I have an auto GT and the thought of a V8 conversion has been on my mind for some time. And someone is selling an SD1 V8 with all the auto bits just a few miles away from me. can't help thinking about an investment for the future as they are becoming scarce.

Graham Moore

correction, not SD1, P5B
Graham Moore

denis. great news. but how are you going to decide which of your MGBeasts you are going to drive each day?
Graham Moore

Easy Graham the supercharged roadster is for nice sunny days and the GTv8 for the rest. At least that's my thinking at the moment, though the v8 will get a bit of a flogging for a while. They are very different to drive. The GT smooth flowing power and I love the T5 gearbox. The SC roadster is more aggressive and fun type power. Not a lot in it between them but my SC car is pretty well developed. My V8 engine came with an auto but Its pretty old tech. If I was going auto it would be no less then a lockup 4 speed. Dellow here in OZ do a bellhousing for the GM and the Nissan 4 speed to Rover. I used their T5/ Rover bellhousing.

D M Hill

Hi Denis
Looks great
I know it's only a little part, but I really like the look of the single bonnet strap
Enjoy the drive----------
Envy green eh

I'm fairly sure it could be made fit, although the Rover bellhousing is quite bulbous it would bemeeting the trans tunnel in an easily 'expandable' area,- as far as the trans itself goes there is plenty of room-
William Revit


I too still wander in here occasionally; an MGB was my first sportscar, so I'll always have an interest in them, even though I walked away from the last three I had ('68 rdstr, '70 GT w/Buick 3.8 V6 & a '74-1/2 GT w/rbr bmprs) as a result of a divorce eighteen yrs ago! At the time I didn't feel too bad for losing the cars, as I did keep my '57 Austin-Healey 2-seater; as of this past April, I've owned the Healey forty (>40) years!

Besides the Healey, I've kind of gone over to the dark side, but still in keeping with the same Rdstr/Gt format; they're just branded with a three (3) letter acronym name instead of two (2)! Nowadays the Healey shares garage space with a '99 M Rdstr (bought 11/00 w/5400 miles) an '01 M Rdstr (purchased new and picked up at The Factory in South Carolina, where ALL Z3/1st gen Z4s were built) and a few years ago, I added a '99 M Coupe to round out the selection.

The M Coupe used to be a customer's car, and in 2006 I fitted a positive-displacement supercharger to it, nearly doubling its horsepower (originally 240, to about 450 bhp). These cars are considerably heavier than the MGBs, at around 3200 pounds, but they're still quite fast.

In any case, I still keep an eye on sites like BAT, looking for just the right BGT to pick up where I left off. After doing the 1st V6 swap (and I then had SEVERAL BOP engines & a TR8 5-sp to work with) I far and away prefer the V6__it's 5-1/4" shorter on the outside and 16 c.i. bigger on the inside, plus has a whole raft of speed equipment available for it (think GN-X & turbos, etc.). Here's an ancient link to my old car (can't believe it's still being hosted, but...):

And here's essentially what my attached garage looks like these days (the 2 M Coupes stacked in the right bay were customer cars)!

Randy Forbes

This thread was discussed between 01/06/2016 and 05/10/2018

MG MGB GT V8 Factory Originals Technical index

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