http://www.avweb.com/news/columns/182084-1.html
One if not THE best article I've read describing engine fueling and overal operations.
Grumpy, I think you might find the section near the end, "Some Old Wives' Tales (OWTs)", to be interesting. I'd like to hear your thoughts.
Once you've read that section (too long to quote) I'd like to discuse it in this thread.
My understanding (and common sence) says that a naturally aspirated engine is far from that of a turbo engine. My valve temperatures will be much lower than yours given the overall size of my engine and it's relative low output. The same is true when running at part throttle and cruising loads. I'd like to see a graph showing the BSFC of a turbo motor similar to yours. The reason I say this is because it appears as if best fuel economy AND engine life will happen leaner than stoich. I think there is an exception to this but at the moment my mind is still in the "absorbe" mode.

 

That was a fascinating article. One to print out and keep. And I'll probably order that book they reprinted. I'm going to have to reread it several times to get the full impact but that's the kind of theoretical stuff I need.

 

Thanks for posting that JPrevost, very intersting stuff.
the parts on removing timing rather than throwing fuel at the problem are well worth looking into.
The case of giving a little to gain alot are excellent points for the everyday driving senarios.
I've printed it and am going to read that one at least 2-3 more times to let it all sink in.

 

...right click...Save As...

 

Over 150 views and 3 replies....
*sniff*sniff* I smell lurkers. Either that or the article is over everybody elses head, but I doubt that's the case.
Maybe I've just been blacklisted, yeah, that's probably it.
So to the 3 guys that thought the article interesting, have any questions? Did you find any of it useful?

 

Not immediately but only because my engine is still on the stand and I haven't even begun to start tuning yet. I do know that it will come in handy.

 

:lurking:


Actually, it's just that I haven't had time to read it through a second or third time yet. I gave it a quick once-over and it seems to be slap-full of information....maybe I'll have a chance to REALLY read it sometime next week.

 

I only have a few comments about it's practicality.

1. We don't have the luxury (or need) of going WOT, and 18:1.
2. If you have a cat, it's not much help.
3. If we had ETC (electronic throttle control), and a kick butt algorithm, we could implement some of this.
4. Most of us want full power at high loads, not fuel economy.
5. We use WB and knock sensors, not EGT, or CHT, and I wish they had used it too, for clarity on everything.
6. When leaning, there's a point when HC's go up, and that is lean partial misfire at least.
7. When leaning, the combustion can slow down a bit, which can actually heat the piston, which in an automobile is a bit lighter and less robust than an aircraft I think. This is just for argument's sake, though, since I haven't personally gone so far as to try leaning it out to achieve piston failure.
8. We use 87-94 octane most of the time.

I'm not bashing the article, just trying to point out some of the shortcomings of airplane technology applied to daily drivers. Also, what I say is definitely not gospel, so if anyone wants to dispute these claims, please do so, I'm listening, and want to have accurate info in the end.

Also, I have a great article somewhere from a friend, but I'm not sure if it's public domain, is that taboo to post here? Oh wait, it's a word document, not a link. It's about gasoline, and I'd like to share it. I'll look it over and check for any print about ownership.

 

No real questions although reading that makes me wantto use EGT more than anything. That with a WB can do alot.
The only other item I can think of that you can lean out the mixture more at high altitudes just because of the air density being less. The same A/F ratio results in less fuel needed to still obtain the correct mixture.
Just reading through the various points of the parameters as the mixture is made rich and lean was good to see the relationships and where the changes in magnitude are reducing at certain levels.
Once I get the new heads and stuff on mine, I'm sure I'll be tuning for the "just less" than peak to get the milage and power benifit. Its not exaclty the same but alot of the principals carry over.
Then I'll use my G3 and switch to fly mode!
With 16 bins to choose from, theres room for some experimental programs.

 

RednGold, I see your points but I don't think you understand what I was asking. I wasn't saying that this is HOW to tune an automotive engine. I was posting this article to give people a better understanding of how engines work.
1. We don't have the luxury YET of going WOT, and lean. Again, my point was to shine some light on the whole engine thermal limits and bring up valid questions that contradict a lot of what is preached on this and other EFI boards. I've read too many times that lean kills engines but my point about running rather lean AND having low horsepower when doing so AND having a rather large cooling/valve size to fuel burn ration... well I hope you understand what I'm trying to say.
2. Having a cat doesn't mean you cant cruise lean. Infact OEM used to do this with "highway" mode. The only time I've seen cats get damaged is when they're run too rich and not enough timing. You CAN put out a cat with overly rich fuel but destroying a cat with an engine at part throttle and lean is highly improbable.
3. I don't know if that really matters as much as you might think. Implementing lean burn at cruise is a lot safer than at WOT.
4. True, most of us do want full power when we press the go pedal but with the price of gas and the expense of engines why wouldn't you want to save money and engine wear? From the guys experience he's got a lot more hours of engine abuse than probably any of us could imagine. The point that he's running WOT AND lean is even more relavent to my point of using a lean burn cruise to increase milage and save engine wear. From his data, CHT's are lower with an overly lean mixture, look right at the lowest BSFC point!
5. Unfortunately we do only use WB and knock sensors. These are good tools but why not use an EGT and CHT? I have my EGT and am looking for an inexpensive spark plug CHT sensor. A CHT sensor would be very useful but you could (and I might) settle for an oil temp sensor. Oil temp is a good indication of piston temps.
6. This is true and why I hope to get my CNP (coil near plug) setup working. A better ignition is going to be a better burn. It also helps to have good fastburn style chambers to get away with running lean mixtures. Good quench does wonders with wedge heads for both power and BSFC.
7. This is where I believe I've gained from running LESS timing in highway mode. By running less timing I was hurting my horsepower a tad but the gains were from running where the engine produced the lowest BSFC. I found that happy limit when I was commanding a 15.5 AFR, the 16.5 AFR was costing me too much horsepower and moved me into the higher BSFC area of my motor. ALL internal gasoline burning combustion engines have a BSFC table similar to the one charted in that article.
8. We definatly do use lower octane fuel but I don't believe this is a shortcoming of airplane technology applied to automotive engines. Octane from my experience is nothing more than engine speed and compression ratio dependant. Higher octane fuels don't actually contain noticably more energy so none of those charts would be different.

I understand you're not bashing the article so please don't think I'm jumping down your throught. I just reread my whole reply it probably sounds like I'm getting defensive... but I really am not. I just want people to understand WHY I posted the article.

Please do post the article about gasoline. I've read a few SAE papers about fuels and am less than impressed with the results. I've run 100 octane in our 14.5:1 comperssiong 14,000rpm racing engines only because I couldn't remove enough timing to get rid of detonation at 8000rpm and higher. Below 8000rpm we actually made the exact same power (accurate to within a tenth of a ft-lb torque). So I run 87 octane unless I find a good deal on premium. Besides, for my motor 87 octane actually keeps things running smoother believe it or not. Low compressiong, low power relative to displacement, high quench, fastburn chamber, least amount of timing needed for the motor to run well, all these things make my car/engine happy with lean burn 87 and my highway milage is rather good.

 

The altitude is a good point. I had thought about that initially but what's impressive is the high load these engines are seeing AND running lean. Things that I've been told were really dangerous might not be so. I think running lean AND advanced timing is probably detramental to engine life but running lean and less advance seems to jive... at least on my motor it does.

 

That has been my experience on previous projects with carbs. I haven't really pushed the issue on my TPI but its looking like something I want to work with. I have reduced timing to reduce the amount of fuel I need to get off the line and it helped (mostly because I couldn't leave at full power without breaking loose)
In using that theory I did have noticeable gains in milage because of the reduced input requirement of PE/AE. I will be working on that again and also with running lean in HIway mode as well.
I have to run at least 98 octane or I get knocks to the point that I have to reduce timing to the point of power loss.
I need a CAI, that would also help.

 

Crizap, I tried to attach a word document, and lost the post. Oh well. I'll find a way, but have to go to lunch. I like it when people post these articles, so there can be more info to draw conclusions. I think we all benefit when we can discuss things like these.

 

CHT for an air cooled engine is the same as a CTS on a water cooled one.

EGT?, isn't everyone?, with that a WB, 2/3's of the work is already done. Add a G-Tech, and you're home free.

Now if he'd just mentioned an ecm bench.

Operating conditions are somewhat different at altitude, so some of what he says maybe slightly misleading, IMO. As air density drops you need to add timing (at a given IAT), to recover as much energy as possible for a given cylinder's worth of air. So in the aero world they're going to benefit more from lean and advanced then the same engine at sea level.

Still nothing beats giving an engine what it wants.

 

I still don't understand how to "tune" with EGT, because it's multi-variable dependant. I'll stick to WB, and dyno, and knock for the knock limited cases (low octane, high compression, hot engine, whatever the cause). From this, the engine gets what it needs (steady state first, then PE, then transient constant RPM, then transient at almost constant load, then sweep around to check), and go from there to get drivability with IAC and more transient tuning. I know this isn't economical for most, in which I must reply: I know, so, get it (VE) close with conservative timing (use stock tables or mimic a conventional advance distributor), fix the major fires like transients and idle, use some math and a WB to get PE to 12.5 or so, then try some more timing in places if you like. Let closed loop fix small problems with VE, and change VE if closed loop isn't fast enough in that area, or if it causes other problems. I just can't recommend spending hundreds of hours "just" tuning, for goals like economy. The money wasted there is a little silly, but if you're on a trip for another purpose, sure try a few things and see what is best, but get some use out of the miles you tune with.
IF you're an open looper, you MUST have a wideband, and you probably have a terrific cam, again, I wouldn't spend too much time for economy, or I would have chosen another cam. And IF I were a big cam guy, I'd make a wideband closed loop system (think about this: LM1 has two outputs, a MAP or TPS based switch can't be that hard - switch from one A/F vs Voltage curve (switch point) to another, and leave the ECU in closed loop with the proper VE jumps at the right MAPs).

This is probably just begging to be trounced on, so I'm bracing myself.

 

Thanks Bruce for your input. I agree that altitude is a big factor and greatly affects the tuning of an airplane enigne versus an automobile engine. I consider altitude a "natural EGR".

I have done a lot of work with my engine in altitude because of the area I live in. And you NEED more timing, just as Bruce said - both for power and for throttle response.

Altitude is like reducing load; you are now not filling the cylinder fully (without a power adder) and the mixture is less volatile. Thus the extra spark advance is to ensure the optimum cylinder pressure is built at the right moment. As Bruce said, NONE of that would work at sea level (and you would encounter massive detonation).

 

I think the volatility difference in the fuel is just to make it "even" with sea level fuel. Like water, fuel boils easier at altitude, but this may cause some excess tank fumes, so the volatility is reduced.

Is it really a problem at altitude (asking because I don't know - please tell and explain)? Thanks.

 

RednGold, I don't trust the knock sensor for anything more than cruising knock detection. At WOT I've gottem more false knock from my transmission shifts than I have REAL knock. This is where EGT has it's advatanges. EGT depends on fuel and spark advance. The EGT also can help with fuel distribution issues where a wideband would only average.... unless you had long tubes and a wideband for each pipe.
I've used the WB to get it close and then the EGT to fine tune the SA and AFR. If you get a slight misfire at lean cruise tip in (happens with TBI unfortunatly) then the EGT picks it up. Also with more advance the cooler the EGT because more of the energy is going into the cooling system and oil.
For the price of an EGT I'd say it's worth a gander. When you get knock from too much advance you'll see the EGTs go low. Retarding the ignition with a rich mixture will skyrocket the EGTs. See how this info is useful? Using a wideband isolates the fuel where EGT has fuel and spark and knock, if you use a wideband then EGT's only other variables are spark and knock .

 

At EGTs of ~2,000dF the exhaust valves start to erode, and try leave the engine thur the ports (Ti raise this some).
You can also get into piston dome failures, and skirt galling.
EGT is just another tool, it prevents one from exceeding one the limits of the engine, ie the thermal one.
BTW, it doesn't take much to get to a 2,000dF EGT. And in a non-N/A application, alot less then you might possibly dream of.

 

I know this is an old post, but id like to read the article that is linked in the first post. The link is gone so I wonder if theres a chance anyone knows and alternate or has it saved?

theres a chance, maybe..

 

I would like to read it also

 

I have a copy of that article saved to my harddrive. Its only 129kb so i can probably send it email style but im on a limited dialup connection. It might be a couple of days before i get back on line to send it.

 

hey that'd be great if ya could. or you could upload that as an attachment here, with the paperclip button above where you type for replies. theres a 1Mb limit i think.

 

I did a search on the original web site but i couldnt find it there for some reason so i uploaded it here so it should be available for future readers. I saved the web page as an html file so its a little bigger than 129 kb. Theres quite a few graphs and charts included with the article.

 

cool, thanks!

 

Sorry to bring this back again, but the link has ben changed. Any idea of what was searched for on the site to locate this 'information from above'?

 

I was able to find it again, they moved it but there was an index when I searched for "breif".
http://www.avweb.com/news/pelican/182084-1.html

 

Thank you.