Quote:
Originally Posted by zenocchio
How many miles can the 2.5L engine go before a major overhaul...
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It varies.
First, miles are probably the wrong unit of measure since freeway miles (at 3,200 rpm) and track miles (at 5,000-7,000 rpm) are not equal in terms of engine wear and tear.
A better measure is probably hours of track use and the general thinking is that most drivers can get around 60 - 80 hours of track use out of a 2.5L engine. You can do the maths but generally most racers expect around 2 seasons of racing out of an engine. But the length of calendar time really depends on how often you go to the track. If you're just casually tracking the car at DE's 4-6 times per year, you can expect something like 5-7 years of track use (assuming each track day is four 30 mins sessions = 2 hrs).
And while the engine might be good for 5-7 years as described above, you'll be replacing many other components on an 18-year old sports car during that time. edc makes a great point in his post about concerns with worn suspension on a car with 120K miles. Be sure to read the Forum posts about what to expect in terms of yearly basic maintenance costs and remember that those basic costs will only go up if you are regularly tracking the car.
Of course, some engines last longer and some last shorter depending on the driver (any over-rev's?), conditions (racing in extreme heat is harder on an engine than mild temps), maintenance (how often do you change the oil?) and how many ounces of unicorn tears Porsche used to pre-lube the engine wear surfaces when they built the engine. So don't be shocked if you only get 40 hours or if the engine lasts 100 hours. Plan for the worst, be grateful for the best and you'll keep a healthy outlook.
My current engine ($1,800) was bought from a salvage yard with 92,000 existing miles and now has an additional 75 hrs on the track. As such, I already have another used engine (105,000 miles/$2500) sitting in my workshop ready to swap in when the current engine fails (which is probably overdue for failure since I certainly have driver induced over-rev's).
As you can surmise, I don't overhaul engines anymore because my personal experience is that a rebuilt engine (even a $10K professional rebuild) doesn't last on the track any longer than a used engine (at least as far as I can tell or have heard in aggregate from talking to many drivers about many engines). And for clarity, we are specifically talking about bone-stock 2.5L engines that are Boxster Spec legal. Just don't buy a used engine with 200,000 miles thinking that it has much life left in it.
Of course, used engines have risk in them also because you have no idea how they were previously treated or maintained, but since they are only about 25%-33% the price of a professional rebuild, the risk is mostly worth the cost advantage.
To answer your question directly, a car with 120K miles probably isn't too many to buy as a street/track car. Around 100K miles would be better but 150K miles or more would probably be too many (as a starting point).
Hope this helps.
Disclaimer: Your mileage (and engine life on the track) may vary.
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