Catalytic converter back pressure?

[ChipBeck_imp]

Gentlemen,

I currently have 3 different exhaust headers for my CB11. One of them is a stock header with the catalytic converter removed. If I install it will the reduction in back pressure screw up the way the bike runs or cause it to run lean or rich? Putting on the Staintune with it's straight through pipe reduced back pressure as the stock muffler has two 180 degree changes of direction and after that my CB still ran fine (maybe better). Will going the next step and eliminating the cat be too much and require a PCV or a reflash? Does the cat have so little back pressure that the bike wouldn't notice? Just looking at it I think that cat produces quite a bit of back pressure but I don't really know. Anybody have some experience here?

Chip

[CIP57_imp]

Gentlemen,

I currently have 3 different exhaust headers for my CB11. One of them is a stock header with the catalytic converter removed. If I install it will the reduction in back pressure screw up the way the bike runs or cause it to run lean or rich? Putting on the Staintune with it's straight through pipe reduced back pressure as the stock muffler has two 180 degree changes of direction and after that my CB still ran fine (maybe better). Will going the next step and eliminating the cat be too much and require a PCV or a reflash? Does the cat have so little back pressure that the bike wouldn't notice? Just looking at it I think that cat produces quite a bit of back pressure but I don't really know. Anybody have some experience here?

Chip

Chip,

You need to put the setup you want on the bike and have a tuner dyno the bike and setup A/F ratio's, this will require a PCV. The bike runs better just above 13.2 A/F as shown on charts. A flash would only be helpful if a map was created for your bike, without your bike being present its a shot in the dark.

My bike had a full Yoshi, flashed with a stock PCV map, although it run much better than stock it was on the rich side. Plug readings showed it running a bit rich on the outside cyl. this could have been corrected by a good tuner. Also, a tuner can check your 10%-100% throttle responses.

I don't believe the CAT creates an enormous amount of back pressure on this bike, very little popping on decel with a full exhaust. (unlike a ZRX1200) Popping will start off throttle above 4500 PRM's and can be eliminated with the pair mod.

So to answer your question, the bike will run richer with a full exhaust with more HP, to optimize have it tuned.

[Motogeezer1949_imp]

IMO, I think the computer will adjust to the situation just fine.

[immgunn_imp]

Honda programmable fuel injection has adaptive fuel strategies. To see if the bike is running rich, lean or at stoichiometry, just connect a digital multi-meter with min/max/average function. Take it for a spin (fully warmed up). On a flat straight-away, start the min/max/average. Stop the min/max/average before running out of flat straight-away and see what the meter says. If the average is in the neighborhood of 450mV, life is good. If it's significantly higher than .45 V, its rich, lower, its lean. The adaptive fuel strategy will try to keep the a/f ratio at stoichiometry (450mV). This shouldn't be a problem with a minor modification or two, but the fuel strategy may run out of authority if the mods are too great (for the Honda PGM-FI). Good times.

[Lord Popgun]

Immgunn,

Where do you connect the meter?

[CB4ME_imp]

What kind of gas mileage are you getting? I have cat free headers, Staintune, TSR air funnel, Pair Valve mod. Bike runs great but I'm struggling to get 40 mpg.

[immgunn_imp]

You back probe the signal wire coming out of the oxygen sensor (HO2S). Leave the sensor connected to the harness. I use T50 t-pins from a sewing store when I can't find my $35 Snap-On back probe. I don't have a wiring diagram, but checking voltages won't let any smoke out. One wire will be power for the sensor heater. There will probably be two (2) ground wires. Heater ground & sensor ground. The final wire will be signal. On a fully warmed up engine, the signal wire should be bouncing between 0 & 1 volt. Slip the back probe through the weather-pack seals of the connector. It doesn't matter from which direction so long as you get a good connection between the back probe and the wire terminal. Twist tie the meter leads to prevent them from contacting the exhaust, moving parts or anything else that could harm them, you or the meter. Although I've never mapped a M/C HO2S, I vision the meter being on the seat between the rider's legs or where ever you can see the meter and press the min/max/average button. If you've never min/max/averaged before, remember you need to start the measurement & end the measurement without any significant accelerations (acceleration enrichment) or decelerations (decel enleanment). Just like a DOT drug (urine) test, capture the sample midstream while at a nice steady throttle on a level road. Straight is nice, but as long as you can maintain a steady throttle, not mandatory.

[Motogeezer1949_imp]

Have flashed ecu and full Yosh. Just got back from the Rally. The riding was pretty tame. 50 mpg.

[emptysea]

I don't want a lot of chemistry and physics talk here, but I do want to know if my stock ecu coupled with my Yoshimura full exhaust (no cat.) would benefit from or be hurt by using a higher octane fuel.

[Motogeezer1949_imp]

FWIW, Guhl told me 89 octane would be just fine for our CB after the computer flash.