Air/fuel ratio tinkering w/PCIII

[tripledigits]

I've recently installed a full Akro exhaust and PCIII, and had it dyno tuned. The shop tuning it used 13:1 as their target a/f. They said running it a bit leaner (about 14:1) saw 2 more hp, but they were afraid to set it that lean.

I'm wondering if their sniffer was out of calibration, since my bike seems to be running rich (sooty tailpipe) and fuel mileage is down a bit. Max power shouldn't be too lean from what I've heard. Does anyone have any input on this? I am able to get the max power map from the tuners, and could easily load it. I'm not so concerned about the last couple hp, but just don't want to burn more gas than I need to.

Thanks for any input on this. I couldn't find my answers on a search.......

[R1000]

It cant be right that the engine produces more power with 14 to 1 instead of 13 to 1 A/F. A ratio of 14 to 1 is normally targeted for emission concerns, and not maximum power.

[bartonmd]

It cant be right that the engine produces more power with 14 to 1 instead of 13 to 1 A/F. A ratio of 14 to 1 is normally targeted for emission concerns, and not maximum power.

This is true in a lot of cases, including low to midrange rpm, but you've heard the "lean is mean" on the top end saying, and it's true... for a short amount of time... If the rpm is high enough that knock is not a much of a factor any more, then, for a short time, you can run at 14.7 and make more power, because there is more heat produced (or rather, more heat left in the combustion chamber), and that makes the engine more effecient at making power (delta Temp between combustion and water jacket temperature), but is mucho baddo for long term high rpm, high power scenerios, like top speed runs, for instance, where you will melt pistons and score cylinder walls and such...

FYI, though, tripple, if you still have the PAIR system hooked up, it pumps atmospheric air into the exhaust ports to burn the extra, unburnt fuel in while it's in the exhaust, so what comes out is about 14 or 15:1, so you may need to plug up the PAIR system to get a good answer with an exhaust sniffer...

Mike

[tripledigits]

I do have the PAIR removed. Thanks for the input, guys. Any other comments on optimum air/fuel?

[EVLXX]

Any other comments on optimum air/fuel?

AFR for optimum Fuel efficiency... I'ld have to dig up my notes. Right of the top of my head...I'ld have to say it varies from 14.2 : 1 all the way to the burn limit for our bikes at 17.8 : 1. But don't go really deep into that lean mixture above 5500 rpm's as the valves and cooling system can't handle it.

Optimum AFR.... for power ..... is between 12.4 : 1 and 13 : 1, depending upon Load and RPM.

And here's a big hint for you... Keep it really rich from 5500 - 6000 rpm, especially since you have the PAIR blocked off and have quadroopled the negetive pressure wave from the exhaust flow.

Later.

[shovelstrokeed]

13.1:1 is too rich, as your down fuel milage and sooty pipes would indicate.

Gasoline is stoichiometric at 13.8:1 ratio. Oxygenated fuels a little richer. I would set for that across the board and, shoot for a gradually enriched condition from say 8000RPM up winding up at around 13:1 at redline and full power. The XX has some pretty good combustion chambers and pretty low surface area at the piston crowns. It will tolerate leaner mixtures quite well. You really have to get most motors radically lean before piston burning and the like will happen. Ditto ping and detonation so long as carbon buildup hasn't gotten too bad. You'll see best economy up around 15:1 but power will be down.

You can't mess around with very high compression engines like that. Big piston domes increase surface area and to some extent combustion pressures but a street engine like the XX, it shouldn't be much of an issue.

[Pete in PA]

A whole book can be written on this subject but in a nutshell...each combustion cycle in each cylinder can be slightly different due to cylinder filling, flame propagation etc.

For max fuel economy you want enough air to burn all the fuel.

For max HP you want enough fuel to use all the oxygen.

For emissions cars are set at the stoichiometric ratio of 14.7 to 1.

An engine will run as lean as 17 to 1 and as rich as 12 to 1.

You can't have one set A/F ratio over the entire RPM band for best power until true variable cam timing goes into production.

[EVLXX]

13.1:1 is too rich, as your down fuel milage and sooty pipes would indicate.

Gasoline is stoichiometric at 13.8:1 ratio.

Ed... your sleeping... wake up.

Copied from...Wikipedia, the free encyclopedia

(Redirected from Stoich) Jump to: navigation, search In internal combustion engines, the air-fuel ratio refers to the proportion of air and fuel present during combustion. The chemically optimal point at which this happens is the stoichiometric ratio (sometimes referred to as stoich), where all the fuel and all the oxygen content in the air of the combustion chamber will perfectly balance each other out during combustion.

For gasoline fuel, the stoichiometric air/fuel mixture is approximately 14.7 times the mass of air to fuel.

Now back to a little more about what I wrote....

Best Power is made in between 12.4 and 13.1 on our XX's at Max LOAD. My bad for not writing that before. Like Drag stip pulls with the rider sitting up.

That's not to say that's where the engine will run under normal conditions after being tuned like that.

Under most Normal Road conditions the ratio will be from 13.1 - 14.2 : 1, thanks in part to the stock ECU.

[tripledigits]

Thanks for the replies, guys. We have 10 percent ethanol in our fuel here in CO, unfortunately. I think I'll do a little experimenting with the a/f and see what I can do for a good compromise between economy and performance. The throttle response with the pipe and PCIII is really an improvement over stock. I'll let you know what I come up with.....

[shovelstrokeed]

13.1:1 is too rich, as your down fuel milage and sooty pipes would indicate.

Gasoline is stoichiometric at 13.8:1 ratio.

Ed... your sleeping... wake up.

Copied from...Wikipedia, the free encyclopedia

(Redirected from Stoich) Jump to: navigation, search In internal combustion engines, the air-fuel ratio refers to the proportion of air and fuel present during combustion. The chemically optimal point at which this happens is the stoichiometric ratio (sometimes referred to as stoich), where all the fuel and all the oxygen content in the air of the combustion chamber will perfectly balance each other out during combustion.

For gasoline fuel, the stoichiometric air/fuel mixture is approximately 14.7 times the mass of air to fuel.

Now back to a little more about what I wrote....

Best Power is made in between 12.4 and 13.1 on our XX's at Max LOAD. My bad for not writing that before. Like Drag stip pulls with the rider sitting up.

That's not to say that's where the engine will run under normal conditions after being tuned like that.

Under most Normal Road conditions the ratio will be from 13.1 - 14.2 : 1, thanks in part to the stock ECU.

Sorry, and you're right. 14.7:1 it is. Actually, I think that is for iso-octane but that is most of gasoline anyway. I have an excuse, posted at 0558 and hadn't had coffee yet also, my blood sugar was 72 that morning, an all time low for me. It was 468 when I was diagnosed 5 years ago.

[tomek]

Quick break from turkey consumption.

As far as top end power motor will make the best power at mixtures leaner then normal in the most cases.

We have to consider factors outside of combustion chambers.Exhaust pipe is designed to boost torque in certain rpm range.The range is determined by lenght of primary and secondary pipes,I.D and all the bells and whistles like balancing pipes,stepped headers,etc.

So the pipe works the best over certain rpm range.Exhaust gas temperature also has influance on that range. Lower EGT will move that range down,and vice versa.

Leaning out the mixture will increase EGT and as result of that pipe will give boost at higher rpms and peak hp will go up.Like variable geometry exhaust pipe.

Another thing to consider.Rich mixtures lowers EGT and makes them denser and effectively make exhaust very restrictive.Engines that are tuned way too rich fall on it`s face on top end becouse of that.

Another thing to consider,on production motors compressed mixture in so called squish area hardly burns and screws up exhaust readings.

Squish area is on the outside of valve pockets,and during compression stroke mixture will get pushed toward the spark plug but on production engines there is always some mixture left there and not totally burned.

I just pulled cylinder head from my 04 R1.Quick test with soldering iron gives reading 1.1 mm.

At peak rpms conrod flex will take about 0.6-0.7 away from that 1.1 mil,but there is a room to improve.

There will be 0.4 removed from the cylinder block,combustion chambers ported so there is no charge trapped and,,,,,,,,whole bunch of other tricks like blend valve job,perhaps valve guides stick out too much,etc

It is very cool when you outmotor newer,more-powerfull-when-stock bikes during the trackday.

Bike will make power at A/F whatever they are,actually you picked up good shop where they understand that tuning to mythical 13.2 will not always give the best power.

How about turbo motors with poor intercooling/high intakes charge temps.They will make power at rich mixtures due to the fact that vaporizing gasoline will bring temps down and charge density will improve.

Whatever works,if rich works,fine,try lean,it might be better.

Now back to the turkey.

[Toynut]

Do you need to take into account the Ram Air effect on the airbox? :icon_think:

[tripledigits]

I've been trying to post the maps here, but the floppy they were put on is having issues being opened.....

[tripledigits]

To follow up on the PC3 custom map, I pulled the map (after dyno tune) off the PC, and it was the same as the map it had when I brought it in. It was a map I had downloaded from the PC website. I was beginning to have suspicions the shop (which recently went out of business) didn't really know their stuff when it came to dyno tuning. The good news is I only paid $100 for the tuning.....

Now it's off the real dyno shop. I'll post map when I have it done.

Jeff