Technical Compression Test Work-Around

I was reading a thread on this forum called good cheating stories. There was one story that I thought was interesting and I wanted some technical advise on how this was most likely done. I think the story was summed up as :

"After NASCAR brought in a compression ratio limit, Larry Widmer
built a motor that used oil pressure to change the compression ratio.

Spinning the motor on the starter, the compression ratio checked legal.
Fire the motor, and at race speeds, the compression ratio was significantly higher."

Does anyone have any ideas how that was done?

 

Haven't heard that one and I am a little skeptical on manipulating oil pressure to change compression ratio. One possible thought would be to somehow raise oil pressure very high to somehow not let hydraulic lifters bleed down sightly and function normally. This would cause intake and exhaust valves to somehow not seat all the way, which would lower compression.......but I don't think any recent NASCAR engines would be running hydraulic lifters vs. solid or roller lifters.

 

i think NASCAR motors all use solid lifters as tractorguy said

i too would like to know how this was done

 

I have to go with what Tractorguy said. you might be able to manipulate hydraulic lifters a bit to change compression pressure but I have never been around a compe***ive circle track car that didn't run solid lifters outside of some low buck cl***es where very few engine mods were allowed.
I'm not sure if the drag of high oil pressure that was changed by causing a deliberate restriction before the compression test was run to slow down cranking speed would have any effect or not. Some guys do say that high pressure oil pumps can rob horsepower though. Maybe by causing the oil pressure to go up the starter with a full charge on the battery was spinning the engine just enough slower to give a reading within specs. You would still have to have a chart that showed how many pounds of compression a certain size cylinder should put outwith a set compression ratio.

 

You could get the desired results just by the cam. Make a cam with a lot of intake duration to allow compression to blow back out of the intake valve at low speed, depend on inertia or ram effect at high speed. Crower and others experimented with this idea and got engines to run very high compression ratios on pump gas without knocking.

 

How about a small hydraulically controlled valve (or whatever) closing a small "leak" from the combustion chamber when oil pressure appears? Legal pressure when tested, way higher when actually running.
Then there's all the four stroke bike engines etc. with compression release by opening the exhaust valve slightly some part of the time it should be closed, to release some compression so the engine is easier to kickstart. Usually a mechanically controlled solution using centrifugal force as far as I know, but nothing rules out other means of control.

 

It was a purpose built 2 piece connecting rod that extended with oil pressure at higher rpms.

 

It was the Rhoads lifters, they're anti pump up don't ya know

 

Nah. They just built loose bottom ends and put a centrifugal clutch on the oil pump drive.

 

2020 will probably be our last season, so check back in October of that year and I will let it out of the bag at that time.