Safest max RPM when engine is cold

[NyteByte]

Okay, here's the situation:

In the mornings when pulling out of my street to go to work, I have to turn onto a busy 4 lane road. The road is curved and has a hill right before my street, so I can only see about 1/10 of a mile down the road for oncoming traffic. I make a right hand turn in the same direction as traffic. The speed limit is 30 mph since it's a residential area, but most people do 60+ (I live in the Chicago area where most drivers are anuses).

If people obeyed the speed limit, I wouldn't have a problem. But, what frequently happens is:
- I'll look down the street and wait for the coast to be clear
- I'll make my turn onto the 4 lane road
- Some butthole(s) will come flying around the corner at 65 mph and pretend like they are going to ram me. Some of the more extreme buttholes will even speed up.

Needless to say, it's very dangerous. Five teenagers were killed a couple years ago coming around the curve. Ricers always drive nuts through there too. I'm lucky I haven't been killed yet. I usually try to accelerate to match their speed by the time they reach me, or at least come close (which is very easy to do in the Cobra). This lessens the danger significantly.

So, the question is:

What is the maximum safe RPM I can turn without stressing the engine. Remember, the engine is cold and has only been running a few minutes.

In order to get movin', I have to get on the throttle a bit and step into the boost a little, but I try to keep it under 2500 rpms. Most of the time I can usually keep it under 2000 rpms and merge safely. Is this OK for our Cobra engines when they are cold?

I have a friend with an M5, and the redline on his tach will change depending on how hot the oil is. On a cold 25 degree Chicago winter day, his tach will show a redline of 4000 rpms at startup. It gradually gets higher as the engine warms. However, the M5 engine is very different and runs a heavier weight weight oil.

So, what do you think?

 

[PowerWheels]

I live on a wide street that people drive fast down, although not as bad as it used to be. Anyway I told this lady across the street I was going to put in a speed bump and to my supprise she offered to help! :thumbsup:

 

[Venomous98Cobra]

I am sorry I can not help you out...but I think that M5s are bad@ss!

 

[PowerWheels]

Wow, that changing redline is cool!

 

[mswaim]

In 25 degree weather you should be allowing your motor to idle a few minutes before moving, but I would think your fine as long as you keep it under 3,000 rpm's for a few miles. Always keep in mind your tranny and rear end also need a little time to wake up on cold mornings. :rolling:

 

[florida03]

I do the same thing but I live in a quiet area.
I let it warm up 5 min and dont push it past 2500
after that. I dont touch the boost until I hit I95.
Your best bet is to let it sit 5 or 6 min(started) and
go on your way.

 

[Brad]

How hard is it to either warm your car up or not run WOT while its cold?

I can pull onto major highways at 1/3 throttle from a stop in my explorer and I don't have any issues. I'm sure people pull out onto this road you're talking about in cars with less than 400 horse on a daily basis without issue.

Its not a good idea to run it hard when its cold so just warm it up or drive normal. I can't imagine needing to peg the boost gauge to get into traffic.

 

[Undy]

Forged pistons have a higher coeficient of expansion than cast pistons do. (they swell more) Until your engine comes up to it's normal operating temperature range it's better to keep your rpms as low as possible. The big hazard is a problem caused "piston rock" The piston actually rocks (minutely) in it's bore because it hasn't "swelled" up to it's normal size. This can cause, in extreme conditions, the piston skirt to collapse. Typically though it causes excessive cylinder wall "scuffing" which results in poor ring seating. This causes excessive blow-by and high oil consumption. The denser the forging the higher the expansion rate. Our pistons are not a high density forging so they don't expand as much as some of the after market pistons do. Technology and refined manufacturing techniques has reduced to expansion problems somewhat over the years too. The Lightnings (5.4s) have much more problem with this than the Cobras do (4.6s). The longer stroked motor moves the piston pin up much closer to the piston's crown. This has a tendency to increase to potential for "piston rock". You'll find a lot more Lightning owners with oil consumption and piston slap problems than Cobra owners due to the 5.4.

 

[wjfawb0]

I just let it run 5 minutes in the driveway and then keep it below 2000rpms for the first 5 miles or so. In your case, sounds like you need to let it run for a while before you get on the road. My fiances 2000 Celica GTS with VVTL-I won't let the rpms go over 6000 on a cold start. after it warms up it redlines at 7500. I guess 6000 to 7500 is where the VVTL-I kicks in too. That is the only rpm band where the motor has any power.

-Jason

 

[PhillyCobra]

I would say that engine load is as important as RPM. In other words, it would be better to go with higher revs and lower boost to get up to speed, rather than short shifting to a higher gear, requiring more boost.

I don't find idling the engine builds up heat very fast. There is som much mass and such a large volume of coolant, that engine needs some load to warm up significantly.

Engine computer holds back timing and runs rich until coolant temp is 160 degrees.

I say just drive moderately. I think it's OK to go over 3000 RPM if you need to get up to speed fast, as long as it's part throttle.

 

[NyteByte]

Thanks for all your responses. Seems that most everyone agrees that 2500 RPM or lower is OK at light throttle, which is all I ever need.

 

[03BlownSnake]

My understanding:

When cold, the engine will start in Open-loop mode, meaning it will not pay attention to oxygen sensors and fuel tables set up by the PCM and will make the engine run richer then normal so it warms up faster. When the PCM sees a certain ECT (engine coolant temp) or CHT (cylinder head temp) it will go into Closed-loop mode, where it will now look at both oxygen sensors and manage its fuel trims as per PCM strategy. When the PCM sets its strategy to close-loop, its ready enough to drive as you would when hot or normal operating temp. The PCM will run in close-loop for about a minute or so.

So in short, let it warm up for 2 minutes, then you should be ok.

 

[trey193]

I never get my car over 2000 until the needle has moved off the cold mark. Once you see the needle starting to move you know the oil is heating up , but I would go about things a little different whether you are starting your car and letting it run for a few minutes before you leave, just keep the revs as low as possible until that needle starts moving!

 

[hwystr]

Just drive it like you stole it - it warms up faster that way. OK just don't bounce it off the rev-limiter.

Oil should be fine @ 20'F if your running 5W-xx or 0W-xx.

 

[coleman]

fyi, my car had signs of piston slap which might be a result of me getting on it when it was cold.

i'm going to have to take it easier with this new block and wait for the temps to come up to operating temp before i lead-foot it.

 

[caveman6666]

Originally posted by johnsonl
I live on a wide street that people drive fast down, although not as bad as it used to be. Anyway I told this lady across the street I was going to put in a speed bump and to my supprise she offered to help! :thumbsup:

Do what I did; find and install a stop sign.

 

[NyteByte]

Originally posted by coleman
fyi, my car had signs of piston slap which might be a result of me getting on it when it was cold.

Every 03 Cobra I've heard had piston slap when the engine was cold. Mine has it too. It's not overly loud, but you can hear it. Goes away after a few minutes.

 

[coleman]

geez, doesn't that weaken the piston?

 

[BuffDigits]

yeah have seen that changing rpm guage in the M3's as well.

Best thing to do is let it warm up in the driveway a little long (like 5 minutes) and then keep it up 3k until you reach normal
operating temperature.