DreamCarrera

Very interesting chart...

Thanks for posting.



I was not aware that the 997 GT3 had a 9,000 RPM redline. Is this true?

mdeleeuw

All good points above. Considering the piston/connecting rod and main bearings only, the peak acceleration of the piston varies with the *square* of the engine speed. So a 20% over-rev means 150% of the loading to the con-rods, pins, and main bearings.

Do you think that Porsche engineers left 50% of the strength in those components as a safety factor?

I for one would not consider an engine with significant over-revs, and understand why Porsche use it as a warranty gate.

Mike

No HTwo O

True, dat.

DGrayling

In the April 2012 edition of Excellence, it states: "A general health plan prescription for the IMS bearing in your 997 might look like the following: ... ... ... ...
6. With the engine at full operating temperature, drive with the engine rpm up; if possible in terms of legality and road safety, accelerate to or near engine redline once or more per driving cycle."

My question is would this be beneficial for the 9A1 DFI engines also?

RED HORSE

Don't know, but that is a regular occurrence in my case.

997_rich

I'm not sure if the piston/rod/bearing strength is the #1 issue with over-revs although it's a still a big deal. I think if you get into the over-rev range the valves are going to probably float a bit and the pistons are going to kiss off on them. That'll bend the valve and trash the valve train and the con-rod and lower end isn't going to like that either.

In most of the over-revved engines(in general) i've seen the valve train gets the worst of it. Anyway, that's the root of the failure but it sets off a chain of events that can take out almost anything.

911SLOW

It's not true.

https://rennlist.com/forums/8801553-post60.html

Macster

There's not any real proof this is beneficial to the older engines that it prolongs IMS bearing life.

A balance is really best. While one wouldn't/shouldn't drive the car around with rpms in the basement like he's driving some kind of farm tractor neither should one drive around with the rev limiter banging off the stop all the time.

My cars see high rpms -- near redline sometimes (not often cause there's nothing to be gained even redline). Not for engine health but for my health, mental health. These cars a blast to drive and sometimes when it is ok at high speeds, an even bigger blast.

If I lived/drove in an area where higher speeds were legal I'd run the car up to whatever the limit was.

Sincerely,

Macster.

Joe6pack

Lurking over from the 911 board and thought I’d add a point. Not the same I know, but when Ford designed the 289 K-code engine which was an upgrade from the 289 A code engine, one of the things they did was go to screw in valve studs as opposed to press in. They also used heavier valve springs to eliminate the aforementioned valve float. The connecting rods and hardware were upgraded and were identical to the rods used on later boss 302’s of Trans Am fame. They also used thicker main bearing caps and high nodular iron for the crankshaft. To my knowledge, the bearings themselves were the same. The horsepower was boosted to 271 at 6,000 rpms from 225 by solid lifters, carburetion, dual point distributor and exhaust. There was no redline as it were, but the rally pacs in those cars went to 8,000 rpms as opposed the 6,000 rpms for the regular 289 equipped cars. The point is that if you want to rev higher, things have to be made beefier. I doubt the redline is there for looks.

sameerg

Ok, so pardon my ignorance,
I have never gone near 6k rpm in my car. Does that mean, that my DME report will show 0 overrevs for all ranges?

jhbrennan

If you have been the only driver (no service techs) and have never bumped the rev limiter and have never grossly missed a shift then I say it's pretty safe to assume 0 overrevs.

cello

I have heard the same thing re the connecting rods. While certainly the valves can be damaged via mechanical over-rev, there is some concern on the part of Porsche that the rods might be a 'weak link' of sorts (factoring in track use, not normal street use). There is a guy with RTR that has done some testing or consultation work with PCNA on that issue. Dont know more than that...

vern1

OK this is too easy. You have never gone near 6K?? Come on??

gota911

PDK won't let you downshift if that action will cause a mechanical over rev.

However, you can hit the rev limiter while accelerating and in doing so you will, in my opinion, get some over revs in ranges 1 & 2, just as you would with a manual transmission.

I don't have a PDK car but would really like to see a DME readout of a PDK car that has bounced off the rev limiter a few times. My contention is that there WILL be over revs in the lower range(s).

To me it is not logical to admit that a manual tranny car can and will have over revs if you hit the rev limiter while accelerating but then turn around a say it is impossible for a PDK car to have over revs from bouncing off the rev limiter while accelerating. I am not talking about a mechanical over rev (a.k.a. "missed shift").

J. Kid

I really hope your car is still in the new car "break in" phase. Buying mine CPO with 7,200 miles already on the engine saved me 3-4 months of the frustration of having such an awesome car and not being able to make it sing.