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Re: Engine kits, rebuilding and Moss Supercharger

To: "Don Malling" <>, <>
Subject: Re: Engine kits, rebuilding and Moss Supercharger
From: "Kai M. Radicke" <>
Date: Tue, 16 Sep 2003 10:22:35 -0400
Don Malling wrote:

> I plan to use the Moss supercharger, and would be interested in any
> implications of that, like which cam etc. Specifically can I install a
> non stock "hotter" cam and still use the supercharger? In the event I
> remove the supercharger for some reason, I might still like to have a
> "better" cam in it. On the other hand I have read that the stock cam
> for  the MGB is pretty good -- very unlike the stock cam for my
> TR250.

The hotter the cam, typically the more overlap between intake and exhaust,
which means quite a bit of wasted potential in a supercharged setup.  You'll
also probably end up moving the power band up into higher RPMs with a hotter
cam, when the whole purpose of a positive displacement supercharger is to
create broad power and torque in the low and mid ranges.

> I think the stock compression on a B is 9.0:1? I've been told to not
> exceed 9.5:1 on the TR250 for 93 octane pump gas. I assume this is
> the same for the B? I assume I must stay with stock compression for
> the supercharger? Again, it would be nice to have a better than stock
> engine should I decide to remove the supercharger for some reason.

9.0:1 is a little on the high side for a forced induction application,
especially in a 40-50 year old engine design that was not designed with
forced induction in mind.  I would be hesitant to exceed 8.5:1 and maintain
a reasonable level of boost.  Afterall, the whole purpose of supercharging
is to ram as much air/fuel mixture into the cylinder as is feasible for your
car and setup.

Austin MG built the MG Metro Turbo in the early 80s and it was a
turbocharged A series motor running at 4psi of boost most of the time (7psi
I think was available in certain RPM ranges), and the compression ratio was
fairly high... 9.4:1 if I remember correctly.  However, the Moss
supercharger setup is no where near as efficient or advanced as the setup
Austin MG created for the Metro Turbo...

> Any way to detune the supercharger -- less boost -- if I have a higher
> compression ratio? Different pulley maybe?

The less boost, the less power output.  Anything below 4psi is almost
worthless considering the cost of the Moss supercharger installation.
Kelvin would know this best, but I suspect the boost range that the Moss
supplie pulley gives is in the 6-8psi range... which is a very modest level
of boost.

> I'm also interested in how the Brit-Tek distributor would work with the
> Moss supercharger.

You'll have to call BritTek on that one and ask questions about the
mechanical advance curve.  When I rebuilt the distributor for my previous
TR6, with supercharging in mind (as I had a TR6 supercharger kit sitting on
my shelf for a year when I finally got around to doing the prep work to fit
it), I used weights that gave less mechanical advance.  If you're going with
forced induction, your timing curve should typically be less advanced above
2500/3000 RPM than even a stock motor.  Don, did you ever buy David Vizard's
Tuning the A Series Motor?, he covers timing for forced induction motors in
excellent detail... in fact the whole section on forced induction is 100%
applicable to the MGB motor, given that the A series is the B series little


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