For some time now ive been considering doing a rebuild on my stock 72 350 olds .It has about 80000 original miles on it and runs good but it is of course lacking in the power department .Can i build it up to say a 350-375 hp engine and still have it last a 100,000 miles.What are a few of the most important things to do to ensure its longevity? GM built literally millions of these engines with tolerances and specs that seem to be all over the place ,yet they lasted for ever .I would have to farm out the machine works and put it together myself as cost is always a factor for me .

 

With better rods and a modern piston ring design, like the Mahle and a roller cam, it should be closer to modern engines, which go a ton of miles. Of course the other two variables are quality machine work and EFI. I got the comment from a long time Ford tech how many less engine overhauls were coming in since Ford switched to EFI. We actually had Ford's come in the dealership being towed in, flooded out. The carbs needle and seat stuck open, flooded the motor. It happened a few times, the Motorcraft carbs were junk. I am having a hot start issue with my Qjet, raw fuel leaking in the motor does bad things.

 

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How many years of driving would it take to put 100,000 miles on your new engine? I rebuilt the engine in my Cutlass back in the 1990s and it might have 20,000 miles on it by now. I drive it a lot, but the longest distance is 9 miles to work and most trips are just a few miles. Several years ago I had to report the mileage to my insurance company as they wanted proof of my annual low mileage and I recorded about 4500 miles per year. I'm guessing most people drive a lot less than I do.

 

Fun 71 I agree I will never put 100 k on this Motor but maybe my son will or his son someday . My point here is I want a long lasting motor that puts out a good amount of power .

 

Yeah, that's absolutely doable if you're gonna rebuild the engine. With 80k on it now, I would just look into a cam change and wait on rebuilding until it needs it. Just about anything is better than the puny cam used in these 350 engines.

 

How long it will last depends on driving style and maintenance. I never had 350 Olds go less than 200,000 miles. In my less affluent years, I ran them to 200,000 or so, and bought another one at about 100,000 miles. They were in anything from Cutlass wagon to Delta 88 Royale.
They were driven or towed to the scrap yard because the front end was worn out and transmission was "shot". Yes, the timing sets, water pumps, U-joints, and a couple sets of brakes (drum and disc) were changed while I owned them. Some were points type distributors, a few were HEI.

 

Not sure I'm reading your post correctly. How does an engine built in the 90's, get driven 4,500 miles per year, and only have 20,000 miles?

 

It got driven 4500 miles per year when I moved to Arizona. When I lived in Louisiana and later Texas I was 1.5 miles from work/school and didn't rack up nearly as much mileage.