Mustang?

[freebeard]

aka Bonneville spoiler.

[Masejoer]

Searching for something else, I found this thread.

Biggest difference will be gearing - I've had 2.73's, 3.08's, and 3.55's in a
'88 Tbird (but only a ~380hp 306 motor). 2.73's were getting me 34mpg highway average on Seattle-Portland round trips I used to always make. 3.08's are what I used for years as my daily - 31mpg. 3.55's dip down to 26mpg highway through a 4R70W. EECIV with a QuarterHorse for tuning. Electric fan helped out quite a bit, with DCControl thermistor-based controller and Mark VIII fan. Stock 225 wide street tires on 16" rims. Electric fan helped the low-load (downhill) sections of the road, but uphill there was no noticeable difference as the motor was just chugging fuel. Car was well tuned up, fully loaded with (modified) a/c and everything. Big radiator allowed the electric fan to rarely run. I spent way too much time making trips on some weekends just to gather data about how the car was doing with certain tunes, and swapping back and forth between mechanical and electric fan.

I didn't see any difference changing gears in city driving, but my overall tank averages would go down due to heavier-foot.

Now, the car sits a lot and I go through tanks at under 10mpg. I have my '00 Insight for the long 70+mpg trips and while I still like to engineer for max efficiency, it isn't a top priority. I will likely go Coyote soon just because I can, and expect to LOSE slightly on fuel economy as there is a lot more mass to move in an OHC motor vs OHV.

Originally Posted by Baltothewolf

Electric fan
Underbelly paneling
Underdrive pullies
Bigger amp alternator (140amp minimum)
LED lights everywhere

The LEDS will probably help a lot. The car uses a ton of incandescent lights that suck a lot of power.

LEDs don't have any impact compared to the friction and drag the v8s motors have, with with driveshaft and wheel weights/drag. I shaved off around 10A just on my tail lights with some custom ones (not dropin bulbs), and negligible amounts from going d2s projection about 10 years ago.

Belly pan would help a lot, or other ways of improving drag coefficient. I plan on going this after I get a shop built on our new home lot, but as a hobby more than for fuel economy reasons.

Originally Posted by darcane

That's going to be a challenge because...

'89 Mustang with a 351W? There's no OBDII in 1989 and most likely the engine swap means it's carbureted now too.

Sounds to me like the OP is building a race car with outdated technology but would like modern fuel economy. Aero and gearing will help some, but mostly this is putting lipstick on a pig. Keep the car a "5.0" with a Coyote motor and a 6-speed, and you can probably hit the same power with significantly better mpg.

No reason one can't build a big stroked out 351W and keep fuel injection. There WILL be more pumping and friction losses with a bigger motor, but the moving mass is far less than DOHC motors. Nothing new or old with ohv vs ohc - both were invented around the same time. The corvette still uses a pushrod motor. Gearing and aerodynamics allows it to still achieve over 30mpg with its 3300lb curb weight and 0.34cd. No idea on its frontal area.

Carb'd setups can also achieve very good economy (carbs have also come a long way), but few people spend the time/money to set them up well. I agree that I'd expect 20mpg out of any thrown-together 351 combo, if not less. With people wanting to go high-performance carb, I'd by default assume they'll go down to 12-15mpg as the builder tries to save money and time.