Fordboy - the above is a very intriguing and informative exposition...
Since -15 inches of water is only about one-half psi, could you be prevailed upon to comment on the following?
How was the vacuum created?
Initial dry sump testing logged a decrease in blow-by cfm. This was unexpected. At that time, blow-by cfm, in conjunction with leakdown %, was being used to evaluate the "quality" of the dynamic/static piston ring sealing. Wider, off the shelf, scavenge stages were then tried, resulting in even lower blow-by cfm. That's when the light bulb went off and the "problems" started . . . . . . . . Eventually, even more scavenge stages were added. The type of scavenge pump becomes important here, due to the pumping efficiency differences between styles. Ie: gear style Vs. lobe & rotor style Vs. roots style. In the end, total vacuum was a result of scavenge capacity/efficiency, piston ring blow-by, AND, the "leakage rate" of air "allowed" back into the engine assembly. It was a "baby steps/mickey mouse" deal.
What was the limitation on the vacuum level?
Pumping capacity, At first there was a LOT of resistance from pump manufacturers. They "knew" we didn't need that much scavenge pumping capability. We solved that by finding a receptive manufacturer who was happy to sell us "stuff we didn't need".
leakage rates, EVERYTHING leaked at first. The bigger pumps would suck cork gaskets into the engines. Standard seals would "gulp" air. It was a major program just to get things sealed.
pan collapse, We never got to the point where that happened, the fabricated pans were probably stiff enough in section. The cork pan gaskets were a giant "pita", and were replaced by "reinforced" pan gaskets. Stamped rocker covers on the other hand, were not stiff enough to clamp cork gaskets, or any other gaskets in place.
blowby etc? With poor ring sealing, or a bad top ring, or a scuffed piston, the whole setup takes a dive.
Something you didn't ask about: We worked very hard to reduce "throw off" oil from various assemblies. This reduces the volume of flow to say, con-rod bearings, cam lobe/tappet faces, cam bearings, etc, etc. Let's just say that there is some "non-quantifiable risk" to doing this. It was a giant learning curve.
Hazard a guess on the relative contribution--reduced oil churn vs. reduced pressure windage? We had a block with a lexan "window" in the crankcase, one of my "brilliant" ideas. It was like trying to look at a hurricane, close up! Not something that was easy to quantify. Just a wild guess, I think we might have been getting a reduction of 50%, most of that from reduced "churn". The later setups yielded "smaller hurricanes".
What were the more troublesome vacuum sealing problems? The cork gaskets and stamped tin were by far the worst. The final solution was to replace all those pieces with parts that were "stiffer" and/or could apply more "clamp load". Look at a Cup engine now, no tin, no cork, only castings, O-rings, printed RTV gaskets, etc. Look at how valleys are sealed now, remember the old cork ends when the manifold sealed the valley? Initially, we just turned the crank seals backwards, a dead giveaway to what we were doing. Double-lip and eventually multi-lip seals solved that problem. Problem was we couldn't hide what we were doing on race engines. Don't ever let anyone tell you that there aren't any "spies" in Nascar . . . . . . .
Interested Observer, et all,
Still a slow and crappy typist. I've inserted comments in your text, sorry.
I have been away from the pressure of "racing every day of the year" for about 11 years now. Looking at a current Cup engine and just "speculating":
1/ As I said above, no tin, no cork, only castings, O-rings and printed RTV gaskets. Stuff that can be really sealed tightly . . . . . . .
2/ "Big" multistage scavenge pumps and scavenge lines . . . . . . . .
3/ Ask yourself, "Where did the engine breathers go?"
I would hazard a guess that the negative pressures now are much higher than what could be achieved 10/11 years ago, with a probable net bhp gain of ?Reflecting back, I would say this as a caution to everyone who wants to be an engine specialist: For every insight I had, it turned out that some "dope" had to go through the drudgery of "developing" the concept into something useful. That "dope" was usually me, so be careful of what you wish for . . . . . . . .
Even something that sounds simple, like replacing a cork gasket, can become a huge task if there are no alternative parts available . . . . . . . . .
And, in spite of what most guys think, technological jumps in performance are mostly a triumph of development over design . . . . . . . Note that this requires time AND lots of money. Unless you have "unlimited time" and "unlimited money", my advice becomes: Stay with a well developed package if you actually want to get to the race track. If you want a modern "treatise" regarding development over design, read the Milwaukee Midget's Build Diary. Keep in mind that he started with an engine that had 60 years of "development" behind it and he was getting advice and parts from well thought of suppliers. . . . . . . . I'm pretty sure he is a lot more satisfied with his effort of 2013 than with his previous efforts. But, you could ask him directly.
If you want to tinker around/fix stuff because that's what you enjoy, well that's a different deal, and you are on your own.
Fordboy
