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MG MGB GT V8 Factory Originals Technical - V8 Conversion brought forward...

I did a trackday at Donington on Saturday which was great fun as it was open pit lane all day and the wet weather made it interesting!

However, on the way my trusty old 1.8 starting smoking heavily on the A50 on the way back
This is how much it smokes from cold....

The temp and oil pressure remained normal when it happened, although the oil pressure was slightly lower when i started it in the morning about 45-50lbs compared to the usual 65-70lbs.

I've ruled out that its not the head gasket as the oil is not contaminated with water, i'm also getting smoke out of the dip stick hole and from the oil cap.

So i think a piston ring has gone although i will find out more when i do a compression test.

But i've now decided that i need to concentrate on getting the v8 conversion done, as it seems the ideal time?!

So this is why i've posted in here :)

So far i have got,

1984 Rover SD1 V8 engine (minus starter motor & alternator)
Block hugger tubular manifolds and exhaust system.
Starter motor in the post - won it off ebay
SD1 LT77 5 speed gearbox

Other bits i need,

I think i need a shorter water pump from a p6 or something similar can anyone clarify this?
8 cylinder tacho - what car can i get one off thats a straight swap? or can i get mine altered?
Remote oil filter base
Larger radiator & twin fans

For the time being i'm going to connect it up to the standard axle to get it up and running until i can afford to get the ratio changed.

Is there any important bits i have missed?

As i'm aiming to buy all the bits i need over the next 2 months ready to do the conversion early next year.

It's a Rubber bumber '78 MGB GT.

Thanks in advance for any advice.

Gavin J


Motormount brackets, new v8 motormounts, altenator cradle from P6 or mgb gt v8, uprated brake calipers, thicker brake rotors, engine stay bar, induction system?, heater valve connector,

I will check my conversion records and get back to you.


I have shortened the P6 water pump shaft by 1" for give some clearance with the radiator, the flange is mini (true mini) provenance pressed on the shaft, I built my own pulley, I built my own ally radiator with core bought to Pace product, two japanese fan, the engine is SD1 "slightly" tuned, LT77 gearbox with close ratio gears bought second hands in Holland, Quaife ATB differential, 3.7 (no 3.07) ratio I use the car for track day, AP racing disc brake all round, pédal box with balance bar, Hopkinson suspension with Bilstein, antitramp, Panhard rod, it's a good car.

Sorry to hear about your GT, Gavin, but maybe this is her way of saying "I need something bigger under the hood!"

Looks like your well under way with the parts you have for a conversion.

My '77 Sebring roadster has been on the road since last January and working great. Most of my parts are from Clive Wheatley through a supplier in Ontario.

Check out Clive's web-site for pictures of the parts.

My car: '80 SD1 3.5 + 5-speed; Edelbrock Performer intake + Edelbrock/Weber 500 cfm carb; stock MGB running gear with lowered springs; CB conversion; Sebring fender kit; cross-drilled/vented rotors with EBC pads; stock MGB rear brakes; 3.07 gears; custom driveshaft (u-joints are common so a shop can make one for you. Cost about $600 CDN); custom rad with two original MGB electric fans (works great at keeping the engine cool); MG RV8 headers; SS single-exhaust; original tach converted to 8-cylinder; all original '72-74 instruments.

Is the starter you've bought an original Rover unit or a high-torque, gear-reduction one? I managed to find a Rover starter with the solenoid mounted on the bottom to fit my car. One day I may change to the modern unit.

I've got lots of pictures if you'd like to see anything.

This is a great project. Enjoy!

Simon Austin

Try these as suppliers, different people whill have different opinions but their parts lists will give you an idea of what you might need.

I'm in the sma espot as you, perhaps a few months ahead- sort your engine first: - carbs and manifolds

You will need to sort out the carbs and manifold - the SD1 SU set up is way too tall. After considering all the options I bit the bullet and got an offenhauser manifold and webber carb new.

You are going down the right route with ebay, it is cheaper but as ever watch out!

At the moment on ebay there is :

MGB = HOW TO GIVE YOUR MGB V8 POWER mg NEW BOOK = MGB Item number: 4594842570
-you will need this, just buy it.

V8 Short bottom pulley. P6, P5B. Item number: 4595543051 (watch out there were different types). This will go for 40+ quid. Your old SD1 one will do - take all the pulley wheels off-I had a groove machined into mine for 40 quid. The instructions for it are in the above book.

WEBER CARB AND MANIFOLD ROVER V8 Item number: 4595348322 - this will go for nearer 300+, you may choose to just buy new from RPI above. Second hand carbs and EFI systems are always problematic, and with EFI systems you need all the wiring and still may have to machine it to fit. The purist would go for an orginial MGB V8 manifold and carb, but these are pricey even second hand.

Water pump -I would buy a new one, about 60 quid on ebay.

Oil pump base (different to the remote filter base -buy off ebay 40-50 quid, 100+ from non ebay suppliers.

Some of the more specialist suff you may need to buy direct from suppliers, both of those above do the gearbox/speedo conversion stuff.

You dont mention if your exhaust is from the SD1 - I doubt it would fit if so-mine didn't, even so it would not mate up to a new system - you may need to buy new or fight with me on ebay when a stainless steel one turns up on ebay!

Wait long enough and it all appears on ebay.

It's great really, I have been secretly buying stuff off my own secret special christmas list!!

Just wish I could find a straight MG!

Cheers for all the replies guys,

I've been looking at the Clive Wheatley site and the prices seem reasonable and theres the added bonus that they are located about 30 minutes from me so i can save some postage costs.

Liam, the exhaust system and manifolds are off an mgb V8 conversion so i've been assured they will fit.

I also seem to have caught the ebay 'bug' at the moment, as the first thing i do when i get in from work is type in 'mgb v8' on ebay!

I've just started a spreadsheet in Excel and priced up alot of the bits i need and its not looking too expensive so far, i think the two biggest(most expensive!) purchases to come is getting the rear axle ratio changed and buying a carb set up.

Thanks for all the links and advice so far i appreciate it.
Gavin Jewkes


You can put off the rear axle ratio change. I have run the stadard 3.9 ratio behind my EFI 3.5 SD1 5-speed for a few years without problem. May change in the future but in no rush.

BTW, never tally up the costs......
Edd Weninger

I disagree really need a 3.07 MG ,or 3.08 or 2.9 diff from an SD1, otherwise you will never be able to use 1st gear, drink petrol faster than you can fill the tank , and twist the half shafts like licquorice.

The 2.9's a little high with 15" wheels ( under 1000rpm @30mph in 5th), but great for most things in life, it's a compromise.

I did track day with mine earlier this year at's great fun, isn't it ?

M Barnfather

Built my SD1 engined car with LT77 about two years ago, and bought most of the conversion parts from Dave Vale at V8 Conversions at Farnborough, Kent.
Dave has all the bits you will need including engine mounts, steady bar (essential), gear box mountings to weld on to the crossmember, uprated oil pump base and remote filter bracket. He also has the P6 mounting bracket for the alternator and of course the alternator itself. He is very helpful and knowledgeable having been part of the original Costello set up. I don't think it was mentioned but you will need to have fabricated an extension to raise the height of the gearbox tunnel to clear the LT77 gearbox. If your car has the forward radiator position the engine and box will fit straight in but you will need the V8 rad.

Daves phone 01689 858716 and Liam has provided the web link in his post above. I also found MGB Hive a good source of reasonably priced parts, they will supply a V8 tacho on exchange for approx £80.00

As you are starting from square one you might like to consider fuel injection, a complete flapper system went a few days ago for £70.00 and there is currently a hotwire system available with a starting price of £150.00 or buy it now for £300.00 some where in the middle would be nice, there is plenty of info in the archives about how to set it up and considering that the carb, manifold filter and ancillaries is about £500.00 EFI is worth thinking about better MPG as well.

You will get all the help and advice you need of this board, and the end result is great plus you get that free permanent grin.

Good luck

Kevin Jackson.

Kevin Jackson

I'm with Kevin on this one, I had (Vitesse)flap valve for about 3 years and changed to hot wire a couple of years ago, for improved fuel consumption, and because parts are cheaper, the downside of EFi is the height problem ( not easily overcome without a lot of ingenious machining)....but I love the RV8 bonnet, and it's a direct replacement for the MGB one.

M Barnfather

Yes, 1st is a bit short but the rest are useable and the diff is strong enough. I have a new 3.07 gearset but never installed it. For my needs a 3.3 diff would work best, but I'd have to convert the whole axle. Will do so when the $$ and time line up correctly.
Edd Weninger

The tacho can be easily altered by buying and applying a two dollar 20Kohm resistor. Check the archives, Zac's tacho conversion.

I'm using the standard 3.9 diff with my 3.9 motor and loving it. The later MG back axle (post'75) was orrigionaly designed for a small truck/van and is very strong.
I can accellerate strongly from stand still in second gear to well over the speed limit which gives me an edge. A low first gear is necessary for parking and peakhour traffic. I've read some people actually complaining that after they put in a 3:1 diff their economy actually got worse, engine working harder. Mind you, who changes their MG to a V8 with economy as the primary motiveation? I would suggest it will cost you nothing to try the 3.9 and see. You can always change the diff' later.
If economy is a factor, you've got to go efi.
Actually EFI is quite easy to set up. Lots easier than carbies I imagine. Heres all you need to know in excessive detail.

You can put a stock 3.9 hot wire system onto a 3.5 engine without any difficulties. This things pretty flexible.
You don't need a swirl pot, you don't need Oxygen sensors, you don't need a speed sensor.
Wiring it in is simple enough. You need to provide 12V for the computer (thick orange brown wire on mine) and a wire from the ignition (green white). It seemed sensible to put fuses on these. Note wire colour codes do vary from year to year, check your Haines manual.
You may (or may not) decide to run the fuel pump through the computer.
If you want to ovoid the programmed speed limiter (which operates by switching off the fuel pump over 120mph) then either; don't connect the Speedo to the computer (I haven't) or simply don't wire your pump through the computer, use the MG loom.
I also am not using oxygen sensors (lambda sensors) in the exhaust. As far as I can tell these are there primarily for antipollution reasons and keeping CO emission within the capacity of the catalytic converter. The engine works very well without them. You might conceivably get better fuel economy with them, I have my doubts, and antipollution is not about good economy. Instead you need to change the tune resistor to a 470 Ohm "green" resistor. Any thing in the range 446 to 494 will do. This resistor is an "external to the computer" plug in and can be found in the loom near the computer/relays. On mine it is a blue plastic plug and a small resistor in clear shrink wrap plastic in a loop of wire about 10cm long. I got a replacement from an electrical shop for about a $1 and soldered it to the plug.

The Manual Gear box resistor is 510ohms. You may already have one. If not, buy one for a dollar and solder it between the wire from pin 34 and ground. Pin 34 might have a thin orange brown wire (check your Haines Manual). You need this because it tells the computer that this is not a auto box in gear and will let you start the motor. A good antitheft device by the way.
Fuel supply can be set up easily-
You don't need a swirl pot in yout tank. You use two in-line pumps.
A very late model fuel gauge sender (pt # ADU 3218) , which has a fuel uptake line incorporated into it, which,(via fuel line) connects to a large cheap filter (Kmart $18) , which connects to a feeder roller vane pump, which connects to a high pressure rollervane pump. Via the fuel line, this connects to the fuel rail on the motor and thence back to the old pick up point on the tank via a second fuel line. The large filter acts as a very effective, external, swirlpot/antisurge tank, as well as being a filter.
The feeder pump is a small high volume rollervane pump able to keep up with the larger high pressure Bosh pump but more able to draw petrol, The Bosh high pressure fuel pump can deliver high pressure but draws petrol very poorly. The feeder pump can pull through , and fill, a filter up to about half a meter above the tank without cavitating and becoming noisy (I've tried this). However I would not place it much higher than the top of the tank (ie the boot) as I expect much higher fuel vapor pressure regulations in the future (translation-noisy pump). Do not be tempted to plumb the return line from the engine back into the high pressure pickup via a Tee piece. Small vapor bubbles form in the warm petrol and make the pump cavitate and become very noisy. The return line must go to the fuel tank, which has its own pressure release set up.
All fuel injection pumps can be destroyed by the tiniest bit of debris. An additional benefit of this approach over the in tank swirl pot is that the pump is better protected from debris; but should it fail, is much more easily got at. I actually carry a spare pump in the boot.
The feeder pump is made by Pierburg in Germany and is called an Auto-suction vane cell pump. Stock no. 12001. It can deliver 0.5 bar when used as a primary pump. It cost $95 Australian (apply exchange rate to get an idea what it might cost locally) The main high pressure pump is a Bosh one pt no 0580464070 and cost $140. You should be able to set this up in a couple of hours with some hose clamps, rubber fuel line and some 'bundy' tubing. Bundy tubing is metal fuel line tubing for your "under the car" fuel lines. Can be got from any hydraulic fittings shop (Yellow pages). Its cheaper than rubber fuel line.
Machining the plenum-you don't have to actually do anything here except provide the measurements to the machine shop.
This will cost about $100 dollars. Just take the trumpet tray to a machine shop and get them to weld up the vacuum take offs; grind off the bumps/left over bits of the take offs and generally tidy up. Then machine 15 or 16mm off the bottom of the tray and up to 10mm off the top. You might also need to have 5mm machined off the top cover as well depending on how much clearance you need.
How much clearance do you need? Set the plenum up on the car; take out the trumpet tray from the middle. Substitute a stack of paper or wood between the intake manifold and the top cover in order that you might see how thick the stack can get while you are able to get the hood/bonnet shut.
You'll also need to cut down the trumpets, depending on how much you have machined off on the top of the tray and the top cover. For the 4 middle trumpets its easy enough, ie 10mm plus 5 off the cover. Before having any work done to the trumpet tray do measure the height difference between the 4 centre trumpets, and the two at the front and back. write this down somewhere. These trumpets start off the same length, but sit on different height shoulders within the tray. After you get the tray back then cut these trumpets to maintain this height difference. The two front trumpets, and two rear-most, need to be shortened more than the 4 middle ones because when you machine 15mm off the bottom of the tray you remove the shoulder these sit on. This height difference exists in order to make the manifold air passages the same length. They didnt bother with this on some 3.5 motors.
You can get the trumpets out of the tray by heating in an oven. Different coefficients of heat expansion. Silicon them back in afterwards. I used Ultra grey which is fuel resistant and sets up firmly.
Note-You need to turn the fuel gauge sensor float around to prevent it fouling on the old pick up line. Just unclip it and clip it in the other way around. An additional bonus I've discovered recently is that if you cut the trumpets 10mm shorter than you strictly need to; you get better air flow into the engine and noticeably more power.

You can put the vacuum take off for the brake servo on the top cover. I replaced one of the three bolts on the stepper valve (back of top cover) with a hose fitting.


I use Elliot tachometer and Smiths "electronic" speedometer with the LT77 OE sensor (transducer)
I use Holley 390cfm with Holley fuel press regulator Holley fuel pump (blue), the fuel filter is Bosch.

Visit Leon Zak's website:

<<<The only part you need is a 100K 10 turn pot. I had one in my junk box, but they're available from Radio Shack, I wouldn't think that they are over a couple bucks.

The pot gets soldered on pin 4 and pin 7 of the only chip in the tach. There's a mark (usually an indentation in the chip case) on the corner of the chip that is pin 1. If you hold that so it's in the upper left corner, the pins are numbered 1-8 counter clockwise.>>>

Then adjust your variable resistor so the tach reads half what it was. at a variety of rev's. I did this by leaving a wire loose during the adjusting process so I could switch in and out the new "circuit".

Thanks for all the input guys..

I have decided not to with injection and go for a carb set up as i feel there is less to go wrong with this option and will make more sense to me that trying to wire the injection system.

I'm going to go for this off the RPI site,

"Weber 500 and Edelbrock Dual Plane carburettor kit, Includes Weber 4-barrel carburettor, Edelbrock or Offenhauser performance dual-plane Manifold, 14in Chrome air cleaner, and fittings ready to bolt on to your V8. Includes throttle linkages, gaskets and all fittings

Complete Systems - All models Only £575.00"

Will i need to have a bulge in the bonnet for that carb set up? i'm hoping i won't need to as it looks like the carb will sit quite low.

Just another question i've got and i thought i'd ask on here before i started another thread,

I've been looking on the RPI website at the alternative cams and heads that can be fitted to get more performance out of the v8. It seems you can anything between 18-25bhp increase out of a cam. But when looking at the Stage 1 reconditioned heads it does not say what sort of performance increase it would give, bhp wise..any ideas?

Gavin Jewkes

I went down this route, but I would contact RPI first, I sent a few emails with stupid questions and they were pretty helpful. They told me the low profile manifold (they can tell you which one you need, JWR dual port I recall) and air filter would be ok from a clearance point of view. They gave me a web link which showed it in a conversion they had been involved in but I can't find it now. They also have a very good FAQ section from their customers on their site. Try searching their web site for the MGB thing.

The carb itself is a work of art, I might just put in a case on a velvet cushion and look at it.

I seem to be going down the chrome bumper route so have the option of test fitting the engine first for clearance - but even if I have to bulge the bonnet it won't break my heart. It seems all very low when you put it together.

You probably also need the carb fitting kit, you might struggle otherwise.

This aint a cheap hobby, but hey!

This thread was discussed between 08/12/2005 and 18/12/2005

MG MGB GT V8 Factory Originals Technical index

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