'60s 427 FE 425 Hp side oiler......mpg?

[AC Ventura]

Before everybody shoots me down, saying don't fit a BB to save money on fuel, I was just wondered highway cruising at 70, running at 10:1 comp, what miles per gallon would be the norm and also average around town?
Anybody actually tested this. Just wondering how in real life it compares to a modern 347 that seems to average 10 -15 mpg.
Also I heard with alloy heads and water pump, weight comes down to 520Lbs. Is that about right?
If there are any real life answers that would be really helpful.

[kevins2]

I have a '68 FE Side oiler with aluminum heads/intake, 10:1 compression and a Holley 750. Mine dynoed at 482 HP/502 Ft Lbs torque at the crank. I've not run a tank of gas out solely on the highway so don't know what that would be, but driving country roads with a lot of stops, starts and some spirited driving I average 11 mpg.

Kevin

[1795]

Would need to know rear end ratio and transmission to give better estimate. With a BB ,4 sod top loader and a 3.54 rear end ratio, I can get 14 mpg's cruising at 70. Average about 13 mpg around town. as low as 11 with more spirited driving.

[Varmit]

I don't get MPG, it get stations per mile

[Bernica]

With a 482 BBF, 10.8:1 comp, 4 speed WR toploader and 3:31 rear I am in the 10 mpg range. Less with spirited driving. Glad I have a 42 gal tank!

[AC Ventura]

Thanks guys tha pretty much answers the question. It's gonna be average of about 11 with typical, enjoyable but non explosive, driving.
The question was really based on find in available range with a 15 gall tank. Incidentally that man sized 42 gallon tank would cost around $325 to fill, here in the UK.
Do we think MSD Atomic or similar EFI would make any difference?

[Bernica]

Originally Posted by AC Ventura

Incidentally that man sized 42 gallon tank would cost around $325 to fill, here in the UK.

One time when I filled it with 100 race gas my credit card company denied the sale because they figured someone was stealing gas on my card!

[patrickt]

Originally Posted by AC Ventura

Do we think MSD Atomic or similar EFI would make any difference?

No. The only way to increase MPG is to put her on a flatbed.

[Young1]

428, top loader, 9.5 CR, 3.31 diff. Did 200 miles today between 65 and 80 mph, 11.5 mpg, 750 holley vac secondaries, 72 primary jets

[DanEC]

GTOs, 427 Corvettes, 383/440 Plymouths, my FE ERA - I've never had anything that got over 13 mpg on the highway - 8 - 10 mpg in town. Only after EFI and high rear ends/overdrive transmission started being installed did I see anything over this. And then the exception is my 2003 Lightning PU with overdriven supercharger and computer tune - gets about 10 - 12 mpg.

[Ron61]

On a good day with my 1964 SO I could get right at 12.8 MPG. My best with the 1969 Cobra was 13.2 once and most of the time it is about 11.5/12.6 and if I get on it the mileage drops to around 9.

Ron

[mdross1]

Of all the vehicles we have owned most of them cared enough to check mile per gallon. It never entered my mind once I decided to build my car. The reason, no explanation needed for all you guys. We look for fuel stops when gauge hits the half full mark.

[COBRAMAN 484]

In the 21 years mine has been on the road. I have used a 428, 454 ( 428 crank ), and 2 different 484s. Compressions were between 9.7 and 11. I've used single quad dual quad and for the last 18 yrs EFI 50mm 8 stack . They all averaged 10mpg. except when I tried a tremec 3550 with a .68 5th, I got 13-14mpg.

[olddog]

I think a good mass flow based EFI would allow more precise fuel metering, which would allow any engine to run leaner, without issues, than you can get with a carb. It will also allow tuning the spark to get the most power out of the fuel being burned. So, yes a good EFI, properly tuned, would squeeze more miles out of a gallon of fuel. That being said, it can only be tuned to the engine it is on. Old Big Block engines have a lot of friction and pump a lot of oil. EFI can do nothing to help that. If EFI gave you a 10% increase in power, on a given amount of fuel burned, a 10 MPG engine would increase to 11 MPG. In other words, you would hardly notice the difference.

If you added EGR, you would likely see much more improvements, as it will allow you to pull in more timing without pinging. I'm not sure that would work so well with a lot of cam, but should with a milder cam. I just do not think the benefit would be worth the hassle and ugliness under the hood. At some point, it makes no sense being on a Cobra.

Speed density and Alpha-N type EFI, I doubt could match mass flow. On a mild engine, speed density could come close enough. Alpha-N is not nearly as accurate on fuel.

[DanEC]

Wow - that's a really well thought out, high-tech, EFI savy response from someone who goes by the logon "olddog"! Maybe old dogs can learn new tricks (technology).

[AC Ventura]

The reason I posted this thread.
I'm based in the UK. I have one of the 480 alloy bodied Mk IVs that Ford and Autokraft built under licence from AC Cars Limited, between '82 and '94. Like most, my car has the 5.0 EFI 302 from the Fox Mustang. The Mk IVs (not Cobra because there was a law suit with Shelby, regarding the name, at the time) were sold as new cars and had to be emission compliant. Obviously the 225 hp EGR, smog etc, ect 302 is quite unfulfilling. In fact potentially embarrassing, is what it is.
So, the default replacement choice is either a 340 hp 302 or a 425 hp331/347 from somebody like Keith Craft. That's the easy option. A simple swap. But I've read that these strokers only get 11-14mpg on a carb.
Therefore I asked the question, what you guys get mpg wise and it seems only 10% worse, which begs the question why not go all out and fit and fit the legendary motor? Well it's not easy in the Mk IV. The chassis, the footwells, the tunnel, everywhere you look there's a problem. Advice from experts here is not encouraging. They all say don't destroy/devalue a valuable car, it will be too hot in the footwells, it will understeer on every bend and will overheat on traffic. Also you'll lose all the boot (trunk) space, cos you'll need a 150 litre fuel tank. But when I hear that I think, no.... the installation that you guys did, overheated and that I'll find a way to do a better job.
It's all made worse by the fact that I've found a good '68 FE 427 that's not been overbored.
One final snag is that we cover 5000 miles in this car all over Europe on competitive rallies and fuel in UK and Europe is $8 a gallon and the std EFI does get 24mpg.
Never the less, I just feel its a 427 body and to hell with what's best. I cant believe I'll regret the big block. Surely it be an event just starting it.
Then somebody says Coyote. That way you'll have 400hp and 20 mpg.................
Anyhow, really agonising here so any advice, do feel free!

[olddog]

Originally Posted by DanEC

Wow - that's a really well thought out, high-tech, EFI savy response from someone who goes by the logon "olddog"! Maybe old dogs can learn new tricks (technology).

Well we can learn new tricks, but if we don't do them every day, we forget!

[olddog]

I have no clue the value of your car or what changing the engine would do to that value. That said you could pull the original engine (after fogging it with oil), then properly store it, so it could be put back later, thus preserving the value of the car.

Now you can install another engine for fun. However to keep with planning to re-install the original engine some day in the future, you need to minimize changes required to fit the new engine.

That would tend to make me go for a 347 stroker. If your budget would allow, I would go with an aftermarket 4.125 bore block which gets you a little over 360 cid. Go with the best heads you can afford and keep the cam more to the mild side. You should be able to make somewhere near 400 Hp and still get decent MPG.

Is the car EFI now? If it is, stay EFI. If not, stay with a carb.

[rodneym]

You'll be ok, going to a carb'd engine, in Europe???!

[AC Ventura]

Originally Posted by rodneym

You'll be ok, going to a carb'd engine, in Europe???!

Yes. There is a little known concession regarding engine replacement for cars when an original replacement engine is no longer available. Basically if your replacement engine is 1968 block, then the annual emission test is performed to the emissions requirements that were in force in 1968. Hence a carb would be okay.