hwyrnr

DeWolf

^ Yeh, I just hold it at redline and then dump the clutch. Not sure I get what your saying. How you use full power from a standstill?

beran earms

Maybe Otis can give his advice!!

OTR18WHEELER

,yes there are several reasons of course...
It will cause increased fuel consumption, increased tire wear, and it freaks out all the minivan crossover and Prius drivers.
It could also add enjoyment to your cross town commute.

worf928

High-load low-rpm acceleration is ‘hard’ on an engine because it is the easiest operating regime to provoke knock and where oil flow is relatively low thus increasing the (small) probability that a knock event will do (a tiny bit of) damage to bearings.

If you hear engine knocking under certain conditions, then STOP operating the engine in those conditions until you fix the problem.

If there’s nothing wrong with the engine it’s not a problem.

On ‘89+, where I can operate the Hammer in knock-count mode, one of my inspection criteria is WOT knock-count at low rpm. Basically, I try to provoke knock. A healthy 928 should have a count of 0. Spec is (IIRC) < 10. GTS’s usually fail miserably.

vanster

Think of that crankshaft turning away at 2500 rpms a suddenly you ask it to spin up. 2500 is not a bad range to ask it to do this because by then it's already even on all its bearings. Lower revs like 1500 it's not. I'm not sure where your motor is "on the cam" but most likely around 3000 so it you ease into the 3k range then nail it, you will not be doing any harm and your engine will thank you.

OTR18WHEELER

Ok, ok, I can be serious too, the weak link will break under high stress loads. The s4 tapered shafts have a known sheer defect, never heard of axles or cv joints failing due to low rpm acceleration.
The use of the correct oil, and gasoline for the engine as it was engineered to use will prolong the life of the engine under normal use.
The entire drive train is composed of many wear items, deferred maintenance and abuse will certainly break the weakest link.
This thread could evolve into a HUGE oil and fuel debate, but I digress on those topics as they have been covered multiple times already.
ps btw, I only use 92 or 93 octane pump gas, and dino Castrol 20w50 oil.
('85 with 106,xxx miles on original gasketed engine. )
OTIS out...

hwyrnr

More or less it’s a 30 year old classic sports car with aged parts. So it’s not necessarily a 928 things, it’s a classic car thing.

dr bob

Hmm. Were I to offer full throttle to my 928 at 1500 RPM, the trans would shift down at least one and usually two gears to allow the revs to increase before full torque loading occurred. There are some advantages to the auto gearbox.

And FWIW, I have a much bigger concern about high-speed detonation, especially in cars that have some miles since injectors were last or replaced.cleaned. Further, the GTS oil vapor ingestion issue contributes more at higher loads and RPM's, compounding my high-speed detonation concerns. The LH brains offer some enrichment to the open-loop map under these circumstances, reducing the detonation risk some from lean-out. The extra oil vapor can't really be compensated fro in LH tuning though, except to drown the charge to try and keep it cooler.

ptuomov

If it’s a street car engine, it should be able to take WOT at any rpm. Race engines are another story.

worf928

Majestic Moose

Well I think the idea would be to avoid lugging the engine. Full throttle at low rpm will hammer the rod and crank bearings. I believe the cause is that the fuel/air mixture in a cylinder will complete its combustion before the piston reaches the end of its stroke whereas at an appropriate rpm, combustion is completed near the end of the stroke resulting in a smooth push to the piston all the way down. Add to that lower oil pressure plus knocking and this becomes something to be avoided. As the rpm increases the ignition deals with this by increasing timing, meaning the spark is ignited earlier. Now I don't know what that rpm is and a V8 is pretty smooth at low rpm so it is harder to sense. You can cruise all day at 1500rpm but I would not go full throttle at that speed. Either downshift or gradually increase throttle till you get to a safe area, and 2500 for me is entering the safe zone.

My daily driver is a 3 cylinder and you can easily tell where it is lugging by rough running and vibration of the engine.

hacker-pschorr

Exactly - this applies to every gas engine ever made.

So never get on it until after 2,500 and yet in another thread people are saying 928's are rarely driven pas 4,000rpm..... What are these, diesel engines?

I have to assume this is about 5-speeds since the torque converter in a properly setup automatic keeps the RPM's above the stall speed which is around 2,500 or higher already. That should tell you something....and in my opinion the stall speed is too low in these cars (and yes I'm changing my 87).

The redline in 928's is very, very conservative. Once engine temps are up I make sure to hit the peak multiple times when I drive my cars, always. Even my Yukon. It's very much an "American" thing to lug engines around relying on low end torque versus horsepower (yes, I just went there).

All that being said, the early US sold 5-speed mucky up this water a bit since they are gutless past about 5,300 - 5,500...but still I run them up since shifting at 5.3 drops you a bit too low in the power band when going for full acceleration. Even still, why would you want to try an accelerate below 3k, these cars are not even making 125rwhp:
https://rennlist.com/forums/928-foru...t-exhaust.html

So no, do not be afraid to rev the snot out of your engines, just don't do it when everything is cold.
If you are lumbering along at 2k RPM and need to accelerate, downshift...that's why there are 5 to choose from.
"Lugging" the engine around is a great way to cause detonation which will damage an engine much faster and more catastrophic than running it up to reline with a warmed up engine.


Our Beetle is at 4k rpm at 80MPH is top gear........

dr bob

Joys of modern FI and ignition... With both mapped to consider any load at any RPM, "hammering" the bearings at 1500 RPM is no longer an issue. Really. By 2/3 throttle we are off the relatively-lean closed-loop operation and into the loaded open-loop maps. Plus the S4+ knock sensors offer additional adjustment for when the mixture in a particular cylinder is lean enough to cause a knock. These aren't early 911's with big carburetor chokes and poor mixture management at low RPM's.

Meanwhile, higher-RPM detonation is not readily heard by the driver's ears over all the other "normal" noises from the engine at speed. Any weakness in fuel delivery shows up first at high flow demand. That's the same as high RPM and lots of throttle. Famous 928 sage Jim Bailey opined that a partially-clogged fuel filter never keeps a car from starting. Reduced pump capacity for any reason (wear, low voltage, clogging) shows up first at the same high-load conditions well before it keeps the car from starting or idling. There's a much greater likelihood of detonation and bearing damage from these "normal" deterioration causes than at lower RPM's even at full throttle.

My driving habits are pretty much the opposite of H-P's: I rumble around with the tach very seldom sweeping the cobwebs from the 4k+ segment of the dial. No need. Yes, I do run it up over 100 once in a while, but mostly to lose casual tailgaters disappointed that I'm only rolling at 65 through the 55-posted mountain lakes highways here. Still that's a gentle roll-on rather than a full-throttle low-RPM blast.

FredR

I fully concur with Dr Bob's observations. Although there is no normal logic for hoofing the car at low rpm's I have done so during my sharktuning runs. To do this on an automatic one has to undo the kickdown cable, run at low rpms in either 2nd or 3rd and then plant the throttle. I saw no issues with knock but then I reckon my motor is reasonably well tuned. Under normal running with the automatic variant and the kick down engaged full throttle operation does not happen at less than about 3k rpm. The region most prone to knock seems to be at about the point where the flappy changes over [possibly because it is changing] and then at around 5200 rpm - the latter probably because cylinders 6 and 2 flow more air and thus run slighly leaner.