ptuomov

If you have the dyno time, try all four combinations, pairing the two main castings with the two throttle bodies.

GregBBRD

This thread got really quiet, really quick....

We're anxious to know what happens when you hold it at 6,000 rpms for 30 seconds or so, with that windage/breather system.

Catorce

Greg,

Carl is busy testing injector combinations right now, and although he hasn't posted on this thread, they are tweaking the motor every day but it's limited by engine dyno availability as well. I'm not sure this motor has even seen 6k RPM yet because the injectors are at full duty cycle at a much lower RPM.

I'm not worried.

What don't you like about the windage system? This thread is meant for the education of all; why don't you tell us what you see.

GregBBRD

These engines are infamous for filling the cylinder heads with 2-3 quarts of oil at high rpms (in each head)....which leaves virtually no oil at the pick-up....leading to catastrophic engine failure. At higher rpms, the crankcase pressure builds up and the oil return passages from the heads to the crankcase are not able to return the oil from the heads, because the crankcase pressure pushing back through the oil return passages keeps the oil in the heads. (Many engines suffer from this issue...Ford had to do extensive work to keep the Coyote engines from doing this. The Boxster engines will regularly fail from the pick-up being uncovered at high rpms. Porsche installed scavenge oil pumps in each cam carrier on all of the post 1998 water cooled 6 cylinder engines to deal with this. Any successful high rpm Small Block Chevy or Big Block Chevy racing engine was dry sumped to help with this problem....the list is endless.)

Of course, this takes some high rpm use for extended periods of time (like you are going through turn 8 and 9 at Willow, or going down the front straightaway at Willow or Fontana) to show it's ugly head....so this may not be an issue for your intended use.

Literally dozens, if not hundreds, of these 928 engines have failed from this problem, alone. The higher output 928 GT and GTS engines had a terrible reputation for rod bearing failure on the Autobaun, when driven hard and fast, because of this issue. Porsche "addressed" the issue on the 928 Marine engines (marine engines tend to run at high rpms for long periods of time) by simply installing a huge capacity oil pan and allowing the heads to fill.

Andy's 600hp naturally aspirated engine that I built (and others) pushed out literally quarts of oil from the valve cover vents at 5500rpms (and it had 4 vents), when held there for 30 seconds. When we looked at the data from that run, it showed that the engine had also lost oil pressure due to the oil pickup being uncovered.....not enough to automatically shut the engine off before we shut it off, but a definite loss that would have been catastrophic if it had been allowed to continue. (Makes a real mess in the dyno cell, BTW.) I was forced to undertake a major redesign of the oiling and ventilation system (6 months of R&D) to keep this from happening......which I've now very successfully used on multiple engines to keep these engines from running out of oil at the pick-up.

The simple/quick test is to load the engine up and run it at 6,000 rpms for 30-45 seconds (can be done while tuning) and see what happens. (Have a mop handy.)

I'm just interested to see how Carl's pieces are going to function under these conditions (from his pictures I don't see how the crankcase is supposed to ventilate.) Without doing something, even with an Accusump, these engines will fail. (Worth noting that even Mark Anderson's dry sumped engines would "suck down" the oil tank several inches from 5,000 rpms on.....as the heads filled up with oil.)

However, different ideas and solutions sometimes can make the most complex problems a non-issue. If Carl has this all figured out, there's a huge amount of factory engine developers that would be really interested....and their companies would pay big bucks to know the simple solution.

ptuomov

To put crankcase breather system issues in the right perspective for each engine, it would be useful for everyone who can to post the blowby CFM numbers at the peak torque rpm (and for the peak power rpm and the torque produced at that rpm.) If the engine produces 10 CFM of blowby then the solution required is different from if the engine produces 1 CFM of blowby. Many dyno cells have a blowby meter, as it's not that expensive compared to other dyno equipment.

Catorce

Excellent explanation, I had no idea. I too eagerly await the conclusion of this tuning, and regardless of what I intend to do with the car, the expectation is that it can run at the RPMs and for the time you are stating without issue.

Really interesting reading, thanks Greg. Let's wait and see.

GregBBRD

I build different kinds of engines, with different kinds of pieces, depending upon the intended use. I've now built so many of these engines that I've got a really broad base of information to draw from. However, it is important to realize that everything I do and build comes through my own "rose colored" glasses....I've yet to find anyone with more knowledge about these engines (than myself) to draw information from.....I find myself always figuring out things, on my own.

I've found that crankcase pressure, in a stock 928 engine (with .0008"-.001"" of piston to wall clearance) is enough to stop the oil return from the heads and fill the heads with oil. Of course, in most street applications, these engines are not likely to spend much time at 6,000 rpms, so I have system which makes some ventilation changes and can generally get away with "passively" addressing the problem, instead of "actively" addressing it. (Andy's engine was an exception to this.....and I intentionally ran it at higher rpms (for extended periods of time, on the dyno) to "test it". See below.)

In a high performance race engine with steel liners and forged pistons (with greatly increased piston to wall clearance) or even in a Nicosil coated engine (with higher piston to wall clearance), the crankcase pressure is going to be higher....it's a given.

Andy's street engine (Nicosil), which he wanted to be able to do open road racing events, was an exception and required active measures.....no passive attempts to cure the problem worked.

Worth noting, Colin's crankcase vacuum system seems to work well on street engines (the vacuum presumably draws the rings into the cylinder walls, reducing blowby, which might also reduce crankcase pressure enough to allow the oil to flow back from the heads to the crankcase.) I have no idea if he has tried his system on a race engine with increased piston to wall clearance, on any high performance 928 engine, or even if he has done any testing to see how much oil collects in the cylinder heads, with his system. Certainly, that would be an experiment worth doing.

It is interesting that all of the dry sump oil systems (which I have tried) have not created enough crankcase vacuum to allow the oil to return from the heads to the crankcase....they have all still produced enough crankcase pressure to keep the oil from returning to the crankcase from the heads (at higher rpms.) I am currently building an engine which will have greater scavenge ability and a completely new approach to the oil pan design. It will be interesting to see if we can create enough negative crankcase pressure which will allow the oil to return to the crankcase from the heads. However, I am a bit dubious and already have a back-up plan, should this not be the case.

ptuomov

By my logic, if the engine is on a stationary dyno, just the average crankcase pressure can't blow the oil into the heads if the crankcase is sufficiently vented from the oil filler neck. Think of this average crankcase pressure thought experiment as a hypothetical experiment in which the oil pan has a very large volume which dampens any pulsing.

The vertical drop of the oil drain passages is about 10 inches. Adjusting for density of oil, the head needed to stop the drain is 8 inches of water pressure differential between the crankcase and valve covers. That's 0.3 psi, and as long as one can keep the pressure differential below that the oil should drain. If the valve covers are connected with a hose, a single non-blocked drain passage will flow 15-20 CFM at 8 inches of water without any improvements. (About 1/3 square inch area and flow coefficient of about 0.6 just ballparking the guess). Contrast that with the 2 CFM total blowby number that we measured for the engine currently on the dyno in my car. It will be very difficult for the average pressurization for like that to happen, given the sizes of the passages with any sensible breather system, at least with the engine on a stationary dyno.

What I think is going on inside the engine that causes problems is not so much the average pressure differentials but the piston pumping pulses. I believe that it's the piston pumping pulses that causes the oil drain problems in some engines. Longer stroke makes the problem much worse, larger bore makes it worse, center counterweights make it worse, shallow pan makes it worse, higher crankcase gas density makes it worse, etc.

To see how dominant the piston pumping pulses are compared to the blowby rate, consider the following calculation. My blue engine had about 2 CFM blowby at 3500-6000 rpm, but a single piston moves 262 CFM inside the crankcase at 6000 rpm! If that 8x262 CFM has to even partially communicate thru the valve covers, the oil drain passages are going to get really busy. That's the elephant in the crankcase, and the average blowby only matters if it's not vented out properly and instead is allowed to increase the crankcase gas density.

Carl's windage tray kit is a copy of Kevin Johnson's windage tray kit. Both kits have four weird looking pieces that stick up into the crankcase. Those weird looking pieces serve multiple functions. One of the functions is that they block piston pumping pulses from blowing directly into the heads, and allow oil to drain down. I've got similar pieces in the blue turbo engine, and I have NA engine too with different pieces performing the same job. I think they work.

The problems get more interesting when one subjects the engine to external forces. Slicks and turns are a difficult combo for the 928.

Carl Fausett

I decided to take a page from your playbook, Greg, and post when I was ready instead of posting intermittent results each day. Have not been happy with my first set of injectors and I have another set coming in. Will be on the dyno again Tuedsay.

As to: that's largely correct, but not completely correct. Actually Kevin had a working 928 crank scraper and windage tray system when I first met him in about 2008. Through the next number of years, Kevin and I co-developed his next two iterations, he making them and I test-fitting them and running them and redesigning them. Unfortunately Kevin's health took a turn, and he was not able to continue to make the intricate 928 crank scraper anymore. That's when I took over manufacture of it.

Since then, I have made several improvements to it (especially in the areas of head drainage). So what we have now is not a copy of the original design at all, but certainly has evolved from it.

These pictures show some of that evolution.

ptuomov

Carl --

You didn't post the pictures of the most important pieces that KJ designed that actually have (positive) consequences for the oil drain from the heads.

Carl Fausett

I am not planning to test 6,000 rpm for 30 seconds under load, as at the dyno there is no oil accumulator installed, no oil separator and catch can system, no oil return to the motor from that oil separator, and no pan-o-vacs installed.

There is nothing to be proven under that set of circumstances as less than half of the oil control system is installed!

I KNOW from experience that when those items are installed correctly, the 928 engine can be run at wide open throttle and max load for extended periods of time with no loss of oil pressure. Even with boost. I've done it.

Carl Fausett

The drain-back diverters? There are 4, on one side of the engine only (the other side does not have the same problem of oil being dropped onto the rotating assembly). It was brilliant that Kevin saw the need for these diverters.

You can see them in these pictures. They have also gone up another iteration since the last manufacturing date.

Carl Fausett

I'm going back to my weekend guys... TTY tomorrow.

Catorce

Well I for one think a 216 mile per hour run constitutes at least 30 seconds under load. Looks like the system works.

Sure, I have skin in the game, but that's why I chose Carl. Because he's done stuff with his cars, personally. I think those achievements speak for themselves.

Catorce

Hi guys,

Sorry for the slow responses. While I wait for the motor, I am literally working on 3 other builds simultaneously, one of which needs to go to Luftgekuhlt which is on May 7th. For you non air cooled types, think of Luftgekuhlt as a kind of Sharktoberfest.

Today I found time to address the aero; the side skirts are complete, and I picked them up. They are nicely rendered in Carbon Fiber and weigh next to nothing.

Before I proceed, let me state my position on race car aerodynamics for the privateer; IT IS ALL BULL****. None of us has a wind tunnel. None of use effectively has the means to test spoilers, splitters, skirts, diffusers, or any of that stuff. Everything I do here is either a copy of what I have seen on another car, or a shot in the dark at best.

It is based on what I consider to be sound principles, but at the end of the day I have NO IDEA if it works, and my seat of the pants will be questionable at best.

So why do it? Easy, because my gut tells me the aero on the Devore car is lacking, if nothing else just by just what aero aids are missing from the car with respect to, say, your average modern GTLM car like an RSR, C7.R, etc etc.

Anyways, I originally planned to mount the skirts with Dzus fasteners but after installing three of them, it was clear that the skirt needs a much more robust mounting scheme. I'm going to revise the mounting, but you can see what the skirt will look like, albeit kind of floppy right now.

I cut the fender to clear the skirt (Yes, I saved the lower piece in case I need to bond it back together) to create the air channel that routes air from the wheel well back to the skirt, thus relieving the wheel well of high pressure and lift.

Next up: I need to make the inner fairing that connects the wheel well to the skirt where the fender was cut.