6.5 City/7.5 Hwy. MPG. ?

[Jeff Frigo]

I've been keeping a log recently. 427 w/428 crank Holley 950cfm HP., 585 hp. @ 6,200 rpm., 3.73 gear, 26.5" Goodyear Billboards, top loader, spedo. is right on the money, runs great plugs are perfect. Is this possible?

[FWB]

Originally Posted by Jeff Frigo

I've been keeping a log recently. 427 w/428 crank Holley 950cfm HP., 585 hp. @ 6,200 rpm., 3.73 gear, 26.5" Goodyear Billboards, top loader, spedo. is right on the money, runs great plugs are perfect. Is this possible?

yes......might squeek 10 out of it with smaller carb and vac secondaries

[Tom Wells]

Interesting...

I have a 557 with likely similar horsepower and a Holley 950 DP in a Zephyr station wagon. On a weekend where I run mostly highway miles, say up to 1,000 miles in three or four days, I get 12-13mpg.

Have you run it while checking with an 02 sensor/AF meter? Sounds as if it might be sucking some unnecessary dead dinosaurs.

It's possible you could do better, especially on the highway.

Tom

[lovehamr]

Trans? If you're running a top loader then yes. To do better you'd probably need an OD trans, steeper gears or both. 3.73s are pretty stiff for a car that light with an engine that big.

[Rick Parker]

Engine is spinning pretty good for a Big Block (unnecessary) try dropping to 3.54/3.50/3.31.

[DanEC]

I'm not surprised if you let the car warm up a little in the driveway, back it out of the garage to wash and then back in again, spend some time tuning it in the driveway, run around town on short drives, etc. None of my 427 Corvette, tuned Lightning truck or 67 440 GTX can beat 8 or 9 mpg for all of the above reasons. 7.5 mpg on the highway is a little steep - my Vette with 4.11 gears can probably beat that very slightly on 55 mph highways.

[philminotti]

Vacuum advance on the timing will definitely help if you're not already running it. That's why it was invented.

[jhv48]

What rpm's are you turning at 65 mph?

[scootter]

My 514 does much better. I've got over 15mpg on the freeway. 600Hp with a 850 Demon. My new for Ford Superduty with the 6.2 gets about 13.5 to 14 mpg highway.
Scott

[Turbonut48]

My Daytona , with 418 EFI 5 speed, 3.50 gear gets about 13-14.
Its still breaking in, and I hope it goes up 1 or 2 mpg.

The Nut

[JBCOBRA]

I realized a 3-4 mpg improvement when I finally figured out what Tier 1 gasolines are.
Look up the stations in your area. I tried Turkey Hill gas for the first time a couple weeks ago and got 3 mpg more.
I was surprised Sunoco was not on the list. Next tank I put Sunoco back in. MPG went back down. Ran that out and put the turkey Hill back in. Car even runs better on Tier 1. Learn something new every day

TOP TIER Gasoline Retailers:

QuikTrip
Chevron
Texaco
MFA Oil Co.
Conoco
Phillips 66
76
Entec Stations
Shell
The Somerset Refinery, Inc.
Kwik Trip / Kwik Star
Aloha Petroleum
Tri-Par Oil Co.
Turkey Hill Minit Markets
Mileage Stations
Chevron Canada
Shell Canada
Petro-Canada
Sunoco Canada

[marcocsx3121]

You may be pleased to learn that your crappy mileage only adds to the authenticity of the car. CSX3121 running a .030 over 427 with an 850 Holley and 3.77 gears only managed a hair over 10 mpg on the highway and 7-8 in town.

[DAVID GAGNARD]

Originally Posted by lovehamr

Trans? If you're running a top loader then yes. To do better you'd probably need an OD trans, steeper gears or both. 3.73s are pretty stiff for a car that light with an engine that big.

[QUOTEEngine is spinning pretty good for a Big Block (unnecessary) try dropping to 3.54/3.50/3.31.
][/quote]

According to any one of the many gear/speed calculators, you should be turning about 2850 rpms in 4th gear @ 60 mph........big cubes,big carb,a lot of rpms, yes that fuel mileage is accurate..........75 mph would put you in the 3550 rpm range on the highway!!!!!!!
By switching to a 5 speed overdrive trans,your rpm drop from 4th to 5th gear will be about 700 to 900 rpms depending on the trans. gearing in 5th gear.......

As stated, the 3.73 rear gear is too much for your set-up, you'd be better off with something in the 3.25 range......
I run a 3.70 rear gear with a toploader in my road race car!!!!!!!

Years and years ago, I helped a buddy drop in a 428 with a toploader and 3.73 gears in his Superformance, I tried to talk him into a 5 speed Tremec,he wouldn't listen,within 3 months he told me he had wished he had taken my advice, he said he couldn't stand to drive it on the hgihway for more than 20 to 30 minutes at a time..........

David

[mdross1]

With the 3.73 gear and toploader sounds right.Our 460 with 1000cfm dbl pmp 3.73 and Tremec does much better,especially out on the highway at 80mph.