Jack:
This is an interesting point. The MGB motor will cruise all day long at
4500 rpm without any problems if tuned correctly.
The problem is that without tuning the car on a dyno or rolling road, it
is unlikely that the tuning is going to be accurate at that speed. On a
typical set of older SU carbs and distributor, the tuning at idle can be
set but linkage adjustment and distributor wear can cause a lot of
roughness at higher speed.
As an example, I've driven two MGBs that were professionally tuned. Both
ran well around town with lots of power. On the freeway, they both felt
rough above 3500 rpm and the fastest comfortable cruising speed was 65
mph.
Getting technical, some quick checks with a timing light showed that
both original distributors were giving far too much advance, which
accounted for some of the roughness. New distributors helped
dramatically.
The interesting thing is that both cars were subsequently fitted with
superchargers. At cruise, all the supercharger does is provide a well
mixed fuel mixture to all cylinders. All of the high speed roughness
smoothed out and both cars felt completely smooth at high speed allowing
comfortable cruising in the 4500-5000 rpm range. No more thrashing and
the engines acted more like electric motors.
The experience showed that it is very important to tune the car
accurately for the anticipated rev range. That the MGB can be as smooth
as a modern FI car if care is taken to ensure that all the systems are
working optimally not only at idle, but at anticipated cruising speed
too.
Sorry for the long answer, but it was an interesting experience that
showed how much potential these cars really have if tuned correctly.
Kelvin Dodd
> -----Original Message-----
> From: mgs-bounces@autox.team.net [mailto:mgs-bounces@autox.team.net]
On
> Behalf Of Jack Feldman
> Sent: Wednesday, June 20, 2007 4:52 AM
> To: A Leveque; mgs@autox.team.net
> Subject: [Mgs] MGB Cruising Speed.
>
> I just got my BGT back after some restoration work. The engin is bored
.40
> over, has larger carbs, a shaved flywheel, and the head is ported and
> polished. It has great torque.
>
> When I traveled in my MGC, I would cruse at 3000 rpm, which gave me a
> speed
> of just over 70 MPH.
>
> Taking into account both the handling and the engine stress, I was
just
> wondering what you folks would consider a safe cruising speed for the
BGT.
>
> Jack
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