race gas is still missing the lead; so, no. (lead is a "dry lube" )

now what's all this about 'cold starts' ?

I don't get it. How often is a warm/hot start?

some race gases do have lead, in fact the only really effective ones for high compression motors do, some are unleaded. If you mix race and premium gas, usually you mix the leaded and at the right ratios you can make a higher octane than either one by itself... this is also why you can't run a cat when doing this.

Randy is not making the cold start thing up... especially in a 911 motor so much wear and tear occurs when the engine is first cranked... believe it or not, to an extent the higher the RPM you when the engine is first cranked, the less certain parts, especially cams, wear. if it helps, forget the "cold start" term and simply think of it as, the 911 engine does not like running below operating temp... start it below it and the tolerances are off and it stresses and wears certain parts differently.

Can't leave it idling . ..can't stop and let it cool down.

So then how do you get on the internet whilst always driving? :cool:

Yes, I'm slightly baffled. But I must be doing something correct. I use 30wt oil, let the engine warm up for at least two minutes, sometimes longer...sometimes much longer...and at 180-degrees, I'm revving it to 5 and 6,000 RPMs, sometimes 6,500 and several times up to 7,000. So far so good for three years now. I'm not saying I'm correct in how I treat my motor and I'm also not saying anyone else is incorrect. It seems as if there are several paths to 911 engine preservation/duration and/or wear. All I figure is the stoutness of these engines make them more idiot proof than any other engine in production. But honestly, I can't see them being too finicky and also retain the track record they have when maintained properly with the required oil changes and valve adjustments.

Wait . . .you start your engine before it's warmed-up? :eek: --that's just all wrong. :cool:

Okay, seriously, someone enlighten me as to why valve wear would be increased by not warming-up "properly."

. ..or for that matter, any other components.

btw, I get that the moving surfaces are relying on mixed-mode at worst, and hydrodynamic lube at best. But 911 oil pressure builds fast. So .. . what's the big issue about warm-up?

It's an air cooled motor! It's not liquid cooled... the tolerances cold are wildly off from when it's at operating temp, whereas a liquid cooled motor has very tight specific tolerances and it gets warm quickly... 911s take forever to warm up, in all seriousness you should not go above 4k RPMS(2.0-3.2) or 4.5k RPMS (3.6) for almost 15 minutes when driving the car, warming up a 911 properly is very important. not warming them up properly is the culprit for most of their leaks, and other little problems like that.

tolerances cold are wildly off from when it's at operating temp
 

Really?

let's see; valve stem spec. clearance (cold) is .030 to .057mm (thats new. ..plus w/ a .15mm wear limit !)

is that too tight when cold?

What if we look at Coef's of thermal expansion?

Alum ~CLTE=13.5 in/( in °F)x10-6

steel ~CLTE = 6.5 in/( in °F)x10-6

difference ~7 in/( in °F)x10-6 . . or, .000007 mm/mm/°F

valve stem ~9mm, and pick an outragously high "warm-up" Temp rise; say 500°F (above ambient)

.000007x500x9 = .032 mm

.032 mm is "wildly off"? . . .really?

"How often is a warm/hot start?"

That would be when you stop the car and then restart it before it cools down. So if you get back to it in 15-20 minutes, that start will be less damaging than if it cools all the way down, or nearly so.

Randy. . .say what?

I think, maybe, you're mixing "cool down" with "drip-down" . .. as in, the oil moves away from the bearings over time.

or are you thinking of something else?

90% of engine wear is caused at start-up, because there's no lubrication for a second or two. This is well documented. This is why I like Accusumps. The new engine will have an Accusump. Why are cylinders made of Alusil or Nikasil? The thermal expansion is the same as the pistons. There is a lot of metallurgical research and engineering in an engine. Porsche engines are really well built, and I have always marveled at the precision of the tolerances in their engines.

Valve guides are not pressure fed, they just kind of drip down the stems of the valves. Because of their unique lubrication requirements, and of the extreme service, they are made of bronze or one of the derivative alloys. They are also the buffer between an aluminum head, and steel valve, and must also compromise the thermal expansion properties as Island pointed out previously. So, the guides end up getting lubed last in the start-up chain. Porsche and VW guides are historically durable, as long as they are installed correctly.

Race gas generally has a much higher VOC, and fewer oily additives compared to pump gas, so it actually has less lubricity. It's actually not as helpful in the regard you're inquiring about than ordinary pump gas.

I have seen evidence tearing down race engines of pitting and very slight surface rust on the valves from race gas use, something not normally apparent in street engines.

Yes, but since the guides are relying on boundary lubrication it really shouldn't matter.

Should it?

.. . boundary lubrication, as we have here, depends on the strong adhesion of the lubricant to the bronze guide and polished stem. When you shut the motor off, you have just as much oill stuck to the sliding surfaces, as when running.

So, again, I don't see how start-up is going to adversely affect the guides.

Airplane fuel
 

I have an opportunity to add avation high octane leaded fuel to my '69 911s on occaision at a local airport. I can drive right up and buy the fuel and my engine seems to run much smoother with a couple gallons of "high test". The last time I was at the airstrip a pilot told me I was risking trouble with the leaded high octane because it has 50 times the lead the pump gas from the '60s had and too much lead will foul the piston ring grooves. Has anybody here got an idea if the avation fuel is dangerous for my engine? I would think a couple of gallons would lube the guides for me. The motor really loves this treat and the difference is amazing.

Start up is start up. Start up adversely affects everything. Warm or cold, there is no oil pressure. (I have to reach back in my feeble mind to fluid mechanics). I think there exist at least three states of lubrication; boundary, mixed-film and hydrodynamic. When you start up the engine, every moving part depends on boundary lubrication, the layer of lubricant residually "stuck" to the moving and mating part surfaces. Once we get oil pressure, we are in the other phases of lubrication, which are more protective of the moving parts. The simple reliance of boundary lubrication for the time period between cranking and having oil pressure in the galleys feeding the moving parts is what causes wear. This wear is on everything; guides, crank journals, cams, everything.

Ever see a commercial where the product shiller will show an engine which has just run 10,000 miles without ever shutting off (I think the old STP commercials), and they show the lack of wear which they attribute to their product? There is no wear, because they only started it once. Once you have hydrodynamic pressure, you are golden!

If you rig an Accusump to your engine, you get 15 seconds of oil pressure in the galleys...hydrodynamic pressure at start up, or mixed-film at worst. You remove the reliance on boundary lubrication, and remove the wear. Following up on your rigorous treatment of clearances, you get a tiny amount of wear PER START UP. Multiply this times (maybe) six starts per day of car use times five days (we all use our 911's for work) for five years...it becomes a big number. How long to get to the wear limit? Are guides more worn than, say, a rod journal? (Engine rebuilders can chime in here) My experience is that exhaust guides suffer at leat twice the wear of intakes due to the heating effects
Pat

Airplane fuel
 

I say; don't fix whats not broken.
The newer guides are designed with unleaded fuel in mind. While it may seem that the guides are wishing they had additional lube, that's just not the case. So, my money is on NOT buying leaded fuel, and just living with the cost of a head-job after 150k or so . . . the valve-seats likely need some attention then anyway.

Also, lead is NASTY stuff to breath.

the fourth is the hydrostatic lube (pressure fed . . floating the big loads). But before that, the bearings are likely to have enough residule to go right into hydrodynamic.

I guess what i'm saying is that I think that too many are simply repeating the line from the STP type of commercials.
[deep announcer voice]90% of your cars engine damage happens at start-up (be afraid, be very afraid) STP addative coats sooths and protects your vital engine components from harm.. . .[/deep announcer voice] :D

IMO, Heat and impurities are what do things in. . .. more so than start-up. (strange thought, I know . . and if EVERYONE says . ...)

okay, Pat, sorry. . . I just read your other paragraphs there. :o (funny though, I choose "STP type of commercials" too.)

I just did a sanity check, and looked it up.. .your talking hydrostatic pressure, not hydrodynamic pressure. Hydrodynamic is where the motion of the journal gives the oil a wedgie, and rides the wave . ..so to speak. Like an oiled bronze bushing in an electric motor.

Back to valve guides; I agree with you. on the exhaust guides. Heat, not start-up, is the brutal component.

Maybe Andy Granatelli in a lab coat...?
FTC busted Slick 50 for false claims, BTW
Can I get an example of hydrostatic lubrication in an conventionally lubricated internal combustion engine?