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Rover V8 and BW65 auto gearbox

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Montesacota Will S
Cheltenham, Gloucestershire, UK   GBR
Hi - I am hoping to fit a RV8 and BW65 in my 77 MGB Roadster Shell. I've done all the research I can on fitting the RV8 and have got myself a rebuilt SD1 9.35:1 engine, MGRV8 manifolds and BW65 box ready to go. Just a couple of questions if anyone can advise please:

1. Is it true that the BW65 autobox is basically the same dimensions as the LT77 manual but does not need the tunnel mods?
2. Will the MGB/C auto shifter work with it?
3. Will a propshaft converted for the LT77 be ok?
4. I've looked into the ratios and the 3.9 :1 axle should be roughly the same as a 3.07:1 when 15" wheels fitted. Anyone had experience of this?
5. Will the SD1 engine fit without needing to be shortened? By my reckoning without a viscous fan and some engine mount juggling it may (just).

oh one more:

6. Can the SD1 alternator bracket be modified to fit? Mine has blanked off top mounts (for a second alternator?) that look like they might work..

Obviously without either a converted MGB or an LT77 for reference its a bit of a trial and error situation.

All advice most gratefully received.
Thanks

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Simon Austin Avatar
Welcome Will! I can't help with questions about the BW65 itself but may be able to offer some advice.

First thing to buy: the book "How to give your MGB V8 Power" by Roger Williams https://www.amazon.com/How-Give-Your-MGB-Power-ebook/dp/B00J9U5ZIY

In answer to your questions;

3) your best option is to have a custom driveshaft made once you have dimensions with the engine/gearbox and rear axle installed.

4) I don't know the final drive ratios of the BW65 so can't comment on that. I can tell you that the LT77 I have in my car: http://www.britishv8.org/MG/SimonAustin.htm needed the 3.07 diff gears to lower the rpm by about 500 at highway speeds. It has 15" wheels.

5) the SD1 will fit your shell. My car is a '77 and needed no mods to fit the engine. I have RV8-style headers as well.you won't use the original fan but will likely switch to electric fan(s). I have two stock RB fans mounted.

6) I don't remember what the SD1 alternator bracket looks like. It may sit the alternator too high but that's just a guess.

One of the best sources of advice and parts is Clive Wheatley http://mgv8.homestead.com/index.html

The photo I've attached is my current project; a 1970 BGT with another Rover 3.5 being installed. This one will have a GM T5 gearbox rather than the LT77.

Keep the questions coming and post photos. We like photos!

Cheers
Simon



"Speed costs........how fast you want to spend?"


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Denis Avatar
Denis Denis Hill
Bearii, Nth Victoria, Australia   AUS
Will I have just finished my 73 V8 conversion and still use the 3.9 diff although with a T5 and ,72 overdrive 5th gear. Its OK but I feel it still revs a bit hard at cruise for my liking. My engine came with a BW65 but it would have been hopeless as no OD. At the moment it is 40kph (25mph) per 1000revs and first gear hardly necessary. Ok around town, very quick, but am thinking 3.3 c&p, or similar when our summer is over. BW 65 is a nice box, I have one in my old Jag but old style and no lock up in top I would not use one in a performance vehicle. Denis



68 B roadster, Daffodil yellow, Moss supercharger, Burgess SC head, SC cam, Mikuni HSR 48 carburetor and engine built for supercharging.

73 BGT V8 conversion starting with a bare shell. Built the engine early in 2016 with high comp pistons and a few other nice bits. Started on the body late 2016 and found Its a lot of work and expense starting from scratch. Did the work myself, mechanical, body. paint etc all except the interior trim.
Finished and going well, great to drive and quick. Future mods, maybe an increase in gearing but not for a while.



Edited 1 time(s). Last edit at 2017-12-06 03:08 PM by Denis.

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Montesacota Will S
Cheltenham, Gloucestershire, UK   GBR
Thanks for the replies chaps. As I said its a bit of a trial and error process but hefting the V8 and box in and out each time is sucking up a lot of my time! I have always found the BW65 to be a smooth transmission in both SD1 and P6 Rovers so it seems like a good alternative. They are also much easier to find these days than RWD LT77s. I was hoping the MG would turn out to be more of a burbling cruiser than a performance machine (We have another car for that). But I am guessing that its a combination of large wheels and low ratio diff on the big Rovers that brings the revs down.

Having said that I don't really want to be doing much more than 70mph in the B.

I'll keep pressing on and address the performance/ratios when I get there...
Cheers

V8MGBV8 Avatar
V8MGBV8 Carl Floyd
Kinggsport, TN, USA   USA
In reply to # 3640959 by Denis Will I have just finished my 73 V8 conversion and still use the 3.9 diff although with a T5 and ,72 overdrive 5th gear. Its OK but I feel it still revs a bit hard at cruise for my liking

Swapping out your 5th gearset to a .63 will take care of that. winking smiley

mgb281 Philip Waterman
Taunton, Somerset, UK   GBR
Will
A couple of years ago I was in a local engineers (in Taunton)having some machining done on a bellhousing and they told me that they used to make an adaptor plate to mount a T5 gearbox on a BW65 bellhousing. The company was sold soon after and the new owner let the business run down and eventually close. If you decide to go to a manual gearbox at least you have a bellhousing option

mgv8glen Avatar
mgv8glen Glenn Towery
Dover, Delaware, USA   USA
Will, the T65 & the LT77 trans. are close to being the same size but the LT77 trans. hump has to go up close to 1.5 inch., the 5 speed hits under the heater box in the front of the trans. hump. I have a 5lb. sledge hammer & I move the tran. hump up. I see no need to cut & weld. You need the Rover P-6 alt. bracket, the alt has to sit fight in front of the cyl. head. The T65 is a 3 speed auto with no O/D & you will need all the gearing you can get! 3.07 & run the 195 65 15 tire you need a big diameter tire you can get. I put a 2.79 ford 8 inch rear in mine (200 fewer RPM). MGC or MGC gear selector is what I have used. The U.S. A/M 1800 auto gear selector can be used also. It all goes in & works well!

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Montesacota Will S
Cheltenham, Gloucestershire, UK   GBR
That's really interesting stuff guys - especially about the bellhousing. Trouble I am faced with is the lack of availability of either T5 or LT77 gearboxes. The box is in danger of becoming the single biggest cost item of the whole conversion these days. Not only scrap Rovers but scrap cars and breakers yards in general are in short supply in the UK these days

Currently I have a good BW65 which cost me £50 and at least it will get the project mobile! If I do find either manual box eventually (or the holy grail R380) - with the BW65 I have done the majority of the preliminary work. I was lucky enough to find an MGB auto shifter and brake pedal at an autojumble. Sounds like I might have to settle for an automatic sprint/hillclimb car instead of the cruiser I planned for.
Cheers
Will

Montesacota Will S
Cheltenham, Gloucestershire, UK   GBR
PS : Re the bellhousing that would figure as BW65 was used on the Triumph Stag and I think there has always been interest in Stag circles for replacing it with various manual options.

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Simon Austin Avatar
Will,

Contact Clive Wheatley and see how he can help.



"Speed costs........how fast you want to spend?"

Denis Avatar
Denis Denis Hill
Bearii, Nth Victoria, Australia   AUS
Will the problem I see is that with a 3,9 reat and the BW65 you will only see about 18mph per 1000revs Tyres only make a small difference and your auto will have a little fluid slip on top of that.
Denis



68 B roadster, Daffodil yellow, Moss supercharger, Burgess SC head, SC cam, Mikuni HSR 48 carburetor and engine built for supercharging.

73 BGT V8 conversion starting with a bare shell. Built the engine early in 2016 with high comp pistons and a few other nice bits. Started on the body late 2016 and found Its a lot of work and expense starting from scratch. Did the work myself, mechanical, body. paint etc all except the interior trim.
Finished and going well, great to drive and quick. Future mods, maybe an increase in gearing but not for a while.

mgb281 Philip Waterman
Taunton, Somerset, UK   GBR
Will
You will come across T5 gearbox's more often than you would think, there are always TVR T5's on Ebay and they come with a 0.8 5th gear. Another bonus is that they use a 23 spline input shaft so you can source clutch plates from many sources, the x type jage and mondeo V6 fit. Although the gear lever is in the wrong position swapping the rear housing from a Cosworth Sierra rectifies that.
Philip

Montesacota Will S
Cheltenham, Gloucestershire, UK   GBR
Hi thanks again for all the info.
Ive done a bit more research and the ratios available from the BW65 are the same as those from the BW35 as fitted to the MGB automatic. I think larger wheels/tyres will bring the final ratio with the 3.9 :1 rear diff to around 3.32:1 which is very similar to them MGB automatic rear diff which was around 3.45:1 with 14 inch whels

I don't imagine the 1800cc motor was doing much more than 3250 rpm at 70 mph. So could I expect the rover V8 to be the same? Is that an unreasonably high cruising rpm?

I love the idea of super quick of the mark 0-60 but equally I don't like the idea of headache inducing revs when cruising.

18mph per 1000 revs sounds like 3800 rpm at 70 mph and over 6000 revs to reach 120mph. Anyone know what the optimum revs range would be for the v8?

mgv8glen Avatar
mgv8glen Glenn Towery
Dover, Delaware, USA   USA
Will, Go out & drive your MGB with it in 4th. gear & you will have or close to 2800 RPM @ 50 mph. With the T-65 auto you will turn close (100 to 150 more rpm) to the same RPM. You are dreaming, thinking you will get the gear ratio you are thinking you will get. My Dads MGB V-8, I run the T-65 auto with 195-65-15 tires with a 2.79 rear diff & I have the gearing that is needed for a MGB that can go all day down the interstate 65-75 mph. Do all the math & thinking of what rear gearing you think you might need, the hard fact is you need all the gearing you can get. The T-65 with 3.9 rear is close to drag race & parade show only.

Montesacota Will S
Cheltenham, Gloucestershire, UK   GBR
Yep - its going to need the rear diff ratio changing. I see that Clive Wheatley does a replacement crownwheel/pinion set 3.07:1. It would need to be done for an LT77/R380 anyway so its just another piece of work to add to this project!
At the end of it I am beginning to think an LT77/R380 is a better arrangement all round.

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