Fuel Mileage Fix

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Nov 23, 2021 | 04:29 PM

66v8baby

Thread Starter

Fleet Mechanic

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From: Southern Maryland

Fuel Mileage Fix

I found the cause of my terrible fuel mileage: The primary jets were 67s! A stock '66 4 BBL 352 as found on a Galaxy used 54s. So that's what I swapped out to today. I wish I had done that before my cross country trip, but I guess I'll just have to do it again next spring. This carburetor was previously set up for use on a 351W with aluminum heads, a roller cam, and a single plane intake. I'm sure I have way more signal on my 352 with a dual plane. It may be a while before I can get a nice long highway drive, but I should notice an improvement immediately just driving around town. With a leaner mix I should also have more part throttle power.

Nov 23, 2021 | 06:31 PM

66F250_4x4

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Joined: Dec 2019

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From: Orange County

Good luck. Watch out for pinging when you get into the throttle - could back off the timing a bit if that occurs.

Nov 24, 2021 | 08:46 AM

hiball3985

Logistics Pro

Joined: Mar 2005

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From: tujunga, calif

I've found running Ethanol type fuels required just a little richer jetting, slight cruising stumble, and I had to go up a litle in jet size, maybe 56s would work if you find a problem with the 54s.. I did it to all of my three engines but they have Holleys..

Nov 25, 2021 | 11:38 AM

Greaser007

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Joined: May 2021

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From: Anderson, California

Quote:

Originally Posted by 66F250_4x4

Good luck. Watch out for pinging when you get into the throttle - could back off the timing a bit if that occurs.

I run conservative timing on my 385 series 429 engine with a 4160 Holley dual feed.
Actually because of pinging issues I am also only running mechanical advance and No Vacuum advance.

Nov 29, 2021 | 08:27 AM

66v8baby

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Fleet Mechanic

Joined: Sep 2016

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From: Southern Maryland

I can't really discern an improvement in city driving mileage so far, but the power band has moved down by 200 rpm and no sign of pinging or detonation using 89 octane 10% ethanol pump gas. Before, 1500 rpm was the ragged edge of where I could cruise in 5th gear, now that has dropped down to 1300, so that was an unexpected benefit.

Dec 30, 2021 | 09:01 AM

66v8baby

Thread Starter

Fleet Mechanic

Joined: Sep 2016

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From: Southern Maryland

After returning from a trip to Charlotte, NC, I got a best of 15.1 mpg. That's almost a 50% improvement in mileage with the smaller jets. I think the quality of gas makes a difference. My best mileage was the first leg where I made it almost to the NC state line before stopping for gas and lunch and could have easily made it across the state line. I was able to get good quality gas from a local Sunoco station that has a lot of traffic.

I'm still driving on what is certainly the worst tank of gas. It would barely idle, and the engine started bucking like there was either water or debris clogging the filter and it was hard to start after it died while stuck in traffic on I-95 (a crash had traffic at a standstill). It eventually cleared up which leads me to believe it was probably water. I filled up that tank at Jenkin's mini mart, a tiny Exxon station off I-85 in southern Virginia that probably rarely sells anything but the lowest grade gas.

I'm absolutely delighted with the improvement! The extended range means I will almost always need to make a pit stop to either eat or for a potty break by the time I need gas.

Last edited by 66v8baby; Dec 30, 2021 at 09:09 AM. Reason: spelling

Dec 30, 2021 | 09:39 AM

ibuzzard

See A Man About A Horse

Joined: Apr 2003

Posts: 4,917

Likes: 667

From: Mariposa, Ca.

That’s great. I was informed, by an FTE member I believe it was, about using only Top Tier gasolines, which have higher levels of additives in them. I always look for that logo on pumps, and have had no problems in the ensuing years. They cost a bit more, are easily worth it.

https://www.toptiergas.com/

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Dec 30, 2021 | 11:16 AM

66v8baby

Thread Starter

Fleet Mechanic

Joined: Sep 2016

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From: Southern Maryland

Quote:

Originally Posted by ibuzzard

When I'm driving cross country I sometimes have to take what I can get to avoid running out completely. I try to find large stations with lots of traffic as they seem to have less problems with condensation or trash in their tanks, but that's good info.

Dec 30, 2021 | 12:29 PM

#10

66F250_4x4

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Joined: Dec 2019

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From: Orange County

15.1 is pretty good, and a huge difference with one change - good catch.
FYI, I measured 9.85 mpg HWY in my 5180lb 460 powered truck w/ a pretty good tuned Carter AFB, 70 MPH at 3100 RPM. Shell 89 octane. (This was a 40 mile test to determine if electric fan might be a good idea) I plan to switch to EFI soon, and will report on any mileage change.

Dec 30, 2021 | 02:43 PM

#11

ChaoticMN

Cross-Country

Joined: Jan 2020

Posts: 59

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From: Minnesota

66V8baby, I'm curious what O/D gear ratio you have in that Tremec 5 speed? I plan on ordering one today for my 66 with 3.5 rear end and 28" tires behind a fresh 428CJ. It looks like I'm at about the same gear ratio as yours with 3.7 gears and 31.5" tires.

I was thinking of using the TKO close with 2.87 first gear and the 0.68 O/D. I hope to use O/D while cruising back road 55 MPH at 1500 - 1600 rpm.

Dec 30, 2021 | 04:53 PM

#12

Becky_is_a_66

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Joined: Sep 2012

Posts: 860

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From: Asheville, NC

Quote:

Originally Posted by ChaoticMN

I have that same TKO ratio setup behind a warmed up 390 with 3.25 trutrac differential. I really like the OD ratio, but with my rear ratio the 2.87 is a little weak. No problem cruising at 55 mph in OD unless you get to about 5% grade uphill - at that point probably better for the engine to use 4th.

Dec 30, 2021 | 07:13 PM

#13

ChaoticMN

Cross-Country

Joined: Jan 2020

Posts: 59

Likes: 3

From: Minnesota

Thanks for the info Gavin. I actually meant I'm going with the TKX 5 speed which is the current one to order. Hmm more to think about. It will be interesting to see what Dirty Harry's opinion is. I asked more on this topic in another thread as I don't mean to hijack this one.
Here's the other thread for anyone interested.
https://www.ford-trucks.com/forums/1...ive-is-in.html

Dec 31, 2021 | 10:15 AM

#14

66v8baby

Thread Starter

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From: Southern Maryland

Quote:

Originally Posted by ChaoticMN

IIRC it's .64. I'm cruising at 2000 rpm at 70 mph. I tried passing a car going uphill at a fairly steep incline in 5th and I had to fall back in behind as the cars behind me were coming up fast. I should have just shifted down, but didn't want to take a chance getting stuck blocking traffic. Cruising back roads at 1500 rpm shouldn't be a problem. My tires are only 27 3/4" tall but with your slightly lower .68 5th gear, it should be very close to the same final drive.