Hi there. Being the Ex-Chevy guy that I am, I have never been driving a really big engine on a regular basis. All I´ve got so far were old small blocks in the 283-327 range,so the 425 / 4bbl nailhead in my 65 Rivi is kinda new to me and I´d be glad to hear what normal fuel consumption would be like. First off, it really runs like a dream, it´s .030 over , and all stock other than the overbore.I was on a 400 mile round trip and got around 11.8 mpg cruising around 70-75mph and taking it very easy. My other V8 cars are between 14-20 mpg , depending how fast i go. The plugs are clean as they can be and even the tailpipes are clean on the inside... What do you think, is 11 mpg ok for a big old nailhead? ( Please delete, if that´s just too dumb a question...)
Im not sure but I had a 65 gs with 2 four barrels, and it would launch you in the back seat quick! Didnt care on fuel economy. I ate up little 240z's and other euro sports cars. One car I do miss.....
Yeah , it really hauls ass as is should! I really love that car and will never let it go. I just got to plan how often I can afford to drive it hahahaha... gas was $280 for 400 miles...
Gears, Trans, and tune? Also if it has a switch pitch that's working correctly ? Close to 20 on both a 400 Pontiac and 428 Pontiac. 66 Gs with 401 300st Trans and 2.7x gears got almost 20 also. That's providing I could keep my foot off the floorboards
i'd say you are probably in the ballpark of about right. the one thing that may net you a little better mileage would be to hunt down the elusive 1 year only Q Jet nailhead intake. I daily drove my 64 wildcat 2drtp through the late 90s early 2000s with sever different set ups. it had a pos 750 double pumper on it when i first got it that on a good day got around 8-10mpg. Changed to a factory dual quad and it did around 10 all the time sometimes a little better if i was easy on it which i rarely was. Switched to a Q Jet set up and moved up closer to the mid teens area. i think i did get it to average 16-17 on a trip across nc once going to a goodguys from the eastern side of the state. Gas prices shooting up are what led me to driving it less and less and eventually regretably selling it a few years ago, well that and the 401 was tired and i didn't have the cash to do it up like i wanted. I have access to a 401 or a 425 that i could put in the 62 f100 unibody i'm building but since it's a daily i doubt highly i'll take advantage of either and will probably use either a small block ford or chevy.....ken....
11-12 MPg is probably pretty close to what was or should be expected for a '65 Riv in stock trim. That was pretty common mileage for big cars back then.
I had a '64 years ago. Swapped the AFB for a Quadrajet on an adapter. (As per Jimmie Vaughn.) Drivability and mileage both substantially improved.
Sounds like the part throttle is fat. Try tuning with wide band A/F meter or a dyno with 5 gas analyzer.
Most Buicks were geared for the interstate. I've owned several old Rivieras including a 425 '66, along with other full size Buicks with 455's, and on road trips averaged anywhere from 15 to 18. Though, to be fair these all did have Quadrajets on them.
Thanks for you input. I don´t want to rant about gas guzzling when I floor the pedal, but it would be nice to do a little better while cruising I just calculated reaend gear ratio, which is supposed to be around 3.02 with 27.2 " inch tall tires and a cruising speed of 70mph at 2600rpm. I´ve still got the stock Carter 4bbl, probably an AFB. But I have a few Quadrajets on the shelf I could play with and try. Why are the Q-jets so much better than the AFBs when it comes to fuel mileage?
http://www.automobile-catalog.com/economy/1965/88520/buick_riviera_425_v-8.html Pretty cool site. And your mileage matches their numbers for 70-75 mph.
1406 Edelbrock should be as good as it gets for jetting and needles. Modern distributor with adjustable vacuum advance will improve things.
That helped a lot of guys save gas during the gas crunch of the early 70's. One thing to think about is that when you start with 11 mpg a 1.1 mpg increase is a whole 10% increase in gas mileage so the little things really count. On my 3/4 ton truck with the same gas mileage changing to electronic ignition and a distributor without slop or play got me two mpg if I kept foot out of it. I'd make sure everything was in top shape but only make changes on one thing at a time. Probably starting with the ignition. Even if you keep the points make sure that the distributor is tight so the shaft isn't moving around changing the dwell and the advance systems are working as they should.
I had a GS with the dual quad version and it got absolutely the worst mileage of any factory stock passenger car I've ever had any experience with. About 8 mpg city, 11 hwy. Truly a bad ass and way under-rated factory engine.
Damn, $280.00 for gas?!?! What was the price per gallon, cause using your figures of 400 miles and 11.8 mpg that works out to $8.25 per gallon!
That's what we pay over here... Around 1.65 euros per liter....today was 1.71... A gallon has about 3.8 liters, and a Euro is about $ 1.30.... That's why I'm trying to get the milage down a bit. I have a pertronix Kit and a q- jet I' m going to try. And Ilike the idea with the vacuum gauge. Is there a Special q - jet i want to use , or will anyone be better than the AFB?
Here´s an update I think I should share with you. I was on a 800 mile roundtrip with the Rivi the last couple of days, and I´ve got 16.8 mpg average.I was going between 75 to 80 mph max, with a few sprints mixed in. Buying a new, fuel (and fool) proof gas caps was one of the best improvements I did. Whenever I was flooring the gas pedal, which I actually do from time to time, the fuel in the tank was slushing backwards, washing the rear license plate and bumper from the inside. Second leak was one of the rubber fuel return lines above the rear axle. Always smelled like gas, but it evaporated so quickly I never saw drops on the ground,I just smelled the fuel. The Pertronix kit I installed may have helped aswell, but I just can´t really tell the differance. Maybe idle is a bit smoother. Thanks for your input guys!
PS: I´m still running the AFB Carb, because I haven´t found a Q-Jet intake yet. I´ll probably stay with the AFB, I think 15-17 mpg is just fine for me.
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