Gas mileage discussion + thread collection

[helowrench]

Dawie, regarding cis. I am definitely a big fan of the system for street use. Tunable like a carb, and rock steady reliable.
CIS is tunable to achieve good mileage in all regimes, with the exception of idle.
Due to its nature, idle is inefficient, but with that being said, idle is inherently 0mpg
Unfortunately, from my experience, parts are becoming harder to source.
I would love to drop it on my bug, but I do not believe that space will allow it.

[madmike]

Back a few yrs ago when I bought the first Laser 917 #25 with old Bias tires, 1500 single port with merged header I got a whopping 62.5 MPG at 55mph,Very boring no topend to speak of and handled like crap,Now have #34 917 and wide Radials 295,50's 1641cc ,40 idf's ,010 dizzy, 1 3/8 merged w/stinger,gets 50mpg @55-60mph but I get 40ish mpg with a heavy'er right foot

[dawie]

What are your experiences regarding running a lean mixture and what was your CHT on type 1 and 4 engines? Assuming spark advance compensated to optimum for this condition.

At what percentage of engine power can a VW aircooled engine operate at around 17:1 afr before enrichment to say 13:1 would be required to keep cht under control. How lean would it have to be to operate at full throttle without overheating, and roughly at which afr ratio would that be? Obviously different engines would behave somewhat differently, and efficiency/power would diminish.

Think aviation people run rich of peak at full load an lean of peak below around 70% load, (depending on engine type).

Was thinking of avoiding the hot area by setting to run either rich or lean but never inbetween. A gap in the power curve would then result, and the driver would have to be aware and compensate for this by changing gears or his speed. One could even switch 2 cylinders to lean and the other 2 to rich while the engine has to operate at a load halfway between. Obviously this would not be possible using carbs.

[Piledriver]

I have overcooling issues at 19-22:1 range and great fuel mileage.
I maintain 19:1 currently to 83 KPA, >2600 RPM.
(decent squish and good ignition help, what your motor will tolerate may differ, or not)
Just have to run sufficient timing, that lean requires significantly more timing.

Max temps are going to be around stoich, and or running retarded of optimal.

[dawie]

Thanks for your informative comment. I always enjoy reading your posts.

[oprn]

I am hoping this thread is not too dead to be revived for more discussion.

I am on the quest for better fuel economy. The background is a glass Buggy with a 1911cc type 4 web cam 86, 40mm Webers, crank trigger ignition with a light cruse of 41* BTDC and 15.5 to 16 AFR. This results in a best to date mileage of 29.9 mpg on 87 octane and Imperial gallons. My goal is 35 mpg, some claim to have achieved that with a glass Buggy but it might be all B.S. too. My bone stock '71 SB did get 34 mpg back before the 10% ethanol days.

The latest attempt to increase my mileage is to switch out the '67 swing axle and 26" rubber for a late Beetle IRS with a 3.87 final drive and 28" tall rubber. The jury is out yet until the weather warms enough for an extended drive.

[Ol'fogasaurus]

Interesting question!

When you got the 35 MPG what did you have for an engine?

Changing over to the IRS rear trans and larger tires is going to take some work mainly adding the pivots (at the trans arms) for the trailing arms; I don't remember if the spring plates are different or not.

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Stock IRS pivots. The aftermarket ones mount differently but in roughly the same place as I remember correctly.

The taller tires also are probably going to take more engine load than the smaller tires would take at lower speeds but then the engine rotation/load is going to be less at higher speeds. Kind of a "catch 22' isn't it.

(Just - incase you are not familiar with the term. https://www.bing.com/search?q=catch+22& ... fb&pc=LCTS

There is one person who posts here that does take is buggy on summer vacations around the US. I know he has gone to electronic ignition and other components and does have a good time doing it. I don't remember seeing him post here for a while.

My buggies are more for the sand but might have some info there that could help.

Lee

[oprn]

The engine I got 34 mpg with was as stated a bone stock '71 1600 DP.

Yes it is going to be a trade off between engine load and engine RPM. Also fan speed comes into it too. The fan must turn fast enough to keep up with the waste heat produced.

The IRS conversion is finished, that issue is behind me now. I took it for a drive yesterday and the engine is turning 2900 RPM at 60 mph. I am running the stock type 4 Bus cooling system so we will see when summer comes if cooling is compromised at that RPM.

With the rapidly increasing price of gasoline these days I would think there would be a lot of interest in this subject. I get that very few people take their Buggies/VWs out on the highway anymore but we do some serious road trips in ours. My main concern here is fuel tank capacity. Presently we are limited to 3.5 hours on a tank and often where we drive that makes for range anxiety and we carry a couple of jerry cans.

[Ol'fogasaurus]

The IRS conversion is finished, that issue is behind me now. I took it for a drive yesterday and the engine is turning 2900 RPM at 60 mph. I am running the stock type 4 Bus cooling system so we will see when summer comes if cooling is compromised at that RPM.

I quick guess is that with the tall tires the engine is working hard ("grunting") at that speed. Also, the gearing in the trans could be off, or the engine build or carbs are off, again, my guess is probably the fuel system then the gearing/tire dia..

Lee