Dennis:
Buy the book "How to Power Tune MGB 4-Cylinder Engines" by Peter
Burgess. It is the best primer I have come across for understanding the
interaction of MG engine components. It offers real world advice for
various stages of tune. "Tuning the A Series Engine" by David Vizzard is
another must have book for anyone interested in really understanding how
these siamese ported engines work.
The powerplant is a complex inter-related machine. All aspects must
be optimised for the type of driving you are planning on doing. The factory
did a really good job of balancing cost, drivability and performance. Any
modification you make from stock is going to change that balance, so be very
careful.
The original cam/lifter/rocker setup on an MGB is a weak area.
These components in stock form tend to wear prematurely. Increasing lift or
valve spring pressure increases wear and reduces engine life. Be
conservative.
Traditionally the 270 degree duration with a bit more lift than
stock, is a realistic cam for street use in a vehicle that will have
"hobbyist" mileage and maintenance. Many reprofiled cams need to be
correctly timed to give the maximum result, so figure you will be spending a
lot more time assembling the engine to get it right. Again power is
directly related to time and care. There is always a trade off. Typically
you give up low end torque for high end horsepower. Keep this in mind when
you are figuring out your driving preference.
I have had two high performance MGB engines built. Both cost lots
of money, both failed prematurely. Both were my mistake because I did not
take the time and trouble to check every part and ensure adequate
maintenance was performed. Not something I want to repeat. I know what it
takes to build and maintain a high performance motor, to be honest I don't
have the time, energy or budget at this time to get too carried away.
Other items. The production quality on the 18V blocks and cranks
was higher than on earlier units. BL put in some nice fancy equipment that
solved some of the core shift problems. The 1950cc overbore is not
something I recommend on early blocks or to people who are not on a first
name basis with a machine shop. One of the liabilities any retailer has is
offering parts that require skill, care or specialized knowledge to install.
It is amazing what incredibly dumb things people will do. Ignoring basic
assembly practices is incredibly common. Then the problem comes back to the
retailer. Sorry, started to go off there.
The Lotus pistons were the Brit's idea of a good conversion piston.
They work, but are not cheap. The piston height is lower than that of the
B. But since they are a substantial oversize the compression is increased
over a stock piston with the same pin height. The amount to be removed from
the block deck depends upon the final compression requirements. The best
use I can see for these pistons is to create an engine that has lots of low
end torque without requiring high octane fuel. This would be a nice plonker
engine for around town use. Oil consumption and blow by from poor ring
seating have been problems if the cylinder walls flex. I am planning on
building an engine using these pistons and a cross flow head, but there will
be a lot of measuring and fiddling before that project gets going.
my apologies for the length. It's a subject near and dear, as I have 4
blocks on my garage floor right now.
Kelvin.
>
> Hi Lawrie
>
> This message brought up the subject of cams. And you mention
> the use of
> a mild street cam. This is where I have some confusion.
> I've looked at
> cams from various grinders and they seem to be sold by specification.
> What I mean is they have 160, 170, 180 and even 190 or
> greater duration
> cams with various lifts. Terms like "mild", "1/4" and 1/2
> race etc. are
> not mentioned. What do you consider a mild cam? What criteria do you
> use in selecting a cam? Like when you would use a 170
> duration and when
> would you use a 180 duration cam. What would be the
> "hottest" cam that
> can be used before you start to have to modify the head, intake and
> exhaust. I know a lot can be said on this subject but I would like to
> hear from experience on using different cams.
>
> Thanx
>
> Dennis
> 67 MGB
>
> Lawrie Alexander wrote:
> >
> > Carl...........
> >
> > I know the old saying, "there's no substitute for cubic
> inches", but I have
> > never been impressed with the 2-litre MGBs I've
> experienced. I know of three
> > in my locality at the moment and not one of them is quicker
> than my 40-thou
> > overbored BGT! My biggest objection is that, with the added
> capacity, you
> > have a need to remove more heat from the engine - and many
> folk already
> > complain that Bs don't cool well - plus you have the
> attendant risk of
> > cylinder wall warpage from having removed extra metal that
> the factory
> > thought was necessary to support and cool the cylinders.
> Then you have the
> > need to change the carb needles and springs (to what? who
> really knows?), or
> > even fit 1-3/4" carbs (again, what needles are best?) to
> make the most of
> > the added displacement.
> >
> > So, my two cents (or does that long paragraph constitute a
> nickel's worth?)
> > says go 40 over and fit a mild street cam, and know that
> you'll be able to
> > get the carbs right and have a powerful, trouble-free motor.
> >
> > Lawrie
> > (willing to race any 2-liter B with either my BGT or my 77
> roadster!)
> >
> > -----Original Message-----
> > From: Carl French <cfrench@cybertours.com>
> > To: mgs@autox.team.net <mgs@autox.team.net>
> > Cc: bfrench@nh.ultranet.com <bfrench@nh.ultranet.com>;
> info@britbits.com
> > <info@britbits.com>
> > Date: Monday, November 29, 1999 7:17 PM
> > Subject: 2 Litre
> >
> > >I have been offered a set of never used 2 litre pistons for my
> > >rebuild, they would be free from a friend. I have a 67B with the
> > >original motor from what I can tell. What would you say
> are the risks of
> > >trashing the block? Other thoughts? Lawrie?
> > >Carl French
> > >
>
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