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MG MGB Technical - V8 conversion

Okay, so I might be in the wrong section but I'll start here anyway.

I have a 78 GT which needs some light restoration (it was fully restored 12 years ago but is getting a little untidy in a few places).

As part of the restoration, I'm thinking of going down the route of a V8 conversion.

As I understand it, a 78 car is ideal as it should almost be a bolt in replacement.

So to the questions:
- Who has done this and roughly what did you budget?
- As well as the engine/gearbox, what other bits did you change - e.g. brakes, crossmember etc.
- What's the best choice of gearbox - price/availability?

TIA.
Jezzer

Hi Jezzer,

Please read Roger Williams' book 'How to give your MGB V8 Power'. It will answre most of your questions - and provide answers to questions you didn't know to ask.

Further details are available on ther engines conversions page of this BBS.

Im enjoying a conversion of a 1978 MGBGT to V8 powerr, using an old ex-Costello engire and transmission. It's lots of work but fun. Contact me off line for further information.

Good luck

Peter
P L Hills

The MGB Engine Conversions thread will be happy to welcome any one who had turned to the "Power Of The Dark side".
Yes, your 78 has the V8 configuration engine compartment. The steering rack is queezed up with the smaller universal joint to clear the exhaust. The rear bulkhead is already cut back and reformed to allow for the V8 head clearance and has the V8 steering cone. The tunnel is also much higher and wider than the earlier cars. If you choose your gearbox carefully,(Toyota box) you will not need to do any panel beating. The radiator is in the V8 location and the core is V8 spec'(header tank a little different but you could work with it if you really wanted to). The V8 radiator was a bit marginal though, you might likly want to upgrade (I did).Nothing worse than sitting in traffic watching the temperature guage soar. The inner guards are also formed to clear the exhaust manifolds, however this is not so important since the RV8 appeared on the market(more about that later).

It seems everyone who does this conversion has their own favoured approach, individualist all.
But this my approach. The conversion rate is about 2.5 australian dollars for every pound.
I'm using a 3.9 motor out of a rangerover(RR). As well as being more powerful, this engine is much stronger than the 3.5 and generally all round better. Much reinforcing in the crankcase. The gear box is a W58 out of a Toyota Supra. This cost $650 reco' guaranteed and is a small, light and strong box with a nice set of ratios. Fifth ratio is 0.78. You can get a 6 gear version if you have breathtaking amounts of money. There is a company here in Australia, Dello Automotive (they are on the web), who make adaptor bell housings and ship them all over the world Australia 02 9774 4419. Other gear boxs are BorgWarner T5, T56 or even MGRV8. These all need tunnel beating I believe, which is why I ovoided them. I had half an inch machined off the RR flywheel to make it a copy of a Rover 3.5 flywheel, which are in short supply here. The Front cover is off an 80's RangeR. You need to use the older style (or RV8 style) so that you might use the oil filter adapter. (adaptor about 100 pounds)You need the adapter 'cause the rover oil filter is in exactly the wrong location wrt the steering rack. By the way most of the V8 Rover and rangeRover bits are interchangeable.
You will need an engine. I paid $2300 australian for a very low KM complete 3.9 with all the efi gear on it. $1600 for reco-gearbox and bellhousing clutch etc. From Dellow austomotive.$300 for a stronger longer tail shaft (local shop).When everything is finaly in place find a machine shop and tell them what you want to match to what and how long it needs to be. 400 pounds for the RV8 exhaust manifolds, bought off Clive Wheatly V8 conversions in England (01902330489 or WEB). The "Through the guards" Rover RV8 approach solves any over heating problems for good. As well as getting the hot exhaust out of the crowded engine compartment it provides ventillation into a low pressure zone. Also gets you another 10 to 13BHP and solves some starter motor problems. Get your starter motor off a SD1, it has the solinoid on the bottom. The RR side solinoid motors don't fit in MGB's.
$600 for alloy radiator, another $400 for electric fan hoses etc. I made my own engine brackets, not hard, but alot of messing around and much 'furrowing of the brow' as to right engine location. If I were doing it again I would save time and effort and get the brackets off Glen Towery 13027341243."Towery Foreign Cars" mgv8glen@belatlantic.net in the US. His set the motor lower and further back than most (like mine do), which solve many problems with bonnet clearance. Once the engine is in place it simplifies things. Gives you a fixed reference point. All you need do then is adapt the old gearbox cross member to the new gearbox mount. An adapter plate, easy enough.
If you can get a motor with efi already on it, it is much cheaper and easier to adapt this than retrofit Carbies and their manifold.

Here's a copy past "all you need to know about fitting EFI" (or at least all I need to know)
You can put a stock 3.9 hot wire system onto a 3.5 engine without any difficulties. This things pretty flexible. In light of that I can't see that there would be a problem with the Higher compression 3.9.
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, this is placed between 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. Cost about $1.

You don't need a swirl pot in yout tank. You use two in-line pumps.
Details-
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 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 tank, which has its own pressure release set up.
All fuel injection pumps will 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.
The air intake set up is too tall to go under the bonnet of an MGB. There is a solution to this. The air intake set up (the plenum) has three main components. Starting at the bottom, The intake manifold, then on top of that, the trumpet tray (has 8 trumpets & three vacuum ports) and finally the top cover that covers the trumpets and has the throttle mechanism on it.
There is also a small water heater on the underside of the throttle. Take this heater off and plug up the bolt holes.

Machining down the plenum-you don't have to actually do anything here except provide the measurements to the machine shop.
This cost about $100 dollars (Australian) to get done at Engine Improvements opposite the St.Kilda Town Hall. Just take the trumpet tray to a machine shop and get them to weld up the vacuum ports; grind off the bumps/left over bits of the ports and generally tidy up for appearance sake. Then machine a maximum of 15 or 16mm off the bottom of the tray and up to 10 or 11mm off the top. You might also need to have 5mm machined off the top cover as well depending on how much clearance you need. Obviously you dont want to machine off more than you need to.
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. Obviously the front and rear channels are longer than the 4 middle ones.
They didnt bother with trumpets on the early federal flapper efi 3.5 motor which did not work as well as the later mannifold.
You can get the trumpets out of the tray by heating in your kitchen oven. Different coefficients of heat expansion. Silicon them back in afterwards. I used Ultra grey which is fuel resistant and sets up firmly.
Note-On the later fuel sender 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. If you dont want to buy a new sender you could simply remove the old sensor to a safe distance and solder a hose fitting into it and that could be the return line. Although this is not as good as having new (larger diameter) pick up near the return, its cheaper.
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 port 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.

Peter

http://www.britishv8.org/mgv8conv.htm
Peter

Peter,

Just to let you know your extraordinary efforts are appreciated. I will save your extensive comments for my eventual V8 conversion, even though I'm not even thinking of one now.

Thanks from a reader who just luckily stumbled on your post.

Allen
Allen Bachelder

"for my eventual V8 conversion, even though I'm not even thinking of one now."

Peter draws another one closer to the Dark Side.
Edd Weninger

No one Can resist the Power young jedi...turn..turn......

Forgot to mention- Pullies/fan belt/waterpump-I had steering rack clearance problems with the RR bottom pully/balancer. You might be OK, you might not. Solution-The bottom pully/balancer off the Rover SD1 has a longer neck and the steering rack tucks in neatly under it. The SD1 pully balancer assembly has many superflous pullies on it, obviously keep the one you need. Many (but not all),80's Range rovers and rovers used a cast water pump pully. I used this and it lined up with an SD1 balancer plus selected pully. I then spacered the alternator bracket forward. You could spacer the RR water pump pully forward as well. I kept/used the RR water pump. On the MG GTV8 they used a P5(or P6) balancer that is the same as the SD1, except it has a fanbelt groove machined directly into the balancer. Up to you, but you likely will need some variety of that longer neck balancer. I happened to start with a Range Rover front cover like the RV8, but a Rover one (like the MG GTV8) might be as good. So long as its got the split down the middle bolt togeter, style oil pump, which was used right up until the early '90s. This is so you might use the RV8 style oil pump base with remote filter.
Alternator bracket is off a Rover P5 or P6 and is the MG GT V8 one. Should cost no more than $20 if you ask for a P5/6 one (or a early '70's rover one); will cost $70 to $80 if you ask for a MG one.
peter

Brilliant Peter. Really useful. I'm using an injected 3.9 myself from a Rangie. I shall file your notes for future reference.

Mike
Mike Howlett

The flat pully out of the SD1 "collection".
Three 20mm spacer blocks under the alternator bracket.
(off cut bin at an Aluminium extrusion place). This allowed me to keep and use the nice looking "internal cooling fans" large 100amp RR alternator that came with the motor. Spacering the pullies forward also solved a clearance problem between the "fan" belt and the bottom water hose.
If you already have the pressed metal variety of RR water pump pulley, you can use that with a 10mm spacer under it. The Outer ring part of the unsuitable "on the crank nose style oil pump" is 10mm thick and lines up with the three water pump pulley bolts. You may already have one if you have the 3.9 motor as these usually have the later front cover. I used this for a while until I noticed the cast type pulley on some RR motors with aircontidioning (and later on an SD1).
The advantage of the cast type pulley is that its grooves are 10mm forward of the pressed metal variety. I did get the grooves machined 2 to 3mm wider and deeper to match the bottom pulley, although the thinner belt seemed to work OK. The machine shop threw that in for nothing, with the work on the plenum.

Also top radiator hose for those using RV8/ rangerover front covers.
Nissan Pintara RWD '86-'89

Grommet GR206
MACKAY CHI564
OEM 2150154500
GATES 05-0598

This radiator hose actually fits better than the RV8 one and costs $15. Compared to about $60!.
Its much longer than the RV8 one which suits my application (and anyone using Glen Towery brackets) of radiator far forward and engine far back perfectly. Infact I had to cut about one inch off each end.
Peter

This thread was discussed between 07/01/2006 and 11/01/2006

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