> First message on the Internet - I've been reading reading the digests
> with great interest.
Well, welcome! Glad to have another B on the list.
> This summer I bought a 1970 MGB after looking at 26 cars (lotsa junk!).
Good choice of years -- you've got the big valves with the dual springs,
reasonable (if not the best) con rods, and the stronger crank. Keep lots
of oil in it and you can't go wrong till it explodes. :-)
> My main interest was a fun car that I could auto-x. I've since
> 'caught the bug' after my first event (dead last, but not by much!)
> I'm already started planning the suspension rebuild, etc. I'm an old
> hand at Chevy engines, with a long history of owning Corvettes, but
> pretty new to anything less than 350 CID...
>
> My two questions are:
>
> 1. Using a completely stock engine, other than a header, is it worth
> using sidedraft Webers? Looks like in most kits you need to give up
> vacuum advance, and I know that too much breathing capacity can make a
> car undriveable at low ( < 4000) RPM. The downdraft (5200-series, I
> think) looks like the best deal for a dual-purpose car.
Downdraft carbs are never the right choice for a B. 45DCOE with, um,
36mm chokes should start you off, but frankly they're not worth the
expense until you add internal mods. The SUs are surprisingly good
up to the last 4 or 5 bhp, which you can't realize till after you've
done the head, cam, and compression mods. The problem with downdrafts
is that they have to make that 90-degree bend, plus making the bends
from the central carb location out to the spacing of the intake ports.
The SUs give you a straight shot from each carb into the port, which
is the right thing to do. If you have the head off or have a very
good shop vacuum on your grinder, you can smooth out the surface of
the intake ports lightly, making them just larger than the intake
manifold; see anti-reversionary in the next paragraph.
The stock exhaust setup is pretty good, too, at least the header and
downpipe are. You can pick up a little extra power from going to a
less-restrictive muffler; a single pipe leading to a Supertrapp is
probably the way to go. While you have the carbs and manifold off,
take your Dremel and grind a whacking great amount of metal off the
inlets to the header -- off the manifold, that is. This gives you
an anti-reversionary lip that works even better than port-matching
at the gasket.
Are you planning any budget for engine work? Blueprinting a B is
worthwhile, to the tune of possibly a couple of BHP but mainly for
increased smoothness. Since you're obviously talking about the
Street Prepared classes, look into lightening the flywheel as well.
Go with the best valve springs you can get, and have the valves
cut fresh and matched for height. Good valve springs will let your
car run at higher RPM without valve float. (Of course, since valve
float is self-limiting, good valve springs can break your bottom end
if you're not careful in shifting. I think this is part of the
reason the motor in The Green Car went grind-grind-grind last spring;
I'd replaced the head but done nothing to the block.)
> 2. I'm really torn about the tube shock conversion, vs some upgraded
> Armstrongs. I like the Spax idea, and the rear conversion looks fine,
> but the front looks like a total hack - the mounting looks very loose.
> I'm looking at running 15 x 6 Minilite clones.
I've got the 14 x 5.5" center-lock Minilite replicas (my car had wire
wheels when I got it). HUGE improvement. The 15 x 6 might give you
fitment problems at the rear, but probably not on a '70; oddly, the
early Bs (before 1972 or '73) seem to fit wider tires than the later ones.
Note also that the B benefits greatly from going to shorter tires, not
only in the handling department but in acceleration. The 185-60 tires
I'm running, when compared with the 155s I took off, make an equivalent
change in my final drive to going from a 3.9 to a 4.1 rear axle ratio.
Shocks... I've run the Moss standard tube-shock conversion. The mounting
isn't all that loose, and in fact the car feels very taut in transitions.
It'd be even better if you could buy just the brackets from Moss, then
get the part numbers for their shocks and get the equivalent in a Bilstein
Sport or a Koni adjustable. The Spax setup is very good but very spendy.
For The Green Car, which is going to be reincarnated as a vintage racer
(right, Daren?), I'm staying original -- I have the competition valves
for the lever shocks in my garage, awaiting installation RealSoonNow.
Other improvements: get a second set of air filter housings (preferably
a banged-up set) and cut off the top plates, so that you have full
peripheral entry for air into the filters instead of the little 1" holes
at the ends of the air filter housings. You can then paint these Chevy
Engine Orange for that extra dose of top-end power. :-) Keep the stock
MGB air-filter backplates, as they shape the intake charge going into
the SUs, something to which that carb is particularly susceptible. (Did
you happen to get my SU carb performance tuning writeup from a week or
two ago?)
I also recommend going to a stiffer front bar. Start with the Moss
standard 7/8" bar (I think that's what it is, might be 3/4"), which
is incredibly easy to install. Once that's in place, you'll notice
*less* understeer -- nevermind what Fred Puhn and Carroll Smith say,
they're talking about real race cars. The B's front end geometry
adds lots of positive camber under body roll, so if you limit body
roll you limit camber gain. Stiffer sidewall tires, not to mention
asymmetric tread designs such as the A008RS series (and this year's
Comp T/A, for that matter) also help in this regard.
As a cheap way to increase spring rate and roll resistance, consider
going with MGA front and MGB-GT rear springs. (I need to look up the
MGA front; I think they're 121 lb/in where the B got 99 lb/in due to
its stiffer unibody, but I'm not sure. The GT rear springs have one
extra leaf, for seven instead of six, and are rated at 100 bl/in to
the stock MGB's 73.)
You'll probably find, once you limit the front body roll, that the
real problem with the B's handling is that there's too much of it. :-)
What there is is good, decent, and honest, it just rolls too much and
is underdamped in stock form. Steering response is very good (unless
you're used to a Spridget), and throttle response -- that is, the ability
to make minor alterations in your line by holding the wheel steady and
moving your foot one way or the other -- is quite sharp and predictable.
A great car in which to learn to race or to autocross.
Have fun and keep us posted!
--Scott
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