I thought the rod bearing problems were caused by not using the right oil and/or not caring enough about the car :dunno:


As to the rest of it, buckle up, it's going to be a bumpy ride





PLEASE NOTE THAT I DO NOT OWN AN M5 AND THIS POST IS NOT INTENDED TO BE ARROGANT. PLEASE READ THE IMPORTANT REVISED DISCLAIMER THAT APPLIES TO THIS POST

 

Yes, I came across those opinions, too. Surely that is a potential wear/failure point, but it does not seem either that common, even with a statistical proportion of poor maintenance situations, or otherwise a design problem that would easily be addressed by substitution with fatter rod bearings (typically, rod bearings seem undersized for what the rod big ends could easily carry). So I'm not particularly worried about that, as the motor in mine has always had frequent oil changes with nice (I won't say "proper"!) oil (10W-60). And I have not heard any informed remarks about design or execution flaws in the OE rod bearings themselves. But maybe I missed something. Of course any teardown of a 100k+ motor is going to show some nonuniform wear on the rod material, a large proportion of which is going to be due to oil starvation on startup.

My semi-informed opinion. Additional info gladly accepted. Stephen

 

There's NO reason to spend anytime at redline... shift 500rpm below it and live a long happy life.

 

Agree with above...there are documented "premature" rod bearing failures in cars where the rev-limiter was raised. I think the stock rev-limiter is fine at 7K, most of us who use the car as a DD don't really go there often if at all. I'm usually going fast enough by 6500K.

There is enough on this topic on this board to keep you occupied for hours or days (maybe weeks?).

 

One thing i can think of is if you have the car remapped to deliver more power late in the rev range, then you might wanna change it according to the remap (ofc at your own risc).
Without knowing where the RPMs will land when you push it above 7k rpm with the shark injector mod, i cant comment if the car actually is faster when the next gear changes comes at a higher RPM, at east my car doesn't feel slow with the stock rev limiter and gear changes landing at 4k RPM
With the stock map the max BHP is reached around 6100-6600rpm?? if im not mistaken so like you said in your first post, no need to hang at the 7k limit

 

Curious about what the high rpm cautions are. Of course hp n torque drop off sharply above the std indicated rev limit, so there's no point in spending any significant amount of time beyond 7k rpm; I'm clear about that. But where does the danger zone lie and what are the consequences?: at what point does valve float start to happen, what's the story on rod bearing failure, and is there a real problem with harmonic vibrations beyond redline? Can the chain handle brief overrevs (e.g.: up to 7400 rpm with the Conforti Shark Injector in order to get a better rpm on the downshift). In other words, what are the mechanical/structural/design limits on our fabulous S62 motor and what would let go first at sustained hi rpms?
If this has been asked and answered, plz advise. Thanx, Stephen

I would like to hear an answer on this too other than just people saying dont do it. I see people rev s54 with stock bottom ends to 8750rpm and those engines have the dreaded rod bearing issues as well... granted they also have solid lifters. A lot of s62 tunes bump up the revs to 7200 and I have also seen 7500. Are there any confirmed cases that this is causing a problem and if so what was the failure mode?

 

Yes but the S54 is giving away 2 cylinders and not far shy of 2 litres capacity. Its much les of a mass to spool up so it isn't really fair to compare it rev wise to the S62.

I agree with others on caution to be taken in raising it. Unless the car was specifically being built to do runs and a gearchange less would help out your trap time on the strip etc i don't see the point of hanging in a gear for that long.

Anything you get regarding information about will be purely anecdotal, as there have been failures with and without rev limits raised on here. There have also been plenty of people who haven't seen a failure at all. Because you'll never get 300 failed engines together at a bench and know every history detail about how its run, looked after, oiled, warmed up etc then the resulting failure or not isn't benched as the "test" isn't fair, hence unfortunately you have to go on opinions.

Its really up to you, but the consensus here i would think for the most part is:

The S62 "can" have issues with rod bearings and so why exacerbate that risk, however big or small by potentially over revving the motor for minimal if any gain?

Of course, you could raise away and live happily ever after, who knows. You have to decide pro's v (potential) cons, because there isn't simply one 100% answer out there.

My thoughts as well as the above on the issue is plenty of R&D by BMW was put into the rev limit, its there for a reason. Its not like any other part of the car where a compromise sometimes has to be made to satisfy something, like cabin noise, emissions, production costs etc etc, its a piece of code that says "let the engine rev to x RPM". If its set at something, you can bet its because overall its for the most amount of performance vs risk of failure, excessive wear etc, and also suited to the power curve of the engine vis a vis, power dropping off so there isn't really a point to set it further.

A remap may give you small gains at the top beyond a standard rev limit but in reality there are other areas of thos cars performance that hold it back, chasing a few HP with increased revs and perhaps increasing a risk of motor failure isn't worth it.

If you want 30HP everywhere rather than screwing the car to the wall for 4HP at a screaming 7500RPM, get a set of headers.

I appreciate the cost is a bit different but thats what happens when you chase performance figures on a performance engine. You simply have to pay

 

All good replies; I do concur that its foolish to try and spend time above 7k rpm - but sometimes it does happen and the question (theoretical more than anything else) arises as to what would fail first if the motor was pushed hard beyond its design limits. I would not want to be that timing chain nor the guides! One specific question is: at what rpm do the valves begin to float?
Thanks for the well-informed comments.

Re the S54 motor: my info is that the rod bearings were a chronic problem area. I have seen some grievously mangled crank journals in those engines.

 

All good replies; I do concur that its foolish to try and spend time above 7k rpm - but sometimes it does happen and the question (theoretical more than anything else) arises as to what would fail first if the motor was pushed hard beyond its design limits. I would not want to be that timing chain nor the guides! One specific question is: at what rpm do the valves begin to float?
Thanks for the well-informed comments.

.

Dinan raised the rev limit to 7300 and there were no issues. He warrantied his work, whether S2 or S3, so I think 7300 is pretty safe.

I have seen motors on the dyno up to 7600 rpm. No valve float, but after 7300, power drops right off the table. A function in large part on the cams. You are way better off at 5600 than 7600.

So if you need to "stretch" a gear at the track, consider 7200 or maybe 7300. Power peak is 6600 so really, by then it is time to shift. But unless you are racing for $$$, not worth doing unless once in a blue moon. There is a rev limiter for a reason (and remember, it can only protect you on an upshift, not a downshift!!!oohhh

Regards,
Jerry

 

I'm not sure this adds a whole lot to the discussion, but last month I was heading into the town of Vienna, VA in rush hour traffic and saw an e39 M5 with the license plate "8000 rpm." I was curious about whether he actually got his S62 to rev that high, and if so how. Traffic was too thick to get alongside, and I posted here in the sightings forum, but so far, no joy.

 

I'm not sure this adds a whole lot to the discussion, but last month I was heading into the town of Vienna, VA in rush hour traffic and saw an e39 M5 with the license plate "8000 rpm." I was curious about whether he actually got his S62 to rev that high, and if so how."

Maybe, but not likely. I would wonder about valve float and about the stiiffer valve springs which would mean more drag and wear at all lower rpms and all the time, too. I don't think the hollow camshafts would appreciate the extra load, either.

 

Basing truth of licence plates. If it was that easy......................................

 

Lol this rev limit stuff is getting funny... Why are people under the assumption that revving higher=faster car?
Unless you've swapped cams, ported your head, and upped the compression this is useless on these motors... Only thing these people are insuring is a shorter engine life... Bmw set this limit right from the factory

 

Lol this rev limit stuff is getting funny... Why are people under the assumption that revving higher=faster car?
Unless you've swapped cams, ported your head, and upped the compression this is useless on these motors... Only thing these people are insuring is a shorter engine life... Bmw set this limit right from the factory

BMW also gave us the crappy 540 exhaust manifolds! Everything is a compromise, and setting a reasonable rev limit is certainly in BMW's financial interest!!! 7k wouldn't be so bad if the power peak wasn't at 6600, not much "head room" to get max power. Adding a couple of hundred rpm to redline gives a slight bit more flexibility if you are running the car hard and are a little slow to shift.

Regards,
Jerry

 

It doesn't matter if your power falls off after a certain RPM, the real question is: for a given RPM and gear, at what point does shifting to the next gear increase torque at the wheels?

For my dyno plot, wheel torque @ 7000 RPM is always higher than wheel torque in the next gear @ the corresponding RPM drop until you get to the 4-5 and 5-6 shift, which is better to shift ~6800 RPM.

For example:
2nd gear @6500 RPM = 2470 ft-lbs at the wheels, shifting to 3rd would put you ~4200 RPM and ~1875 ft-lbs at the wheels.
2nd gear @7000 RPM = 2230 ft-lbs at the wheels, shifting to 3rd would put you ~4600 RPM and ~1890 ft-lbs at the wheels.

So even though 7000 RPM is 240 ft-lbs less at the wheels, it's still greater than any RPM in 3rd.

Long story short: let it rev!

 

Yeah, really. The way I see it, the car comes with "X" amount of fun in it. You can either use it up as fast as you can or you can dribble it out over a longer period of time. To each his own.

 

Con rod bolt stretch, anyone?? I will stick with ARP

 

Con rod bolt stretch, anyone?? I will stick with ARP

- Oooo, I don't want to think about that . . . . .