AFR suggestions for max mpg at cruise

[Steve Arndt]

An easy to implement idea would be to try the 1.9 Vanagon dizzy. It is an SVDA with hall effect pickup and high output inductive coil driver.

[volkaholic1]

OK - here is the plan, step 1, now that I bumped up the advance, run 1/2 tank, see where I am at, I will step up the AFR 0.1 at a time until my cylinder head or oil temp start creeping up.

step 2, I checked and I do still have all the MSD gear that came with the CB set up. I could try it again, using the normal MSD advance springs and stops for more total advance, sounds like if I could get like 34, that would be better. yes? no? maybe?

step 3, lock out the MSD advance that try the CB program again.

The problem with steps 2 & 3 is my fear of getting shocked again. OK - I must be a p*ssy. Is it just the 40K coil? How does that compare to the typical bosche blue coil? or I am doing something wrong? no, I was not standing in a puddle when I was checking my timing. I realize these are high tension wires, but I did not even touch the wires, just got like an 1" away. Is that to be expected? I assume this was related to my electrical interference issues I was having. All parts, wires, coil, etc are brand new. Anything I should double check?

[Steve Arndt]

Research "lean of peak".

[Piledriver]

I recall an ~87 MonteCarlo SS 4.3 that came in one evening running rough...
(HEI ignition with separate coil)

Opening the hood (running) it looked like the whole top of the engine was engulfed in a violent lightening storm.

The coil wire was open... the plastic guts were ~completely gone (I cut it open to see), but it continued to run.

I'd run an HEI ignition in a heartbeat, and the LS2 coils I am running are probably capable of more current output, and close on the voltage.

Your limitation is the little stock distributor cap...

If you got bit by being in proximity on a connected system, you probably had a bad wire.

Put the CB setup back in, and fire it up at night, in the dark you can literally see issues with HV wiring.

It will not kill you, or even really hurt you, but you will learn respect

[Piledriver]

I've been doing a little mental processing on this, and "lean of peak" on aircraft vs. an auto differ somewhat in the details.

The CHT delta is very real and easy to see (and on an ACVW it is worth doing for that alone) but one thing the aircraft guys miss is when they go lean of peak, they SLOW DOWN 10-15 MPH... So a not insignificant % they are saving in fuel is from that--- In fact, that could be the majority %.

Cars... cannot slow down when in cruise and running lean of peak... in the end the same speed/HP requirement
They ideally will be running more throttle position/higher MAP, so most efficiency improvement comes from reduced pumping losses from the (slightly) increased throttle position/MAP at cruise.

I suspect the "trick" is going to be cooled EGR throttling... Something that is becoming common on OEM solutions, even the old TDis have it, but it is not restricted to diesels.
That would allow for significantly reducing pumping losses, as you would be running at WOT, with recycled inert gas (exhaust) diluting the mix.

This would of course require a "richer" mix vs. the AFR gauge in the exhaust, (waves hands frantically) blablabla.
What's the easy way to cool/meter ex gas?
Thoughts?

[volkaholic1]

I guess I really did miss a step, I will call it step 1.5, I could go the SVDA route. At cruise, I am pulling about 14" Hg, would the SVDA dis give me the vac advance I need to better mpg?

[Piledriver]

If you are running a basically stock >very mild cam and ~stock manifold vacuum it will work far better than a 009.
That may sound like damning with faint praise. It is.

It's basically just a primitive analog computer to set some predetermined RPM and load based advance.

You still have a distributor.

[subwoofer]

I've been doing a little mental processing on this, and "lean of peak" on aircraft vs. an auto differ somewhat in the details.

The CHT delta is very real and easy to see (and on an ACVW it is worth doing for that alone) but one thing the aircraft guys miss is when they go lean of peak, they SLOW DOWN 10-15 MPH... So a not insignificant % they are saving in fuel is from that--- In fact, that could be the majority %.

Cars... cannot slow down when in cruise and running lean of peak... in the end the same speed/HP requirement
They ideally will be running more throttle position/higher MAP, so most efficiency improvement comes from reduced pumping losses from the (slightly) increased throttle position/MAP at cruise.

I am no expert at light aircraft operation, but AFAIK constant speed propellers are fairly common. So the RPM stays the same just like when you back off the throttle when you have reached your desired cruising speed on the freeway. Slowing down an aircraft saves fuel in the exact same way it saves fuel in a car - once air resistance becomes significant at 40MPH or so. Doing 60MPH you are probably not producing more than 15 or so HP, way less than the aircraft boys, they reduce power output to 60-70% from WOT.

The BSFC curves are telling the real story. It is fairly flat from 14.7AFR to 16AFR (appr.), but going higher AFR means more safety against detonation. Too high average AFR and you have a cylinder very much down on power, the "lean miss".

It think there are several mechanisms at work here. Less fuel falling out of the mixture in the ring land crevice is one thing, optimum speed of combustion may be another, pumping losses are certainly one

[Steve Arndt]

PLease post your experience wrt to temperatures vs AFR when running lean with extra timing during cruise. I would like to see some data for the difference in temperatures compared to say running mid 13:1 AFRs and just a little extra timing vs full load (like the SVDA which only add 8*).

[Piledriver]

PLease post your experience wrt to temperatures vs AFR when running lean with extra timing during cruise. I would like to see some data for the difference in temperatures compared to say running mid 13:1 AFRs and just a little extra timing vs full load (like the SVDA which only add 8*).

I haven't run <19:1 AFR at cruise for so long I can't say I have any current data, but I have some old VE/ignition maps I could pull in to get a comparison... All I can say is @19:1-22:1 target, I only worry about overcooling if OAT is <70F.
From memory, 50-75F delta vs 13.1:1>14.1:1 (latter is ~stoich w/E10).

Most of my AFR target map is @19:1 as my current WB only reads to 20:1.

My previous WB setup (JAW1.03) had basically zero filtering, and could see a single event misfire, managed to spot a code bug with it, as well as ID some setup issues on my end (LS2 coils dwell/voltage curve was wrong)

The fine point iridium plugs driven by the LS2 coils seem to be able to light it off very reliably, no problems.
Running iridium Pulstars (just to try them)

[luftvagon]

Here is some data I collected, albeit not very accurate due to the location of temperature sensor probe:

http://i.imgur.com/pVmRgRa.png

[luftvagon]

Here is my GM Coolant Temperature Sensor adapter, and it fits in the stock TSII location

[Steve Arndt]

CHT data only please, not warmup (coolant) temperature sensor data. (reason being is those basically flat line once warmed up).

Keep it coming.

[luftvagon]

My CTS sensor goes up to 200F, and my CTS location is right on the head, albeit not under the spark-plug. It still shows the relationship between RPM, AFR and temperature. The scale may be different.

[Steve Arndt]

My CTS sensor goes up to 200F, and my CTS location is right on the head, albeit not under the spark-plug. It still shows the relationship between RPM, AFR and temperature. The scale may be different.

Up to 200F? I'm looking for data concerning the 275F to 400F range as measured at #3 plug. My thermostat flaps don't open until its been at 270F for quite a while.