I am not sure if it would or not. I would expect that if the valve's are opening and closing at different timing, relative to what you currently have, it may.
However, I'm not sure. I've only run a modified cam in one car and in that I had put in domed pistons and raised the regular compression up to 12 or 13:1. However I ended up having about 250/1000's shaved off of the head, which was all I they could take off, before I even got to where I could get the ignition to ping. Once I did, it ran like gangbusters, with probably 30% more power and about 20% better fuel economy. However, I never did a compression test on it, after I finally got the darn thing to run.
My personal conclusion was that you start fiddeling with it and you can either make it better or a lot worse. I decided to opt for what something came with from the factory.
In your circumstance it seems to me like a cam switch would be very likely to show a noticable, significant increase in mileage, on top of what you already got from the transmission change.
Do you know if the XFi has different pistons, or anything, from what you have?
I had to check -- thank goodness it's not a pushrod!
At any rate, I think this test may have some potential for members who are stuck with a powerful engine that have access to less-aggressive cam designs for their application.
I'm excited to see the results. If the redline is the only conern, then that's entirely manageable with or without an ECU. Otherwise, cam swaps are fairly common in the horsepower scene -- but to change it for economy is brilliant.
Any concerns with tuning, or will it be install and go?
You can build a DET CAN for detecting knock...it's always amusing when mechanical solutions are better than electronic.
thanks for posting that DaX. i made one on the weekend and tested it out.
works pretty good, you can hear everything your engine is doing. quite amusing actually.
anyway, i advanced my timing and went for a drive, i could hear ping from moderate to high load, so i pulled over and retarded it a bit, took a while to find the right spot and im not even sure how much ive actually changed it from where i began. anyway thats enough threadjacking for me, sorry MetroMPG
nah it actually didnt help me out a whole lot. my car lacks sound deadening and the little bit that it did have (ie carpet.) i removed.
if however you have a car which you cant hear the engine too clearly i can see how it would help. it made it easier to hear the ping but i wouldnt say i needed it. i could however hear other engine sounds which i wouldnt be able to make out without the det-can.
if you have the parts laying around id say go ahead and build it. its worth it in amusement alone
I'm a bit of an automotive hypochondriac (immediately assume the worst whenever some new sound appears, or the car doesn't idle like it normally does...), so maybe I'd be better off not hearing the noises that I couldn't otherwise hear.
Here's a serious question though: exactly how bad is pinging? EG: If I have my timing set so that I'm just beneath the ping threshold for 98% of my driving, but it does ping on those rare occasions when I load it up (say on a really steep hill, or to accelerate faster than usual), am I playing with fire? Going to wreck the engine?