Originally posted by moerom
Ok I am going to chime in again:
Finding comparable FI and N/A engines is not exactly jusitfiable.
An N/A motor is built differently to be reliable than a F/I motor to be reliable.
I want to ask one simple question:
If forced induction was not as reliable as N/A, why would huge auto companies use F/I for their cars?
The answer is that with current technology, an F/I motor can last just as long as an N/A motor given comparable variables.
Well for one, it's cheaper and easier for the automakers to force-feed their engines than developing new engines to keep up in the ever increasing HP wars.
That being said, there are a number of things to consider in the F/I vs N/A argument.
F/I *can* be just as reliable as a N/A motor, provided it's factory built. Nearly EVERY aftermarket supercharged / turbo-charged motor is going to be under greater strain than a N/A motor, or a factory built forced air motor. The biggest reason behind this comes down to the simple engineering dollars spent on making the car reliable (for at least 100,000 km anyway) while under warranty. With a factory build F/I motor, they've looked at all the underhood cooling requirements, airflow etc, etc, and have the resources to move / relocate equipment easily to make it the best it can be. With the aftermarket it's much tougher to do this, without spending significant (often making the investment poor) $$$$.
Let's also look at what the requirements for the motor are. If it's an engine that you're planning on running on the track regularly. First of all, a N/A engine provides more linear throttle response, which makes the car easier and smoother to drive, and doesn't have the overly boosted nature a F/I car does (especially mid-corner).
Also, on the track, you're spending most of your time north of 4,000 RPM, which means you're generating significantly more heat, and putting more strain on the engine overall. It's easier for a N/A motor to handle this, though a factory designed and built unit can be pretty close.
Sure, F/I can be cheap HP, and it's one of the reasons why factory's do it for themselves. It's cheaper for force-feed an existing engine than it is to build a new, more powerful engine from the ground up.
Same thing goes for aftermarket kits. Much cheaper to drop a turbo on to a 3.2L M3 engine than it is to build an engine which puts out 400+ HP N/A.
If all you want to do is rip around the streets with it, then F/I can be every bit as reliable as N/A.
On the racetrack, it's a different story.
It's best to know what your intentions are first, and go from there.