EFI Discussion

[Dan Filetti]

Well maybe if you add some back pressure back into that exhaust system and get a good tuner to have a play with the cam timing you would see some real improvement.

But of course no-one's ever done it before (that you know of) so it's no doubt not possible right?

Or perhaps it's just that kind of engine with such a gutless bottom end it's never going to be efficient at anything but ludicrous engine speeds.

Wow, WTF? what crawled up your ass and died?  

A few points in response:

1. 'a good tuner' has indeed spent hours working on this bike, after 10, dyno runs, and 7 different custom map iterations, the fueling and power characteristics are nearly perfect for me, for this bike.  Note, fuel economy did not factor into what was trying to be accomplished with the tuning.  

2. Who EVER said EFI on an FJ could not be done? -certainly not me -maybe you need to go back and read the post.  I simply did not know whether anyone had ever actually accomplished it.  As I said, I have seen several attempts just never heard that one of them was actually successful.  That's why there was a question mark after the sentence -'has it ever been done?'  It certainly could have been the case that someone did it, and I missed it.  In fact, I expected someone to come back and say, 'oh sure, Hank Scott has done it to 3 different FJ's...' or some such...  I was actually a bit surprised that no one did.  Same thing with Big Piston forks, I'm surprised no one has done it on an FJ yet yet.  This is a really smart and innovative group of people.  

3. The Gixxer does not have the low end that the FJ does, that is certain, nor will it ever -no matter how much tuning is done.  The Gixxer's design principles are simply irreconcilable with that of the FJ.  But the Gixxer is well more than a hundred pounds lighter, benefits from another 15+ years of R&D, over the FJ and with proper thrashing, it has it's own kookaloo, I can assure you.

4. Sorry to hijack the thread...

Dan

[andyb]

Backpressure is mostly required for 2strokes, and is a term thrown around by people who can't get a fourstroke motor to properly run.  It's up there with mistaking midrange power for torque.

Adding an exhaust that's designed for a significantly different engine specification than the rest of the motor (i.e., head, cams... the airflow path) is going to cause mismatches.  It's totally possible to put an absolutely open exhaust on something and retain both torque and low-rpm power, if everything is designed as a matched system rather than a jumble of parts, without having to resort to "adding backpressure".

FJ engines have been successfully converted to FI for years and years.  They're sold under the name "XJR".  Trying to fit a different FI system on is another matter, but mostly I'm being pedantic.

While I'm moaning, tuning a bike for A/F ratio is a bit silly to me, and it seems that I'm not the only one. Tune for power while keeping the A/F at safe levels, and tune the idle/cruise ranges for reasonable mileage.

Don't compare 3krpm on two engines when one revs to 15k and one redlines at 6k.  That's when you start getting into the moronic harley arguments.  Compare two engines at a % of their redline (say, 30% of redline on an FJ is ~3100rpm, but on a 600 could be 5000rpm or more).  Given two dragbikes with the exact same amount of power but two very different redlines, the higher spinning one will win every time, as you can put more gearing on it, and increase the torque multiplication advantage of gearing.

Anyhow....

[fj1289]

I've got an old book (written in the early 70's I think) about motorcycle tuning.  The best quote out of it is "power is where you find it".  His whole guidance in the book is change one thing then test - using a measurable result - and optimize the fuel and spark by incrementally go leaner or richer until it slows down and then back up a step. 

I agree about not tuning to a specific AFR, just like I can't tell you to use a 112.5 jet.  You can use it as a starting point and then you have to test it, try a 115, or a 110 (depending on how your test went) and test that, and so forth.  Don't see how that is different from trying to achieve an AFR of 12.5, see how it performs, try 12.0 or 13.0, etc, until you see what the bike wants.  A generic AFR map will get you in the same ball park as the base line jetting recommendation in a jet kit.  It's up to you to fine tune it from there. 

Whether you're tuning with brass or pulse widths, it's still tuning!

[Pat Conlon]

Whether you're tuning with brass or pulse widths, it's still tuning!

True....but it is sooooo much more precise with fuel injection.