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

[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!