GregBBRD

I'd guess that the pressure is significantly higher....almost has to be.

Stock 5.0 engines blow rods out the sides, too. I think the problem is systemic.

john gill

Hello All

After spending hundreds of hours in my own dyno testing and tuning , I know that there are many on this list and beyond that have spent a lot of money on strokers and such and like my own experience run on the verge of destruction (a wing and a prayer ) .

With my own GT , I originally planned that I would rev this thing to over 7000 rpm given the work done to the engine (shown here in this link for its history...... ://www.emtec.net.au/928GT_engine.html).

I found that every time I was mapping approaching 6000 rpm I was noticing that the 928 GT catch can was filling and spiiling , I run all the covers breathers into the can and from this can had to provide an overflow to an external container to catch the surplus oil that was generated from the heads. When you do the maths you quickly realise that when this fills there is not much left in sump , any wonder it goes bang as the 26 is the first to weld .(see air)

As GB has mentioned the heads chronically fill with oil and then if not adressed empty the sump .

In my case I would simply shut it down , as I plan on keeping my 100% record of not destroying any engines on my dyno.
Anyone who is chasing higher performance is kidding themselves, if they do not address the oil control issues.
I believe the only way is to dry sump it , if you take the time to research this as I have ,you will find that all the performance cars are dry sumped , even the lowly speedway car . if the oil pools in the heads there simply has to be a larger supply of oil available from somewhere or the inevitable will happen .
THe early engines had less area in the rocker cover to store the oil , this I believe only delays the problem not in any way eliminates it .

I was about to start my next project with higher (custom ) pistons and set of the CJ cams , but alas I now know that I cannot exploit the potential of this combination without a system of dry sumping in the stock GT car or I will have an expensive pile of trashed metal .

I know Kibort will stick his head up here and add his bit , as having his own personal god has certainly helped him.

So the development of a dry sump in the stock car is a must to be constructed as I want to keep the stock look of the handsome GT with all the creature conforts , happy to share ideas.

IcemanG17

I agree....I have personally seen many 944's with ventilated blocks....and 928's with "blown" engines...but I haven't personally seen a ventilated 928 block yet....key word is YET...

I just wonder how much the crankcase pressure vs stroke & rpm is correlated? I would think it terms of "air" moved the higher the stroke + RPM (piston speed) has to increase the pressure that is generated?

Here is part of my inherently flawed thinking....(NOTE I am not an engineer...I am a COP, who likes racing 928's and doesn't want to grenade my $300 engine) a friend who has built many 928 engines (not doc of course) and owned a GTS...found that when he kept the RPM under 6000 the oil consumption just about dropped off the chart.... My Estate that I keep below 6000 doesn't really consume much oil, other than the amount it leaks that is not correlated to the issue being discussed..... I wonder if the "overpressure" in the crankcase occurs at a certain piston speed (+time) that can be achieved by high RPM in a stock engine or lower RPM in a stroker.... My thinking from engines i have personally destroyed or know were destroyed is yes...there is a magic #.....

Since the oil problem in the tested stroker is above 5000rpm thats 52fps piston speed, which in convential standards is quite low... but maybe that is near the magic "trouble" area...since my bucket never goes over 52fps piston speed?

Of course my theory goes straight in the bucket when you factor in known successful wet sump 928's strokers...like the Beast and the Devek white car before that...they should have grenaded many times over....you can explain away Andersons due to his dry sump....but not Joe Fan and the other accusump strokers?

Once again....I just want a 928 engine design that WILL survive under harsh conditions, not matter the RPM or if corners are involved.....

Lizard928

I have been thinking about filling some of the cavity in the heads as well. It would be fairly quick and easy with some aluminium and the TIG welder. It could attach with the cam cap bolts, and would add very little to no weight.

Brian,
do you have pictures, or links to the vented 944 blocks?

IcemanG17

Colin
No.....I have been at the track were 3 different 944's grenaded....two were track days cars...one was a "lemons" racer.....

Hilton

Is it possible that building to the tight end of factory tolerances produces low enough leak-down that crank case pressure takes longer to build? i.e. there would be a longer period of sustained rpm's before a burp became an issue?

As an aside - I wonder what they did for the marine engines? Unlike a car, boats see sustained high rpm's for long periods of time, so either they blew them up regularly, limited the throttle to 5k rpms, or had a deep enough sump and oil capacity that even when the heads were totally full of oil the pickup was still well covered?

This thread also brings to mind the bizarre mystery oil pan baffle that was discussed this time last year, which appeared to have a factory part number, but remained unidentified.

https://rennlist.com/forums/928-foru...lies-heel.html

It looks to be a separator to catch oil thrown off the crank, and I now wonder whether it was an attempt to reduce the upwards pressure on the head drains, by eliminating interference from crank thrown oil?

daveo90s4

I've got a couple of photo's of Jacky Ickx's 748HP S4 32 valve twin turbo boat engine taken at the Porsche museum in 2009 but can't post them. If someone wants to add them to this discussion email me at doveringtonATozemailDOTcomDOTau and I'll forward them. One photo appears (but uncertain) to show a very very deep sump at the front (no steering system or ground clearances to contend with - did they just have a bigger sump with more oil??)

Vilhuer

andy-gts

wow what a beautiful engine......that oil pan has to hold a gallon or more of oil don't you think?

andy

928er

well the stock pan already holds 2 gallons (8 quarts) so this should hold much more than that...

m42racer

So after many posts that all seem to tell the same story, it appears that the answer here is to run one of these engines on a Spintron and see exactly what is going on.

We can all guess and think what may be happening, but this would tell us. May take a little to to fit, but the end result would be well worth it. I happen to know someone who has a Spintron, so I will see what can be done.

That marine engine has always inspired me that more should have been built.

GlenL

Vehicle motion is a big problem as well. The front sump and slightly-sloped pan mean that, in action, the oil isn't returning to the sump even when it drains from the heads.

Check that boat motor with the huge rear sump. You can expect a boat to be noise-up and the motor to be tilted. When a car is accelerating the g-forces are doing the same thing: pulling oil towards the back of the engine.

James Bailey

Also note they were oiling the turbos by tapping into the oil galley of the heads which by some degree might reduce the amount flowing to the heads. And yes that deep oil pan would easily hold another gallon of oil down far from the crankshaft....

GregBBRD

John:

Thanks for your addition!
I have yet to find a suitable spot, in a street 928 that will accept a decent sized dry sump tank. I think it will require a 5 gallon tank, in order to allow the oil to sit there and have enough time for the air to separate from the oil, so that. While there are several places that are possiblilities, none are this large and they all will transfer heat to the inside of the car. I think you will love what we figured out as a solution, for this engine.

GregBBRD

John:

Thanks for your addition!

Notes, below, in blue.