ptuomov

I was writing strictly about the stock setup.

I think that the theory and reality have converged pretty closely in the design and understanding of an internal combustion engine. I am not claiming that I know all that theory, just that the state of the art is close.

Does the 928 stock engine's piston pin batter the circlips? I haven't seen any evidence of that, but I have looked at pistons from a couple of 928 engines, not from thousands of 928 engines.

I think the bearing will always be centered under the rod beam as long as it hasn't lost its crush, in which case we'd have bigger problems. The rod small end has room to move sideways on the wrist pin. The rod is guided by the big end with crankshaft. The stock rod side clearance is something like 0.25mm per two rods. Furthermore, the oil pressure tends to center the rods back on the journal if they stack in one end. With the rod length being 150mm, center to center, and piston to bore clearance tiny, my instinct says that the tilting or rocking of the rod shouldn't be an issue for bearings that are 24mm or even just 20mm long. But that is just instinct, not theory or practice.

I don't think there's any reason to expect the rocking to be a less of a problem with shorter rod bearing. I just don't immediately see why it would be a big problem with 20mm long bearings that are used for most other engines. That doesn't mean it wouldn't be, just that my instinct about magnitudes says the rocking shouldn't be a problem. But it's just instinct.

Personally, I believe that whether or not the shorter bearing will work well depends on whether it can hold the load at the set oil clearance, oil viscosity, rpm, and weight of the components.

mark kibort

i run all stock set ups and my experience has been different. the fastest times ever recorded at laguna seca on DOT slicks for over 10 years now, and no issues. ( as reference. Anderson 1:40.1 in 2000 w 420rwhp, and then 1:36 with the big 500wHP in the 2004 range , while running 1:30.7 on real slicks as his best, while ive been running 1:36-7 for 6 years now at laguna on used DOTs). the point is, the 928 can survive some amazing racing forces and not blow up.

ahhhhh You are not there young jedi Knight. 2:02.xx on slicks is close, but rememeber we ran 2:01 on DOTs at 3000lbs, 2:04s on DOTs at 3100lbs 290rwhp, and also 1:57.xx on slicks at a much better HP/weight. Point is, we are pulling much more gs to run those times and still have no issues, again, even marks hay day, he was running 1:40.0 at Laguna with WC with the original work horse on DOTs. Ive run 1:36.1 on DOTs with a lot less HP.
again, this is not a driver comparison, i'ts a car going around the track, creating forces on the engine, comparison.
(scot, you , me, Petty has been running, as well as my old engine somewhere in arizona too!)

No issues what so ever. and most shifts are right around redline and has been for many many years. current engine is up to 50 race days, the holbert engine was 120race days and when it was pulled apart, there was no unusual wear on the #2/6 bearing.

slate blue

Perhaps, I can add something here just for general information's sake, engines that batter the circlips are engines that might be detonating but the best example of an engine that pushes hard on circlips is a top fueler. They don't use clips but alloy plugs that are trapped by the cylinder wall. So those plugs actually run against the cylinder wall. So they stay in place because they can't get out.

To address the fact that the crankshaft assembly does move backwards and forwards as allowed by the thrust bearing clearance. I read and through my own information gained by talking with Pankl Engine Systems, that in top end race setups that piston guided setups are used but sometimes the specification is double guided.

My understanding of double guided is a safety feature just in case of excessive bearing wear during a race. GB did comment about how the stability of the narrower bearing would behave in relation to a rocking movement.



Many would ask, what has the rod oil clearance got to do with stability. A piston guided cannot work with a normal bearing clearance. A piston guided rod is a very high quality piece and this allows a tight rod bearing clearance along with the correct bearing shape. The tight clearance steadies the rod and these bearings are short. When I implement this setup I will get the longest bearing I can, just for long life.

One advantage of the piston guided setup is that rubbing friction on the rod big end cheeks. A piston guided setup is always perfectly centred and this can add to bearing life. I would have thought any of the current strokers have a bearing about 20 mm long. In short, lots of bearing area equals higher friction but long life and of course the inverse is true also.

Courtshark

Tracking a stock oil system-equipped 928 and expecting to drive it like Cole Trickle is a recipe for disaster, based on the vast majority of experiences here. I've done 3 track weekends, so my input pales in comparison to the veterans here, but FWIW, I've added the 3/8" pan spacer, and I should be adding an external oil cooler here shortly. So far so good for me, knock on wood. When I installed the pan spacer, all of the rod bearings appeared to be in excellent shape. Like new. Remarkable for an engine with over 100k miles on it.

I thus wonder if those, like Doc, who experience a 2/6 failure, have an engine that missed an oil change at some point, or used an inferior oil, or just had bad luck (defective bearing?). I'm also concerned about the cooling, as in coolant, system of cars that have suffered this classic failure, as the oil is symbiotic of that, and hotter oil will foam/slosh around more easily. I've got a new aluminum radiator and mostly water for coolant, with Zerex G-05 and water wetter mixed in.

I use BG 20W50 oil, as recommended to me by a guy who professionally raced various V8s before getting into the lube business. It helps that this oil is free to me, but so far I can say that I've not burned a drop on the track, and the engine seems to run much cooler with it, too. http://www.nowearracing.com/bgpm1.HTML

Shifting below 6k RPMs is strongly recommended, as well as not taking turns at over 6k RPMs. This latter issue will come up for me next weekend at VIR, as at the end of the very long backstretch, I'm at the end of 4th gear and have to get down into 3rd in a hurry for the roller coaster. I'm not out there to win races, but obviously going as fast as possible is a lot of fun, so I will have to be mindful of this turn. In this video (START AT 2:16; the link I provided included that editing but RL starts it from the beginning) you can hear/see me baby it into this turn: I actually get to the end of 4th way before the turn in this version, and lift like a pansy.

Iceman, Mark Kibort, John Venniger, Mark Anderson... all these guys have beat the crap out of 928s far more than I ever will. The bottom line: is the 928 a solid track car? Absolutely, but definitely not on a "stock" set up if you intend to really push it. It's great to take out to the track as a weekend warrior in stock form, provided you don't think you're Johnny Mario Andretti and make sure to keep it below 6k rpms. And make sure your cooling system is in proper shape.

GregBBRD

This whole oiling and rod bearing issue gets pretty complex.....and "theories" with "conclusions" run rampant in every engine that is built And not just in the 928 world)....especially when built for high performance use. Once you get beyond the "rookie" level (which I consider myself to be) and start talking to the people that are involved in "big time" race engine preparation, you find that the debate over bearing failure and what causes it, gets worse, not better.

Cross drilled or not. 360 degree oiling or not. What bearing to use. Hugely debated topics.

And the people that use these engines have them fail every weekend.....even with the very best pieces, built by the very best people.

What works for one application may not work for another application. What works at one track may not work at another track. What works for one driver may not work for another.

It would be great if there was a "magically solution" that fixed every engine every time.

The reality is....there is not.

I offer about a dozen different solutions for different applications. Some people can get away with a stock crank. Some people need a "Chevy" drilled stock crank. Some people need a custom crank with custom rods. Some people need a pan spacer. Some people have detonation problems and need a system to eliminate the oil out of the intake. Some people have problems returning the oil from the heads and need a system to return that oil. Some people are turning more rpms and need a higher quality bearing. Some people have a home track like Willow Springs and need a complete dry sump system. Some people pull .8 g's with slicks. Some people can pull almost 2 g's with slicks. The same thing applies to "street" tires.

The whole trick is to recognize that there are different solutions for different applications and different drivers, be skilled enough to know the different solutions, and always build that particular engine one step farther than that owner needs....so it is reliable for him.

That's what I believe I am good at.

IcemanG17

nuff said

docmirror

Nope. Good fresh oil, right at the middle of the mark. It was Nov, so not too hot but I was watching the cooling and the oil temp and they were rising but still well in the zone. I used Castrol Dino oil in the engine which is pretty good stuff, and was rated for the engine. I'd driven about 20k miles prior to the track day without a problem except for some oil seeping into the plug wells and causing some misfire which I solved months earlier.

I was flogging it hard, and my plan was to keep up with the 997T that was just ahead of me on the track. He was getting a bit flustered with a doggy old 928 on his behind and he was on it pretty hard as well. I could see the tail slip out on two of the hard left hand corners but I didn't have enough pull and tires to get him on any straights.

In fact, things were starting to look up cause I was smelling brakes from him and thought I might try a pass inside on a decel zone. Two more corners and it was going great - right up until the rear tires skidded and a lot of red lights came on the dash...

mark kibort

There are things that make sense here, and others that are guess work. point is we have cars that are surving sustained high rpm straights , into long 5--7 second carocells at 1.5g or higher and not having any failures, and its not just one curve, its THOUSANDS! .... not like the "thousands of engines youve seenn apart" but (which is more like 100s). a g forces on the engine is a g force. it doesnt care about the driver or the tracks location. a turn is pretty much a turn for the most part. the only thing im concerned about with all the failures is the RPM the engine is turning, the duration and the oil used. I think many of the failures are guys being too careful with the engine, getting the engine RPM too low and the pressure becomes too low as well. this could be an issue. I try to always keep the engine in the prime operating range, of 4500rpm to 6500rpm for the entire race (30 to 50mins).
I also think warm up procedures are a good thing, and i cant tell you the number of idiots that think by reving the cold engine, that it warms up faster.
there might be damage that is caused by this, that shows itself on the track as a failure, seemingly oil related, when its actually some bearing damaged caused by abuse.
the soft Gycol bearings?? thats all ive used over the past 17 years of doing this spanning over 7-8 engines that are all still running today (or have never been damaged due to oil starvation) as well as the varied number of tracks visited , INCLUDING Willow springs (albiet it was in my early racing days, only running a 1:34 with a 280rwhp 3200lb 928. But add to that list, Buttonwillow's 4 configurations, Laguna , sears point, thunderhill , even Road America, and you see that if my engine is surving, its due to something worth understanding, not discounting because you think im driving around turns at .8gs on slicks Again, the times speak to the forces and they are as high as any have been seen with the 928, for 95% of all the track miles any of them have ever seen (sans when anderson got the 520rwhp and found pirelli slicks).

so, my point is, start doing what others are doing sucessfully and then go from there. that means, right down to the oil, shift points and oil levels. custom engines, all bets are off. once you start varying off stock, you are on your own here. you saw what happened when you changed out rods for anderson's beast because of a arguably defective, or weak design rod? the new design blew up in the motor for unknown reasons. previously, that motor had run for many years without failure,using stock 968 pistons, and your original crank and rod design. So did Joe Fan's and his is still running today, without a dry sump, turning almost the same times as Andersons car, and surving willow springs for countless laps.

some engines were dooomed from the start , with suspect beginnings.

I dont have many answers, but what i do know is that what we have done up here, has worked for more racing than any group of 928 racers in the country.
between Scot, Brian, petty and myself, we are not seeing engines blow up. forget about brians automatic, look at what he is doing now, on slicks with 270rwhp and running some very fast times at Thunderhill, which has some classic 928 challenging track characteristics.

if eveyone starts a bettter warm up procedure, keeps the oil level mid range, uses a real good oil like Amsoil/redline and keeps the RPM between 4500 and 6400rpm for the entire session, (but doesnt use high or/redline RPM around turns, and goes up a gear, meaning goes around sweeper turns at 4500 to 5000rpm ) you should see good results. (as long as the engine is good to start with.



your last point is well taken. You should be able to beat up these cars like almost any race car out there. and for some reason, they were designed right. but, like any machinery, they need to be taken care of and there are some precautions, like i mention above. one of the most important things, is oil. if you have oil that clicks on the oil pressure light after a few laps at a track near you ........... you have a problem or you are using the wrong oil. if you are putting around the race track, near idle around sweepers at high g loading, you are asking for problems, ironically because most do this to be "nice " to the engine. these cars can take the abuse and need the abuse to survive. high rpm causes high oil flow, and cooler tempuratures (ironically).. why, because high rpm drives the oil and water pumps, and those fluids are the life blood of your engine. I noticed a few times on cool down laps that the oil pressure drops significantly when i drive at the lower rpm.. so, when i do that, i reduce my speed to match, as to not get that drop in oil pressure.

mark kibort

try and find some spot on this video from 2008 a full 6 years ago , where i was going easy, or the tires werent screaming at the edge of adheasion.

these cars are MEANT to be abused and raced!

GregBBRD

Thank you for the same mantra, Mark.

Three points:

Parts inside race engines can and do break.....regardless of who makes those parts and how much they cost. Formula One, Indy Car, Nascar teams transport many millions of dollars worth of replacement parts around with them, because of this reason. We know why that rod broke. You have no clue, so any speculation or comment by you is just beyond worthless.

Everyone here knows that your experiences with the 928 engine are unique. I'm looking for solutions that the other hundreds of 928 performance oriented owners can use.

In all the time you have posted here, I have never seen you concede one solitary point. You have theories and no amount of evidence or fact will ever dissuade you from these theories. That makes any discussion or counterpoint a complete waste of time.

GregBBRD

The position of the oil pressure sender and the restriction make it virtually useless for track use. Any momentary uncovering of the oil pick-up will not be noticed. If people were to open up the oil sender restrictor and install it up in one of the cylinder head galleys, information from the oil pressure gauge would be far more valuable.

docmirror

You sir, have keen hindsight, and a very good grasp of historical situation.

I always enjoy words like 'virtually'(having the appearance but not the fact of an attribute).

I bought a Porsche, one that said it was "race bred", I even bought one that's a GT which is supposed to be top of the line, ready to go. I went on ONE track event not knowing that the 928 engine gurus put the oil sender in the wrong place, and I paid the price.

I'm not on here whining about it, I'm an adult, I take care of my mistakes(or the engine designers). The guy asked a question, and I try to fill in so someone else doesn't suffer. But - once again, we sure do appreciate your 20/20 retro-vision.

BC

This.

BC

Just knock out one of the small plugs on the head galleys? And stick a pressure sensor there?

GregBBRD

Sort of. Obviously going to need the thread the cylinder head. And the stock sender has huge threads, so a different VDO sender is required.

This is just one thing that makes Kibort's theory that the failures are totally about oil and oil temperature so silly.

Anderson, before he went to a dry sump system, would bring his car back into the pits, at Willow, with the lifters clattering like crazy. The only way that is possible is if the pick-up ran out of oil and sucked air. I don't care what oil you use...if the pick-up gets uncovered, the engine is going to fail......and they did.

The stock oil pressure sender has a tiny, tiny restriction in it. This restriction is there to "dampen" the sender, which is great for the person driving down to the 7/11 store who doesn't want to see flickering needles....but not so good for a race car.