Blackfly XFi?

[MetroMPG]

Thanks to a certain website overlord who shall remain nameless, I now have in my posession a camshaft from a Metro XFi (year and mileage unknown).

This cam will find its way into the Blackfly's engine compartment in the not too distant future, replacing the extravagantly wasteful OEM cam that came with the car.

[Bruce]

Wouldn't you need the ECU as well?

[MetroMPG]

Apparently not.

[Bruce]

Originally Posted by MetroMPG

I'd really like to do some A-B-A to get an actual number, but cam swaps at the side of the road on a hot engine may be problematic.

Should only be about as tough as changing a flat without stopping.

Congratulations. I wish I were able to make some practical tradeoffs of power for efficiency in my car, e.g. a smaller engine, but I haven't seen anything yet that wouldn't require major surgery or drastically impact the reliability.

[MetroMPG]

Thinking more about this.

[DaX]

You can build a DET CAN for detecting knock...it's always amusing when mechanical solutions are better than electronic.

[TomO]

hmm, that sounds like a good and cheap thing to do. Thanks for posting that DaX!

[DaX]

Originally Posted by TomO

hmm, that sounds like a good and cheap thing to do. Thanks for posting that DaX!

No problem. Just don't let the police see you driving down the road with headphones on! Imagine how strange it would be when a cop looked in the car and saw hoses running from the headphones to the engine!

[MetroMPG]

CoyoteX posted a cheapie microphone-based ping detection method too. One or the other will come in handy, yes.

[Matt Timion]

I would love to see a side-by-side comparison of the two cams. My functional engine knowledge is not the best.

[MetroMPG]

I also found a post that confirmed I may have to watch the ignition timing after the swap.

[Coyote X]

I would set the timing back to 6 degrees advanced like the factory calls for. I don't think you will have any problems with it knocking unless you have really bad gas or something. A knock sensor out of something from a junkyard is pretty cheap but if you have good hearing then you don't really need it.

Also I got better mileage out of my xfi when I have the cam advanced to 11 degrees

[MetroMPG]

Do you have to run higher octane with the cam advanced 11 degrees?

[Coyote X]

Nope I am still running 87 with the cam at 11 degrees and .040 shaved off the head so I am at 10.5:1 compression ratio. I am only running 4 degrees of ignition advance but the car seems happy with this combo. I just need to get it to run for 3 weeks or so straight without breaking down to get a good mileage reading.

I would put the cam in straight up with the ignition at 6 degrees and get some time on it before changing the cam/ignition timing just so you get a feel for the mileage with the new cam before changing more variables.

[Ted Hart]

Originally Posted by MetroMPG

Apparently not. My understanding: the different cam profile - lower lift & duration - raises the cylinder pressure and shifts the torque peak downwards, so less throttle is required at low RPM. It's a mechanical thing.

It lowers the XFi's HP rating from 55 to 49, but the torque value is unchanged (the RPM at which the max occurs is lower). (EDIT: The cam alone may not be the HP limiting factor - it could also be ECU.)

A number of people have done similar swaps including GeoMetry on this forum,

I sense a bit of "misunderstanding" here....
A lower lift and/or duration cam profile (opening the "doors" to gas flow later, closing them earlier, and holding them open for a shorter time) is going to raise the BMEP? ...and shifts the torque peak downward? How so? If gasoline is the source of power (pressure), then how is less of it gonna make more?
Torque is what moves the vehicle. Power is the rate of producing this torque.How is less of it going to move it better? Easier? More efficiently? Are you aware that HP = torque (by definition) at 5252 RPM? The two are tied together so tightly that "nothing moves without them". Check your physics book!

[Gary Palmer]

MetroMPG: I would go ahead and make the cam swap. I would also set your timing up to match whatever the Xfi specification is, certainly to start out with.

The cam basically controls when the valves open and close, relative to the crankshaft and pistons. It won't change the actual compression ratio, but it can change the effective ratio. Additionally, the cam lobes can be ground to have different ratios of opening and closing, how long the valves are open/closed and when they are open and closed. Depending on the engine rpm, they are optimized for a specific rpm, but are generalized at the same time, to allow the engine to operate over a wider rpm range.

It is possible to get cam's set up that are optimized for lower rpm, but they typically run more poorly at higher rpm's. When Honda introduced their VTEC technology, it basically allowed them to have two different cams in the engine, one optimized more towards the low end, one towards the high end.

I would doubt it you will need to change the ecu. To a large extent because of your driving style, I expect the engine is generally in closed loop, so that it is monitoring your O2 and other factors, to control the engine parameters. In open loop mode, the setups in the ecu are probablly already close enough, for what your asking it to do.

I've thought about pulling a camshaft off of a 91-94 CX and putting it into my 89 Wagon, towards the end of improving the fuel economy. However, it's rather far down my list of things to do and preceded by issues of more a more pressing nature, which seems to be the way things go, more often than not.

Make the change and then let us know how it goes, in comparison to your previous mileage.

[MetroMPG]

I'll be the first to admit I'm not a cam expert. You can see I've mostly quoted things I've read elsewhere.

[MetroMPG]

Originally Posted by Gary Palmer

It won't change the actual compression ratio, but it can change the effective ratio.

Yes, I had read this also. Which addresses Ted's question, "If gasoline is the source of power (pressure), then how is less of it gonna make more?"

It is possible to get cam's set up that are optimized for lower rpm, but they typically run more poorly at higher rpm's.

That's true.

It's mentioned in the source I linked in the previous post. The shorter duration on that Olds cam meant a higher lift rate was used, which resulted in a lower red line (the valves would float at a lower RPM because of the higher lift rate).

The same is probably true of the XFi cam - and perhaps that's another difference in the XFi ECU: a lower rev limit.

[Gary Palmer]

One of the items which is on my list of I'd like to do, is to get the HF transmission I have, rebuilt, so I can get it into the Wagon. After I do that, my rpm should come down substantially and then I may try to make a cam swap to more adapt to that change.

In your car, I believe you already made that change?

[MetroMPG]

Yes, I've swapped transmissions and have a much taller final drive. So you're right: the cam swap and lowered torque peak should match the engine better to the gearing I have.

[MetroMPG]

Here's a question: if the cam is going to raise effective compression, would that show up if I did a before & after compression test?

[Gary Palmer]

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?

[MetroMPG]

Engine wise, differences I know of on the XFi (besides the cam):

- slightly smaller throttle body,
- 2 rings on the pistons (vs. 3 on the regular) for reduced friction,
- and the different ECU.

[rh77]

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?

Keep us posted and good luck!

RH77

[MetroMPG]

The Actual Unit - 6 lobes of fury

[Peakster]

Originally Posted by MetroMPG

I'm itching to get this done, but it'll have to wait until winter retreats a little. It's -22 C / -7 F outside. That's Peakster weather, not Blackfly fixin' weather.

Ha haha! Thanks . By the way, it was only -10*C (14*F) in Regina today and it's going to get above freezing this upcoming week .

[nathan]

Originally Posted by DaX

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

[MetroMPG]

No that's OK. You're not threadjacking at all - it's relevant.

Question: how much of a difference did using it make? I mean, could you think the timing was OK to the "unaided" ear, but when you used the det can did you discovered it was actually pinging?

[nathan]

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

[MetroMPG]

That's funny.

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?