#41  
Old 10-09-2019, 06:31 PM
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Quote:
Originally Posted by moontower69 View Post
TRUTH = only marginal gains. Def not a 20+ MPG highway cruiser. At the end of the day, you're gonna improve mileage from a stock 7-10 city and 12-14 highway about 15-20% max.
FWIW - My 1964 GTO convertible, with 3.08 gears, 27" tires and the original Muncie M20 - gets 17 MPG on the highway and I don't live in "flat" country.
  #42  
Old 10-09-2019, 06:52 PM
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Originally Posted by moontower69 View Post
NOTHING is gonna give you a 20 MPG set up. I've tried the 2.56 rear end and had the 700R4 with the lockup and the Q Jet "tuned" for high gas mileage, etc.
Disagree, pure highway cruising we got just over 20 MPG.
80 Firebird with two men. 455 engine - 310 CFM heads, hyd roller, 2004R with PTC 3200 stall - locked up. 56 Miles/ 10.2 Liters of gas consumed. RPM was right about 1700 RPM for the drive. Owner spent many hours tweaking the fuel and timing curves. Autometer speedo was calibrated less than 1% error.
  #43  
Old 10-09-2019, 07:32 PM
gr8 goat gr8 goat is offline
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I have a Lonnie Diers Extreme Automatics 2004r stage 2 hooked to my 800 cfm quad rebuilt by Cliff Ruggles. All I can say is he is the best for a spot on rebuilt carb. I am currently running an SD Performance stump puller cam, cnc'd 320 cfm round port edelbrock heads and a 455 stroker set up from Len Williams. The mileage is very good but due to the right foot it still likes to hear the tires chirp when downshifting from drive to second and then hear that torque chirp the tires in drive once more. The transmission is hooked to a Bowties Overdrive cable and throttle kit set-up so don't be afraid to call them and tell them exactly what you want to do and they are more than capable to get you on track. The quad has not acted up at all in well over nine years now. You can call me if you need more info on the carb or set-up.
  #44  
Old 10-10-2019, 09:44 AM
goatman1970 goatman1970 is offline
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Quote:
Originally Posted by footjoy View Post


Here is my carb I don’t know anything about it. It came on an engine I bought. Would like to get it built for my 400


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Don Johnston of DCI Motorsports in Akron, OH is a carb expert (especially Q-Jets, and he rebuilds Pontiac motors as well), he rebuilt this exact same carb for the 400 be built for me, and the carb runs awesome, if it's anything other than a stock motor you will want the carb tweaked, it will need the idle air passage drilled out among other things. I would swear by anything Don does, give him a call!
https://www.dcimotorsports.com/
  #45  
Old 10-11-2019, 04:20 PM
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Originally Posted by pastry_chef View Post
Disagree, pure highway cruising we got just over 20 MPG.
80 Firebird with two men. 455 engine - 310 CFM heads, hyd roller, 2004R with PTC 3200 stall - locked up. 56 Miles/ 10.2 Liters of gas consumed. RPM was right about 1700 RPM for the drive. Owner spent many hours tweaking the fuel and timing curves. Autometer speedo was calibrated less than 1% error.
My experience as well. '67 GTO convertible, TH400, 2.56 rear gear, stock Q-jet, stock distributor, original 400 engine with small valve #15 heads for 9.3CR. Average for the past 8 years or so for highway drives is 20-21 MPG at sustained 75-80 mph, and best was 23 mpg on a 140 mile run at a steady 65 mph. My '65 GTO with a 4 speed and a 3.36 rear gear with tripower gets 15 mpg highway at sustained 70 mph. If you're not blipping the throttle all over the place and are steady and smooth, not an issue. Around town, not so much.
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  #46  
Old Yesterday, 12:39 AM
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I really enjoy these wild mileage claims. Here are the 1971 Pontiac GTO Convertible 400-4 V8 4-speed (man. 4) specs in stock form:


•Pontiac GTO Convertible 400-4 V8 4-speed (man. 4) , model year 1971, version for North America (up to September)
•manufactured by Pontiac in USA
•2-door convertible body type
•RWD (rear- wheel drive), manual 4-speed gearbox
•gasoline (petrol) engine with displacement: 6558 cm3 / 400.2 cui, advertised power: 190 223.7 kW / 255 300 hp / 258 304 PS ( SAE net SAE gross ), torque: 461 542 Nm / 340 400 lb-ft, more data: 1971 Pontiac GTO Convertible 400-4 V8 4-speed (man. 4) Horsepower/Torque Curve
•characteristic dimensions: outside length: 5164 mm / 203.3 in, width: 1948 mm / 76.7 in, wheelbase: 2845 mm / 112 in
•reference weights: shipping weight 1651 kg / 3640 lbs base curb weight: 1723 kg / 3798 lbs
•how fast is this car ? top speed: 188 km/h (117 mph) (©theoretical);
•accelerations: 0- 60 mph 6.6© s; 0- 100 km/h 7.2© s (simulation ©automobile-catalog.com); 1/4 mile drag time (402 m) 15.2© s (simulation ©automobile-catalog.com) 1971 Pontiac GTO Convertible 400-4 V8 4-speed (man. 4) Detailed Performance Review
•fuel consumption and mileage: average estimated by a-c©: 22 l/100km / 12.8 mpg (imp.) / 10.7 mpg (U.S.) / 4.6 km/l, more data: 1971 Pontiac GTO Convertible 400-4 V8 4-speed (man. 4) Specifications Review
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Triple Black 1971 GTO. 455 + .040", Block zero decked and align honed. SD Forged rods, forged SpeedPro pistons, crankshaft oil holes chamfered, polished and balanced. 6x-8 heads with 1.77" exhaust valves, bowls blended, port matched and smoothed. Crane 284281 (234/242 @ .050 duration w. .488/.505 lift), Crane 99838 Springs & retainers. ProComp RPM clone w. 770 Holley Street Avenger, FlowTech headers, TH400 w. Hughes GM25 convertor, 3.55 BOP 10 bolt.
  #47  
Old Yesterday, 01:00 AM
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Quote:
Originally Posted by NeighborsComplaint View Post
I really enjoy these wild mileage claims. Here are the 1971 Pontiac GTO Convertible 400-4 V8 4-speed (man. 4) specs in stock form:

•fuel consumption and mileage: average estimated by a-c©: 22 l/100km / 12.8 mpg (imp.) / 10.7 mpg (U.S.) / 4.6 km/l, more data: 1971 Pontiac GTO Convertible 400-4 V8 4-speed (man. 4) Specifications Review
Estimated doesn't mean real world.

Another key specification not listed is the rear gear ratio.

The devil is in the details.

Real world, actually measured fuel mileage (duplicated multiple times) with a 462 c.i., Quadrajet, 4spd Muncie M20, 27" tall tires and 3.08 gears driven on rolling terrain in MN and WI is 17+ MPG.

I'm sure someone with 2.56 gears or an OD transmission can easily brake 20 MPG.
  #48  
Old Yesterday, 08:38 AM
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I probably wouldn't have started this thread except, I have owned two Pontiacs.

1. 1964 GTO 389 bored ,060 tri power other than the bore everything else was stock. 4 speed and 3:23 rear end. At 65 mph it got 18-19 mpg.SOLD

2. Currently 1965 tempest conv. 400 bored .040 crower 60240 cam #15 heads(small valve)
performer intake 735 cfm Quick fuel. Overdrive with 3:73 gears final 4th gear
2.55. at 65 mph 12 mpg.

Thursday I am taking it a shop and they are going to run it on there dyno and check AFR all the way through the gears.

I'm thinking put a tri power on it maybe lightning will strike twice. lol

Thanks

Last edited by footjoy; Yesterday at 09:18 AM.
  #49  
Old Yesterday, 10:56 AM
Formulajones Formulajones is offline
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Fuel mileage is something I've always paid attention to since we drive our classics daily. They have to be at least somewhat respectable on mileage or they'd drive me into the poor house.

These classics can be pretty darn good on mileage, and you don't necessarily need an overdrive to do it. As long as the engine is built to run efficiently, tuned properly and the rest of the cars details are looked at.

My 70 RA Formula, with a 400 RAIII, 400 turbo and 3.31 gears will consistently get 17 mpg highway cruising at 70 mph and 2800 rpm. Gets right between 13-14 around town driving. About as good as any new SUV with it's fancy 6 speed overdrive and fuel injection, cylinder deactivation etc...
I'm pretty happy with it. A simple overdrive would easily put that car at 20 mpg or better.

Our 69 Z/28 with a 302 running a fat 780 holley, M-20 and 3.55's out back gets 14 mpg around town and a solid 17 on the highway cruising at 65 mph which is 2900 rpm. I just recently installed a TKO600 in this one. 70 mph cruising is now 2100 rpm but have not checked the mileage on the highway yet. I fully expect this one to top 20. Around town it's already improved to 15.5 mpg.

The 79 1 ton pickup with a 454 and 3.73's gears out back runs a 400 turbo. This thing weighs 5300 lbs. and is shaped like a brick. 65 mph cruising is 2800 rpm and it gets a solid 14 mpg.

We have a ton of examples here, they are all pretty respectable on mileage.
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