Tuning EFI for economy.

[Sam Powell]

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

Sam

[pgfpro]

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.

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

[Sam Powell]

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

Sam

[pgfpro]

Originally Posted by Sam Powell

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)

[Sam Powell]

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

Sam

[kafer65]

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).

[slownugly]

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.

[Occasionally6]

Originally Posted by Sam Powell

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

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.

[Sam Powell]

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

[kafer65]

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?