Gas mileage in my Ford Zetec modified:

Gnichols, that all stands to reason, I have been thinking of building a roadster with the space frame under the skin and an early aero influence. It would be interesting to have a reference of what the early aero tricks actually worked out to in numbers (I'm sure there is one somewhere, I just don't know what it is). In case I'm being too subtle, yes I am asking if anyone knows of a book that contains said info.

 

Nex and Rex!
As Rex knows, one of the primary goals of the fenderless 27T closed cab pickup I have on the drawing board is mpg - be it from a diesel (heck, it will be a TRUCK after all!) or an I-4 or V-6. I gotta have a car I can afford to drive cross country or even to Europe / Japan in my old age! On the "good" side, if the aero is SO bad, then keeping the weight down might be less of a problem. Might have to bump my wet weight up to 2000 lbs and go for the Caddy ride!
Belly pans are neat, but a maintenance nightmare. A shorty pan in front around the nose stopping about at the water pump might help, along with smoothing the toe boards down to the level of the lower frame rail starting around the tranny? Who knows...
Later, Gary

 

Rex,
Congrats on making the big time... December 2008 Rod & Custom article on modern 4 bangers for hot rods by Kev Elliott has a photo of your little Ford motor. One of these little animals is probably going in my new build (unless I cop out and go the SC V=6 route!). Later, Gary

PS Another interesting article same issue on modern fuels and hot rod mills.

 

Aero really is the problem with our cars. All those things that stick out in the air, like the headlights, tires, straight up radiator, hanging axle, etc. all add up to a crappy Cd number. To help some understand this, think about motorcycles. Most bigger bikes, from Harley's, to Sport bikes with 1000cc to 1800cc motors only get 35-45 mpg! A motor 1/4 the size of the average SBC and only 400-850 lbs and that's all the mileage they pull in real world riding! Although Cycle World just did a comparison of mileage kings and a Honda 250 Dual Sport type got around 95mpg! Of course it pretty slow and not any fun on the freeway
The point being that Aerodynamics are incredibly important.
And as a side note, the wifes PT with a 5 speed manual used to get only 20 mpg no matter how hard she tried to improve by light acceleration and slow freeway cruising! the main reason she dumped it! Sounds like the HHR does better!
Last comment, Rex did you drive to Bonneville? Any changes?

 

A couple of additional thoughts on the mileage bit.

Aero as noted is tremendously important and in this case, probably the reason for the not-as-good-as-expected mileage.

I've found that lugging the engine in 5th can kill mileage as well.

I suggest you get a large diameter (2 5/8") S-W vacuum gauge and strive for the highest vacuum you can get at highway speeds.
This may mean running with the overdrive locked out.

Case in point:
We took our 6 month old 88 Mustang GT, 5.0 liter, 5-speed, etc. to Idaho from Central California.

Speeds were usually 65 to 75 on the highway.

The trip up returned 24.5 mpg and the car was in 5th when on the highway.

The trip home returned 25.5 mpg and I was following the dictates of the vacuum gauge.
When on the long subtly uphill desert upgrades I down-shifted to 4th and vacuum went from 10-11" in 5th to 15-17" in 4th.
Spinning the engine during highway travel isn't all bad.

Even on a car with fair aerodynamics such as the Mustang has, higher speeds really drag the mileage down.

A co-worker - cheapskate, but honest - bought an 89 Mustang GT (new) similar to mine.
On the long flat highways of Central California he'd plug 55 mph into the cruise control and mileage went to 30 mpg.
Higher speeds, it was similar to what my Mustang got.


Next step for me is to plug the 3.00 diff into my 32 and see what happens.
I'm guessing in-town mileage won't change much, but it looks like 18 mpg is reachable on the highway.

Interesting post and lots of good, intelligent comments by many posters.

 

Hotroddon,
Did not drive my modified to B'ville this year as I was having some wiring issues with the injection, changed a bunch of things and it started to run, no idea what one of the changes fixed it!! But it is running and actually pretty good but I am still very rich. C9 is right about lugging the engine, at least with my car it doesn't do any thing for the mileage. I drove to the Billetproop meet in Antioch this weekend about 180 miles round trip and got really shitty mileage, less than 18 but I know that I am not back to the ECU tune that I was at before I had my problems. My plan is to go to smaller injectors, 25 lbs/hr from the 30 lbs/hr that I have now, decrease the inside diameter of my ram tubes to 1.75 and also go to a 4.8 QC ratio and lean it down a couple of points. All of these should help and I actually think that the acceleration performance should get better at the same time as I know that I am still way to rich.
Car is running great right now and just want to enjoy and gets some miles on it.

Rex

 

Hi Rex. Good to hear that you've got it going again. Nice to meet ya at Bonneville and visit for awhile. My track roadster ran better at Bonneville than it has anywhere. Gonna bump the idle circuit and main jets one more size up. It can only get better...right?

Charlie

 

here's something to add to C9's post and maybe simplify it for those who don't wanna run a vacuum gauge. the most efficient running condition for any engine is obviously the highest vacuum but what creates that condition can be observed without a gauge. RPMs in the mid to high range and a small throttle opening are what create the condition because it atomizes the fuel much better so basically, run the RPMs 2/3 to 3/4 to the shift point with the least throttle angle/pedal push for any given gear. i do it on my '08 triumph at all times and where other guys report real-world mileage to be 35-40, i consistently average 45-48 and i don't ride easy. instead of cruising at around 1800-2300 like most do (highest gear without lugging) i keep it down one lower and hover around 2700-3000 and get HUGE mileage gains. plus it sounds cooler with the RPMs up a bit and i can take off quicker when i want