What is Considered Low RPM Driving?
 

The bore scoring video had suggested that one hypothetical reason for bore scoring was low RPM operation. Something like piston rod angle if I recall. So, what is considered low RPM driving? My manual suggests shift points at 3K RPM. What about cruising RPM? Under 3K? Over 3K? Just curious about others opinions. I have a hard time shifting at 3K BTW. Usually 4K and over.

Thanks,
Kyle

I recall a post by a respected member of the forum noting don't drive above 3k RPM when cold and not below 3k RPM when warm...I subscribe...and don't give a rip about the gas mileage.

Perfect.

And avoid cruising at 2200-2400 rpm.

The builder of my engine, Flat6Innovations, advises: "This area of the RPM range (2,200-2,400 rpm) is where the most stress is placed on the valve train components due to the variocam arrangement which does cause accelerated wear of some components". So i don't cruise at that range and recommend to others to avoid doing that. Better safe than sorry.

I need to make a t-shirt that says "2200- 2400 = DUH-DUH-DUH-DANGER ZONE!"

I just put red tape over that section of my tach to remind myself to drive faster.

you have to remind yourself? :burnout:

I'm not convinced. Tips shift at much lower RPM and I don't believe they are more prone to bore scoring.

Valve train wear isn't the same as bore scoring.

So, I've been driving under 3K until it gets to operating temp and over 3k after reaching operating temp for the past two weeks. My mileage has increased by 2 MPG. The higher RPM seems to be more efficient?

I keep things 3K rpm and above cruising.

You should believe! This was discussed (might have been in the IMSB sticky) and explained a few months ago by some of the best in the business.

The m96/7 engine seems to me to be happiest at 3k rpm, when not idling, keep as close to that as possible until you are ready to RIP !! :burnout:

This I can totally agree with. Seems most happy at around 3K RPM and I have not used 6th gear in years. Plenty of highway cruising in 5th gear.

Same here, 3-4K all day long!

It seems difficult to "cruise" at 30 to 35 mph... between 2nd and 3rd Opt for the lower gear, just maintaining speed...??

Drove 80+ miles today trying to avoid the 2,200 - 2,400 rpm range, what a nightmare! I have a 03 C2 w/tip.

I had to drive in manual mode the whole time and I realized that I had been cruising a LOT in that range. In 5th it's at about 65mph, 4th about 55mph, as you can see, what a pain, but I will keep doing that if there's a big benefit in the end.

Argh! hope this is all worth it...

Carve this in stone.

TC

I feel a decided bump when I get to 3300-3400 rpm’s with my 3.6. I always thought that was where the vario cam changed and never looked into it. Hummm, you learn something new every day.;)

TC

My 3.4 Variocams kick in at 5k. I try and cruise above 3k - but it can get pretty noisy at a constant 3,500!

If you are just "cruising along" with very little throttle at 2500 is that a no no?

Because I do that...then if I need acceleration I downshift one or 2 gears and acceletate at over 3000....good?

The tip seems to "cruise" in the dreaded RPM zone on the highway. I also find myself often using manual mode for cruising to avoid that RPM range. But, you know, the 6M guys have to do the same, so I guess one can survive. :)

Is it worth it? Don't know what the typical valve train repair bill is, and I never want to see one.

The learned advice is to avoid 2200-2400 so i would think 2500 is fine.

Assuming is bad but I would think the middle of that range (2250-2350) is the real bad place to be so following the advice would keep you far enough away from the danger zone.

I just stick red tape with a big $ on it over that RPM range as a subtle reminder. :rolleyes:

Good stuff here. Warm meaning water temp or oil temp? I assume water.

Both. They are related. Water temp should be close to 180 or above for 10 mins because oil temp lags water temp by 7-10 mins in this car.

I actually find the car drives really well in 3rd and 4th gear unless I am on a highway, she stays around 3k if I am not ripping it.

Maybe I'm just dense, but I've spent a couple hours reading threads dating back as far as 2008 on this topic and I'm still confused about a couple of points.

My main question is about steady(ish)-state cruising conditions: meaning situations like a fully-warmed-up engine, flat/gently rolling hills, and empty highway (no need for sudden passing power) where it's easy to just set the cruise control and enjoy the ride. I just did my first longer commute (about 100mi) in my 2002 C4 MT Cab and thanks to working a really early-AM flight I had mostly empty roads along the way. I did some experimenting and found that in the 68-73mph (Waze GPS speed) ranges that I was cruising at I could either be in 5th at 3100-3300ish RPM or 6th at 2600-2900ish RPM. The engine seemed pretty happy cruising at those speeds in 6th and if I gently bumped the throttle it didn't seem to struggle at all accelerating, so I'm relatively sure I wasn't anywhere near "lugging" territory (and well-clear of the dreaded 2200-2400 range), but when I came on here to do research I saw a lot of debate around these conditions in the 2008-2013 timeframe and not much since (the more recent comments seem to focus on warm-up procedures and/or more spirited/traffic driving conditions where punching the throttle to pass makes more sense of keeping >3k RPM).

A couple of the threads/posts that have simply left me more confused are ones like...

This 2019 one where @Charles Navarro seems to indicate that 2200-2400 really isn't something to be actively concerned with on the 3.6L engines (not that I'd want to cruise there anyway, but it'd be nice to know one way or the other as general knowledge). I got the impression that this is the range where variocams are flipping open/closed like light switches on the 3.4Ls and the variocam plus' on the 3.6L aren't affected because they actuate over a much wider range, but I've also seen other threads saying completely different numbers for the variocams on both engine types.

This 2013 comment from @Flat6 Innovations where Jake implies that the lower RPMs from people using 6th gear has made him a bunch of money, but doesn't specify exactly how. I'm guessing(?) he's referring to lower RPMs causing IMS failures, but is 6th@2500+ cruising still in that danger zone? How does having an IMS Retrofitted/Solutioned car (mine has the Retrofit) affect this discussion? I don't recall post warm-up cruising revs being mentioned in the bore scoring series, but are there other non-IMS concerns about this range?

I've also seen a bunch of older references to the idea that the "keep it above 3k" rule is more of a carryover from the air-cooled days than anything else, but I'm not sure if time has proved that right or if it's still true for the M96.

So, I guess bottom line: are Dak and Az968 right that 2500+ is fine as long as you're at low load/cruising/going easy on it?

I've only driven my new (to me) C4 Cab MT 3x's so far.

Haven't over reved it at start up but haven't paid any attn to the revs at time yet either; will in the future.

Have seldom had any problem keeping it over 3K rpm while driving and I haven't had to use 6th gear yet; been mostly using 2nd-4th.

Only hit the redline cutout once at 7k+ while doing a pass on a narrow backroad; was paying more attn to the road than the tach.

Don't think the revs,have dropped much below 3k except when stopped at a light. Will pay more attn to this in the future.

With direct injected engines, the zone where LSPI occurs is below 2000 rpm with high engine load. Also, with direct injected engines you don't get good atomization of the fuel at low speeds. That's one reason manufacturers are starting to use port injection and direct injection simultaneously, as port injection works better at low speeds and has the added benefit of keeping the ports clean.

With 5-chain engines Boxster 97-02 and 996 99-01, the Variocam kicks in at 1500 rpm and kicks back out at 5500. For sake of the variocam wear pads, it's good to not run the engine around either rpm where the variocam is going in and out repeatedly.

The later 3-chain engines use a vane-cell adjuster for varying the cam timing, so this isn't an issue.

The drive it like an aircooled Porsche recommendation is a safe one.

The biggest thing is keeping your foot out of it until the engine is to full temp. Remember, the oil isn't at temp when the coolant is reads the engine is warmed up. Depending on the ambient air temps, it can take quite some time for the oil to get to temperature. The ZDDP and Moly additives in the oil need temperature, pressure, and sliding to activate and don't work their best until the oil has warmed.

With older vehicles, if you see mayo on the oil fill cap, it's likely your oil isn't getting and staying at temperature long enough to vapor off moisture and shortening drain intervals to 3 months or 3k miles is probably a good idea.

As far as steady state, the only real concern there is during break-in on a fresh rebuild (or new engine) - you need to vary loads and rpms and lugging the engine too helps with seating the rings.

Like we always say, drive it like you stole it (but with the caveat that the engine needs to be warmed up first)!

I see Charles was posting when I was and ge gives a mucho better technical explanation because he knows what he's talking about.

So I'm going off advice from Jake that the 2200-2400 issue has to do with the variocam/valve train wear (can't remember specifics but i'll try to find my notes), not the IMS. My car has the IMS Solution and he still advises avoiding the 2200-2400 range for sustained periods. So I would believe cruising at 2500 is not an issue.

The warm-up advice around seems to be "under 3k when cold, above 3k with hot". But for long cruising not under load what you are doing should be just fine. Car is more responsive about 3k, because Mamma, that's where the fun is!

Its not just the rpm, its a function of the rpm at what cylinder load (how much throttle). You want to avoid situations where you are lugging the engine at low rpm and having to keep it going by really planting your foot on the gas.

If for example you are coasting down a slight hill and you're in 6th gear with a tiny touch on the gas to keep it going (like barely off idle), its fine to be at 1500rpm, you never want to be that low rpm going uphill with your foot planted down.

What you are doing is perfectly fine. Charles’ advice is spot on. Jake’s advice about specific RPM range is probably a vibration resonance problem on specific components...

The 3.4 Variocam turns on at near 1300-1400 RPM and then back off again above 5900 RPM and below 1300. So every time you come to a stop, the Variocam switches. I don’t think we need to worry about those switching components for that reason.

Thanks for the clarification and especially the reminder that the oil takes a lot longer to get up to temp than the coolant. Sounds like I should be ok cruising in 6th under those conditions. If only Porsche had been kind enough to give us a reliable indicator so we wouldn't have to do so much guesswork on warm-up! It's going to be a year-round DD for me, so I guess I'm going to have to go spend some time reading those threads about people endeavoring to add real oil temp readouts...