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.

002.jpg

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

[Bruce.m]

I’d guess an open top buggy if fairly “draggy” aero. No smooth roof etc.

Only suggestion I can add is measure the manifold vacuum & aim to maximise it at cruise / light throttle. However your advance & AFR already pushes efficiency

[oprn]

Yes the wind resistance is against me. I am also thinking the 96mm bore is not in my favor either. I think that effects flame travel. Dual spark plugs would help but that is beyond my budget at the moment. My 944 has a bore of 100mm, weighs double and still gets 35 mpg but the car presents so much cleaner to the wind.

Next time I am out I will rig up to take some vacuum readings. The car cruises pretty effortlessly at that speed, not much peddle. The change in gearing could have effected the cruise vacuum value a few "Hg so I may need to adjust my timing map now.

[Clonebug]

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.

My engine turns slower than yours at 60 and I've never had an overheat problem. I do almost 66 mph at 2900 rpm with a 28 inch tire.
I turn 3100 rpm at 70 mph.
Personally I love this gearing as it allows me to make decent time without feeling like the engine is screaming...I still think it's turning too fast and I usually try to do around 60-65 mph but when traveling long distance you don't get anywhere unless you do 70-80 mph. Once I get used to the engine turning that rpm I can maintain 70 plus mph but the wind noise gets fatiguing in a fairly short time. I only go that fast if I'm by myself as the Wife doesn't appreciate that much wind in her face.

[Ol'fogasaurus]

Dune house diary 081 copy.jpg

Dune house diary 082 (2).jpg

These pix were taken when the cage was built and brought back to me. I would recommend doing the convertable top after the cage is built but... a good cage builder can do the fitment very well.

On my "blue buggy" I had a convertible top built for it. Side windows that are removable and the rear window rolls up. The roll up rear window is a good thing but for higher speeds the side windows (not shown) worked but usually were removed for several reasons.

The big problem was the windshield. There was a track in the frame that a fold in the front of the top was tucked into but in my case one side of the frame's track was a bit wider than the other so the top would slip off the windshield. I have seen snaps used but there can be issues there too.

Dune House trip Aug 2005 026.jpg

Lee

I forgot to mention that my blue buggy was street driven when I bought it and started to play with it both on the street and in the sand. Can a buggy be OK for both sand and street... the answer is yes and no! In WA turning brakes are not legally allowed on a street legal vehicle (with some location exceptions). Part of the reason is the brake assembly's balance of the front and rear brakes combination.

Again, there are other yes and no things in WA and in other states.

If you noticed, the front end are spindle mount rims... no brakes as they can lockup on the sand, dig in and rip the steering wheel out of one's hands (yes, it can and does from personal experiences).

Lee

[Bruce.m]

Saw a YouTube video the other day where the guy modelled the aero of a beach buggy. It was bad .
Adding side screens made a big improvement. Other changes to the front did little to help

[Clonebug]

It makes a big difference in cruise kpa if you draft a vehicle in front of you