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Gas Mileage SU vs Webber

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SilentUnicorn

SilentUnicorn

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In another post the subject has been asked what kind of mileage should we be getting ? An interesting question. This weekend My neighbor and i made the run to Stowe Vt for the Invasion, about 100 miles one way. We ran up and back together and ran milage checks. the results kind surprised me. I was running just over 30mpg, normally during the week on my 10 mile one way to work i average 20 or so. mine is a 1500/webber and his is a 1275/su. now here is what blew my mid, he got almost 45 mpg! Are SU's that much better on gas?
i am not sure what his wife gets during the week, but i will find out.


Before i swapped my rear end out form a 3.7 to a 3.9, i was pulling high 30's on trips like that. i understand that many things can affect your mileage, driving style, state of tune, rear end ratios, gade of fuel, tire inflation and so on. During the week i might tend to be a little heavy footed (Spirited) on my commute, but i have to admit, i am somewhat dissapionted in my mpg's.

i guess i am totally amazed at his mileage and rather envious. So i put it out there, What is your milage and what carb?


mark
 
This is NOT meant as accusatory, so please don't take it as such, but: Weber carb has an accelerator pump, and every time the loud pedal is pushed it delivers... SU's are demand only: no pump to squirt a shot of petrol inna pots. You may be a bit "spirited" in your pedal application without being conscious of the act? Try an "economy run" of a hundred miles or so being oh-so aware of driving techinque. See if that runs up some different numbers.

My single 40 DCOE Weber has delivered 22~25 MPG on 250 mi. trips as long as my boot is testosterone free /ubbthreads/images/graemlins/wink.gif

When the "poison" sets in, that number drops like a rock. Thrutchin' it rewards me with an ugly 16~18 per in the villages. But if I can humble some boy-racer in his nip-sled I consider it a privelege /ubbthreads/images/graemlins/smile.gif
 
I think one of the other factors in the difference in fuel milages you guys had (in addition to what Dr.E pointed out) was the difference in displacement. The smaller bore engine will naturally pull less air and there for fuel in to the pots to burn.

I just re-evaluated my milage with my stock '76 B(Zenith Stromberg) with complete emissions. This past week I pulled off 19MPG'ish (190miles on the trip Odo with 10 gallons used). 90% of the driving was in morning and evening "rush" traffic on surface streets (average speed while moving 45-50). The final 10% was on freeway, or streets with very few stop signs (average speed 60-70). My driving for the duration was not in the best interest of fuel milage. Seems kind of low to me. There are a few things that I need looking into to see if I can bring that up.
 
I got 20+ with my 73 B GT this week. Since this is the first full week of driving it there was a lot of ZOOM ZOOM. I have SUs. Still better than my 3/4 ton 4x4 Chevy.
 
My B with the weber 38/38 / outlaw (heavily modified engine) averaged 28+ on the Boston to Stowe trip to British Invasion this year (230 miles on about 8 gallons). I have not calculated city driving..but a guestimate would be 23 or so mpg.

Paul
 
hmmmm... something tells me there's something amiss under my bonnet...
 
I average around 22 in mixed driving. All my driving is mixed as I live 5 miles from town and drive on 50mph roads mostly. 78B

Guinn
 
This may be apples and orangutans, but in the interest of mileage/displacement/carb(s) it may be germain: the 1750cc T/C Alfa Spider, with dual 40 DCOE Webers I flog as a commuter is thirsty. 18~20 in traffic and a paltry 22~24 with Interstate use. The Elan with the same carbs and a 1600cc, T/C would get 25-ish in town use, with a bewildering 35 on interstates. This is likely due to power-to-weight considerations as well as aerodynamics. The MG with a single 40 DCOE, cammed up, falls somewhere in-between even though one would think it'd return some more impressive numbers on the open highway side. When fitted with a rock stock engine and twin SU's the B would deliver highway figures in the 30~33 range.
 
hmmm... so, what can cause the ZS variations to deliver the poor milage that I'm experiencing?

I rebuilt my charcoal canister yesterday in the hopes of maybe unclogging it. Unfortunately, it didn't seem clogged when i pulled it, but the charcoal within definitely reaked of gas. I assume that this means the charcoal within was near saturation if not already. Whoever rebuilt it last used poly foam at the top and bottom. The stuff was really brittle and stuck to the screens. I unrolled pure cotton cottn balls and wrapped them around the screens.

While I was under the bonnet, I also looked at my carb a bit. I noticed that my choke idle adjustment effects the normal idle adjustment. If the choke idle is set too high I cannot lower my normal idle beyond some RPM. Finally, I think my choke is enriching too much, but there doesn't seem to be anything I can do to change that due to some PO modifications. Starting the car with the choke on is ok, but it won't fast idle for more than 5 to 10 seconds before it settles into the "I'm way to rich" rhythmic idle pattern.
 
20. No matter how I drive the B or where I drive the B. Back roads, around town, interstate. 20. It rather annoys me.

I have the dual SUs I plan on dropping in her this winter (anyone want a nice ZS?) Is that going to make a difference? I hope so!
 
Forgot to say my carb is a Weber DGV and I drive with the top down. If it rains I drive the F150 and get 15. /ubbthreads/images/graemlins/smile.gif

Guinn
 
Jaybird: Assuming no engine mod's the SU's should get you in the "25+ club" with the lower compression engine. Highway with O/D should kick it into the 30+ range for cruzin' speeds.
 
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