I think i found out what B&S do to restrict torque in their engines.
They simply restrict AIRFLOW into the engine.
This picture shows a "intake manifold" that sits between the carburator and the engine head. As you can see it has a smaler diameter in the end.
This view is the way air og fuel is flowing into the head.
I didn`t mesure the diameter, but a guess is that the carburator is 30mm and this part has 30mm diameter at the begining and then mayby 20mm at the end.
This is the end that sits against the head, as you can see it has a different shape that match the intake opening of the head.
This will restrict the engine from breathing especially at higer RPM`s.
I found this out after i startet taking down my new (2hour run) engine for some tuning. I have opened up this diameter so it is a straight tube
As you can see in this picture.
I also milled down the head, did a valve seat job, porting of the intake and exhoust and tuned the ignition spark
I can`t say you what difference it will make to open up this "plastic manifold" since i did all the above modifications at once, but i can say that it did a huge impact on
the power of this engine. I`m impressed of how i handles heavy snow now!
It also have a deeper tone now ( under heavy load) and you can hear that it flows alot better and have bigger "throat".
The snow thrower just takes every thing you throws at it, and newer bogs down.
This message was modified Feb 23, 2010 by Geronimo332