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MG MGB GT V8 Factory Originals Technical - wich gearbox

Gooday all from Australia.
Rebuilt a 69 roadster a couple of years ago and very happy with it.
Now concidering a 3.5 rover transplant. Question is, will the original gearbox with overdrive handle the extra power output. As to the engine, what model vehicle (in aus at least) has the correct water pump position.And finally, is it worth getting the hugger manifolds or the rv8 style.Ahh. one more.I am guessing there is an adapter plate for the gearbox. are these hard to find?
Thanks in advance for any help revieved and hope to join this site in the next 6 months (don,t want to put the car off the road just before the summer fun)

re: Thanks in advance for any help revieved and hope to join this site in the next 6 months (don,t want to put the car off the road just before the summer fun)

Not a problem! Relocate to North America for the next 12 months...that way you can do the conversion during our winter, drive it during our summer, then relocate to Australia to enjoy yet ANOTHER summer driving season!


I would recommend the RV8 headers as they allow more rapid heat removaol from the engine compartment.

rick ingram

Hi Cactus,

Welcome to the place.

Do you have an engine yet? If not then I would look for an engine with gearbox attached to help with the swap.

The availablity of the Rover engine here is limited by a few things like which models were imported and also the Rover cars people looking for the same engine to keep their cars going so it may well be a case of taking what is on offer and adapting it to suit what you want to do.

The original B box is about at the limit and any amout on heavy right foor will see a very short life indeed.
The Borg Warner T5 (Holden Commodores and Ford Falcons and variants) can be bolted to SOME Rover V8's depending on the bolt pattern.

Have a browse in the archives and also have a talk to someone in the MG car club ( to save reinventing the wheel.

Oh yeah join the board now. If you are going to do it dometime now is a good time.

Cheers , Pete.
Peter Thomas

Hello cactus,
I used a toyota supra gearbox with a Dellow bell housing. Dellow automotive in sydney make adaptor bell housings and ship them all over the world. Cost about $500. reco guanateed Gear box cost $700. Got the gear box off dellow because you can specify the W58 variety (0.78 overdiven 5th gear) and the D (21in) gear lever length, with is the longest variety. The supra box is very light and strong and SMALL ie fits without any cutting and welding. You prbably could pick up a supra box at a wrecker for around $300. If you get dellows bell housing , specify the larger slave cylinder set up of around an inch. The supra slave of three quaters of an inch is useless, as I found out. I sustituted a one inch range rover slave, which has the same threads as MGB.

Don't know anything about the commodor connection, would be very interested to know more.

I Used a range rover 3.9.
If you can get a 3.9, do so, they are a much better motor. You can buy a new short motor for around $3000, It'll cost you nearly that to rebuild a 3.5 . The heads are virturally the same as '80's motors. Also get the hot wire injection, heaps better than Flapper style. From about 1985 the intake manifolds on the flapper style were the same as the Later hot wire. Your best stagegy might be to pick up a cheap 3.5 with a cracked block (most of the 3.5's seem to have this problem eventually) and salvage the heads and intake manifold and front cover, then buy a new short 3.9. You need the pre 92 front cover with the split oil pump so that you might fit the RV8 oil pump adaptor.
EFI is much easier to set up than carbies. The alterations to the intake manifold will cost you about $100 or less. There's some small amount of welding and maching to get done. There's a guy opposite the StKilda town hall who's done a couple for me, Engine Inprovements. Also you need to spend about $300 for a late modle fuel guage sender and a couple of fuel pumps for the fuel supply.
Get through the guards RV8 style extractors. i have them and have never showed any signs of overheating problems ever. Also they add about 12 BHP. Also they cure the "starter motor overheating" problems that block huggers have. You can buy Clive Wheatlies stainless ones as I did for about $400 pounds (plus 25% customs duty), or you can buy Adrian Ackhursts of AAA Automotive in Adelaide. These are mild steel but may be coated in ceramic "jet hot". These cost about $1300. next time I do a V8 I'd get these, they are VERY nice, tuned etc.
"Race Radiators" out in Dandenong make pollished alloy radiators to specifically fit MGB V8 conversions. They charged me about $600. Suggest you fit a fan on the front top RHS and one on the back bottom LHS.
I have the largest Craige Davies fan I could buy ( on the back of the radiator). It's massive overkill. Two smaller fans driven by a two stage therostat would be a much better solution.
Brakes- You can fit brakes from a volvo. You need the wider calipers suitiable for the thicker ventilated disks. These need to be cross drilled so you have one outlet, not two. The mounting holes need also to be redrilled to suit MGB's. For disks you can use redrilled peugot 505 turbo diskes or buy the brake upgrade kit (I did) from MG Workshops in Melbourne. If you are doing part of this brake upgrade yourself, you can still buy their (MG w'kshop) braided stainless brake lines which have volvo fittings on one end and MG on the other. These fittings have an ADR number on them, vital for registration purposes.
I have heard roumors that Ford Falcon brakes can be adapted, don't know more than that, would like to hear more if anyone elso knows.

Thankyou gentlmen. Most informative.Even going to the states.
Peter Thomas....Thanks mate. Am already a member of the board,just not the v8 section.

Peter,Moomba. Very detailed and thankyou for spending so much time with your reply.It does answer a lot of questions i was thinking about.I will do the conversion myself but do need to keep the costs down,ie new short motor etc.I was fortunate enough to have the car given to me originaly as it was about to go to the tip.Rusted away and in 5000 pieces. Spent 3 months full time on it and have been offered 25g for it.Owes me 5 g so i guess the extra dollars spent on the conversion would still see a low overall budget.
While spending 6 or so thousand would be nice, budget restraints force me to do it as cheaply as possible so all work will be done by myself (other than bellhousing etc.)I can appreciate the fuel injection would be the way to go, but would a holley 350 or similar be ok.I realise bonnet clearance is an issue but dont mind the idea of a "shaker" a la xw ford.(have a spare bonnet just incase it looks terrible)
Power output is not high on the agender .Just like the sound.Brakes work fine for my style of driving and hopefully will be adequate for the 8.(figure stopping from 100kph requires the same amount of stopping power whether 4 or 8 cyl)And finally, i was led to believe that registration in Victoria was not a problem,re engineers report,as they were fitted with 8s from the factory. You would no doubt be aware of the requirements.

Thankyou again

Best to contact an engineer before you start. They'll tell you the requirements such as how much body to engine clearance is required etc. They might require a brake upgrade, might not. They did with me, even though the car ended up about 30Kg lighter. With a 3.5 you might need to have the MGGTV8 brakes. These were thicker disks and involves getting hold of the outer half of triumph calipers. If you don't do a brake upgrade they will need to do a brake fade test in any case. In this case you need to have first class MGB brakes and might consider removing the brake splash sheilds (I have, you don't miss them))and putting cooling ducts from the front valance.
Collin at Enkelmans was most helpful, he does the MGworkshops conversions. When I'm back home in melbourne (two weeks) I'll look up his number for you. Or it might be better to ring the RTA and ask for a list of engineers near to you.
The cheapest conversion around is to use the motor and gearbox from an old Leyland P76. This motor was stroked larger to 4.6(I think). Disadvantages are the gearbox is only three forward gears and that the block is about half an inch taller, so you really have to get the motor as low as possible. Might want to discuss mounting on the front crossmember with the engineer. Is it allowed? etc, it's certainly a better option, I wish I had thought of it earlier. many of the P76 parts are interchangable with Rover stuff.
With carbies, it's often more expensive to make up adaptor plates etc. Cost is all going to depend on what you start with. If you end up with a motor with fuel injection already on it it obviouly cheaper to adapt that, than try and fit carbies.
With 3.5 motors be very careful to inspect around the main crank shaft bearing cap bolts. The bearing cap bolts are inclined to work a little loose, the crank moves a little and cracks develope in the block. You will see fine cracks either side of where the bolts screw into in the aluminium. I looked at 6 or 7 3.5s and all were cracked. If the seller doesn't want to remove the sump for you to look, he's hiding somthing. I'm told the cure for loose bolts is to either clue them in with locktight, or use studs.
You might find someone to make up extractors for you, or you might even do it you self , if you are very patient.

Thanks again peter.
The idea is to collect the parts required over the summer so that i can convert during the winter.
Engineers.I used to work at the Healey Factry in melbourne a couple of years ago and we always had something to do just to keep them satisfied.I was led to believe (probably by the niave) that the 3.5 was simply installed (niave again) and no engineers report needed as it was a factory conversion.That was my main reason for sticking with the 3.5.I assume that the range rover motor is ok except for the water pump position. i can only guess that there are a lot more of these motors around than rovers.My only reason for carbs was to avoid having to have a computer wired in for the injection.I have done no home work on this subject.It may be a simple install but knowing my luck, someone will charge me heaps for the knowledge.
I think the supra box may be the go ,as per your advise,as the old p76 gear is hard to find now days. Even the 4.4 is getting scarce.Extractors are a little beyond my patience levels to manufacture but i have a friend who is in the business.(fingers crossed) I have read a few posts regarding tyre clearence being a problem with the rv8 style.Does this mean THE rv8 exhaust which i guess some use?.Clutch. Is it the supra or the mgv8 one or the 3.5 or a mixture.
Tacho,easy to convert or is there another that will fit.(so many questions once you start to think)
I am down in the otways in victoria so geelong is my nearest city but i know theres not a lot there as well.
Thanks for your patience and time peter and yes, i am saving these answers so i dont have to ask later.

Cactus, my first conversion was a RB model with the smaller tach & speedo gauges. VDO Australia converted the tach for about $100 & a local instrument mech converted the speedo to Kph for $66.
My second conversion was a CB '71 with the larger gauges. I used the speedo & tacho inners from an SD1 Rover sedan & fitted them into the MG gauge cases. The dials ( made from perspex )had to be reduced in diam. by an 1/8" & a couple of extra holes drilled for the ign. & hi beam lights. Also a few extra holes in the cases.
Finding a flywheel will probably be your biggest problem as most Rovers in Oz were autos. One from a Range Rover can be machined down to size by skimming off a about 1/2" from the face & have it drilled to take a Ford Falcon pressure plate (your cheapest option) The driven plate is supplied by Dellow.It has to fit Toyota splines. whether it is a stock Toyota part or not I don't know.
The Toyota Celica gearbox is also an option. It has a cast iron case as to the ally case with a Supra. Back in '89 I was advised to use the cast iron case version if I was fitting it behind a V8. This info has since been refuted, but that was the thinking back then.
Barrie E
Barrie Egerton

wrt taho's
I culled this from the archives.

Visit Leon Zak's website:

<<<The only part you need is a 100K 10 turn pot they're available from Radio Shack, (Dick Smiths etc.) 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.>>>

Zacs site has lots of pictures for the electronicaly illiterate like me.
For my car it worked out about 20kohm. Since I don't have fancy electronic monitors, wave form detectors etc I simply left one of the wires loosely attached; I adjusted the resistor until I had the tacho reading about half, unhooked wire, check reading, reattached and fine tuned etc . Did this for a number of RPM's. The only glitch was that Dick Smiths sold me the wrong resistor (100ohms) to begin with, had to go back. This little resistor is blue, and about 20 by 6 by 6 mm. Cost $2.00, plus I had to buy a cheap $9 soldering iron, which has come in very usefull. Took a couple of hours of not unpleasant fiddleing.
The range rover motor was used in the RV8 as is and infact I'm using the front cover from one so the position of the water pump is no problem, in fact it's quite usful since the pump is displaced up and to the right this leaves room for the motor from the more centraly placed fan.
Barries suggestion of the celica box is a good one if you wish to save money. Obviously the celica box is cheaper and plentiful. Disadvantages are that the celica box is heavier and has a smaller main bearing so not as strong, but still well up to handeling the power output from a 3.5 I'm told, eg Barries car.
You want to get the longest box, thats the 21inch, or "D" size. The different lengths (4) are determined by the length of the (bolt on) part of the box that the gear lever attaches to. The supra W58 box I have has a 0.78 over driven 5the gear. There's heaps in the archives on various toyotas and their gear boxes, ratios etc.
I was initially a little intimidated by EFI, but it tuned out to be dead easy. The people on this board helped out and there's heaps in the archives (scroll down to V8's), fault sections from manuals etc. The range rover sites are useful since its the same motor. Esentially the EFI is stand alone so all you need is a 12V wire for power to the computer, a wire off the ignition and thats about it. I put fuses on these wires to be on the safe side. I also wired the fuel pumps through the computer but later realized this was unnecessary and infact something of a hinderance. You also need to change a couple of resistors, one to tell the computer your driving a manual, and one to tell it you don't have cat' converters/oxygen sensors etc. I'm not a home at the moment and cant recollect the details but this is all in the archives anyway. There's a thread running at the moment called :"why do I need a swirl pot" ( or something like that) that answers the fuel supply problem very comprehensivly.
Tyre clearance and RV8 extractors is a problem with an easy answer. On full lock one of my tyres comes within a few mm. This is because I made a silly mistake fitting them and I suspect I'm not the only one to do so, I put them on backwards! This is because the RV8 extractors collect into a down pipe, that is not centraly placed, It's off by about 2 inches. I assumed that this displacement would be toward the back of the car to clear the brake down pipes, wrong. It's not any real problem but at some stage I'm going to swap them over, just to be tidy, plenty of clearance then.
Clutch-I bought Dellows set up, didn't use the spring plate, used a rover one instead, didn't use the slave cylinder, used a one inch range rover one. I bought a machined rangerover flywheel from Triump and Rover spares in Adelaid but would have done better to get a range rover one machined by a local shop as the bolt holes had a very corse thread (bad) and I had to drill and place some dowls to locate the rover spring plate.

Roger Williams has written a couple of very good books on MGB V8 conversions. Infact he's got a new updated book due out next month. There's "How to give your MGB V8 power" and (my preference) "How to improve your MGB, MGC and MGV8". vast numbers of pictures, diagrams etc. Good summer reading. If you check back though the archives you'll see him giving reams of advice. The technical book shop in Melbourne stocks them (they;ve moved from swanston street to round the corner) and a few other outobook shops around town.

Ebay item: T5 xsmn + all adaptation bits for sale
Graham Creswick

This thread was discussed between 24/11/2005 and 29/11/2005

MG MGB GT V8 Factory Originals Technical index

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