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Gas Mileage and current tuning strategy
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Author:  Sam Powell [ Sun Jul 20, 2008 5:47 am ]
Post subject:  Gas Mileage and current tuning strategy
The first tank of normal driving, with no power runs or long idling for tuning produced 24.5 MPG. I was quite pleased, and surprised. Seventy five percent of these miles were commuting a short distance to work. I was surprised because it was running richer the entire time than I intended for it long term.

The warm up coefficient curve was tuned to raise the AF ratio a little as the ECT temp went above 200. This was a reaction to having the engine stumble and run rough after it sat for ten minutes (a trip to the store) and went into heat soak conditions. Raising the number a little at 205 degrees seemed to make this better. But perhaps I raised it too much.

Anyway, then I put in the Evans Waterless coolant, and didn't think about the tuning, but realized part way through the week that now the engine runs hotter, and as a result is now operating in that richer/hotter part of the warm up enrichment table. I had a highway trip yesterday that produced cruise temperatures of a stable 210 degrees ECT. This pushed the mixture higher into the richer part of the warm up curve. It was cruising on the highway at between 13.5 and 14.1. I thought this was choke-on mixture levels. I never had a way to check what AF ratios are with the choke on, I just thought it might be around that since that is the ratio this engine shows during most warm up driving, which is the entire 4 miles to work.

I was thinking, "man this tank of gas is going to stink gas-mileage wise".

Imagine my surprise when it produced 24.5 MPG after topping off the tank, and squeezing every last drop of fuel into the tank. I put a new gas gauge in with the new dashboard, and I must have wired it wrong, because it doesn;t work, and I just fill it up after 100-150 miles to be sure I don;t run out. I just don't want to take the dash back out again at this point.

So last night, my wife and I went up to an insane car cruise I will likely not participate in again, and she retuned the warm up curve for me, and refined a few of the VE cells so it cruises on country roads at 14.8 to 15.2.

Now, here is the interesting thing. I have always assumed that up to the point of running badly, lean was more efficient. Is there a possibility that an AF ratio of 13.5 on the highway is the most efficient mixture for highway cruise? It seems unlikely to me. But I will check out this tank and see. I will need to take it out on the highway and tune there as the lower AF ratio numbers might have been partly due to VE bins needing tweeking in the range of the map where highway cruise would happen. This would be with higher KPA numbers than country road cruise.

BTW the previous tank showed 22 MPG and that was with a few power blasts, and alot of time spent idling in the garage as I worked out the start up mixtures, and the warm up curve. That number was the best to date, and seemed good to me, but I kind of assumed that perhaps I did not get the tank filled all the way. If that had been the case, this latest tank full would have showed less efficiency. But it did not, it showed better. EFI is finally beginning to seem like it was worth while.

Now, here is the really big question,: if I can get a brick of a car like this to yield 24.5 MPG only partly tuned, with old technology, why in the world are many new cars still sturggling to produce these numbers with all their modern aerodynamic styling, and millions of dollars of R&D? What's wrong with this picture?

Sam
Author:  DusterIdiot [ Sun Jul 20, 2008 7:46 am ]
Post subject:  Emissions...
Quote:
Now, here is the really big question,: if I can get a brick of a car like this to yield 24.5 MPG only partly tuned, with old technology, why in the world are many new cars still struggling to produce these numbers with all their modern aerodynamic styling, and millions of dollars of R&D? What's wrong with this picture?
You have to remember if you're going to bring your Dart into the 21st century with the new models... you will have to reinstate the EGR to pass the current strangled laws, as well as being able to pass a full sniffer test...
so in other words, tune the car up, turn all the accessories on and see if you can dial it in again with your engine strangled to death with the EGR charge and at the same time making sure the exhaust Gas analyzer shows very minimal CO levels at all driving levels.

One strategy to combat some of these things automakers use is to retard the cam (a heck of a lot). I had a buddy with a chevy 305 that could wring out some nice power and get in the mid-upper 20's in mileage with it... the cam was stock... he found that while degreeing the cam the factory retarded the cam 11 degrees to combat NOx, after getting it truly centerlined and settinging it up for 4 degrees advance, it suddenly 'woke up'... but he'd never be able to smog it in the portland area to get his tags renewed, so he had to register the car in an exempt town at a buddy's house...

-D.Idiot
Author:  SlantSixDan [ Sun Jul 20, 2008 7:55 am ]
Post subject: 
Hold on, Rob, you're talking in 1970s-80s terms, not 21st-century ones. The Chev 305 is a fading nightmare, and EGR is no longer the strangulation device it was in the '70s and '80s; now it's used in small amounts to permit aggressive spark advance and high compression, thus increasing net performance and fuel economy — when it's even used at all. Virtually every car had EGR from '73 to '90, but it's no longer universal. And retarded camshafts? Not in this century; that kind of slapdash (cheap) strategy for reducing emissions worked when nobody cared about gas mileage, but not any more.

That said, you do have a good point: Sam's Dart doesn't have to pass any Federal emission certification tests, and probably doesn't even have to pass any state emission inspection for registration. That removes a significant constraint on engine configuration and tuning.
Author:  Sam Powell [ Sun Jul 20, 2008 7:59 am ]
Post subject: 
Oh That! I guess that 'splains it. :wink: I wonder how dirty the exhaust is on this car. You cannot smell it after it warms up. Not like the old carburetor. And with the new gas tank, I have not smelled raw gas. I could always smell gas before. What do you think of the notion that 13.5 might produce better economy than 14.8?

Edit: Dan's post showed up after I read DI's and before I entered mine. In other words, I didn;t see his post until after I entered mine.

Dan, nice to see your post. I thought maybe you were out of town.

Sam
Author:  SlantSixDan [ Sun Jul 20, 2008 8:02 am ]
Post subject:  Re: Gas Mileage and current tuning strategy
Quote:
The first tank of normal driving, with no power runs or long idling for tuning produced 24.5 MPG. I was quite pleased
I would be, too!
Quote:
The warm up coefficient curve was tuned to raise the AF ratio a little as the ECT temp went above 200.
When you say "raise" the AF, do you mean you added more air, or added more fuel?
Quote:
This was a reaction to having the engine stumble and run rough after it sat for ten minutes (a trip to the store) and went into heat soak conditions.
What are we including in the term "heat soak conditions"? Are you just referring to the physical (fuel got hot under the hood), or is there a heat-soak protocol in your ECM?
Quote:
It was cruising on the highway at between 13.5 and 14.1.
Just offhand, this seems too rich to me. It's close to the optimal power ratio of ~13:1 which is desireable under hard acceleration, but not helpful at cruise (not much power needed to keep the car rollin' down the highway), and leaning it out to 14.7 or higher would save you fuel. The question is how far you can take this before encountering ping or driveability problems.
Quote:
Now, here is the interesting thing. I have always assumed that up to the point of running badly, lean was more efficient.
There are a few exceptions and complications, but that is close enough to reality to be a sound assumption.
Quote:
Is there a possibility that an AF ratio of 13.5 on the highway is the most efficient mixture for highway cruise?
No, I don't think so; you're going to be throwing a bunch of unburned fuel straight out the tailpipe at that ratio.
Quote:
EFI is finally beginning to seem like it was worth while.
Hoorah!
Author:  SlantSixDan [ Sun Jul 20, 2008 8:04 am ]
Post subject: 
Quote:
Dan, nice to see your post. I thought maybe you were out of town.
I leave for India tomorrow afternoon, and don't get there until Tuesday night. :-( :roll:
Author:  Sam Powell [ Sun Jul 20, 2008 8:16 am ]
Post subject:  Re: Gas Mileage and current tuning strategy
Quote:
Quote:
The warm up coefficient curve was tuned to raise the AF ratio a little as the ECT temp went above 200.
When you say "raise" the AF, do you mean you added more air, or added more fuel?
Quote:
This was a reaction to having the engine stumble and run rough after it sat for ten minutes (a trip to the store) and went into heat soak conditions.
What are we including in the term "heat soak conditions"? Are you just referring to the physical (fuel got hot under the hood), or is there a heat-soak protocol in your ECM?


There are a few exceptions and complications, but that is close enough to reality to be a sound assumption.
Quote:
Is there a possibility that an AF ratio of 13.5 on the highway is the most efficient mixture for highway cruise?
No, I don't think so; you're going to be throwing a bunch of unburned fuel straight out the tailpipe at that ratio.
Quote:
EFI is finally beginning to seem like it was worth while.
Hoorah!

"Heat soak" the way I am using it is to describe the situation where the coolant stops flowing and the hottest part of the engine, the head, procedes to get hotter, and the rest of the engine either cools down, or stays the same. It seems as if the heat becomes condensed in the head. The ECT at the head will read 195 when I cut it off, and 210 when I restart it. And the "fix" was to increase the fuel by raising the warm up coefficient in that 205 range. This was before the EVans coolant.

One benefit that the Evans brings to the table is that warm up seems to go faster. We will see how it behaves in cooler weather, but since it does not draw as much heat out of the engine, more of it stays in the engine during warm up, thus reducing the warm up time. I think this is why I got decent mileage in my short trips to work.

Your comments about leaner being more efficient are encouraging. It seems as if I can do better with more tuning. I will continue to lean it out.

Sam
Author:  Dart270 [ Sun Jul 20, 2008 12:49 pm ]
Post subject: 
Nice work, Sam. Sounds like you are getting there.

Knowing how you drive (Mr. Low RPM), I could imagine that 14:1 AF might be good for cruising around at 1200-1800 RPM and may actually give you best mileage. Just a thought. The problem with running too lean can be that you try to compensate for lack of power going up an incline by putting more foot into it and/or lugging the engine. If it is under load and high AF, I have found mileage to be a little worse. I think you can run leaner at higher RPM (higher vacuum) and get good mileage.

I just got back from Wilkesboro race and did about 18 MPG if you include 30 1/8th mile passes (also at Radford, VA track Fri night), a bunch of idling, lost of WOT tuning on the hwy and street, and 380 mi of mostly hwy 70-75 MPH. Just the highway cruise part was 24-25 MPG. Almost got the car into the 10s in the 1/8th - 11.06 @ 63 MPH. Getting fun to drive again.

Dan, India? I gotta hear about this...

Lou
Author:  SlantSixDan [ Sun Jul 20, 2008 1:52 pm ]
Post subject: 
Quote:
Dan, India? I gotta hear about this...
Well, start here. Product development nightmare...big boss specified 3rd-world manufacture for a new lamp, because everyone knows that's how you save money. Except we are now 9 months behind, we don't have lamps to send to our customers, and we've wasted enormous amounts of time and money on pathetic samples from India. The trip idea (not mine) is that I'll wave some kind of a magic wand I don't actually have, and *presto*, the Indians who for most of a year have been lying and sending us garbage that doesn't even come a little bit close to meeting our specs, will suddenly become capable of first-world quality. It's completely freakin' idiotic. We could have had super premium, top-flight, military-spec, USA and/or Canadian manufacture for less than we've wasted on this fiasco with Indians who very obviously have no capability or intent to do what they claimed they could. This is what happens when we disregard the difference between price (the number the Indians put on the quote) and cost (the pile of money we've wasted chasing that "price").

22 hour plane flight there...two days there...22 hour plane flight back. I said I'd bring back a souvenir. I hope it's not dysentery. :roll:
Author:  Sam Powell [ Sun Jul 20, 2008 3:05 pm ]
Post subject: 
Maybe the higher cost of travel will bring some jobs back home. Just be sure to leave the by-product of dysentery there in India. :wink: I hope you have an Uncle Dan story to write up for us.

Lou, I have given your ideas on RPM lots of thought. I certainly no longer intend to lug the engine in the idle territory. I got into the habit of that with the 2 bbl carb. It would idle along in OD at 1200 RPM at 40 MPH and pull incredible MPG numbers. Sometimes as high as 28-29. These numbers held up as speed increased until it got over 60MPH, whereby the power valve apparently started to open, and MPG would go down. If I could keep the vacuum above 10 inches she was very, very economical.

Now with the EFI if it gets close to the idle cells in the VE table, then the AF ratio goes rich for sure, and any benfit from lower RPM's goes away. However, it will happily cruise at 1800 RPM at 60 MPH on the highway, and seems to yield good economy this way. Now tht I have leaned it out a bit, I will check the highway mileage again, and see if it gets better or worse. It is really hard to run good scientific experiments with this stuff since the conditions are never the same twice in a row. It is fun to try though.

Sam
Author:  Wizard [ Sun Jul 20, 2008 3:43 pm ]
Post subject: 
True. This looks like a bell curve where you get good MPG vs amount of mixture. Too lean, lousy mpg, too rich again lousy. :D

I got same. I just touched the mixture screw around 1% richer from lean and engine responded big time with power yet MPG stays GOOD. :D

Cheers, Wizard
Author:  Dart270 [ Sun Jul 20, 2008 5:30 pm ]
Post subject: 
Interesting on the 2bbl result. Too bad you probably don't know the AF it was running then, or the exact timing curve...

I guess I'm a higher RPM biased kinda guy, but it has worked pretty well so far. Course my record for mileage is 26 not 29...

I'd like to try some aero stuff sometime.

Lou
Author:  DusterIdiot [ Sun Jul 20, 2008 6:36 pm ]
Post subject:  Yep...
Quote:
Hold on, Rob, you're talking in 1970s-80s terms, not 21st-century ones.

Well most people don't want to chime in about dialing in a spark knock sensor, or rigging up a megasquirt/XFi combo that at certain instances turn off the injectors and drop the spark from certain cylinders for better emissions, or better mileage at cruise...

I just wanted to 'start' in an 'era' that most of the board members understand better/ have had 'hands on'... most people dont' go poking around trying to figure out why their 2003 Ford F250 gets better mileage on Premium than Regular unleaded.....(knock sensor/timing map)...


To add into the equation also, we are dealing with fuels that only have so much 'energy' or heat, and are 'watered down' by a product that has much less energy/heat potential... so the mileage will continue to decline a bit as they reformulate things.


-D.Idiot
Author:  SlantSixDan [ Sun Jul 20, 2008 6:45 pm ]
Post subject: 
Good points...and yeah, sometimes the math gets a little "creative" when we're assured by our politician "friends" that concerns over reduced fuel mileage with ethanol are baseless (no, they're based in, um, the laws of thermodynamics...)

What I haven't really got a very good explanation for is why my truck ('89 D100 318/TBI) runs noticeably better on regular than on high-test.
Author:  Sam Powell [ Sun Jul 20, 2008 7:46 pm ]
Post subject: 
Dan, isn;t there actually more energy available in regular? Doesn;t it burn faster than high test?

This ECU does have a knock sensor circuit, and the engine has a GM knock sensor installed and working a gauge. It seems to work correctly. That is, it does not seem to show knock when it is not there. If I could figure out how to interface the Accel ECU with my knock sensor I would do it. The thing is, as I have said many times, Accel's tech support is miserable, and the knock sensor kit they sell has no real wiring diagrams. Only a harness with no circuit diagrams supplied. It is essentially another black box in their instructions. So, I don;t know how the knock sensor is supposed to be wired in with the ECU, especially if there is a gauge. I might be able to research this on a Buick GRand National site, as the knock gauge kit came from a company that specializes in Grand National parts and support. I think I am just a few wire connections away from having automatic knock induced timing retard.

Sam
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