Startup RPM vs Engine Wear?

[TheLoneRanger]

Which is a better situation:
1. Having an engine rev to about 1800 rpm at startup, and drop down to a normal 700 rpm idle?
2. Having an engine rev to about 900 rmp at startup, and drop down to a normal 700 rpm?

The higher revving engine (at startup) will get oil pressure faster, but will also be running faster before the pressure builds.

The lower rpm engine will take more time for oil pressure to build, but will be running slower before the pressure builds.

Which startup situation creates less engine wear, or does it really matter.....?

 

[Patman]

I honestly don't know the answer but I do cringe everytime I start up my Firebird on a sub 0F morning and it momentarily revs to 1500rpm. I'd much rather it only revved to 1000, although I'm sure there is some emissions related reason for it to rev high at first.

 

[digitaldrifter91]

hehe another dealer phrase "we will look at it but its going to cost you"

 

[TheLoneRanger]

Originally posted by Stuart Hughes:

quote:

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A d(st)ealership would probably tell you their favorite phrase:"It's within spec."

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Originally posted by digitaldrifter91:

quote:

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hehe another dealer phrase "we will look at it but its going to cost you"

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Ha Ha, you got that right, guys.

Patman, I have the same feeling when I crank the Explorer over. Those high revs when the engine starts make me grit my teeth. I've listened to several, and they all do it. I'm going to take a good look at the throttle body, to see if there's an easy way to slow the initial idle. I don't have a lot of hope, though. Anything I change will probably also affect the curb idle.....

 

[Bio-T]

I have a Cold Air Package on my 01 Ford diesel, it starts and goes to the normal idle RPM. But when all parameters are correct it raises the idle to 1100 RPM after about 2 minutes. Then if I don't move it after about 3 more minutes it goes to 1300RPM. When I touch the brake to put it in gear, the idle drops back to normal. In weather above about 40F, it does not effect the starting at all. I do realize differnt fueled engines, but I do like this CAP method. It sure can warm up the cab in short order when the weather is in single digits.

 

[digitaldrifter91]

hehe...i dont think u can change that startup idle.

 

[digitaldrifter91]

my uneeded 2 cents...isnt the reason for the idle being that high is because the engines emmissons allows the engine to be high until the system has reached optimum temperature, therefore closing the valve. i really forgot how it worked though, but i was reading about it somewhere. o maybe its called the starter valve that lets in a little more air when cold and closes when warm. its normal i guess if it goes down hehe.

 

[UncleS2]

No matter the temp outside, my Neon always idles at ~1100 rpm on cold start, dropping to ~900 rpm when warm. It's done this since new.

I guess there's some good reason for the higher(~1800 rpm) to be built in to the car, be it oil pressure or cat warmup or something else. A d(st)ealership would probably tell you their favorite phrase:"It's within spec."

 

[Patman]

quote:

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Originally posted by digitaldrifter91:
hehe...i dont think u can change that startup idle.

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In some cars you can. I already asked about mine, and a custom program for my car's computer can adjust that rpm. Unfortunately those reprograms run about $500 (although a good tuner can also wring out 10 more hp from it too while they reprogram your fans to come on sooner, adjust shift points in automatics, etc.)

 

[digitaldrifter91]

o thats cool, i didnt know that. i want to do a custom ecu in the future for my car, hehe its going to cost me about 750 dollars for one.

 

[TheTanSedan]

Well, guys, if it's "an emissions thing" then why does my 1971 Chrysler call for cold (full-choke) idle of 1600-rpm? (Emissions-exempt now, I set the in-gear idle to 600 rpm for warmed operation, lower than the emissions-stated 700 rpm). Experimenting with cold idle speeds doesn't seem to produce a benefit: any higher and the thermostat doesn't open sooner, and any slower and the car balks at wanting to move after the recommended period of highest idle is complete.

The motor has to warm up all that metal to support combustion without excessive fuel use. The fastest way to do it is to get the block and heads warm as fast as possible. As to what computer-controlled cars do, it would seem that the idle is controlled to quickly get a handle on all facets of operation, not simply emissions.

I've read somewhere that Cadillac or another manufacturer has thousands of lines of code (if I have stated this correctly) simply to control idle functions.

 

[JohnBrowning]

Well a modern vechile has what is called a cold start circuit. This circuit enrich's the fuel based on coolant temp. It does this to keep the engine running until "Thermodynamic Efficeniycy" is reached. Cold cylinder cases do not like to keep the flame kernal going. You need to maintain enough RPM to carry you through poor combustion until temps come up in the cyclinders. The only way around this is to have a re-light cabability. If the ECM/PCM can detect a failure to light or that the flame went out and can re-spark the cylinder then you do not need to idle it up so high. Most cars today have pre-cats and postion them in or close to exhaust manifold to heat up quickly. Some even have heaters built into the cat and the O2 sensor. My Dodge hits about 600-650 rpms when cold and then imediatly drops to 500 rpm idle reguardless of temp in about 30sec. Lower rpms creat less emissions. I doubt that the normal idle charteristics of a car are going to be significat if proper weight of oil for temp. and quality oil is being used. I can not belive that as fantical about oil and performance that anyone on this site would use anything but synthetic in the winter months!!!

 

[Calvin]

With respect to the origional question of time to build oil pressure.... I have always been a Chevy / Mopar guy and have had 305,327,350,427,454, 225,318 and 440 engines and all of them would show full oil pressure on a mechanical guage (mostly Autometer) within 1 second of the engine lighting off.In these cases it didnt matter if it was 35 deg F or 110 deg F
it was always nearly instant.Every one of these had straight 30 weight in them.I dont live where it really gets cold so I cant offer any examples of real cold weather observations....I would think that with the so common use of lightweight multi vis oils it the oil circulation would be as quick or quicker.

 

[widman]

It's going to run smoother at a higher rpm until warmed up a bit, and the older engines with manual chokes or the first versions of automatic ones over did this considerably to make up for always being way of ideal.
For the first few seconds, you really want the crankshaft turning as slow as possible but the oil pump as fast as possible to build pressure in the bearings. Since they are attached they have to run at the same relative speed, and the sooner you get pressure IN the bearings (not the guage) the better.

 

[Calvin]

I agree what shows on the guage and what is at the bearings are slightly different.Oh I guess it was back in the middle 80's a kid at work put a 350 Chevy in his 65 Chevy II.It was a fairly stout engine with a large solid lifter cam.He used a Gear Drive on it and decided to make an oiler for it.On the passenger side just above the timing cover on some small blocks there is a tap into the main oil feed that is plugged from the factory .He used of all things the plastic mechanical oil press guage line to make an oiler to a drilled hole in the top of his timing cover to supply oil to his gear drive.For some reason he felt he needed this.Well it did work and being that he used the plastic line you could see the oil flow from the main feel above the cam to this gear drive oiler.I remember watching him fire up this engine and while I didnt actually time it, it had to be between 2 and 3 seconds when oil flowed to his gear drive oiler at an approx 1100 idle rpm.(Big Cam).

During those years I was also able to be involved in a little over 200 engine Dyno pulls.Hennan Freud and SuperFlow Dynos.On one occation while doing some testing on intake manifolds the owner of the engine wanted to see the amount of oil that ran past the lifters.In this case a mechanical roller cam.So we pulled the lifters out and just using a drill and a good preoiler tool spun the oil pump.I was abit taken aback at the voloume and velocity of oil was flowing through the (empty) lifter bores with what was just drill speed...far less than idle speed.Again this was a Small Block Chevy.Granted it would be of far higher pressure with the lifters back in but all in all I really think it takes only a couple of seconds for a good oiling system to supply oil to all the vital parts of an engine.I cant say for these modern engines but by the time you got it up to 1800 RPM it should have plenty of oil flowing.

 

[Ray H]

quote:

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Originally posted by TheTanSedan:
Well, guys, if it's "an emissions thing" then why does my 1971 Chrysler call for cold (full-choke) idle of 1600-rpm?...

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I think you just answered your own question. A 32 year-old car with a mechanical choke on a conventional carburetor. You had NO computer emmissions controls in that era, but you DID have cranky engines that could only be made to run in cold weather by feeding them an excessively rich mixture and a high idle speed until they warmed up enough to release the choke. About the only mechanical emmissions devices were the PCV valve and a vacuum operated NOx exhaust gas recirculation valve from one of the exhaust manifolds. I don't even think air pumps were in use yet, but I could be wrong. I had a 1971 Plymouth Satellite (first NEW car) with the 318 cu. in. V8. There was NO air pump on that engine. The EGR valve went out within 5,000 miles. I had to fight with Chrysler for an in-warranty replacement. When the second one pooped 6,000 miles later, I left it alone and figured the tree huggers would just have to lump it. Drove better without it anyway...

Getting back to the original question, I think that the high RPM initial startup speed is an effort to minimize emmissions and still have a minimally rich mixture during warmup. These engines could probably be programmed to start up and idle at the normal speed, but I suspect it would take a significantly richer mixture to do so. With the catalytic converter stone cold, it doesn't take much imagination to conclude that tailpipe emmissions would be off the scale - not to mention the liklihood for premature catalytic converter failure.

[ May 13, 2003, 01:16 AM: Message edited by: Ray H ]

 

[ikeepmychevytoo]

I've heard this somewhere that the cold-idle speeds were durability optimized rather consumption optimized in the 60's and 70's. And this speed was close to where engine operation is most optimum, close to the cruising rpm. I bet a couple hundreds higher and the Tan Sedan's Chrysler is a cruising motorcar.

My LE2 (173) from '84 has a multiple stepped choke cam. At coldest it starts right at 2000 rpm then drops gradually in three steps, but it is very rare. Usually starts at 1000 or so. @2400rpm it does 65mph in hi range. Matching with the theory.

With whatever technology if you can idle smooth at 650 rpm at most intemperate weather then you probably wouldn't want to ruin cat and 02 sensors unnecessarily. But I think this brave(?) attempt of low cold-rpms comes from mostly from advance in oils, not because those engines wouldn't idle with carbs. Because I can play with the cam calibrations or idle kicker solenoids. Before I heard this I thougth that the original rpm specs was ridicilously high, because that LE2 could actually tick like a watch at 1000 rpm at the given cold temp while the emissions label specs 2000! However it'd drop fast, but consumes more when cold comparingly. Again comparably, it would probably more reliable with '80s SF oils.

 

[Gary Allan]

I think the initial surge in idle is merely to assure that the engine is fully lubricated and that the cylinders are warmed just enough that the normal fuel atomization from the injectors can sustain the idle. It only last about 30 seconds.

But as far as the oil pumping up and potential damage? I think this is highly over rated for the most part. You've go no load on the engine.

 

[mechtech]

Most car Mfrs. program the vehicle to rev up 1200-1500 or so at start up, even with precise fuel injection.
It makes sense to me that it is for oil circulation, and that they concur that this is the best way to get the oil flowing.
So I like the slightly higher start up speed.

 

[Patman]

Wow, this is an old thread!

I no longer have my Firebird, and the Corvette I now have doesn't show me the startup "spike" rpm at first, since the needle sweeps all the way to the redline when you first start it up (all the gauges sweep to their maximum then down again)