Air/ fuel ratio opinion

[Truckedup]

Would you please explain what you mean by not getting a proper A/F reading?
What was the problem?

The pipes on my bike don't have sensor bungs so the thin wand was put up the exhaust pipe...The readings were way too lean for the power being made, 18-1..The operator changed O2 sensor but same result..The computer diagnostic said all was fine with the O2 stuff....Same thing occurred when I first built it and used another shop with a different dyno brand..
I don't find A/F readings at full throttle useful...There's no standard A/F for these engines,it's just one engine, I tune by best power on the dyno and best speed on the track while keeping alert for detonation...This isn't like a Chevy..The competitors are tight lipped .Running this vintage junk you're out there alone more or less to figure out what works...In fact the only real help I got was here on Speed Talk

A lambda sensor on a wand inserted in the exhaust pipe is virtually useless because of ambient air leakage back into the pipe. So why does the engine not have proper lambda bungs brazed into the pipes at the correct location?

A properly installed lambda sensor reveals much more than a simple A/F ratio (which it does not do). It will show engine misfires, shortstopping, transitional mixtures, mixture spikes, lean sports and much more. Do not look for a "standard" value since the correct mixture is dependent on conditions and specific blend of fuel used.

Vintage "junk" is not different than advanced engine development; you're on your own to figure out what works.

.. What is A/F going to tell me that jetting for best power and speed hasn't already told me? That it's jetted to lean?

[David Redszus]

A properly installed lambda sensor reveals much more than a simple A/F ratio (which it does not do). It will show engine misfires, shortstopping, transitional mixtures, mixture spikes, lean sports and much more. Do not look for a "standard" value since the correct mixture is dependent on conditions and specific blend of fuel used.

Rich fuel ratios are often used for temperature control, detonation avoidance, throttle response and other reasons that have only a slight relation to maximum horsepower.

[jmarkaudio]

Fuel completely vaporized during the intake cycle replaces air mass

It's all relative. If fuel is better vaporized early then distribution is better, so less overall/leaner mixture makes more power. And with better vaporization a larger carb can be used, or two carbs to lower pumping losses. At the carb shootout we were rule limited to individual cylinder peak O2's of 13.9, and the closer we got the more power it made.

[Truckedup]

A properly installed lambda sensor reveals much more than a simple A/F ratio (which it does not do). It will show engine misfires, shortstopping, transitional mixtures, mixture spikes, lean sports and much more. Do not look for a "standard" value since the correct mixture is dependent on conditions and specific blend of fuel used.

Rich fuel ratios are often used for temperature control, detonation avoidance, throttle response and other reasons that have only a slight relation to maximum horsepower.

Dave I' understand what you are saying and I know you have way more experience than me with this stuff....I could do that and then using my A/F values from the track when the bike runs it's best speed to use that value when to rejet for different conditions as you say....
I'm only familiar with the size of O2 sensors commonly used in cars/trucks...The problem is anything like that sticking into to the exhaust pipe kills power on top end...The engine has two 1-1/2 x 34 inch individual pipes, no collectors or megaphones and imagine the restriction of an O2 sensor...Is there some other O2 option?

[Warp Speed]

The Bosch 4.2 and 4.9 lambda sensors only require the very tip to be exposed.

[Truckedup]

The Bosch 4.2 and 4.9 lambda sensors only require the very tip to be exposed.

During the many dyno pulls to tune the bike I tried to limit mid range reversion by inserting a 1/4 bolt 3/4 inch long near the pipe exits...Improved the bottom end by a few ft pounds and took the same off the top end...with only 55 rear wheel HP (40 ft lbs torque) to push a naked frame bike and rider with as much air drag as a car ? to over 130 mph , even one HP is precious...

[David Redszus]

The Bosch 4.2 and 4.9 lambda sensors only require the very tip to be exposed.

During the many dyno pulls to tune the bike I tried to limit mid range reversion by inserting a 1/4 bolt 3/4 inch long near the pipe exits...Improved the bottom end by a few ft pounds and took the same off the top end...with only 55 rear wheel HP (40 ft lbs torque) to push a naked frame bike and rider with as much air drag as a car ? to over 130 mph , even one HP is precious...

Engine performance as measured on a dyno is quite different than that developed on the track.
Assuming a vehicle with a frontal area of 8.0 ft^2, a Cd of 0.42, we still need to know the ambient air conditions.
Further assuming a baro of 29.0 inHg, 80F deg, and RH of 30%, at 130 mph it would take 45.8 hp to overcome aero drag.

As mentioned earlier, a lambda need not be fully inserted into the pipe to obtain adequate readings.

[Belgian1979]

you make it sound as if using a dyno for tuning is irrelevant

[user-23911]

you make it sound as if using a dyno for tuning is irrelevant

It depends on how you do it.


Like dynoing a car that's got a hot air sucking pod filter on it.
Dynoing it with the bonnet open when it's closed when you drive it.

Does that make any sense?

[MadBill]

...As mentioned earlier, a lambda need not be fully inserted into the pipe to obtain adequate readings.

http://www.ebay.com/bhp/o2-sensor-spacer

[Truckedup]

...As mentioned earlier, a lambda need not be fully inserted into the pipe to obtain adequate readings.

http://www.ebay.com/bhp/o2-sensor-spacer

They function properly if not projected into the pipe at all, let's say the tip is flush with the pipe wall?.......You guy mentioning the chassis dyno.....My bike runs it's record breaking speed at the track exactly as tuned on the chassis dyno. Changing tuning at the track offered no improvement other than gearing...I know this normally may not be the situation ...

[Warp Speed]

...As mentioned earlier, a lambda need not be fully inserted into the pipe to obtain adequate readings.

http://www.ebay.com/bhp/o2-sensor-spacer

They function properly if not projected into the pipe at all, let's say the tip is flush with the pipe wall?.......You guy mentioning the chassis dyno.....My bike runs it's record breaking speed at the track exactly as tuned on the chassis dyno. Changing tuning at the track offered no improvement other than gearing...I know this normally may not be the situation ...

The portion with the multiple holes should be flush with the pipe id, leaving just the center tip exposed. This will keep influence to output at a minimum, and also help with overheating during extended high temp use.



Not sure about the re-locators Bill posted above, but I would imagine they could lend to false readings and slower reactions but?
I feel if the testing is done properly, a dyno can give relative information for the track. Especially in low g force environments.

[nyesgym]

I have a question. my base motor runs on m1 alcohol mechanical injection, but nitrous system runs on C23 gasoline. what do i set my racepak sensor to read for best results > gas or alcohol

[Walter R. Malik]

Using just an 02 value for tuning the air/fuel ratio is only an indication, not actuality.

[MadBill]

Seems to me (but I'm prepared to be wrong) that if you selected λ rather than AFR, you'd be covered regardless of the fuel mix.