Re-jetting with a wideband

I'm not on here to impress you, and I've made it clear from the start that I'm no expert, and am relating my observations based on my experiences. I'm not here to argue or get into pissing contests.

I will tell you I've burned over 100 chips and/or .bins for my Firebird; all of the WOT tuning done on a chassis dyno with a wideband tuner, many more .bins done after I installed a wideband sensor permanently in the car after upgrading to a late model GM truck PCM with much more computing power and an emulator which allowed me to tune without burning chips.

I can tell you I've made enough minute adjustments to the fuel and timing tables and tracked the results to state my opinions based upon significant experience, not just conjecture. I will tell you that while I am certainly no automotive engineer, the DIY tuning forum I've participated in since buying my Firebird 5 years ago has a number of expert engineers, freely lending their expertise as dozens of DIY tuners worked on the same projects.

I will tell you that I made a number of modifactions to the car, got nowhere near the performance increases I felt I should have, and turned to the PCM to get the rest. Since doing so, I went from 264 rwhp and 309 lbft torque to 302 rwhp and 375 lb ft torque, all with a crappy 2bbl throttle body injection system that everyone swears won't support 350 hp, and all from tuning. At the same time, I went from getting 17 mpg in town and 21 mpg on the highway to getting 22 mpg in town and 32 mpg on the highway (when switched to the economy tune).

I can tell you I've run my highway tune as high as 15.5:1, and burned the tips off my spark plugs doing so when I got disgusted with fighting the knock sensor and disabled it to "see what would happen". I did.

I can tell you I've seen dozens of tuners in my forum over the years ignore the advice given by those more knowledgable and do major damage to their engines because of it. Everything from catastrophic detonation to combustion chamber temps so high they overwhelmed the cooling capacity of the car and even warped aluminum heads.

If you don't buy what I'm selling, that's fine with me. I started this thread simply as an observation that I'm suprised wideband tuning isn't more common here. I only went further into it because posters appeared to be going off in a wrong direction, and i don't want to see someone take a misimpression from here and find out the hard way that it wasn't a good idea.

Regardless of whether you agree with me on this, though, THIS discussion is about tuning CARBS. If there's going to be any "challenge" here, then I challenge you to show me a carbed application tuned leaner than stoich.

Post edited by: seanof30306, at: 2007/07/28 13:25

By the way, as an example:

en.wikipedia.org/wiki/Charles_Lindbergh

Scroll down to "World War II"

or:

en.wikipedia.org/wiki/CVCC

or:

en.wikipedia.org/wiki/Stoich

Post edited by: seanof30306, at: 2007/07/28 11:11

based on this thread and an hour of research, i walk away with the impression that max fuel economy is generally at about 15.5. some sources talk about better mileage with leaner ratios (into the 17s), but seem to suggest they rely on special run lean technology.

anyway this source supports the 17 to 17.5 ratio:

www.autospeed.com/cms/A_1595/article.html

this suggests 15.7:

www.hondatuningmagazine.com/tech/0510ht_...my_tuning/index.html

the following page comes from a book on tuning bosch fuel injection. the pic in the upper right corner says minimum fuel consumption comes at 1.05 times lamda = 15.43...

Those clearly come from people much more knowledgable than I, however, they are discussing fuel injected applications.

With MPFI, you not only have fueling which is much more precise than a carb, but you have almost unlimited control of the timing, as well. When a knock sensor detects detonation, for example, the mixture is immediately richened, and the timing is immediately retarded. Depending on processor speed, these adjustments can be made up to hundreds of times per second.

I don't believe there is any way you can safely run a carbed application at 15.7:1, much less 17-17.5:1.

i stumbled on this article about wideband tuning an EFI motorcycle. a bit off topic for our old kaws, but interesting:

www.nightrider.com/biketech/Pro_tuning.htm

Link no worky :silly:

seems to work for me ok.

just noticed there's 2 more articles there about tuning with the wideband:

www.nightrider.com/biketech/innovate_lm1_intro.htm

www.nightrider.com/biketech/diy_exhaust_probe.htm

if the direct links don't work, maybe try the front door and find them from the inside?...like

type www.nightrider.com
click 'motorcycle performance guide'
scroll down the right side and look for 'How to get Professional Tuning Results at home'

good hunting! :silly: :lol:

Post edited by: duncan, at: 2007/07/29 09:14

seanof30306 wrote:

You want to be at your leanest under cruise conditions, at steady throttle. The closer you can get to stoich (14.7:1), the better your economy and the lower your emissions.

13:1 would be the number you'd shoot for at WOT, and maybe 12-12.5:1 under transitional conditions, between cruise and WOT.

I personally found that if the transitional conditions result in 12-12.5, I'm lean. I get the lean surges while cruising and it runs like crap until it warms up completely.

Now that the bike is pretty much jetted for the best overall performance (not necessarily best peak power, just overall smoothness and street-ability), I notice the transitional periods go down below 11.5 briefly. This is probably because carbs are so innacurate. But it definitley runs better under these conditions.

So would it be ideal (for best power) to get the mixture to stay in the 13:1 (or 12.5 or 12) range under all conditions and transitions? I guess I'm asking Lorcan if his bike stays at the same mixture all the time or if it varies under acceleration etc. And if so, by about how much?

I realize this is unnatainable with carbs, but I'm just asking if that's what I should be shooting for, or is there something inherent about the motor that makes it require richer transitional conditions.

Post edited by: loudhvx, at: 2007/07/29 09:45

Duncan's link provides a little support for my rich-transitions finding, (and also mentions reasons for richer when turboing) :

www.autospeed.com/cms/A_1595/article.html

A well-tuned engine used in normal road conditions has an air/fuel ratio that is constantly varying. At light loads, lean air/fuel ratios are used, while when the engine is required to develop substantial power, richer (ie lower number) air/fuel ratios are used.

Bosch state that most spark ignition engines develop their maximum power at air/fuel ratios of 12.5:1 - 14:1, maximum fuel economy at 16.2:1 - 17.6:1, and good load transitions from about 11:1 - 12.5:1. However, in practical applications, engine air/fuel ratios at maximum power are often richer than the quoted 12.5:1, especially in forced induction engines where the excess fuel is used to cool combustion and so prevent detonation.

There is no one air/fuel ratio where all emissions are minimised. At an air/fuel ratio of 14.7:1 oxides of nitrogen peak, while hydrocarbons and carbon monoxide (CO) increase substantially as the air/fuel ratio richens.

Duncan's link also states something I found throgh trial and error:

During acceleration the engine requires a richer mixture than during steady-state running, with the extra fuel provided by acceleration enrichment. Under strong acceleration, the air/fuel ratio will typically drop 1 - 1.5 ratios from its static level. The amount of acceleration enrichment that is required is normally found by trial and error, and this is best done on the road rather than the dyno. The acceleration enrichment should be leaned out until a flat spot occurs, then just enough fuel to get rid of the flat spot should be added. This approach usually gives the sharpest response. Note that both over-rich or over-lean acceleration enrichment will result in flat spots, and that a greater amount of acceleration enrichment is needed at lower engine speeds than higher speeds.

That may explain why the ega shows so rich when I accelerate very hard from idle. And I know the bike runs much better when it does this on the ega.

So it seems to me I really only need the wideband on the bike to set the top-gear top-speed WOT condition between 12 and 13, then the rest is going to be trial and error anyway. Since I don't have an infinite number of needles, I may have to compensate on the main jet to get the transitions right. This is what I've been doing anyway, because the main seems a little rich right now to make up for transitions.

Post edited by: loudhvx, at: 2007/07/29 11:18

To be honest I don't pay much attention to what the A/F gauge is saying during normal riding. My bike has been mapped on a dyno from idle upwards and rides just like any other bike. I know it dives for the rich end as the boost piles in and goes super-weak on a closed throttle (as you would expect) but as long as it's driveable without hiccups the only reason I have wideband on the bike is to watch it at high speed to check it is nice and safe. "High" being above 170mph or so. Up to that it accelerates so fast and wheelies or wheelspins so quick it's all I can do to look where I am going, let alone look at gauges. I have a friend who uses a wideband on his DTA-fuelled nitrous GSX1100G, he's never had it on a dyno, he rides it to work and downloads the datalog in the evening to tweak his map for the best street manners. The WBC and the LM1 both have datalogging capability, if I was running carbs and looking for streetability, that's what I would be doing too (plus tapping his brains for what to look for of course).

Thanks, I figured there'd be a lot of swing in the mixture (since the stationary ega shows that). I just needed confirmation that I don't want to see a constant mixture all the time. It nose dives rich under load and returns to between 13 and 14 when the throttle closes down. It tends to idle around 13.25.

Stock jets in my carb were 15 pilots and 102 mains I had that with free flow exhaust and pods. I'm not sure what my air fuel ratio was but I'm sure it was closer to stochiometric then it is now with the 17.5 pilots and 110 mains. It seems the more fuel I feed it the more the pull is.
Gear ratio plays a roll in this too if you were to have a ratio of 2.4 it would like more fuel. Compaired to a ratio of 2.8 it would like less fuel. This is what I have experienced on my bike. These are facts.
My plugs were black when I had the ratio at 2.8 (15 front gear and 42 rear gear) this was with the 15 pilots and 102 mains. Now my ratio now is 2.4 (17 front and 41 rear) and the plugs are clean with 17.5 pilots and 110 mains. My milage has changed very little. I still average almost 150 miles to the tankfull.