TheSamba.com :: View topic

Mon Sep 26, 2022 10:20 am

I would really like to get timing and tuning detail from yours to compare to mine. You must be doing something different. I see 3.88 final drive and 9.3/1 CR, is that enough to get another 5 mpg?

Mon Sep 26, 2022 8:41 pm

32* total advance on a Pertronix billet distributor. Jetting was set with a wide band sensor. Heads have a modern heart shaped chamber and I run tight decks in all my engines.

Tue Sep 27, 2022 6:41 am

Any vacuum advance? What is your AFR at cruise?

Tue Sep 27, 2022 8:26 pm

Mechanical advance only. 13ish :1 cruising.

Wed Sep 28, 2022 3:50 am

Has to be gearing then, I'm at 41* and 15.5 to 16/1 AFR at cruise.

Wed Sep 28, 2022 8:14 am

Here are current entries in the mileage log for my somewhat aerodynamic kitcar with 1600dp, twin 32mm carbs, and 009 distributor:

MPG figures are indicated miles per US gallon. The very most recent fill-up entry is almost all highway miles; to and from a car show that got cancell'd, but still had some VW people which made the trip worthwhile. On the way there, I tried to get an estimate of how far off my odometer's indicated miles are from what interstate mile markers show. Unfortunately, I-95 has lotsa curves; never got even one straight mile! Best I could do was average a few 4 or 5 mile segments. So I can't be real certain about correction data accuracy, but my odometer came out 10.2% high with current tires, which have been on since last fill-up of 2021 (an even larger correction is needed for MPGs before that, due to worn-out tread). Applying this correction factor to the latest entry, for example:

35.3 / 1.102 = 32.0 actual MPG

BTW the complete top and plexiglass side windows were on for ~40 miles of the trip there and again on the way back, both times due to rain. All the rest was with driver's side T-top and both side windows removed, stash'd. On longer highway trips, I like having the shotgun side window up. Just that 1 side helps alot on my buggy because it not only reduces turbulent airflow; it also helps direct air into my cooling air inlet scoop, ram charging air into the duct which feeds directly to fan shroud inlet. This may reduce engine load caused by the fan, further helping MPGs. And it probably helps to have windshield laid back more than 45° from vertical.

I used to get better MPGs, back when gas was leaded and my buggy's engine was 1600sp with a 28 PICT-1 and JC Whitney mechanical advance only. Once got over 50 actual MPG on a mostly downhill run at night with top and windows up coming out of the Smokey Mountains. Here are a couple typical pages from my log for 1987 and an additional page from 1990. All the following MPG figures are already corrected from odometer indicated to actual by 8% to 12%.

Although mileage was better back then, I never really liked the way it ran. I'm not heavy footed, only wanna keep up with traffic, and can do that better with current setup while getting just mediocre MPGs.

Wed Sep 28, 2022 8:43 am

Now there is some religious data keeping! Thanks for that! So - that once again blows the theory that dual carbs get better mileage than single carb engines.

I would love to try ethanol free fuel for a run and see what the difference is. Not available here in 87 octane which is what my CR is suited best for. I could try a higher octane fuel with the hopes that it doesn't contain ethanol (no guarantees on that though) and I suspect that being a slower burning fuel it would not show any increase without changing my CR to suit it. In fact I would expect the mileage to be lower with the higher octane.

Wed Sep 28, 2022 12:41 pm

Gearing isn't all of it. Like I said b4, not only are you pushing a big flat vertical windshield thru the air, you are also pulling it. My seats put people 4" off the floor, not up in the wind as most buggies do. The floor us flat and nothing gangs below it, suspension parts have been changes and things are a lot more tucked in. Every little bit helps.

A tight deck and more efficient chamber design help a lot. My rotating mass is relatively heavy, c/w crank, h-beams, stock flywheel, but things like springs, pistons, pushrods, rockers, are as light as they can be. Since it's a toy I also run tolerances a little different than most would.

Wed Sep 28, 2022 5:34 pm

Mine has pretty much the same body and seating as yours. Maybe you have side pods?

Wed Sep 28, 2022 7:57 pm

oprn wrote: Mine has pretty much the same body and seating as yours. Maybe you have side pods?

No, no sidepods, just all the litthe things i told you. If you want to see a big improvement.........Get rid of your windshield.

How can you run tgat lean and not burn pistons and heads? 14:1 is stoichiometric. I've only seen 16:1 once and it ended like this.

Wed Sep 28, 2022 8:23 pm

So you don't run a windshield then? That is how you get 35 mpg?

Yes stoichiometric is in the 14.3 to 14.5 range. That is the hottest mixture possible. You never ever want to run in that range AT FULL THROTTLE! Above that range AND below that range the engine runs cooler. I run 12.9 to 13.4 at full throttle throughout the RPM range. At light throttle cruise I jetted for the mid 15s to low 16s. Some guys shoot for 16 to 17/1. It runs cool there but you need more advance because a mixture that lean burns slow.

I believe you will find most all modern cars with FI run in that range at cruise too.

My engine has been running this way for 3 summers now. I don't do short trips, minimum is 1 hour, lots of 4, 6, and 10 hour trips on this engine at that AFR range so yes it works. Back when I first got this engine running, it ran in the 12.5 to 13/1 range at cruise. It got 18 to 22 mpg and you could actually smell the raw gas in the exhaust when following it on the highway!

Wed Sep 28, 2022 8:38 pm

slalombuggy wrote: oprn wrote: Mine has pretty much the same body and seating as yours. Maybe you have side pods?

No, no sidepods, just all the litthe things i told you. If you want to see a big improvement.........Get rid of your windshield.

How can you run tgat lean and not burn pistons and heads? 14:1 is stoichiometric. I've only seen 16:1 once and it ended like this.

ooh, streamlined exhaust system. :shock:

Sat Oct 01, 2022 4:25 am

That piston had more than just a lean mixture, my guess is it went lean under full throttle, full boost and maybe some nitrous too!

Sun Oct 02, 2022 10:49 am

oprn wrote: That piston had more than just a lean mixture, my guess is it went lean under full throttle, full boost and maybe some nitrous too!

Nope, it was at break in, in a sand rail. The guy couldn't shut it off and ran the buggy around his yard till the carb ran out of fuel. No nitrous, no boost, no full throttle

Sun Oct 02, 2022 12:44 pm

Luftwagen 2180 wrote: I realize that this is an old post, but I found out something that surprised me. My wife and I just got back from doing Route 66 from Wilmington IL to Flagstaff AZ. I've had the Buggy for 51 years now and had never been on that long of a trip with it. Almost all of the trip was dry and VERY HOT! Most of the driving west was full of stops along the way. I had the roof on for shade but the windows out for the air flow. When we stopped at my sisters in Phoenix for a week visit I figured out our gas mileage. The wife's Gremlin was getting about 18 MPG, which was kind of expected, but the Buggy was only about 22 MPG. It's a 2180 with a Holley progressive on it with a stock cam. I'm running a 68 transaxle with 255/70/15 rear tires. I was hoping for better. We rarely went over 63 MPH.

However on the way home heading east it was cool the one morning so I had the windows in for awhile. It didn't take too long to get too warm, so I removed just the drivers window. Good airflow for staying cool and much less wind noise then both windows open. Total fill ups on the way home was 14. I was keeping track of the mileage and noticed that the mileage jumped to 30MPG whenever I had at least 1 window in. I was hoping to have the back window removable before the trip but that didn't work out. I was surprised with the difference the roof without the windows makes.

I had one of those Circus tent tops on my buggy back in the 1970s. With the side curtains out the top acted like a parachute. If i ever figured mileage i don't recall what it was. Engine was a 1679 with Holley Bugspray and a cam about equal to an Engle 110.

Mike T

Sun Oct 02, 2022 3:27 pm

My street /strip Dunebuggy I get 20 MPG combined city/highway driving. 2007cc (approx. 120 HP) 044 heads, W-120 cam, Bosch 034 SVDA, dual 44 IDF's with 34mm venturies. Bugpack 1 5/8" header with Hide-Away exhaust 8.6 CR and run 89 mid-grade gas. I run 4.12 R&P with 3.78/2.06/1.48/1.04 gears. I have 2 sets of rear wheels. 26" for the track & 29" radials for the street. I usually drive 65-68 MPH on the highway. Buggy weights 1350 Lbs. without driver. I jetted it for drag racing at 12.7 AFR at WOT. I shortened the windshield 2 1/2" from original height.

Sun Oct 02, 2022 5:59 pm

I never realized how much of a 'Wind Drag' tub buggy's were ,until I picked up mine with Fresh Paint ,strapped it on the bed of my lil Ford range (4 banger), went to jump back on the e-way I-75 north,wth?? , Ranger wouldn't pull 5th gear :lol: