John Veninger

I had finally hooked up my oil pressure sender to my AIM data
acquisition system in the track car. Love this unit.

I ran the analysis software and was surprised at how big of an oil
pressure drop there was during the left hander at Lime Rock. The OP is
at 5+ bar during most of the lap with a drop to maybe 4.3 in some
sections. The left turn at LRP created a drop to 3.1 bar! The spike
down is quite interesting as you see the G force transition. The drop
happens for only about 3 seconds (don't have it in front of me).
There are other parts of the track (all right handers) that create
almost the same G force transition, but don't spike the OP down as far.
I'll try and post a picture og the graph in the next day or so that
shows engine speed, g force, and oil pressure during the lap.

Happy I have a drilled crank and an accusump!!

SteveM928

Isn't that drop in oil pressure exactly what the Accusump is supposed to be preventing? If I had gone to the trouble and expense of installing one I don't think I'd be very happy at all about it if I saw those oil pressure drops.

John Veninger

Just think what the pressure drop would be without an accusump!

Keep in mind that an accusump only give about 3-5 seconds of "protection".
3 bar is still about 44psi.

worf928

Ay yi yi!

That puts the nail in the coffin of tracking my '91 anymore.

Hmm... but John - you're running R-rubber yes? Do you have any data on what the pressure drop might be on good Max-Perf street tires?

Hmmm.... part 2... any data on what the pressure drop might be WITHOUT an accusump on street tires? (I don't suppose you'd turn it off for a lap when running your wets?)

Hmmmm.... me thinks the nails are still in the coffin. If the drop is significant with R-Rubber and an accusump I suspect the drop is just as significant with street tires and no accusump.

Accusump goes into the '89 right after the suspension work is done. That was the plan anyway.

SteveM928

The general rule of thumb that's often mentioned as far as sufficient oil pressure is 10psi per 1,000 RPM. In that case, that 44psi would be acceptable for up to about 4,400 RPM. Doesn't exactly give me a warm fuzzy feeling about the Accusump being the solution that some might think it is.

Do you know what kind of cornering G-forces were occuring when the pressure drops happened?

John Veninger

Running Hoosiers. No data on Max tires, there to slow

I would be happy to run on my wets if you want to bond the motor

John Veninger

About 1.2G. The left hanger at LRP puts the RPM in the 4K+ range, so were safe

mark kibort

Dont forget Im not running an accusump or any other mods at all for the Holbert race car. going on 3 seasons, running Amzoil, and have video of my oil pressure around a track like Sears Point ( very close to as many turns if not more, than LimeRock) the carocel is a 80mph half circle turn that hasnt dropped my oil pressure, nor do the other turns. (3rd gear, going into it at just under redline, hard brake and a 80mph lefty, 4500rpm or so, constant power through the turn). At tracks like Laguna (almost all lefts), there are very few places where the duration of a high g-load, would last over a second or two.

to keep a measure of the type of gs im pulling, my times are over 1.5 seconds FASTER than Mark Anderson his first time there in Speedvision back in 2000 on simular tires. (since, i have 100less hp, you know im making it up in other areas, like braking and cornering). Now, of course, Mark A is running 5 seconds faster there than i am on the same tires but with now, 150 more hp. the point is, the stock 928 can run some pretty hard and fast laps, without an accusump, if the right oil is used and attention is paid to RPMs and duration through the turns.

(yes, still knocking on wood!)

Interesting that even with the accusump, the oil pressure dipped?

what type of oil were you using???????

Next question, is how accurate is the oil pressure gauge and sensor? I would imagine it is fairly accurate!

Those are my thoughts .

MK
PS, check out the videos posted below on these sites, and grab a stopwatch and see how long you stay in a high g mode though turns at sears and laguna. the electricsupercharger site has under( prove it) in the video area, a couple laps at sears or laguna, while the 928motorsports site has a couple of high bandwidth video clips at laguna and sears as well of the Holbert car running against either a cup car on slicks or Don hansons 420hp beast on slicks as well. (vs my hoosier, 5 liter mouse motor Holbert car)

www.electricsupercharger.com

http://928motorsports.com/othervideos.htm

worf928

Hmmm.... let's see....

my money and my pain if the '91 shreds a 2/6 bearing...

or

my money and your pain if you shread a 2/6 bearing...

rob rossitto

http://www.performance928.com/cgi-bi...ss_parent=1128

there's more!

drnick

why is it left hand corners?

SteveM928

Okay, so now we've got two examples of pretty clear evidence that there's a left turn issue, even with an accusump in each case.

Mark Kibort,
I know the question of whether your cams may be somewhat different has come up before, and I think your recent cam chain issue is also a pretty unique thing. Obviously others have had oiling and rod bearing issues where you haven't yet in the Holbert car. Have you ever had the oil pan off, or engine apart, and taken a good look in there or at the crank? Maybe some sort of other possibly a little different than other 928s stuff going on there as well?

bshaw

Tha Accusump has to detect a pressure drop before it can kick in. The electric valves come in different ranges. Mine is the 35-40 PSI valve, as I would guess is John's.

glenn faken

john

curious if you still have the early oil pick up and screen covering the sump area or have you updated to the later version.

glenn

John Veninger

My accusump doesn't have the "new" pressure valve. It releases oil as the pressure goes down.

I'm running the new style pickup.

I was always aware of the "left hander" proble via the excellent work by Mike and Louis. I just haven't seen actual G force, oil pressure and RPM on one graph.