Improve gas mileage on a 427 so ?

[Etype66]

Hello guys
A question that would get me into trouble.
How can we improve the consumption of a 427 so? I already hear some laughing and I expect to have ironic comments but, but ...

In the USA you are very lucky (for now) with the fuel price. In Europe, regarding the price of a single gallon, we pay more than $6.30 per gallon ...
Ok ? You understand now that my question is not that silly?

I have several Cobra 427s in maintenance and my customers often ask me this question and I am sure there are other solutions than "an egg on the accelerator pedal ...."

A smaller carburetor? (even at the expense of some horses)
Any other ideas?

Let me know your expérience
Many thanks
Eric

[MKS427]

Short of tearing it out and using for a coffee table, it's going to use generous amounts of fuel (about 740 cfm air/fuel @ 6000 rpm). The only things that come to mind are a smaller cam and possibly an EFI. The cam will impact power and the EFI benefits depend on how well your carb is working. Running the engine lean is not recommended, so there are limits to what you can actually save.
I'd recommend evaluating initial cost vs long term savings vs fun factor sacrificed vs how much you drive. The price of fuel may be the least bitter pill.
Good luck,
Mark

[joyridin']

Smaller cam, put on EFI, install a 6 speed. Those things will help you get a lot better mileage on the highway. If you do not have aluminum heads, that would also be an option as you can run higher compression on the same octane. That will squeeze a few more hp out of the engine for free.

[Dwight]

Ok I'm going to give you the short story

A few years back I installed a dyno-ed 530 hp 408 in a Cobra for Mike. He drove it 130 miles home and called me about the gas mileage. 6.7 MPG.
I told him to bring it back and I would let Coach tune the carb.
We called the shop that had build the motor and they told us they only tune for wide open throttle because they did not know what air filter, alternator, headers, exhausts system, etc that we would use.
Mike brought the car back and Coach tuned the carb. Trip back home he got about 13 mpg.
The next year I drove it to the London Cobra Show. Round trip 1150 miles and I got 16.7 or 17. something, don't remember for sure.
Moral of the story is check the power valve and get the carb. tuned. There is more to tuning than adjusting the idle screw. Jet size, air fuel ratio, cam plays a big part.
Air Filter is a big issue on fuel consumption.
I had a 351 W one time that would not rev over 4300 rpms in any gear. Stopped on the side of the road and removed the 8" air filter and the motor would rev to 6,000 in any gear.
I'm with Eric on this gas mileage thing. If I can change something to get another mile out of a gallon of gas, I'll do it.

[1795]

In addition to the above mentioned things, take look at the differential and go with something in the 3:54, 3:31 to3:27 range.

If you keep the rpms down you will get better gas milage. A 427 running at around 2,000 rpms will have more than enough power move a cobra. Do not run the car at 5-6,000 rpms, no real need to on the road.

[FredG]

My Roush 427r loves gasoline but it is still much better that my old 427 66 Vette. It has an 870 Holley on it. If I wanted better mileage, I would switch to EFI.

Fred

[bobcowan]

The big "trick" is EFI. A carb is not a bad choice. But it will never be spot on. A good tuner on a road force dyno can get it pretty close, but never spot on. There are just too many variables in road driving.

Closed loop EFI, OTOH, will keep mixture and timing where it needs to be all the time. Which also means that the engine will make more power under the curve than a carb will.

A carb is like a shot gun. EFI is like a sniper rifle.

In the end, though, big cubes will consume big fuel. No getting around that.

[Anthony]

I like simplicity.

I'm guessing the easiest is to get a tuned smaller carb. I don;t personally know of anybody I trust, but talk to quick fuel ? I've heard very good things about them.

Next step, maybe tranny / rear swap ? Dodge got it right with the viper, 3.07 rear, with T56 ( wide ratio 4 spd w double overdrive ) great all around performamce and economy.

final step - rv style hydraulic cam, maybe ford's 390 standard passenger car cam, or GT cam. I'd forgo on this though.

[olddog]

The number one thing is making as much power at a given cruise condition, at stoichiometric, as possible. Rich is not burning all the fuel. Although slightly lean can get better fuel mileage, it causes more emissions, and if we are talking a 427 FE the combustion chamber design will not tolerate lean burn without pinging. So what does that leave us with? Getting the timing right! The number one MPG killing thing I hear people do, is they don't use vacuum advance. That's fine for all out racing, but no good for MPG.

Nothing will allow you to dial in the best timing at a given condition like EFI. It also allows you to dial in the fuel. You should try to target a slightly lean condition at cruise conditions and then find what timing gets you maximum break torque (MBT). If it pings, you have to go richer towards stoichiometric. If it doesn't ping you can try going leaner. Note that as you go leaner you will need more advance, so you have to find MBT again at each fuel ratio change.

Tune and valve timing is your biggest opportunity.

Other things:
1) thinner synthetic oil. Engine, Trans, & Differential.
2) lower volume oil pump. Wastes less energy, too little and by by engine.
3) pump less coolant by slowing water pump, if you can. Watch temps.
4) parasitic loss from belts. Many designs out there. Do your research.
5) Tires. Bending rubber wastes energy. Narrow low profile tires wast less energy.
6) Gearing. Cruise rpm should be lowest RPM engine can tolerate.
7) low friction rings.
8) Cam that allows engine to tolerate lower cruise rpm.
9) Reduce rotating mass where possible.

All these thing have trade offs. Narrow tires, not good for traction. Low profile make a harsher ride (feel driving over a grass hopper). Looks may not be as pleasing. The cam for best MPG is not going to make as much power, nor will it have the rumpity rump idle that we love.

[ERA174]

This old post by Grubby on vacuum advance distributors may be helpful.
vac advance or not for FE Cobra

[6TNCRZY]

Simplest thing I don't think anybody mentioned. Install a distributor with a vacuum advance if you don't already have one. It makes a lot of difference in cruising mileage, you need more timing when the mixture in leaner and less dense.

[xb-60]

If you:
-Change to a smaller carb
-Change to EFI
-Change the diff. ratio
-Change the gearbox
-Change the cam
-Have a dyno tune

These options would help reduce fuel consumption, but would cost from a few hundred dollars to a few thousand dollars. If you spent that sort of cash, how long would it be before you showed a net gain in $ ?

Just my opinion....but the biggest influence on fuel consumption is whose foot is on the accelerator

Cheers,
Glen

[twobjshelbys]

Seriously? You're looking for a way to irmpove fuel consumption on a 1960's Gas Hog becasue all you're going to do is take a 9MPG engine to 11MPG. There is no miracle going to get you from 9MPG to 40MPG. After you do all the things mentioned above 2-3mpg is all you're going to get (yeah, but that's still 25% ). In the end, you'll get close to 200 miles on a tank. Less if lots of city/stop-n-go, a little more if pure highway cruising with a Tremec in 5th. If gas mileage is what you want then a 427 Cobra isn't the right vehicle.

[olddog]

But you are missing the explanation of why. The original poster is in Europe, where he pays over $6 per gallon (Euros, Kilometers, and liters converted). I've been there and done that. I get it.

5000 miles per year at 9 MPG * $6.50 = $3611 / yr

5000 miles per year at 11 MPG * $6.50 = $2954 / yr

Difference is $656 / yr.

A 3 year return on investment is considered worth doing in most business models. So spending $1969 to get there would be considered good business.

EFI conversion will cost too much, unless there is some other driving factor where you can get two birds with one stone.

I do think I read where there are some distributors out there that you can program a timing curve into them, similar to EFI. I don't no the cost.

I do think the cam swap is very doable on that budget. However this depends on what the existing cam is.

Changing oil is just routine maintenance.

[olddog]

I will toss out another thought, but I doubt this would be acceptable. I am assuming this is a 427 FE and not a Windsor based engine. If so pull the FE out and replace it with a stroked 5.0. My 347 gets about 15 MPG just driving around. I estimate it makes around 400 HP or a tad more. Dwight drives to the London Ohio Cobra show from Alabama (I think). He told me he gets around 20 MPG on that trip. He can correct me if I'm wrong. We both have stroked 5.0 engines with EFI.

If the OP is indeed getting 9 MPG then a 17 MPG 3 year return on investment would be a budget of $5100. If you sold the FE engine this would be easy to do. However anyone who has a FE 427 SO is not going to like this idea, unless they want to drive the car a lot and do not care about the legacy of the car

[MKS427]

[quote=olddog;1472263]

Difference is $656 / yr.

A 3 year return on investment is considered worth doing in most business models.

You have some good points. However, the WOW factor that a tuned 427 Cobra delivers, cannot be appreciated in a business model. That's a sacrifice for the thrill of the beast.

[MKS427]

Eric,
I did see the idea of going to a 6 speed thrown out there.
If you are running a 4-speed TL a Tremec TKO-600 w/wide ratio OD may be a good solution. The lower gearing is different, so the ring and pinion will most likely have to be changed.
FYI: 351W based 427 Dart (tuned as far as pump gas will allow) 572/582, EFI, TKO-600 WR OD, 3.08 gears, 25.4" tall tires. 2000 rpm @ 80 mph in 5th gear, gets 15 mpg combined getting on it/cruising.
With 26.5" Billboards, TKO-600, and 3.27 rear gear would net about 50 mph/80 kph @ 6000 rpm in first.

[twobjshelbys]

The ROI works for a daily driver, not for a toy driven a couple of weekends a month.

[Dwight]

Old Dog I got 21-22 mpg for the 1150 mile round trip with about 11- 12 runs down Main St.

[Dwight]

Great question about his tranny.
I changed my 390 '66 Fairlane from a top loader to a 5 speed.
I went from 2800 rpm at 60 mph to 2100 at 75 mph.