Quote:
Originally Posted by akashic
The internals of cars are a new thing to me, so please excuse me while I try to apply my limited experience with engine-talk...
I'm getting that the idea of this mod wrt FE is to lower the resonance of the intake and shift the peak torque -- and simultaneously the island of minimum BSFC -- to lower RPMs. Is that right?
YEP, YOU GOT THE IDEA.
I guess maybe what I was asking was if a car already tuned for more low-end torque would benefit less from the same spacer than one tuned for more high-end torque. At least with given thickness of spacer, the car with the shorter intake would increase it's intake-length percentage-wise more than one that's built with a longer intake. If that's actually how it works (and I didn't completely munge that explanation), then it seems sort of mathematically obvious that a lower-tuned engine would benefit less from the same thickness of spacer.
And to go with that thought, a car tuned for high-end performance has the most interest in a retuning mod like this, to get the BSFC curve into an accessible range for a hypermiler's driving style. Yes? No? (wtf?)
IN THEORY, YES, A CAR WITH LESS LOW-END TORQUE WILL BENEFIT MORE, IF THAT LACK OF TORQUE IS DUE TO THE AIRFLOW AND RESONANCE PROFILES ASSOCIATED WITH IT'S INTAKE STROKE.
btw, I understand a little about "tuning" from the acoustical world. It occurs to me that little hacks like this can accidentally work to your advantage if you happen to disrupt the response curve in such a way as to make a little bump in the "right" part of the curve. You might end up with a bizarre profile with several low peaks, but if you only care about 1900 rpm or whatever, then it might just work for you. So I suppose as you said, this is something that you just hack at until something works, maybe even without a predictable pattern.
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Christ: "I believe, generally, that anything you can do to maximize the power output of your engine without increasing the fuel it consumes to do so will give you better FE." (
in that specific RPM range, relative to the power produced)
Conversely, any mod which creates more torque almost always will change the linear power profile of the engine (torque curve), although not necessarily "across the board". That said, even if you do something that adds power at 2k RPM, and you're typically at 2300 RPM, you'll see a benefit from it. If you add torque at 3k RPM, and you're typically at 1900 RPM, you'll still probably see a benefit from it, but not nearly as drastically.
The above statement was kind of generalized, with certain assumptions:
- You're an ecomodder, so you're looking for efficiency gains
- You're not looking to make more power where you can't use it.
- You ARE looking to make more torque where your engine "sits" during your drive
- and you're looking to do it without introducing more fuel.
Basically, the only way to increase your engine's output without changing it's fuel intake is to change the way it uses the fuel it already uses. More specifically, to change the dynamic losses associated with using that fuel.
- Increasing VE (assuming you haven't added fuel) will nearly always net you more torque.
- Reducing frictional losses will net better torque for a given RPM range.
- Ensuring that you're actually USING the fuel you're using.
Those are just a few ideas that might help clarify the thoughts I was attempting to evoke with that statement.
Thanks for catching it!
In addition - If you're ever thinking about changing TB's to a smaller size, since you can't exactly "port match" and you
don't want to create a wake in the intake tract (this is not opinion... you really don't.) use a spacer that will smooth the transition of airflow from the smaller throttle body to the walls of the plenum. It'll probably also prevent the high-pitched whistle that you'll probably hear.