depami

Excuse my ignorance, but if it is pressure differential between the CC and heads, couldn't you just plumb those "top center" openings to the cam covers to equalize things?

hairywithit

tying the CC to the heads will equalize the pressure but will, most likely, lead to massive oil leaks from the cam covers, end caps etc. The vents in the cam covers are there to provide a slight negative pressure to stop the oil seals from leaking.
If you look at the size of the oil return passages and remember that they inclined at 45 degrees (effective incline angle is increased/decreased by cornering) you can see that the oil has little inclination to return.

IcemanG17

hard to argue with the amount of time the Beast has spent at high RPM at WOT....I doubt any other 928, including track racers, have as much time at WOT..... which brings up a ???

Do you have data logging? Something that shows the amount of time spent at WOT during a run? I would guess its a fairly high % of time on course?

Bill Ball

You don't want a closed circuit here. The inherent blowby in the crankcase needs to get out of the motor, not into the heads. I crudely calculated about 75L blowby per minute in a 5L motor at 6000 RPM. That's assuming an effective 1% blowby. So, at that rate you would need to evacuate over a liter per second. Feel free to critique that.

James Bailey

I would be more interested in knowing the RPM on Tim's car at various speeds.

Bill Ball

I need to back up for a moment...

Greg, you've built and I presume dyno'd bunches of these motors. What's different here that produced such a pronounced problem? Is it simply that you had 4 extensions on the cam cover breathers this time?

James Bailey

Right you must vent the blowby but figure out how to keep the oil in the sump so the oil pump has something to pump. Who was it who plumbed into the exhaust used a angled fitting to create a vacuum then on a group dyno run fogged up the shop which oil vapors ???

James Bailey

Bill this was the FIRST engine dyno runs where you can load it and hold it at high RPM. All the dyno jet runs are over in SECONDS . Even Greg's chassis dyno can not dissipate heat fast enough for a sustained run.... So the HUGE delta is the dyno and extended running ....like an open road race or California auto club Speedway !

Bill Ball

Understood, and nothing I have seen so far keeps the oil from traveling out the breathers. The oil vapor and droplets in the high-speed stream just fly around the various diverters. The copper mesh people have added probably just makes it worse once it gets saturated as there is no way for the oil to go backwards against flow as long as you are on the throttle.

GregBBRD

I've never had any disrespect for Marc's engine building abilities...sorry you took it that way. One needs to really appreciate all the early development that he did..or was done by...I forget who started that company.

It was just my belief that he never got very far in solving the oil issues, with these engines.

As I mentioned, I've got engines with Accusumps on them...and I believe that is the only salvation, for these engines. Certainly, your engine is also going to pack oil into the cylinder heads and thus not have much oil "left" for the oil pump...it isn't much different than all the other 928 engines...except it is bigger. The Accusump is able to provide enough of a "buffer" to keep things supplied with oil.

I don't think is the "cure", I think this is a "patch" (which I've used) to keep these engines "alive". If anything goes wrong with the Accusump, I'm sure that disaster would follow, very quickly. There's enough to "pray" about, right there!

Clearly, a lot of things have changed, since Marc built your engine....development on these engines has made that technology very "old school". The current pieces barely resemble the pieces that Marc used. We have finally gotten to the point where we've worked through a lot of the problems that these engines have had, but there are still some nagging problems that are left over (oiling is one.)

However, it is great that your engine still runs well and still satifies your needs. That is a testimony to the careful assembly work that Marc did!

Rob Edwards

The day before SF10 we did more than a dozen separate Sharktuning runs over four hours with Mark's racer on Greg's Mustang dyno. If I open all the plots and count all the WOT dots in all those runs, I get about 1300. Since we're logging at 10/sec, that means that there was a combined WOT time of 130 seconds. And anyone that was there can vouch for the amount of smoke that was coming out of the dyno's cooling vents.

130 seconds of WOT on the engine dyno takes, uh, 130 seconds.

James Bailey

Craigs list add for a hotrod chevy.....guy said it made 270hp at the rear wheels and went 167 MPH.......on the dynojet

Ducman82

there is a guy in town here trying to sell an 82 with 50k miles for 16.5k. told me he went 197mph in it, with a factory top speed of 215..... uh huh....

GregBBRD

Edwards and I collaborate quite a bit these days...he's my main "go to guy" for a ton of things.

He's the smart one...

GregBBRD

Only if tested by dropping from a C-130 Hercules...it is New Mexico...and Lord knows there's been more than one thing dropped, out there!