Something is going on with the fuel these days!

[klatinn]

Interesting point. But how does that pressure translate to power? BTU has a conversion factor to translate it into HP units. Also feild experience has shown alcohol to not take you as far down the road compared to gasoline (measured by volunm).

My question about the ideal ratio was in reference to using an A/F meter to help jetting carbs. Like Ray was pointing out, the O2 sensor sences when there is no o2 left in the exhaust, so that is what it is about, except for the other considerations such as CHT and what not. Its just with Alcohol the jetting required is different, since it is more resistant to being sucked through the jet. However when mixed with gas, it might not be directly proportional to the % of mix.

Ron

BTU can be converted to HPhr, because both are energy units. But a gasoline internal combustion engine can only convert 25-30% of the energy contained in the fuel into mechanical work. Engines running on alcohol have higher efficiency numbers. This offsets somewhat (but of course not completely) the lower BTUs of the fuel. If an engine is optimized for alcohol (high compression/boost, direct injection and so on), it can get about the same milage as a gas car on a volume/mile basis.

Regarding tuning with alcohol fuel:
Do NOT use a A/F meter based on a regular O2 sensor. When richer than about 14.1 gasoline AFR (0.96 Lambda) they are much more sensitive to EGTs than to AFR (or Lambda). Alcohol fuels typically have lower EGTs, which means a NBO2 sensor outputs a higher voltage. People have been fooled into thinking this is richer and leaned out their engines dangerously.
Use a wideband meter instead. Use Lambda as indicator and tune to about the same Lambda as when using straight gas.

[Plastermaster]

thanks for the explanation Klatinn, I follow the thinking on the efficiency being the other part of the equation.

As for the A/f monitor., I just started running a single wire sender and guage from CB. Not interested in "exact" and a friend is lending it to me. I had the same thought about the EGT. The single wire needs to warm up in order to work, so it seems temps would effect the reading. So far I have found the guage to be erratic, but still have some predictable behavior related to my right foot. It is interesting to see its opinion, but I'm not going to let the guage overide healthy CHT and good performance. BTW, I'm not running alcohol, just gasoline with ethanol out of the pump. The pumps say "up to" 10% ethanol.

Ron

[klatinn]

Hi,

These things (NBO2 based meters) can tell you reliably only 2 things:

1. You are rich of stoich
2. You are lean of stoich

They can't tell you any more despite the numbers on the gauge.
Because with a carburated ACVW you want to run rich of stoich in almost all conditions, they are IMHO absolutely useless for indicating anything.
If you want to know why, read this thread and the math behind them:



http://www.innovatemotorsports.com/foru ... php?t=3127

[davygrvy]

Here's a recent post from the diy_efi mailing list about NBO2 sensors..

Code: Select all

Subject: Re: [Diy_efi] O2 says rich, car runs lean..
From: "Michael Richards" <[email protected]>

The narrowband thing is not really an opinion, it's based on scientific
fact. Narrowband sensors are designed to discriminate between richer
than 14.7 and leaner than 14.7. Nothing more. You can get a vague idea
of the actual AFR is by looking at the actual output away from the
switching point but it is by no means accurate.

OEMs have been using narrowband sensors for years because it is in a
fixed and tested location and since the tuning is fixed the temps are
also predictable. In the original poster's case we're dealing with a
modified engine producing more than stock output numbers. Very difficult
to predict the temps of that sensor and the setup is outside the OEM's
designed application.

-Michael

and

Code: Select all

Second, your readings may be related to the position of the O2 sensor.  If you overheat a narrowband they will frequently read rich when in fact you're running lean. This too can sometimes be caused by an ignition timing issue too much retard will over heat the sensor as well.

Narrowband sensors need a bit of "decoding" from my experience, but they do help tell you something. Ron, I remember you telling me about your 2K ping issue. Ping/preignition makes more EGT, thus putting the sensor out of balance toward richer (when already richer of stoich).

My guess if the guage isn't showing richer when you hit the ping condition, you are in fact leaner at that point than indicated. But take it all with a biggrain of salt.

There is, of course, the wide band option, but the sensor alone (with no indictor display and associated electronics) is around $200 <- NTK one used in Hondas.

Keep us informed of your findings.

[Plastermaster]

This is all interesting info. The erratic behavior I posted earlier, in light of the info on the NBO2, is that it heaves back and forth from way rich to way lean when it is crossing the line of Stoich. With a jetting that puts you about at stoich, the needle will swing with the slight variations that occur from load changes and slight throttle position changes. When the guage is behaving that way it is telling you you are about at stoich and need to go richer. So, then I go up one size on the main jetting and when I am into the mains the needle says pretty much pegged rich, which is probably about right since I went up one jet size. All this would be assuming the EGT is not too hot. If it is I could be pegged on the rich end and STILL be lean.

Unfortunatly my carbs acting up so it is hard to see the readings in light of good performance. For example, before reading all this, I was pegged on the rich side and reduced the mains 1 size. I went for a short ride and the enging seemed better, more crisp, yada yada yada. Next day I take it out and it is stumbling all over the place like it has no fuel. I hate it when IT changes overnight with out me doing anything! Time to re-examin the fuel delivery.

Ron

[Plastermaster]

Back to the topic of something going on with the fuel these days, I removed the carbs and cleaned them as I seem to do about every 4 months or so. I am runninf 4 filters on the car which keeps debris out pretty good. Also I go to extremes with the air intake being clean. What I find over and over again is gum build up. It does not seem to bother ny other FI cars, but It collects in the idle jets and in this last case, I was unable to blow air (from my lungs) through the fuel inlet and out the needle valve fitting. The carb cleaner did not flush out debris but just seemed to disolve some amber colored stuff.

Ron

[Plastermaster]

Narrowband sensors need a bit of "decoding" from my experience, but they do help tell you something. Ron, I remember you telling me about your 2K ping issue. Ping/preignition makes more EGT, thus putting the sensor out of balance toward richer (when already richer of stoich).

My guess if the guage isn't showing richer when you hit the ping condition, you are in fact leaner at that point than indicated. But take it all with a biggrain of salt.


Keep us informed of your findings.

Well, with the carbs cleaned up the engine is running great, but there is still the ping between 2200 and 2600 rpm. It happens if I give it just a bit of gas and I am on a hill. If I floor it or close to floor it, it goes away. I would not say I am lugging the engine either, because with plenty of pedal the car accellarates up the hill quickly. Its that partial throttle that finds it. The A/F guage swings way over to lean when I give it just a little gas until I am up around 3500 rpm. My floats are set pretty high to enrich the transition from idles to mains. that might seem low for the transition, but I found that main jets do affect performance as low as 2200 on this one. Timing is about 24-28 in that rpm range. I have full advance at 30 at about 2800. I could play with the E-tubes, but I kind of doubt they would do anything at that low RPM. (?). When I am not giving it the gas and just going at a steady speed the A/F needle stays pegged rich, which means from the above info that I am probably richer than 14.7. I have 36 vents and 155 mains, and 70 idles, so I doubt I am lean. CHT stays between 275 and 300, which may be too cool for evaporating the fuel...just a thought. Any ideas? other than the ping all is darn near perfect.

BTW this has anything to do with Jakes work, these are my old carbs that I am trying to get dialed in. I am fortunate to have a strong beast of an engine to put up with this trial and error and continue to run strong and cool.

Thanks
Ron

[Stufenheck]

Ron,

Your Dellortos may need different emulsion tubes, suggest that you email Art at ACE. http://aircooledengineering.com/index.php
Had the same kind of transition issue between the idle and main jets with my Weber DCNF's. Emulsion tube he suggest took care on transition issue (flat spot), resulting in size drop on idle jets from .60mm to .55mm.

Just make sure to let him know everything about your Dell's; ie 40 vs 45, float height, emulsion tubes, venturi size, idle, main and air jets sizes. The RPM, timing and driving instance when pinging occurs as you noted earlier will also be helpful.

Jesse