Tuning EFI for economy.
 

I have a 69 Dart slant six with electronic EFI which is fully programmable. I can set fuel ratio, timing, and warm up enrichment rate to anything I wish. First goal was drivability, which is now pretty good. I am eager to learn more about tuning tips to improve economy.

The first big, positive change came a month ago. I took a 600 mile round trip with it from the DC area to Blacksburg VA. On the way down the car got 21.5 MPG. I raised the cruise timing from about 40 BTDC to 55. The mileage on the way back was 26.7. I would like to get this car over 30 MPG, and from what I have read here, this should not be impossible.

The car has a Ford Mustang 5 speed which is much more efficient than the old auto.

Any ideas about tweaking the tuning would be appreciated. Maybe a link to another thread would be a good place to start. Thanks in advance.

Sam

Since you have a steel / cast iron rig its best to play with timing when cruising along, sadly you still have aluminum pistons which you could blow holes in though.

You could also setup lean cruise, you would need to determine what gear / RPM you typically cruise at and the coresponding load then create an island where you go in open loop or if you have a wideband end up with a lean burn situation, most engines run fine at 15-16.5:1 so long as you are loaded up between 40-80% (fluffy numbers), too light of a load and it won't fire, too much and you burn holes in pistons.

There are a couple folks on here who made vehicles go lean, higher compression and knock detection are a must when running lean, high percentages of ethanol work well for leaner than normal AFRs

have fun.

Thanks for the reply. The engine is built with Forged pistons and does have a knock sensor that works well.I also have a wide band O2 sensor that feeds both an in-dash gauge and the ECU. I have been cruising at 16.5 with no knock. However the cooler weather has caused some pre-ignition at 3000 RPM under light load right before shifting. I could go a little richer there, or dial the timing back a bit there. The system has a self tune that will change the fuel map to match the AF table, (user set). Others using Megasquit II have experienced lean conditions when it gets cold outside. I think most have simply dialed up the mixture a bit across the board.

Tell me what you mean by "loaded up". What is 40-80%. Percent of what? Thanks. Car cruises at 2000 rrm at 62 MPH. Compression is 8.5:1. It was intended to be turbo charged, but that never quite worked, so I removed it. Now economy is the game.

One of the things I have tried to figure out is if at 40 MPH it is more efficient to cruise in 5th at 1200rpm, which it will do, or in 4th at 1700 rpm. The AF ratio gets leaner in 4th, and the map reading drops. But I have not had the time or commitment to go out and drive 100 miles at 40 in 4th gear and then drive another 100 miles 5th an compare actual mileage. It would be difficult to find a place in the east coast here where one could actually do that. I suppose if I worked the math maybe I could figure it out. The computer does give me milliseconds of injector open time as one of its readouts. But it does not do the match as scan gauge does.

One feature this ECU has is an overrun fuel cutoff. When coasting in high vacuum, it cuts fuel off completely and starts it again when you open the throttle a bit. Until I enabled that feature, the excess fuel would cause a miss that was quite disruptive to the RPM read on the ECU. I was forced to find out about this fine feature and put it to use.

I am one of those guys who uses Evans coolant. It has been in there for 3 years. There are open questions about what temp to run the coolant, and what temp to have the fans turn on. There is one 16" two stage fan, with separate temp controls on the radiator itself, not in the block. I feel certain wit6h the right solid state controller I could get the sending unit in the block to control the fan. I think the ECu can be made to do this but not two stage (I think).

I am very interested right now in figuring out a way to automate a radiator block when cold. Does anybody know of an easy way to do this? Are there products intended for other uses that can be adapted? Are there OEM pieces that can be modified and put to use? I read on another thread that the Chevy Cruze has such a feature. I know the newer Mopar trucks and cars employ this also, but have not looked into it. Maybe there is a thread already working that discusses one. Thanks again for the response. I feel this is going to be a big help in my tuning and tweaking.

Sam

You could create a true DFCO configuration and it might stop the pre-ignition, when you fully lift your foot off the throttle and RPMs are above a threshhold (maybe 1200rpms) just have them completely off, you could then learn to just fully lift your foot before shifting and pre-ignition would be minimized because there would be no fuel.

by loaded up i mean a percentage of max output, lean burn works best with more fuel (and more load and air), lots of turbulence and warm temperatures,
you might consider a warm intake mod and see if it affects knock.

Can't help much on this, generally higher load trumps lean burn but only to a certain rpm which varies from engine to engine.

My guess is the lower rpm wins as the difference between 4th and 5th is too great on a relatively sizable motor.

Shame you have such low compression ratio. I think with 91 Oct gas you could have went higher.
I think you are on the right track with the 16.5:1 air mixture. Have you tried higher to see when you start getting knock? I believe Honda had 22:1 but this was on an engine that was designed around that idea.
Can you have the higher air/fuel mixture only kick in under certain conditions? Cruising only. Turn off when you step on the gas pedal.
Who much control does the Megasquit II give you?

I get it now. You mean to make the ratio richer when the engine is under load. And to answer ron22's question, the Megasquirt is pretty flexible. I can make the ratio richer under the higher load conditions. That is very easy. And yes, I think one key here is to make a warm air pickup that can be engaged during cool weather. The air filter picks up air from out side, in the wheel well. I would have to think about it, but I think I can redesign the pickup so there is a flap inside the box that would switch over to a second pick up tube that routes to inside the header heat shield. There were lots of stock set ups back in the 80's and 90's that did this. I think I would have to cruise a junk yard and see what I could find in the way of temp sensors that control a airflow diverter of some kind. I love going to junk yards.

Ron, You are right about the compression ratio. The low ratio is because it was intended to be turbo charged initially. There is no squish chamber on these old heads. They are an ancient, 1959 design. This makes preignition a challenge. Thinking about it now, one would wonder if it would be possible to fill part of the chamber with weld material to create a squish area. Maybe next time.

This air box came from a late 80's Cadillac. The pick up goes right straight down into the wheel well. The battery is in the trunk.

http://i881.photobucket.com/albums/a...6/CIMG0767.jpg

Sam

I am no expert on Honda and the "lean burn" mode. But I think for best cruise MPG you would want to try something like that.
Under the right conditions you lean out as far as possible (will need testing) if any of the conditions change go back to "normal" mixture ratio. I think you might have to play with mixture and timing here.
Example you step on the Gas to accelerate. The engine load goes up (going up hill). I think you get the idea.
Now how many times can you change the mixture and timing?
Have one for gas pedal to the floor (max power & max load)
Have one for normal acceleration (medium load)
I think you get the idea.
I think you will find 1 AF ratio and 1 Timing is not going to cut it.
That said sounds like you have a lot of fun experimenting ahead of you.

Fueling andtiming are extremely flexible with MEgasquirt. There are 3 primary, basic tables, and many trim tables. The basic ones are a 12x12 AF ratio matrix, a 12x12 fuel amount (called a VE table) and a 16x16 timing table. In each the rpm which is user defined is across the bottom of the table, and the MAP (load) goes up the vertical axis of the table. Every cell can have its own number. This means for every RPM and load you can have a specific timing and fueling amount. The wideband O2 sensor adjusts the fueling within the parameters the user sets to match what is in the AF table. The actual amount of timing or fueling is an interpolation of the number in the cell, and the numbers in cells around it if the RPM or MAP load is on the edge of two cells, or even 4 if it is in a corner.

I can make this engine run any way I want to. I just need to know what to try. I am not an IT person. Getting the soft ware downloaded and talking to the ECU was not easy, as I needed my daughter's help. So discussions of trying to get mileage feedback recorded and readable go over my head. This does not mean I am not interested in doing it some day. I can tune the actual ECU now, which was an accomplishment for a 68 year old man.

Right now the engine idles at 13.5:1 which is a little rich, but this is batch fire, multipoint injection, not sequential. There is fuel behind the valve awaiting its opening, which can get sucked into another cylinder and disrupt the AF ratio for that cylindar. However it runs at speed nicely at 16.5:1 as long as the load is low. It will cruise down a level highway at 45 MPH and 18 inches of vacuum all day. If I ever get the ECU reconfigured to read the pick up wheel and sensor instead of the distributor, I can set it up as sequential. But it runs now, and am not eager to shake things up much at this point.

The trim tables are such things as warm up enrichment, start up enrichment, start up timing, cold timing, etc. etc. There is an idle timing trim table that will bump extra timing into it when you first crack the throttle for drivability.

Thanks in advance for any tuning suggestions you can offer.
Sam

I plan an extended cruise soon with a friend to play with the timing. The strategy, when a dyno is not available, is to advance timing until the detonation gauge begins to light up, and then back off a degree or so. With a dyno you look for max HP, but sadly I do not have one. All the ones around here are not steady state dynos, which is what is required to set timing for cruise. Read above post for description of tuning capabilities of Mega Squirt.

Thanks as always for advice and ideas.

Sam

Good work. Subscribed!

I will begin reading the posts about tuning for economy. I am sure there is much information already written here. Thanks.

Sam

Do you have any logs of the 40 MPH in 4th and also in 5th?

No. I will add this to my to do list. What should I be looking for?

Sam

I was just going to see if you have the P/W logs we could do some efi math and figure out whats more efficient.(4th or 5th gear);)

Thank you. I will be sure to select the pw in the log.

Sam

I'm so jealous of your slant setup, Sam! Its exactly what I'd like to do to my pickup. I even toyed with a light boost setup as well. I've thought about putting MS on both of my old vehicles. As for tuning ideas, you want to run the lowest revs as possible to reduce the friction of the moving parts in the drivetrain until you hit a point where you have to consider if you are getting sufficient oiling of the engine AND the engine is having to require too much throttle (load) to deliver enough horsepower to push the vehicle through the air. If you apply some aeromods to reduce the effort it takes to go through the air at highway speeds you will reduce the load at the rpm cells and lean the air/fuel mix and gain mpg. Some of the old VW gurus were running 16:1 airfuels in their buses in dinky aircooled motor. My old camper got 28mpg, but it was way too lean and I couldn't go very fast without getting the heads too hot. It weighed 4000 pounds and 1600cc engine couldn't push that brick without needing extra fuel to cool the combustion. Your engine has a lot of torque and displacement in comparison. I've heard our slants have peak torque at about 2500rpm, but I know it will require less fuel at lower rpms if you can be sure to keep the load on the engine down enough to get the air/fuel up. What's your final drive ratio(rearend ratio + last gear).

very cool build im doing somthing similar but with carb. vehicle is a 68 rambler american. shooting for the same goal of 30 mpg. im using the same transmission.

Particularly with low CR you may not be knock limited in terms of the best ignition timing. That's something that is very difficult to determine on the road.

As lean as possible doesn't always produce the most efficient operation. Leaner does reduce the pumping loss but too lean and not all the fuel gets burned.

I think it is time to install the EGT gauge. I am told by folks who fly small airplanes that 15 degrees off of max EGT is where best economy lies. Go lean until temp tops out and back off 15 degrees. I have a gauge in a drawer but never installed it.

Sam

I know these engines like a lot of timing which I attribute to needing a lot of timing to allow the mixture time to burn efficiently. I don't know if you can do it with your combustion chamber/pistons or compression ratio, but at some point you can lean it out so far that the flame front doesn't reach the cylinder walls and it will run cooler. I'm seeing more and more pistons that have a raised center bowl to give it squish area around the periphery and give the flame kernal an area to propagate around the plug with a lot higher compression and less timing to burn completely. I can get at about 38 degrees for my beetle normally aspirated at 8-9:1 compression. I understand with the right cam and pistons and up around 13:1 compression they can run cooler and use somewhere around 20-22 degrees of timing to complete the burn. At 9:1 compression I have to back timing way back into the low twenties when I'm using a turbo with the old tech combustion chamber flat top pistons. My heads get warm quickly on boost but they cool quickly off boost too. I don't think I'd want to be running above 1400 F EGT too often unless you have real confidence in your valves and seats. I would even suggest 1200 would be much safer. Slants stock would make the manifolds glow at highway speeds, but I don't know what temp that is maybe 800 fahrenheit?

Wow, Good info. Thanks. You are right about the turbo. I took the turbo off mine for several reasons, but one was that it went into detonation way too easy. I had to back timing off so far that is was hardly a net gain. There are ways to work around this, but I did not wet the engine up properly to begin with.

Sam