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Tuning for economy?
The 4r70w and 3.5 or even 3.7 gears would make a huge difference in driving enjoyment for sure.

73 Grandé H Code. Headman long tube headers, T-5 Transmission, 3.70 Traclok, Lowered 1" all around, Aussie 2v heads w/ 2.19 intake, 1.71 exhaust, screw in studs, full roller cam 608/612 lift 280/281 duration LSA 112, Quick Fuel 750 CFM double pumper, AirGap intake.

- Jason

[Image: 082-hot-rod-power-tour-2017-1970-1970s.jpg]
On your trip your ratio of highway miles to in-town miles will go way up, and I would expect your mileage to go up also.

I agree, with a lower geared rear axle and the overdrive your overall mileage will go up. If the axle and transmission aren't approved by headquarters a higher stall torque converter may help your seat-of-the-pants feel on take off.

You could even go down to the 3.73:1 rear end and have a final ratio of 2.61:1 with a 0.70:1 overdrive.

If you haven't already done so, you can download the spreadsheet here to play around with axle and transmission ratios.

“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
(01-21-2019, 08:41 PM)mbrew2 Wrote:
(01-21-2019, 01:18 PM)Hemikiller Wrote:
(01-21-2019, 11:54 AM)mbrew2 Wrote: The plugs are NGK ur4gp. The mallory does have a vacuum advance, currently connected to ported vacuum on the Summit carb.

Excellent. I'd say verify that it's working by temporarily hooking it to a manifold vacuum source (or a vacuum pump if you have one) while the engine is idling. You should see an immediate increase in rpms. If not, you'll need to troubleshoot that issue.

You probably have a 4756701 Unilite unit. Should be stamped onto the tag on the base casting. Attached a 2005 catalog below for reference.

Yes, thats the one.

Lets see, trying to follow up on all the tuning tips received, and finding nothing out of the ordinary so far: choke works, carb property tuned, plugs OK, engine is tight with no abnormal noises or pings, cranks at first turn of switch hot or cold, holds 75lb oil  pressure cold, 45-65 warmed up depending on rpm, drops to 20-25 at idle hot. Its responsive and appears to generate good power for what it is. Haven't checked timing yet but am 95% sure its OK and well within range.

So, not finding anything terribly wrong, I am led to the conclusion that the mileage issue is MY BIG Right Foot! I am also convinced that the 2.75 gears and FMX contribute to my problem. I have noticed that in everyday stop and go traffic, I have to be on the gas WAAAY more to keep up with the little girl in that Honda in the next lane leaving the red light. Much, much more than I would need to if I were in our Highlander for example. So I'm thinking that with 3.50 gears, It wouldn't take as much throttle to achieve the same speed over the same relatively short distance. But, and there's always a but, I really like the 2.75 gears for highway travel running 75-80 without straining the motor.

If you haven't figured it out yet, I'm lobbying for a new 4r70w and 3.50 gearset that would be more efficient both in-town and on the highway. HA, I can even see telling the wife that it would pay for itself eventually in fuel savings, not to mention not having that blast from the Flowmaster 40s when I'm just trying to keep up with traffic.

Thanks to everyone for the advise/tips. I have learned to love this car and this forum.  

If something jumps up out of the ordinary with the timing, I'll be back for more help.

You should definitely be getting better MPG than that!!   My motor is a 408C Stroker with around 600hp and with my new cam I went from 7 MPG to around 12 MPG. Not that I care about MPG but I did check it this summer. And my trans is an old built C4 and 373 gears. An I tend to destroy the back tires quite often! Haha You may want to go with a little more gear in it, but not too much as to hurt you on the highway. I like my 373's. They are a little steep for long cruises on open highway but GREAT around town. I am running around 2800-3000rpm at 65mph.


1971 Mach 1
408C Stroker
C4 w/3,000 stall
8.8" Rear w/3.73's
Disc brakes all way around.

[Image: 28ivsix.png]

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