I have a 460 that gets only 6 mpg on the highway. This doesn't sound right to me. It only has 4,000 miles on it. This is a list of what I have into the engine: 9.8 cr, bored 30 over, 750cfm Holley carb, stealth intake, Holley electrical fuel pump set at 14psi, L&L superflow headers, Summit Cam 218,228 duration and .503 of lift, Comp cams roller rockers, flex fan, Accel super coil. I have the timeing set at 4 degrees. I have 35 inch tires with a gear ratio of 3.50. Do I have the carb tuned wrong or is this all I can expect. Thanks for your replys in advance.

Bob
1978 F-150

 

that does seem low my 460 powered 4x4 ran about 10 mile to gallon
with 33s and 4-11 gears my comp was about 9.5-1 and i had a speedpro cam about the same duration and lift as yours also a eldebrock 650
but my timing was set at 10 degrees you say you have a holley carb double pumper or vacum secondarys.at 4000 mile your engine should be broke in engine genearly use more fuel while breaking in.

 

Try adjusting your fuel pump to about 7psi. 14 is too much for a carberator. Timing may be retarded too much as mentioned. Try 10 deg. and see if it helps.

Nathan

 

My truck is EFI, and I get about 10mpg unloaded, city driving, and about 6-7 pulling the boat. Timing is 12 degrees w/SPOUT removed. Mileage sucks, but is still way better than the boat.

My brother "says" he used to get about the same mileage in his stock '85 carb'd version. I drove it for a bit once and think he's waving the BS flag.

Your numbers seem a bit low. I'm wondering if those tall tires and gears require you to put your foot into the throttle farther to get/keep rolling? But then again, healthy engines can have healthy appetites. Do you have a heavy foot while driving?

How do the plugs look? Tail pipes sooty? Have an extra carb lying around? Its worth a try. A 3mpg improvement translates into almost an extra 60 miles before fill-up.

Chris
'88 F350 XLT Lariat CC DRW/7.5l/C6/4.10
'93 Mustang LX 5.0l/T-5/3.55's/Flo's/K&N/Synthetics
Nissan p/u (DC commuter)
Volvo 940

 

yea i agree that's way to much fuel pressure for a carb. motor. i do believe that's what were talking about. shoot i had a stock fuel pump on a built motor that was only putting out 2 p.s.i. and it wasn't hurting performance. and it's running on all 8 cylinders? look at the spark plugs they tell the whole story. CJ. ....

 

oh and you might want to try to advance the timing alittle to see if you can get more performance, but do it in small amounts like about 2 degs. at a time. drive it, and make sure you don't get any spark knock.

 

[font size="1" color="#FF0000"]LAST EDITED ON 28-Sep-01 AT 03:55 AM (EST)[/font][p]I will check the plugs tomorrow. As for timing I will try bumping it up a little. I set it that low because a couple of months ago one of the pistons detonated and didn't want to deal with that again. When that happened I had it set at 12 degrees. The carb has vacume secondaries. I didn't have a heavy foot at the time I checked the mpg, just going up north to my uncles. When I bought thefuel pump I asked a mechanic what he thought the psi should be set at. He said just leave it at what its at, the carb will just take in what it needs until the float bowls are full. I will turn in down to about 4 or 5 psi for now.

Thanks Alot!!!!!!!
Bob

 

Silly question for you Bob, have you corrected the speedo? With those 35's on, if not, then this may be some of the low MPG. Granted, not a whole lot but 10 or 15 percent off/low would help a little. Agree with everyone else here, bump that timing a little, mine is around 10-12 deg. with a slightly quicker curve.

 

[font size="1" color="#FF0000"]LAST EDITED ON 29-Sep-01 AT 01:11 AM (EST)[/font][p]No I did not udjust the speedometer. I know it is slow by 5 mph. How do you do that? I read in a magazine a while back, but I forgot. I think they changed a gear in the transmition or the speedometer cable.

Bob

 

You didn't mention what distributor you're using or total degrees of advance. If it's a vacuum advance, check to be certain that the advance is working properly. To me, it sounds like part of your problem is low static advance and something with the vacuum advance. Your C/R is low enough that you shouldn't be experiencing detonation unless you lug it down in 2nd or drive and then try and accelerate before it can shift down with those big tires.

With your setup, you need more static advance at the flywheel, 8-12 degrees, depending on what the distributor is putting in and when it hits.

34-36 total degrees is the norm, 8-12 static and with your cam the rest should be all in by 2800-3000rpm.

35" tires, 3.50 gears, the duration on your cam and a stock stall converter isn't an ideal combination but you should be getting 8-10mpg on the highway.

 

I agree with the other responses about reducing the fuel pressure as well as bumping timing up to 12 degrees or so. You mentioned you had a Holley carb, does it have vacuum or mechanical (double pumper) secondaries? If it's a vacuum secondary model make sure you have a BLACK spring in where the secondary diaphragm is, any other color will allow secondaries to open sooner and cause depleted fuel milage.

Todd
BB79RANCH

 

Hey Bob, to change the speedo, there is a gear inside the t-case at the end of the cable. If I remember right, it should be color coded. Ford dealer can tell you how many teeth it has and which way you will need to go with the tooth count to get you close. I took mine to the local speedo shop and they hooked me up and even tested to see how close it is (very, with 35's, 60 mph indicated, actual 59.something!).

 

You commented that one of your pistons detonated - make sure to check the distributor springs - I lost 2 motors to the same issue before someone mentioned these 12.00 springs.. Before the new springs (and distributor rebuild) the dyno was showing low HP (220) and the timing was really moving when put under a load, after the springs, well over 300 and no detonating.

 

[font size="1" color="#FF0000"]LAST EDITED ON 11-Oct-01 AT 00:05 AM (EST)[/font][p][font size="1" color="#FF0000"]LAST EDITED ON 11-Oct-01 AT 00:02 AM (EST)[/font]

Ok I changed the timing to 10 degrees and fuel pressure to 5 psi. I checked the spark plugs and they look ok (Grayish brown).
I will check the mpg again in a couple of days. The vacume secondaries on the carb has the silver spring in it so if the mpg don't improve I will change it to the black one. And for the vacume advance it is working properly. I am planing on buying an adjustable vacume advance in a couple weeks for the stock distributor or should I just buy one of those MSD distributors. Any dramatic proformance gains from it??? Also George, what do you mean by static advance at the flywheel? How do you check it? Thanks for your help.

Bob
1978 F-150 4x4

 

Big affirmative on the MSD setup. throttle response and overall smooth power increased dramatically on my last setup. (I have since converted back to Ford's Duraspark Mag-Breakerless, but Still highly recommend MSD setup.)
Im running 14 deg. initial, 36 total, on 87 octane. 8.5:1 comp, over 350 hp, and still damnnd near 20 miles/gallon.. 3.00:1 rearend, 1:1 top gear.. but small tires. Im at 3000 rpm doing 68 miles/hour, and getting gobs and gobs of power and economy. But, I also have a lot of time invested in my engine.

I think you'll notice a difference if you get an MSD setup.. It really helps fuel economy... Other than that, it sounds like you got all the major problems worked out. You should be getting at least 10 mpg when you done.
Best of luck to you!!!


J/.c

1965 Ford Galaxie 500 (okay, so not quite a truck)
ANOTHER 460/C6 @ 365hp/519 lb.ft.
14.36@100.4, 16-18 mpg AHHAAAHAAAHAAA!