OT: Redlining cold engines
10-10-2009, 08:00 AM
#31
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OK, i just got to get in on this one. I bought my first 911 6 months ago, 99 C2, with a factory replacement engine in 03. I've put 13K miles on it and that's more than it had when i bought it. I'm going to go out on a limb and say that the most important thing you can do to preserve your M96 is a slow, careful, loving warm up. Ask yourselves, 'why does Dr. P put the laminar flow oil-water heat exchanger in there?' Why does he put in a thermostat that opens so late? Chevy V-8's are beautiful things, just try to beat a well prepared 944-LS2 conversion on the track. (EVERYBODY hates those things) That has nothing at all to do with a German made small displacment flat six. Apples and oranges. I run swepco 201 in my transaxle, heavier than P recommends, (I would bet that if the engineers did'nt have to account for the everyman the'd spec heavier) I double clutch UPSHIFTS until it's warm. FEEL it people!! That transaxle has cold sincros, and when it's nice and warm the 201 works beautifully. Part of the culprit here is these fantastic computers that make a cold engine run like it's nice and warm.........it's not. Love the site, all very interesting. My 944S2 has 240,000 miles and 2 track seasons and has never been opened, I warm it up very carefully. Cheers!
10-10-2009, 11:31 AM
#32
Race Director
As for #2, remember most race engines are not the mechanic's engine. Somebody else pays for that engine. If someone would pay for my engines I wouldn't care about red lining them cold either. (Well, I would care and I wouldn't red line the engine cause I know the potential for what can happen to a cold engine treated this way.)
For races where there is big money involved. a race car engine will not see red line cold. The engine will be treated with all the care and consideration a very expensive and very precision assembly that it is deserves.
If I were a race team owner and caught a mechanic redlining a cold engine I'd give him a chance to work for a competing team.
Sincerely,
Macster.
10-10-2009, 11:50 AM
#33
Race Director
Yeah, wrapping a motor to redline cold in the North would more than likely have catostrophic effects 100% of the time. In the South where I live, probably be ok even in the coldest conditions.
Hmmm. I am trying to figure out how this would create uneven heating. So, your combustion chamber and exhuast side of the engine would be hot while everything else is cool when idling to operating temps. This would be the differentiation I'd assume.
So, does the friction from (friction bearing, metal to metal contact) loads really warm up the engine that much quicker or is it the heat dispersed from combustion that ultimately is responsible for engine temps?
If it is the former, then I could see uneven heating.
We never got that into depth in school for aviation reciprocating engine theory (same as a car engine).
Hmmm. I am trying to figure out how this would create uneven heating. So, your combustion chamber and exhuast side of the engine would be hot while everything else is cool when idling to operating temps. This would be the differentiation I'd assume.
So, does the friction from (friction bearing, metal to metal contact) loads really warm up the engine that much quicker or is it the heat dispersed from combustion that ultimately is responsible for engine temps?
If it is the former, then I could see uneven heating.
We never got that into depth in school for aviation reciprocating engine theory (same as a car engine).
From cold, even at idle there will be temperature differences. Various areas of the combustion chamber, piston, valves and so on will heat up at different rates.
But at idle the degree of heating is at its minimum simply cause the engine is burning so little fuel.
A higher load from cold will of course produce more heat cause more fuel is being burned.
This also heats up the various components but does so much faster and as a result there are larger differences in temperature between the various components.
For instance, the piston crown can get quite warm compared to the cylinder wall and combustion chamber. These have more metal mass and of course coolant around them to absorb the heat.
It is possible the piston could get hot enough to momentarily stick to the cylinder wall. This damages the outer diameter the piston and of course the cylinder wall surfaces. This lets more combustion chamber blowby get down to the rings, subjecting them to more heat from the combustion and negatively impacting the very thin but very critical oil film that exists on these rings both between the ring and the cylinder wall but also between the ring and the wall of the ring groove and the top and bottom of the ring.
Will this result in catastrophic failure? Probably not. But it does result in accelerated wear/tear. This results in more blow by. The engine is less efficient. Uses more gas. Produces less power.
More blow by means the oil gets more contaminated with the by products of combustion. More water makes it into the oil. More unburned gas. More compounds that combine with mainly water to form acids in the oil.
All this can affect the oil's ability to provide suffiicent lubrication under high loads and high temperature conditions. Thus failure down the road could occur, but not at the ring/piston/cylinder wall interface, but at a rod or main bearing.
Sincerely,
Macster.
10-10-2009, 12:28 PM
#34
Rennlist Member
Regardless of whether or not the IMS bearing prefers high rpms or not, you should always let the engine get up to operating temperature before hammering on it. For those without oil temperature gauges, you have to realize that with upwards of 10L of oil, it sometimes takes a few more minutes for the oil to get up to temp after the coolant reaches that oil. Driving the car hard or 'like you stole it' still means you have to take care of your engine. Just wanted to make sure that one point was clear.
Secondly, on the whole IMS and RPM thing, driving habits are what we're talking about. Don't be 5th (or 6th) gear happy. I try to make sure the rpms are above 2500 all the time, if not 3000 rpm.
Secondly, on the whole IMS and RPM thing, driving habits are what we're talking about. Don't be 5th (or 6th) gear happy. I try to make sure the rpms are above 2500 all the time, if not 3000 rpm.
10-10-2009, 01:40 PM
#35
10-10-2009, 02:06 PM
#36
Addict
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i guess we have more in common than just owning a porsche...now do you forget to stop before you shift from drive to reverse? 
It always makes me wonder why rental cars feel like they have 75k miles when the odometer says 10k.
It always makes me wonder why rental cars feel like they have 75k miles when the odometer says 10k.
10-10-2009, 02:10 PM
#37
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My suggestion is not to redline any engine until the oil reaches operating temperatures. Oil pumps put out flow and that's related to viscosity. The colder the oil, the thicker the oil and the less the flow for a given pressure. Porsches in particular have tight tolerances between moving parts and require sufficient oil for lubrication. It's not to say you'll have a catastrophic failure; it just is not optimum lubrication as the engineers designed when the engine is cold.
On my M5, the engineers provided lights inside the tach that show maximum recommended RPM until the oil reaches operating temperature. They start off with a max recommended rpm of 4k when cold then they gradually go off as the sensor in the oil pan detects the oil has reached operating temperature. Eventually, they all go out except the last one at 7k rpm.
This photo shows some of the lights off because the oil is warm. When totally cold, they are all on initially.
On my M5, the engineers provided lights inside the tach that show maximum recommended RPM until the oil reaches operating temperature. They start off with a max recommended rpm of 4k when cold then they gradually go off as the sensor in the oil pan detects the oil has reached operating temperature. Eventually, they all go out except the last one at 7k rpm.
This photo shows some of the lights off because the oil is warm. When totally cold, they are all on initially.
i was about to mention about the M cars having a cold temp RPM. I always follow the same principal as to warm up on the Porsche. i suppose it couldn't do any harm to be safe than sorry.
