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Upgrade Holley 500 2BBL to Small 4BBL incr perf and economy?

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Upgrade Holley 500 2BBL to Small 4BBL incr perf and economy?

Post #1 by 62Ranchero200 » Tue Jan 13, 2015 9:17 am

Greetings Ford Six Fans,

Quick summary: '62 Ranchero, 250 with CI AL head, Clay Smith 274/274/108 cam, DUI, Holley 500 CFM 2-BBL.

Took the Ranchero on it's longest road trip yet, a 150-mile round trip from Houston to Bryan, Texas, this past weekend. The 250 ran perfectly for the entire trip, despite the fact that it never warmed up ... the temperature gauge stayed pegged out at the lower end of the range except for brief stops, when heat soak brought it up to maybe 140 degrees F. It was about 40 degrees F out and the entire trip was on the highway at 60 mph. I doubt I would take it out in much colder weather (there's no heater), but if I did I would block up the front of the radiator with cardboard.

In spite of the smooth operation, the trip highlighted the poor fuel economy of the 250 ... about 10 mpg. Some of this is undoubtedly due to the 3.50 gears (~3,250 rpm @ 60 mph), and also to the engine never reaching normal operating temperature because of the cold weather.

Initially, I didn't want to try to fit a 4-BBL because of fitment issues with the shock tower, but this fuel economy has me wondering ... if I could make a small 4-BBL (maybe a Holley 390 or slightly larger, because I'm more familiar with the Holleys and tuning them) fit, could I see an increase in fuel economy (because the engine would run only on the smaller primaries at cruise) but also in performance (with the secondaries)? Of course, in addition to the fitment and possible throttle cable changes, I'd have to start carb tuning all over again.

One of the reasons I starting thinking along these lines is that I saw low profile float bowls for Holleys online, which could help me clear the shock tower; and also I know that the CI intake can be milled quite a bit if needed to add shock tower clearance.

Bob the Builder
62 Ranchero, 252 cid, 300 rods, RaceTek pstns, ARP mains bolts & studs, balanced & blueprinted, CI AL head, 1.6 adj rckrs, Smith Bros, 274/274/108 cam, CI int, Holley 500, DSII, CI SS hdrs, PowerMaster strtr and 1wire alt, Optima, V8 rad, T-5z, 10" organic clutch, 5 lug 8" w/3.80 Trac Loc, rear drums, front 5 lug discs, Centerlines. Next: ?.

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Re: Upgrade Holley 500 2BBL to Small 4BBL incr perf and econ

Post #2 by ausxb » Wed Jan 14, 2015 2:03 am

Sounds like a plan. Gearing & Temp. probably didn't help economy any but a 4 barrel with small primary's should help.
250 2v XB Falcon.

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Re: Upgrade Holley 500 2BBL to Small 4BBL incr perf and econ

Post #3 by THE FRENCHTOWN FLYER » Thu Jan 15, 2015 1:37 pm

before trying a 4-v I would try a different 2v - like a Rochester 2gc or autolite 2100.

even with a cold engine it should have done better than 10 mpg.

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Re: Upgrade Holley 500 2BBL to Small 4BBL incr perf and econ

Post #4 by pmuller9 » Thu Jan 15, 2015 8:49 pm

You should not be having a problem getting the engine up to temperature in 40 degree weather.
I would say that the thermostat is not working and is stuck open.

What temperature thermostat do you have in the engine?

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