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MG MGB Technical - What makes the MGB's Have different HP ratings?

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Brett Sinclair

Polution equipment!
Robert Dougherty

Lots of stuff. Type of carburation. Cam spec and timing. Valve sizes. Ignition specs, ported or vacuum advance. Catalytic converter on later cars, as well as other various emmission sundries. Sorry I can't be specific on when all this applies too, but it's pretty involved when you start trying to pinpoint all the change dates in production. Besides, lots of original specs have been changed by various owners over the years, so often times the subject is moot.

-Jared
Jared Snider

The U.S. government began imposing emission controls in the late 1960's. The modifications to comply resulted in loss of HP. The later models only have one carb and catalitic converters.

As an aside, one of our political mental giants thought the headlights were too low. The result was the factory raising the suspension with a reduction in handling.

There are numerous modifications that can be done to significantly increase HP. On the extreme end the car is only usable in competition.
Lee Sheldon

Brett. Do not know where you are located, hence you may live in an area that was not affected by the US safety and emissions requirements. The safety requirements were a driving factor in the modification of the MGB, in the 74 1/2 version, to rubber bumpers and a raised height above the ground. Headlights were not the problem. There was a big push to have all bumpers at the same height so that, in an accident, there would be bumper to bumper contact. The insurance companies, and their lobbyists, were major players in this legislation as they were in mandatory seat belt usage legislation.

With the introduction of the 18V engine, the North American specification cars got a low compression engine. This lowered the power output somewhat. Prior to that, all that had been required was, from 68 onwards, an air pump. The air pump took a little power away from the stock engine. The lower compression ratio took a little more power away. The re-curving of the distributor to meet emissions requirements rather than performance requirements took a little power away. There was also a change in the exact method used to measure horse power output during this period. In 75, MG went to a single Z-S carb (Z-S is an old Anglo-Saxon word meaning " a piece of defecation, left on the ground, which you have just stepped in), along with a very restrictive exhaust manifold.

In reality, most of these "horse power losses" are on paper, not for real. If you take a late model RB engine, replace the Z-S with a set of twin SUs (or, perhaps, the Brit-Tek Weber 38/38 carb), a set of headers and use a 62-68 spec LC distributor, the actual power output will not be all that different from a 67 engine. My daughter's 77 B, with a Weber DGV 32/36, headers and a Euro Spec dizzy will hold its own against my 68 GT. Theresa's car has all of the factory pollution control equipment hooked up and will pass the state emissions testing requirements with no problems. The concept that the later cars were "down on power" is not a hard and fast statement. The way that "power" was measured was changed and the two main problem area--intake/exhaust manifold and carb, are easily changed out. Les
Les Bengtson

to add to Les's comments, you may also wish to modify the cylinder head and change the cam. Horsepower can be increased by modifications suggested by Peter Burgess in his books on this subject.

Putting a hot carb on a RB is like placing lipstick on a pig, it's still a pig....after i installed a modified engine in my RB i understood the pleasure of driving an early B that i read about...in my state an Antique license exempts one's car from emission testing.


rn
RN Lipow

Lee,

The raised ride height of the RB MGB's was due to bumper height standardization, not headlight height. But you're right. The raised center of gravity played heck with the handling.
Paul Noble

Sorry, Senior moment - I stand corrected - Bumper height was the reason.

I guess they forgot about that with the advent of the SUV and the jacked-up pickups that require a tall ladder to enter.
Lee Sheldon

Les - I noted in my Road & Track road test compilation that the 1980 RB they tested had the same 0-60 times and torque figures as the last chrome bumper they test in 1974 - mid-13's 0-60 and 94 lb/ft. The first RB they tested (1976) had a torque figure of 72 lb/ft and a 0-60 time of over 18 seconds.

They also had an intermediate test of a RB in 1978 with 88 lb/ft and 13.8 secs.

The only thing that I believe changed on the RB's during this time seemed to be the ignition. Points on the 1976, first gen electronic in 1978, and second gen for 1980. I am speculating that the factory retarded the timing on the initial points system to meet emissions (which you mention in your post), but that they were able to advance their timing with more modern ignition systems.

Given your experience, does this ring true?

BTW - while the HP figures go up and down as well, the torque figures more closely fit the trend line, and I committed them to memory. The fastest tested CB was the '68, with 110 lb/ft and 12.1 0-60.

BTW #2 - and yes, the 1980 RB was fractionally slower - 13.5 sec, to the last CB - 13.4 sec, a difference I'd put to the added weight of the bumpers. The CB was NOT "Sabrina-ized".

RB's may need help in the handling department - particularly the early ones without the anti-roll bars - and if you can improve your RB's power through simple timing changes, then putting your FIRST real dollars towards the handling side of performance might be the wisest course.
John Z

This thread was discussed on 03/03/2003

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