MG Engine Swaps Forum

Trying to plan a build that I have in mind. I would like to do a engine swap of some sort but want to know if the rear end should be swapped as well. What kind of HP figures can the stock rear-end handle? Could it handle 150? What are some of the easier rear-end swaps that work well for under 200HPish?

I think I am only shooting for around 150hp. But if I was going to swap rear ends it would be nice if it would handle enough for future improvements up to around 200hp

MG started using a Salisbury (tube type) axle in about 1967. Before that, they used a lighter duty "banjo" type axle. The four-lug version of the Salisbury axle should be easily strong enough to endure most 200hp swaps.

The main reasons people change axles when or after doing an engine swap are (a) to get a better rear axle ratio economically, or (b) to get a limited slip differential economically. The combined cost of "MGC" gears and a "Quiafe" limited slip differential to upgrade a Salisbury axle would almost certainly be higher than buying Ford or Chevy axle (with limited slip differential and appropriate gears) and having it professionally narrowed.

The Salisbury axle isn't lightweight. An eight inch Ford axle with aluminum third member would be a significant weight reduction.

So it sounds like a later stock rearend would work fine with a stockish 3.4 v6, right?

FWIW, the factory limit the output of the MGB GT V8 to 137hp. Of course they would be conservative for warranty reasons and also if it was too fast it might 'nibble' at the bottom end of their own E-Type's market.

Curtis is right, should easily handle up to 200hp. Of course if you fit slicks and are drag racing then you are probably going to have problems. It's really not the horsepower numbers that you need though, it's the torque that breaks axles. The original Salisbury type MG axle is pretty comparable in torque capability to the smaller Chevy 10 bolt, so small V8s up to 350 cu in and probably around 250 foot pounds of torque would be a reasonable limit.

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Bill Young
'73 Midget
'59 MGA

There is a fine line between a 'hobby' and 'mental illness'.

It would work... I would recommend finishing the engine installation and driving the car for awhile. You can always do an axle swap at a later date. That's what I did - I found the stock axle ratio (3.909:1) absolutely intolerable, but all axle ratios are a bit of a compromise. What roads do you drive, what tire size, etc., etc. - and then it largely comes down to personal preference.

I drove Brian McCullough's V6 last summer, and I really liked the combination of ratios in that car (with stock axle). Notice though that Brian's not quite content with them yet: http://www.britishv8.org/MG/BrianMcCullough.htm


If that was the issue, it was surely more so because of the gearbox. Remember, they started with overdrive on third and fourth, and found quickly that they needed to restrict overdrive to just fourth. However, I don't think for a moment that the MG factory wanted to use the lower compression version of the engine... It's clear they were losing political battles left and right within the larger BL organization. The earliest prototypes used higher spec versions engines. A little more info about that is here: http://www.britishv8.org/MG/CliveWagerfield.htm

That is correct. The 1st and 5th gears are about where they should be but the gears in the middle and ultimately getting the power useful within the entire bandwidth is the issue. It's 83.7% good enough for me and 100% well enough for others. I want the extra edge that the conversion axle will give plus the plan for 5 lug rims that are otherwise stock looking as just something to set the car off when people bother to look. The limited slip will not hurt either..

-BMC.

As Dave Vale of the V8 Conversion Center (former Costello Motors) told me many years ago, a Sailsbury axle can handle up to 300 BHP before the half shafts start to fail.
With the 3.9 B setup, you should go for larger tyres to compensate for a more direct gearing or try to find a 3.3 MGC rear axle that works very well with 195/60-14 tyres. The C has different brakes bolted on, but they can be changed for the B drums, a simple bolt an.

My Rover 3.5 was tested with 188 RWHP on a RR and the 3.3 MGC rearend in my car has never given any trouble within nearly 30 years of service.

Ralph

Just for reference I am running the V6 conversion with a Banjo and a Qualfe Differential. My Axles, spline hubs and rims were new. Now have 2100miles:

http://www.rc-tech.net/MGB/suspension/ax.jpg

http://www.rc-tech.net/MGB/follow/diff2.jpg

http://www.rc-tech.net/MGB/follow/diff3.jpg

Hi Guys,

When I converted Dave Kirkman's car, we decided to keep the stock axle until it broke. So far it has held up flawlessly after many 1000's of miles, track days and drag strips.

http://www.britishv8.org/MG/DaveKirkman.htm

Dave's 302 (stroked to 342 or 5.7 liters) put's out 390 ftlbs of torque (dyno'd at the flywheel), he also uses 205 Goodyears.

If the stock Tube type Salisbury axle can handle 400HP or 390 ftlbs then 200 HP should be a walk in the park.

Unless you have the budget or desire to change ratio's then start with the stock axle and upgrade later.

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Cheers

Pete

69 B 302 V8 - 78 B 215 V8 - 80 B 302 V8 - 58 ZB Magnette - 69 CGT 9004 - 69 CGT 7666

http://www.mantellmotorsport.com/

I entirely agree. I ran a stock axle behind many high output engines including the Eaton blown 215 which I conservatively estimated to be in the ballpark of 300/300 (that was with 16 psi of intercooled and injected boost and injector times correlated pretty well with those power levels) I did wear out a ring and pinion but that was after many miles and much abuse (tires were 265/50-14). The axle shafts were fine and went into the replacement housing for continued thrashing. At lower power levels the axle should have a long life, but you might want to check the play in your spider gears and install thicker washers if it needs it just to head off a possible trouble spot.

Jim

I put a total of 95000 miles on my GT with the stock rear axle.
While the GT was a devoted race car SCCA the alxe needed some minor attention, such as the spacer washer replace twice. this was with a V6 260 hp race engine.
then the car became a street car with the same axle, replaced the washer and still in the GT. Finally it is going to be replace, only due for better axle ratio trans combo.

Hi torque and a light vehicle do not need 9 inch rear axles. Very low mass to move forward.