Very ON-TOPIC, Let's talk fuel milage

joe- i think we talked about this before... your best gas mileage will be obtained running at the engine's point of highest efficiency- YES timing can help, a little lean setting can help, and possibly the spread-bore carb, but all that aside, if you're running a vac-sec carb, the engine will take what it needs, ie a 600cfm or an 850 will meter only what the engine needs to obtain a desired rpm..... that said- the highest point of efficiency it your point of peak torque, in your case the fact rated torque on that 383 is at a claimed 2400 rpm... early- match the rear gears such that you run at 2400 when you're cruising at your most common speed.... so if you;re taching 3k at 60 with 3.50 gears.... want to step to a cool 3.00 gear and you'll be set... stop over and borrow a 9" 3.00 center section and see... but you'll still only see a hi-teen at best... my 59 tops at 18mpg, 3800lbs, 3.23.... christine however in town gets about 9..... but on the highway at peak torque [4300 that is] it gets an amazing 15mpg... and anyone who drove to CT that year knows i never stopped for gas to back that one up!

 

Interesting point about the engine being most efficient at peak torque...but I bet you'll get better mileage by running at a lower rpm than peak torque! (assuming constant speed operation)

Peak torque is measured at full throttle. We don't worry about mileage at full throttle, we worry about mileage at part throttle.

 

My daily is a 63 Impala wagon, bone stock original 283, 2bbl., glide, 3.50 rear. One of the slowest things on the road, mileage was 15 mpg ish when I bought it 2 years ago. I've since tuned it, used one of those cheap, ebay 60,000 volt HEI distributors, switched to synthetic fluids, and keep my tires at 35 lbs. I take it on lots of long trips, so when I'm measuring mileage, I'm LOADED to the roof, often pulling a trailer, and rarely do less than 10 over the posted limit. But, now it gets 20-23 mpg on trips, fully loaded. Low 20's isn't setting the world on fire, but for a huge wagon, I'll take it. (Always looking to trade it for a Mercury wagon, though). My 57 Ford Ranch wagon has a 302, 500 cfm 4 bbl., AOD and 3.25 gears. I haven't calculated it yet, but it seems to get even better mileage than the Chevy. Once I put a hitch on it, I'll use the Ford. Either way, the peace of mind in knowing I'm in a tank, surrounded by little cars with "crumple zones" is worth a few mpg.

 

i recently swapped my 194 / PG (which got a best of 13 mpg ALL highway) for a bone stock 305/200 in my 64 nova wagon . it has dual exhaust and i added a edelbrock 500 . i've been mesing around with carbs , went to a 600 eddy and my mileage dropped pretty good by about 4mpg. i have a quadra-jet waiting in the wings and have yet to try it out.
the 305 is way more stout than the 194 (duh) and i average (town and highway) just at 20 mpg. the wagon is mainly a "drive it when i wanna" car but will be making long trips from time to time so i've been trying to find the best balance between fun and mpg.

 

Intersting about the nova getting that bad of mileage with the 194, maybe the engine was TOO small! My kid's 70 camaro with the stock 250/pg/2.73 rear gets 19 most of the time.

 

If you're a leadfoot like me, the fastest route to economy is a 2bbl carburetor, plain and simple.

Mechanical condition is the next biggest killer, old V8s can be solidly over 20mpg at 50K miles, but pulling 15ish at 200K miles. Even little ones.

 

I have made a few observations of my own.
- My late model (a '73 Eldo Convertible) gets the same fuel mileage in town as my friends brand new Navigator (13-14 MPG). This is a 5000+ Lb rolling living room with 500 CID.
- The EPA released their anual report at the end of 2006 on national average fuel economy. The 'cars and light trucks' number was WORSE than the 1976 number. The cars only number was better by less than 1%.
- Religeous maintenance (as opposed to whot most people do) is worth more fuel mileage than anything else.
- Benefits of Synthetic oil in a normal street engine is dubious at best. Synthetic trans fluid, diff oil, wheel bearing grease, etc improved mileage in every case we've tested. Byproduct of going faster, don'tcha just love it.
- Carb size: max efficiency requires the RIGHT sized carb. Too small, and you are in the secondaries too much. Too big and the throttle response goes to heck, as does the feul consumption during throttle position changes. The beauty of a spread bore is more carb for WOT and smaller, more efficient primaries during conservative driving. You can run a bigger spread bore than square bore without it being 'too big' for mileage purposes. 'Too small' however, is amplified. I would bet on a progessive 3-deuce setup over a square bore carb any day, but nothing beats the mighty Q.
- A given rate of acceleration in a given vehicle requires a given amount of power at the wheels. Optimizing fuel economy on the dyno means regulating the load to simulate normal road conditions, then tuning for maximum engine efficiency at normal constant road speeds. Optimising carb size and tuning, ignition curve, cam timing, etc to get max efficiency out of the engine at a given speed can improve mileage noiticeably. Engines are usually most efficient when right on the verge of detonation (or even a little past it, but I don't recommend that as general practice). Max power and max economy (and lowest emmisions) are all usually very similar tune ups, because max efficiency gets you very close the the best of each of the 3 factors all at once. Caddies are efficicent by design, even when properly modified for increased performance, so we have it easy.
Note: I care about fuel economy to the extent that I want the best fuel mileage I can get without sacrificing performance or style. Cad Company is not in the fuel economy business - no one who really cares would call us, anyway (who says 'fuel economy' and then thinks '500 CID!!!'?). I'm just sharing observations from emperical testing, because I can.

- Putting a Pinto engine in your street rod worked in the 70's - that's almost traditional now, right?
- You can flame me for that last bit, even though you know I was joking. I deserve it. </SARCASM>