Air/Fuel ratio, is there a quick answer? Options

[veekry9]

No quick answers,because it's complicated,many factors.
https://www.google.ca/search?q=fuel+mixture...WMeAvEQ_AUIBigB

A lean cruise condition at low loads is at one end of the spectrum,highly loaded under acceleration is at the fat,rich end.(1910s)
Change the fuel and the chemistry changes with it,as with methanol/water additives.(1930s)
A turbo application at high boost pressure benefits greatly,stalling detonation and piston holing.(1930s)
Those holes can be had by a lean loaded condition with air cooled engines,as some of you here know.
All of this has been sussed out for 80 years,the military aircraft application the primary impetus.(1930s)
A direct injection fitment to the Type 4 hasn't been done yet to date,and would yield great results with a fine 'smart' mapping.(2017)
A constraint that aircooled engines have is the physical heat dissipation capacity,the mass and size of the fins and the amount of air that passes over them.
Adiabatic cooling systems are a proven upgrade and an easy fit,tho only practical for above freezing climates.(1970s)
Changing out the pistons and heads for a high quench design with piston squirters,a leaner mix can be had,and the application of ceramic coatings will shield them from the heat of combustion.(1970s)
Carburetor jetting is best done on a dyno these days,less time consuming than road testing and plug reading,as was done in the past.(1920s)
Double plugging your six or four has some advantage in flame-front size and expansion,so a leaner burn can be had.
Ultimately,the engine's ability to dissipate conducted heat is the limiting factor,so,the simplest course is to cool the engine and intake charge.

[url]https://www.google.ca/search?q=direct+injection+flame+front+simulation&espv=2&biw=1229&bih=598&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjPmJ7T2anSAhWG4IMKHW13AsEQ_AUIBigBue
(IMG:style_emoticons/default/smile.gif) (IMG:style_emoticons/default/happy11.gif)
Great advantage.Be the first.
Be cool.
/

[pete000]

I picked up one of the PLX Blue Tooth AFR systems and it works really well. Display is easy to read although I do wish it had a record feature though. I had a bung welded in my Bursh muffler at the main collector as to read all four cylinders.

Did a small drive today for an hour on some hills here and was getting pretty consistent readings in the 15s cruising fairly flat roads, under WOT saw it dip into the high 14s. Climbing with a fairly heavy pedal it would also dip into the 14s.

Coasting down hill throttle closed it goes to full lean condition as expected.

After following this thread, sounds like I am a tad lean? Should I be in the 13s under WOT and 14s for cruising vs 14s and 15s I am seeing now? I do not have a CHT gauge, so not too sure what the heads temps are.

Might have to crack the lid off the flapper box and ritchen it up a few teeth. I have read a lot of adjusting the Bosh AFR over on the SAMBA.

My car is also a 74 1.8 L-Jet

https://youtu.be/owYGugwTguE

[Mark Henry]

Yes 15:1 cruise is too lean for an aircooled 14:1 would be the max and even then I'd want a good headtemp gauge to be sure they're not getting too hot.

That chart might be OK for a watercooled, but not aircooled. WC big advantage is they can control head temps way better than air cooled.

Aircooled has a much narrower burn AFR range.
This would be my aircooled chart;

About 11:1 is the max for rich burn
WOT power between 11.5 and 13
Max performance WOT 12.3 to 13 maximum
Lean burn no higher than 13.5-13.7, nickies can run 14:1-14.3

The exception to the above is decel, AFR on decell is of no concern, of course it's a high reading, you just took away all the fuel, but no load so it's not producing heat.

You can run richer than 11:1 without really hurting the engine, but your power and tune goes to poop.
Anything over stoich you better have a damn good head temp gauge to monitor your temps, you are getting into dangerous territory.
As you head temps go over 350f you will start to lose power as a heat soak condition starts to set in.
Running 17-18:1 and you will have a hole in a piston PDQ.

Basic rule on heat temp and heat soak is you can go over 350f on a long hill, as long as the temps recover on the downside. Once the temps are not recovering on the downside of the hill you have a heat soak issue. Even a cheap VDO gauge you can easily see this heat soak/no recovery condition.
Head temps consistent 325f is about perfect, 350F is OK, but I don't want to see much more for long periods of time.
On my LN nickies I don't see much over 300F unless I'm really hammering it on a hot day.

[McMark]

I agree with and support everything Mark Henry has been saying. (IMG:style_emoticons/default/wink.gif)

[malcolm2]

My PLX rig showed up Friday. Looking forward to getting it in the car this week. Turns out they sell on Amazon too. $169 was a little better price.

[pete000]

My PLX rig showed up Friday. Looking forward to getting it in the car this week. Turns out they sell on Amazon too. $169 was a little better price.

You got a great price, mine was 180.00 direct from PLX via Ebay...

I have a second AFM flapper box and will be trying it to compare to the rebuilt unit I am currently running. Will start turning the wheel to see if I can get this thing closer to Mark's recommendation numbers..

[timothy_nd28]

Be careful. The air flow meter has a wound up clock spring that will take off on you when you loosen the retaining screw and if you don't keep constant pressure on it. There is a air flow meter bible that you should read and re-read 3-4 times before making any adjustments.

[malcolm2]

Be careful. The air flow meter has a wound up clock spring that will take off on you when you loosen the retaining screw and if you don't keep constant pressure on it. There is a air flow meter bible that you should read and re-read 3-4 times before making any adjustments.

http://www.itinerant-air-cooled.com/viewto...f=50&t=7761

[pete000]

Sounds like these early FI cars are set from the factory lean compared to today's fuel.
I have a couple Flapper boxes to try out to compare. I think that they will require to be turned to ritchen the mixture.

Here is my O2 sensor and PLX installation.

Video on how to richen the AFM.

https://www.youtube.com/watch?v=yQukm7lNux4

[malcolm2]

I do like welding stuff.... but man you can screw things up in a hurry.

Here is the result of my BUNG HOLE (IMG:style_emoticons/default/piratenanner.gif) (IMG:style_emoticons/default/piratenanner.gif) welding.



It took 3 bungs and some patching of the areas I screwed up, but I am not too proud to show the world.

Point of interest here. I did not really screw up on the welding of the bung to the pipe. I saw a YouTuber that installed the plug that is supplied with the bung. He then welded. His thought was to keep spatter off of the inner threads.... makes sense to me.

Well the bung gets hot and ends up galling up the plug so you can't get it out.

I ended up covering the hole with a small bolt dropped in the bung and a large washer.

Repairs are complete, I'll add some Hi Temp paint to hide my grinding work and start working on where the wiring goes this weekend. Good garage day, it is supposed to snow in Nashville. (IMG:style_emoticons/default/WTF.gif)

[Mark Henry]

Was your wire feed sticking?
You likely need a new whip liner, but you could also try to make you whip as straight as possible.

[malcolm2]

Was your wire feed sticking?
You likely need a new whip liner, but you could also try to make you whip as straight as possible.

I had the heat set high (3) to begin with and it ran nicely. But if I did not keep moving consistently... I burned some holes in the thin pipe. Turned down a notch and I got no holes, but did get some spatter and wire sticking on the work piece.

Did not think of keeping the whip straight. I will pay attention to that next time.

[malcolm2]

PLX is now installed. The guage is temp'd in with a shoe box and a clip.

Reading was 13.8 to 14.5 last night. I closed my CO screw one full turn. Cruising and hills reading is now 12.7 to 13.5.
Heading to NC at lunch. 5 hour drive. I will enjoy monitoring it.

[pete000]

I have been playing around a bit with my AFM. I have a couple of them so I figured one would be a good test mule. I read about a mod the VW Bus guys were doing. The later Bosch AFMs had a jumper wire installed to help the conductivity. This is an easy upgrade to do by soldering a jumper wire from the wiper arm to the large connector bar (See blue wire). I also cleaned all the contacts while I had it apart. I did a before and after OHM test and the numbers seemed to smooth out a bit after the mod and tune up. There are You Tube videos on all of this.

Now to try to get some time to get out and test the AFR results. (IMG:style_emoticons/default/driving.gif)

[malcolm2]

My AFM has that jumper. Did not know it was an add on.

5 hours of interstate driving. Several big hills.

Cruising at 3400 between 70 and 80 the a/f guage was between 12.2 and 12.7. CHT went to 375 on the hills but was 325 to 350 the rest of the time.

I'll fill up with gas today. It seemed to get good mileage. I think 25 mpg was the last i remember with the now bent AFM. 320 miles and still above 1/4 tank.

[malcolm2]

5 hours of interstate driving. Several big hills.

Double post

[Porschef]

Hey Clark,

PM sent

Joe

[timothy_nd28]

Sounds like you are around 26 mpg. I think with this system correctly dialed in, you may get closer to 30 mpg. I'm curious what the spark plugs look like after this trip of yours.

[timothy_nd28]

I take back what I said. Maybe you are already getting 30mpg, driving through the Appalachian mountain will skew any MPG readings.

[pete000]

Tested out my AFM mods and seemed to work well. Was a bit lean but a few teeth adjustment on the flapper wheel and I was able to get it to settle around 12.9 - 13.5 cruising and dips to the low 12's under load.

Re adjusted the timing and will try it again tomorrow. So far seems to be much happier.