Optimum cruise speed/fuel efficiency

[Qikbbstang]

I was looking at some boating forums on how to obtain optimum fuel efficiency and there was a universal "put the throttle right on the edge of, but don't open the secondaries".  Granted boats are "stuck" with one gear and they must shove through water rather then air as does a car but there must be similar characteristics.
   Marine engines get fairly hefty cams: the Ford Ind Marine 460s got the same cam from hyd-Boss 429s, the 351 Lightning motor uses an off the shelf marine shortblock.   Both a short and longblock 351/460s were sold in the Ford Racing Cat.  Obviously the stouter the cam the more rpm it needs to get happy.  Sure as speed/throttle increases the greater the drag on the vehicle but of course the motor runs less time because it gets there faster. 

   I believe the blind eye toward optimum speed/mpg must consider the fact that marine motors and your typical modified FE get hefty cams and the stouter the cam the more throttle/rpm the motor cam needs to get happy.  So how do you figure "optimum" cruise?
   Also I get the feeling using these modern 5 & 6 speeds that can drop revs to 1500rpm at 75 mph behind a carb'd/cam'd FE must yank down the motor to the point all scavenging and power curve goes out the window. 
Here's from a boat guy that must run an F1 motor LOL:

Re: "I'll go out on a limb.. But I would imagine any RPM range, cruising, that keeps the secondary's on the carbs out of the equation is a good start. I would think that a 20K-22K cruise around or just under 3000 RPM would give you the best economy"..

[cammerfe]

Hey Quik---

As you have set the question, the answer may just be as you've concluded. My own experience, at least in so far as the FE is concerned, is as follows:

When my new '64 Custom 427 was only a couple of months old, I went from here in Metro Detroit to Sebring for the 12 Hour Race. In prep, I traded my 4.11 for a 3.50 and installed a pair of 8.20-15s on the back of the car. I disconnected the speedo so I wouldn't run out the entire warantee---only 3000 miles---and decided to run with the tach readings. A little practice helped me discover that with an educated foot, I could get 3K on the tach in 4th and still be in only the primaries on the primary carburetor.

The tire/gear combination resulted in the 3K being about 70 MPH. But being young and hot-blooded, we decided to run at over 100 MPH as much as we could. US 75 was not yet complete and the remaining two-lane stretches made for a deal of frustration as we went along. I achieved 16 MPG for one particular tank of gas, but the trip average was 11.7.

The real answer is to get rid of the carbs and go to EFI! Then you needn't worry about primaries and secondaries and the effects of accel pumps!

KS

[Qikbbstang]

Speed Trap Towns in those days were definitely there. Never forget my first time seeing a Mopar Cop Car in McRae Ga that had the real-deal forward facing Mopar Super Stock hood scoop on it w/ air filters and carbs on display. Those good ol boys would a had a real time chasing that Ford with Yankee license plates down I-75.  They had a bunch of towns where the jail/police station/fire station/city hall was all in one. 

     Buddy of mine had both Fl & Ga Hwy Patrol chasing his ass in of all things a Bandit Edition T/A. He likely would have made it IF the dirt road he chose to get lost on for a few hours had not been the Dep Sheriffs driveway....D'oh!

[Heo]

the previous owner of my Galaxie put in a 2.82 gearing
and with 28 in high rear tires it consumes more fuel
at 55 mph(about 1700 rpm) th at 80 mph
Then on the other hand not much that was right
in that Engine combination
Not exactly related but my wifes car lower it self about
1 inch at 120 kmh and you se the fuel consumption go
down from just abow 1 liter/10 kilometers to Just under
on the fuelconsumtion meter. About half of the Galaxies
consumption. About same wheight more hp but fuelinjected
and a lot better streamlining i Think

[My427stang]

Certainly not scientific, but my original 427 build for my car was .040 over center oiler, Isky EE-390 (250@.050, 108 LSA on 105) 1000 Holley, Portosonic, Hookers, iron heads and a close ratio 4 speed

With a 3.70 gear and 28 inch tall tires, from Las Vegas, NV to Bishop, CA ,  540 miles round trip, cruising speed limit or higher on the way up and hauling ass on the way back, I got 14.1 MPG

With a 3.00 gear, same setup completely, Las Vegas, to Anaheim, CA, also 540 miles round trip, cruising speed limit or higher, but not horsing around, I got 13.0 MPG

Now the roads were way different, the first run went up and down a bunch of good hills and much less traffic, but there certainly is a sweet spot. 

Funny though, now that I have EFI, more cubes, a much better setup I'd expect on the highway....I have no place to go  

From Omaha NE to ?  everywhere I think of tends to have a potential for hail or some other ugly weather....go figure

[cjshaker]

To me, it's a little simpler. Best engine efficiency occurs at just above the cams bottom torque curve. That's where you're producing the best torque at the lowest rpm. If you're not in the cams torque curve, then the engine is not being efficient. The rest depends on tire size, gear ratio, coefficient of drag and all the other variables. Especially the carb tuning. If the engine is only on primaries at the bottom of the torque curve, it's going to be most efficient. If it's into the primaries even a little, it's gonna be a guzzler.

So if you can gear/tire/tune for your average desired speed at the lowest part of the torque curve, you're going to achieve your best efficiency.....whether it's 6mpg or 26mpg.

This is all based on highly scientific guessing 

[RJP]

Certainly not scientific, but my original 427 build for my car was .040 over center oiler, Isky EE-390 (250@.050, 108 LSA on 105) 1000 Holley, Portosonic, Hookers, iron heads and a close ratio 4 speed

With a 3.70 gear and 28 inch tall tires, from Las Vegas, NV to Bishop, CA ,  540 miles round trip, cruising speed limit or higher on the way up and hauling ass on the way back, I got 14.1 MPG

With a 3.00 gear, same setup completely, Las Vegas, to Anaheim, CA, also 540 miles round trip, cruising speed limit or higher, but not horsing around, I got 13.0 MPG

Now the roads were way different, the first run went up and down a bunch of good hills and much less traffic, but there certainly is a sweet spot. 

Funny though, now that I have EFI, more cubes, a much better setup I'd expect on the highway....I have no place to go  

From Omaha NE to ?  everywhere I think of tends to have a potential for hail or some other ugly weather....go figure

Thats why you and Michelle need to come back to the west coast...Oh, yeah....Bishop is coming up.

[plovett]

I also think this is one area EFI has a clear advantage over carbs.  That is low rpm/max mpg fuel metering.   Getting there with a carb takes a really good tuner and the "right" carb for the job.  Can it be done?  Maybe, but not by me. 

JMO,

paulie