Engine longevity and ignition/induction types?

[letitsnow]

From what I have read and experienced, the sbc (carbed and hei) has gone from lasting around 100,000 miles to lasting around 225,000 (efi and pc controlled ignition) over the years.

Do you think that the main difference was the switch to efi - the motors no longer run way to rich or lean when the weather changes?

Or was it the introduction of knock sensors - the ignition can account for weak gas (etc) without detonation?

Maybe there is something else that I am missing?

 

[b454rat]

EFI is more efficient at atomizing the fuel, so it doesn't wash the oil off the cylinder walls. That's why way back when, whenever someone was selling a motor or a car, it had "highway" miles. Running down the road at whatever RPMs, it's not washing the cylinders out. Stop n go still isn't the best, but smoking the tires off every green light sure doesn't help. I've had many trucks lately that had hi miles. Some weren't maintained well, (not by me) over 250k and still ran great.

 

[kennythewelder]

Carb or fuel injection has very little to do with it. In the 1980s Toyota was killing every other manufacturer with there trucks that would go 500,000 miles plus. So GM put a ton of R&D into the 400 series trucks. Part of that was the engine tolerances. Toyota engines were built to a lot stricter tolerances. GM stepped up there tolerances to complete. The older engines could leave the factory with 15,000 clearance before the 400 series trucks. On the 400 series, they went from around 15,000 tolerances to 5000 or less. That is a very big difference. The 400 series engines are good for around 500,000 miles or more. I have seen several with over 400,000 miles. My 97 has 256,000 plus, and it runs grate. The engines that are in GMT 400 trucks are the best GM ever built for longevity, and dependably.

 

[PlayingWithTBI]

^^^This - plus oil quality has gotten better/more stable through the years too.

 

[Pinger]

Carb or fuel injection has very little to do with it. In the 1980s Toyota was killing every other manufacturer with there trucks that would go 500,000 miles plus. So GM put a ton of R&D into the 400 series trucks. Part of that was the engine tolerances. Toyota engines were built to a lot stricter tolerances. GM stepped up there tolerances to complete. The older engines could leave the factory with 15,000 clearance before the 400 series trucks. On the 400 series, they went from around 15,000 tolerances to 5000 or less. That is a very big difference. The 400 series engines are good for around 500,000 miles or more. I have seen several with over 400,000 miles. My 97 has 256,000 plus, and it runs grate. The engines that are in GMT 400 trucks are the best GM ever built for longevity, and dependably.

That would be around the time that the most important computers weren't the ones controlling fuelling and ignition but controlling the machine tools in the factory?...

 

[kennythewelder]

That would be around the time that the most important computers weren't the ones controlling fuelling and ignition but controlling the machine tools in the factory?...

That I wouldn't know. But I do have a very good understanding of machine tolerance, and the machining process. I am a welder in a machine shop. I can run an old school lathe and mill. 5000 is max tolerance for our shop, and 1000 to 3000 is preferred depending on the job. Some jobs call for rite on spec with a max of 1000. Even on a welding fab job, we don't like anything more than 1/16" out of spec and that's on big jobs only. Small welding jobs need to be spot on.

 

[Schurkey]

EFI is more efficient at atomizing the fuel, so it doesn't wash the oil off the cylinder walls.

Sort of. EFI does not atomize the fuel as well as a carb, but it's much better at METERING the fuel so the engine doesn't run rich at start-up. And with a carb (or TBI) the atomized fuel puddles in the "wet" intake manifold anyway. Port FI avoids this puddling even if the spray isn't as finely-atomized to start with. With any feedback fuel injecton, (the kind that has an O2 sensor to fine-tune the mixture) the whole fuel curve is more precise.

So one of several functional differences that have increased engine durability is that you're not washing the oil off the cylinder walls with excess gasoline.

Carb or fuel injection has very little to do with it... ...GM stepped up there tolerances to complete.

I don't deny that the engines were built more precisely. But feedback fuel injection was a major factor in improving engine durability. Feedback carburetors helped a little, but not as much as feedback fuel injection.

Other factors in no particular order, and acknowledging that some of these changes happened before the GMT400 came out; the comparison is more to 1950s--1960s engines, somewhat to 1970s engines, and somewhat less to early 1980s engines:

Better oil (Don't get me started on "zink" or "ZDDP". It's not the problem it's been made-out to be.)
Overdrive transmissions--lower RPM, less piston motion per mile
Lower-tension rings--less ring-to-cylinder wall friction leading to reduced cylinder-wall wear
More-precise spark timing over the life of the engine--more complete combustion leading to less fuel washing the oil off the cylinder walls.
Higher-temperature thermostats evaporate moisture in the oil, reducing acid buildup. Higher cylinder wall temperature (within reason) leads to lower friction.

 

[Schurkey]

5000 is max tolerance for our shop, and 1000 to 3000 is preferred depending on the job. Some jobs call for rite on spec with a max of 1000.

I don't understand "5000", "1000", "3000" and "1000".

Do you mean 0.005 (five thousandths of an inch) max, 0.001 to 0.003 preferred, with some jobs calling for max 0.001?

Automotive crankshafts, cylinder bores, connecting rod big-ends, and block main saddles are routinely cut/honed/polished to better than 0.0005 (called "Half-a-Thou", as in "half a thousandth of an inch", or (less accuratly) "Five tenths" meaning five ten-thousandths.) I can hold runout on valve faces to 0.001 pretty easy, and as good as 0.0002 to 0.0005 sometimes; although I'm still dial-indicating every one unlike a "real" shop that dial-indicates one every now and then. The used valves I ground for my Lumina came off my valve grinder with LESS runout than the brand-new "famous name" aftermarket valves I bought to replace a couple of damaged valves. (I stuck the new valves in the grinder and then dial-indicated them as if I were going to cut them. When I saw that I could do better than they did, I took a "cleanup cut" on 'em.)

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[Supercharged111]

How about block material? I'd heard the 87+ 1pc RMS blocks were a harder material that caused less bore wear?

 

[kennythewelder]

I don't understand "5000", "1000", "3000" and "1000".

Do you mean 0.005 (five thousandths of an inch) max, 0.001 to 0.003 preferred, with some jobs calling for max 0.001?

Automotive crankshafts, cylinder bores, and main saddles are routinely cut and honed/polished to better than 0.0005 (called "Half-a-Thou", as in "half a thousandth of an inch"; I can hold runout on valve faces to 0.001 pretty easy, and as good as 0.0002 to 0.0005 sometimes; although I'm still dial-indicating every one unlike a "real" shop that dial-indicates one every now and then. The used valves I ground for my Lumina came off my valve grinder with LESS runout than the brand-new "famous name" aftermarket valves I bought to replace a couple of damaged valves. (I stuck the new valves in the grinder and then dial-indicated them as if I were going to cut them. When I saw that I could do better than they did, I took a "cleanup cut" on 'em.)

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Yes, that's correct. And yes also on the 1/2 a thousands. We don't do automotive work in our shop, or very little. Also remember that the first GMT 400s came out in 1988, so yes the late 80s was a big improvement over the the late 70s. I also agree the fueling and oiling does plays a part in longevity, but today you can get a SBK 383 that will hold together as well as, say a vortec 5.7 350 will, or very close to it, and that's with a carb and HEI distributor. When GM dropped the old 350 SBK and went to LS, again they spent a ton of time and money in R&D and tooling.