Quote:
Originally Posted by Greg Holmberg
I dyno'ed my car (with cat) and got 192 HP and 176 ft-lbs torque at the wheels. Other people have reported up to 196 HP at the wheels.
Given that there's about 15% loss through the gearbox, 196/.85 = 230 at the crank.
What do you think of my logic?
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My car dyno'd with similar results; 196hp at the wheels. And you're correct, removing the a/c and SAI parasitic drag along with the UDP will certainly bump up the horsepower at the wheels a bit.
I haven't seen an actual measurement of the 15% driveline loss specifically for a Boxster so I try to avoid using it. Thus, I usually quote either horsepower at the crank using factory numbers or at the wheels as measured by a dyno.
Quote:
Originally Posted by Greg Holmberg
Regarding the engine, I know you had a professional rebuild and didn't like the results. I think the power was the same, and reliability wasn't, shall we say, ideal.
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The reliability of a rebuild depends entirely on who did the rebuild. As you remember, my experience (with two full rebuilds) was unsatisfactory but that doesn't mean that other shops can't produce an excellent result.
Quote:
Originally Posted by Greg Holmberg
How has the reliability of used engines been? How many racing hours would you say they go before being down on power to the point of being non-competitive?
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My experience with used engines has been excellent. That engine that dyno'd at 196hp at the rear wheels came from a salvage Boxster with 90K miles and only cost $1800. Its still in the car today and running strong with around 75 hours on it thus far. I am expecting it to expire soon so I already have another used engine ready to swap in.
Quote:
Originally Posted by Greg Holmberg
What does a used engine cost? And then just replace the IMS, RMS, water pump, and timing chain--ready to go racing?
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I have bought three used engines: one cost $1800, another $2700, and the third cost $2500. They are often listed for much more so you'll have to shop around a bit and do some negotiating but they can be bought fairly inexpensively.
I have never replaced the IMS, RMS, water pump, or timing chain unless there was an obvious problem. I race them "as-is" under the assumption that the engine was running well when it came out of the donor car so it should continue to run well in my car. And so far, that assumption was been accurate but I can also imagine a day when its not. I kind of roll the dice and take my chances.
But for $2500 (and a DIY install), I can afford four used engines for the cost of a single professional rebuild; four-to-one is a pretty good factor in taking the chance on a used engine. As long as I get one of the four engines to last 80 hours, I am doing at least as well as a professional rebuild. The odds (and thus lower costs) are definitely on the side of employing a used engine strategy.
And last, the other advantage of a used engine (that has never been opened) is that there are no questions about the legality of the engine. For example, there are often questions about what valve seat profile was used during the head rebuild? The stock 2.5L heads have a factory 3 angle valve seat but that often can't or isn't recreated during the rebuild process when the head gets a 5 or 7 angle grind. Does a head with a 5 or 7 angle grind flow better then the stock 3 angle grind? That answer is hard to know. Another question: Has the head been decked to any extent? If so, what does that mean in terms of performance? What about piston rod weight? What if the shop has 50 used piston rods to select from and can pick the 6 that are best matched rather than simply re-installing the same 6 rods that came with the engine? What does this mean in terms of performance? Was the engine re-built to better than factory tolerances (some engine tolerances are not even defined by the factory) that all stack up in the direction to improve performance? If so, does this really improve performance and if so, to what extent? And so on - you get the idea. Its not about blatant performance enhancements but even a "stock" rebuild generates questions that often can't be answered. The bottom line is that no one questions the legality of a used factory engine that's never been opened.