MG Engine Swaps Forum

Is there a rear end that is a bolt-in swap into an mgb?

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Pogo is right.
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The power of reasons is an illusion. The belief will not change when the reasons are defeated. The causality is reversed. People believe the reasons because they believe in the conclusion.

Nope. They all have to be narrowed and modified except the 72-75 CJ or Postal Jeep. Those need spring perches moved and flanges on the axles modified.

Okay, thanks.

Let me ask the question differently: where can I obtain a rear end already narrowed and modified for the mgb?

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Pogo is right.
—————————————————————-
The power of reasons is an illusion. The belief will not change when the reasons are defeated. The causality is reversed. People believe the reasons because they believe in the conclusion.

Dan LaGrou used to sell a GM that was made to bolt in. Not sure if his son, Mark, still offers it.

http://www.aluminumv8.com/

Thank you.

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Pogo is right.
—————————————————————-
The power of reasons is an illusion. The belief will not change when the reasons are defeated. The causality is reversed. People believe the reasons because they believe in the conclusion.

This:

http://www.britishv8.org/Articles/2007-TechSession6.htm

I think you can get one direct from Moser. Likely as not that's going to be where Mark goes for them.

Jim

Buying an complete assembly from Moser looks like an expensive way to put together a rear end for an MGB project..

How necessary is a stronger rear end after a motor swap? I hate the gearing of a stock unit and have no intention of doing burnouts. Sort of figured a MGC diff swap was the way to go but keep wondering if 250+HP thru any MG diff will end badly.

Buying any axle complete and ready to install is going to be rather expensive, no matter what it is or where you get it. Moser's prices are probably about as good as anyone else's and their business is axles. That does make a difference.


It mostly depends on your engine's torque output. Even if you drive conservatively an engine with good torque numbers is going to stress the drivetrain every time you use even moderate throttle so the idea that you can baby the car and make the axle last is not altogether a sensible one. Back when I was running 215's I went through 3 stock axles and depleted my stock, and I'll tell you that swapping out the axle because you just happened to feel like you wanted to see how hard it would go up the driveway is something that gets old the very first time it happens. The spiders were not the only thing to go either. I wore out one ring and pinion set just because it wasn't strong enough to take the strain. The wear curve is such that it drops off rather sharply. Below a certain point the gears will last for the life of the car. Above that the gears will hardly last any time at all no matter how carefully they are set up. It pays to be on the right side of that curve. (the left actually) If you want to retain your stock axle your best bet is to use the factory configuration with the trousers intake and factory cam. You'll get about 137 hp but it will still be enough to make the car a pleasure to drive. There's a guy on BritishV8.org right now selling one of those intake systems for very reasonable money. Between that point and about 250hp it gets increasingly risky until at the upper end you are very likely to need a new axle before too long. All the above sort of explains why MG used a truck axle for the MGB. They rarely failed in service because they were well on the safe side of the breakover point. Race car axles are usually right around or frequently beyond the breakover point because changing them out between races is a viable option. If it only has to last one race it doesn't have to be very durable and less weight means more speed. Not at all what is wanted on the street. This is the practical and experienced viewpoint, YMMV naturally but if you want an axle to last it should be spec'd out slightly oversized. A ring gear of about 8-1/2" diameter fits very nicely into the role here for size, weight, and strength and be aware, ring gear diameter is the primary determinant of axle capacity. Gear metallurgy has not changed appreciably in the last hundred years and neither has design. You can go with smaller gears and more than a few have but it's a risky proposition. You will hear hype about things like the smaller lighter axles used by say BMW for instance but I ask you this: What does Ford use? The 8.8" is very common for a reason and it's not because it is light and compact.

Jim

Randy,

For 250+ horsepower I would strongly consider a rear end swap as Jim mentioned. That being said if you were in the 200 hp range you should be able to use the stock rear end (as long as you don't abuse it) that is in good shape as there are lots of conversions out there that do.

The main issue for most is the less than desirable gear ratio for V8 applications. One option is a 3.3 gear set which is just about ideal for most V8 conversions, the draw back is that they can be a little hard to find and somewhat expensive. BPNW does have one set in stock according to they're website https://bpnorthwest.com/mg/mgb/ring-and-pinion-3-31-mgb-68-to-80/

If you want limited slip, then that adds about $1500 or so to the cost so by the time you do a gear swap and limited slip it starts to get fairly expensive. At that point most just opt to do a rear end swap which is what I did 40 some yeas ago by going with a Mopar 8.75" rear end that came with 3.23 gears and limited slip.

Bill

Which begs the question, Randy, are you speaking of flywheel or rear wheel HP?

Flywheel, then I agree with Bill. RWHP, then I still agree with Bill.

One thing to keep in mind is the MGB is a light car therefore much less strain, a 10 bolt GM V8 Camero or a Mustang 302 7.5 are more than adequate for high hp MGB.
One of those with the correct gear ratio is the ticket.

If those differentials were used in car that weights 3200-3400 plus lb then the those differentials become heavy duty in a 2200 plus lb car.

Using a 9" or 8.8 in an MGB is just adding dead weight and sprung weight.

Gear ratio is important for a V8 Ford 3.0 or 3:23 GM or 3:35 Ford couple to a T5 with 2:78 first gear and .65 fifth gear. Or stock Mustang trans with 3:35 first gear.

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It is our attitude that will determine the outcome

The PO claimed over 250 HP crank. I tend to believe based on a few local drives. Not going to do burn outs, have not even gotten past 2/3 throttle as it buzzes through the revs in any gear so fast. But it is a concern and something to budget for. Sorry to hijack the thread.

Every time I get reading these topics I start to wonder if I'm doing the right thing. My GT is still a work in progress . I've kept the stock Salisbury save for putting in a Quaife. My transmission is a 4L60E whose ratios should be 3.06/1.63/1/.7. But I have no idea of the BHPs or torques. According to Wikipedia the factory quotes up to 340 bhp (254 kW; 345 PS) and 350 lb⋅ft (475 N⋅m) of torque. I don't intend leaving licorice straps on the road but am I expecting too much?

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Mk1: CKD 11/66 first registered 8/5/67; owned since 3/77. 18GB +40 balanced. Peter Burgess BVFR head. Piper 285. 123. FidanzaFW. 4synch c/r box. Lots more as I did a nut and bolt rebuild; finished 2015. Tartan Red.

GT: December '78. VW Golf guards, flush fit front and rear valances. Torana XU1 vents, frenched indicators & Mk1 rear lights. 'Worked' Rover V8 with Monsoon ECU for EFI. GM4L60E, Lokar tiptronic & Quick4 controller. Vintage Air A/C. FC IFS. CCE 4 link rear. Salisbury with Quaife. Jaguar Storm.