Gas mileage discussion + thread collection

Fuel Supply & Ignition Systems

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helowrench
Posts: 1923
Joined: Wed Aug 11, 2004 8:20 am
Location: East of Dallas TX

Re: Gas mileage discussion + thread collection

Post by helowrench » Sat Aug 10, 2013 11:51 am

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
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Location: Atlanta,Michigan

Re: Gas mileage discussion + thread collection

Post by madmike » Mon Aug 12, 2013 7:39 am

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 8) 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 :lol: :lol: :lol:

dawie
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Location: Cape Town, South Africa

Re: Gas mileage discussion + thread collection

Post by dawie » Wed Apr 30, 2014 6:20 am

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.

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Piledriver
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Re: Gas mileage discussion + thread collection

Post by Piledriver » Thu May 01, 2014 1:42 am

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.
I, for one, regularly embrace our new robot overlords, as I am the guy fixing the robots...

dawie
Posts: 123
Joined: Sun Jan 20, 2008 4:56 pm
Location: Cape Town, South Africa

Re: Gas mileage discussion + thread collection

Post by dawie » Thu May 01, 2014 8:08 am

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

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