Walt,

I don't think that there is negative pressure in the cylinder during the exhaust stroke.

The exhaust stroke takes place at a nearly constant atmospheric pressure because the exhaust valve is open to the atmosphere throughout the stroke. There is (theoretically) no work done on the exhaust gas during this process. The random motion of the gas causes exit from the combustion chamber and cylinder as the volume is decreased by the piston motion. The pressure and temperature ratios are both 1.0 during the exhaust stroke.

The flow of the exhaust gas past the valve guide, however, does result in a suction pressure being developed and the faster the flow the greater the suction.

The high oil consumption we experienced with Coventry Climax engines only became an issue with a Rally car when events with a duration of 250 miles or greater were considered. These engines also used a wet sump which didn't help with oil capacity.

I would agree that for short circuit and Autocross events this wouldn't be an issue.

The engines generally ran well, didn't exhibit smokey exhaust behaviour they just used oil. The 1 litre engines we used produced around 120BHP and in a very light car were a real hoot.

We used this type of engine at the start of our Rallying activities and since then we have always used stem seals many of which were specially developed to suit high revving race motors such as the Ford BDA/BDG which we used for many years.

We built another one in 2004 and used it in the British Historic Rally Championship where it won its class on every event entered but couldn't keep up with the 911s so after 2 years we traded up to 1966 SWB car.

http://i197.photobucket.com/albums/a...ps52yztd5v.jpg

It is rear engine BUT unfortunately is water cooled :)

As a paved circuit track driver, I have a lot of respect for the road rally drivers. The seat makers Racetech cater to this market, and I place a lot of credence in what they say about seats and seat mounting, because their rally customers are great crash test dummies, flying off over cliffs and into trees on more occasions, I think, than we do on our tracks, the best of which were designed to have lots of runoff to minimize the effects of our blunders or bad luck. My home track here in Colorado has not even a bush on the property, much less trees.

It is generally a sad day when it all goes horribly wrong.

This resulted from a broken check strap and a 'rear swing axle'.

http://i197.photobucket.com/albums/a...psxmpwbs4o.jpg