Is this real? (Page 1/3)
ls3mach JUN 08, 05:21 PM
I had a post I was making about how I don't think GM should even be in business, but I came across this:


"The Fiero was redesigned to use a fuel efficient version of GM's 2.5 L (151 cu in) four-cylinder Iron Duke engine capable of 31 mpg‑US (7.6 L/100 km; 37 mpg‑imp) in the city and 50 mpg‑US (4.7 L/100 km; 60 mpg‑imp) on the highway with the economy-ratio transmission option."

Search terms "Fiero MPG"

I have never seen or heard anything like that even when new.
I have never even seen 37MPG on the interstate in any configuration I've owned, which I think is probably all by this point/
Rsvl-Rider JUN 08, 06:01 PM
It is my understanding that the 50 mpg claim was based on the the 84 Fiero with the MY8 transmission. I believe only a very small number were produced.
fierofool JUN 08, 06:04 PM
Pretty much true. The Economy Transmission available only in the '84 essentially skipped 4th gearing and went from 3rd to 5th, which was a much lower ratio than any of the Fiero 5-speed transmissions. I guess you could call it 5.5th.

Test track MPG is probably obtained by constant speed and on what is pretty much a level track. Or maybe they do it on a dyno. I don't know.
RWDPLZ JUN 08, 08:39 PM
Not so fuel efficient with the automatic, I always got a consistent 23mpg in town, MAYBE 30 on the highway.
theogre JUN 08, 08:43 PM
Top Statement Maybe "True" If Based on EPA Estimated MPG numbers.
While those numbers look good in Ads, EPA CAFE scam, etc... You Never get those numbers in real driving anywhere.
Sound like a quote from GM Marketing or Written by a GM Fanboy w/o a clue.

"Iron Duke" is a "replacement" for the Aluminum Engine used in Vega and some others that had Huge Problems.

EPA and Cars makers got Sued some years ago because of Hybrid and Full Electric vehicles have very Bogus EPA Estimated MPG numbers etc. May still be in US Fed court because often take Years to go to court or settle.

Other statement(s) here have "problems..."

Because The Fiero 5 speeds 5th gear is 1 100th dif of gear ratio of MY8 4th gear.
code:
MY8	Getrag (L4 econo)	4th 0.73	Final 3.32
MT2 	Isuzu (L4)        	5th 0.74 	Final 3.35
MG2 	Getrag (V6)     	5th 0.72 	Final 3.61

See my Cave, Gear Ratio

The 4 cyl trans are so close is near 0 dif in MPH even on highway for a full tank.
V6 might get worse MPG just in Gearing because Final in pushing 4:1 plus 5th gear is a bit lower... (Ignoring V6 uses more gas, big/wide tires, etc.)
code:
Tran	Top G *	Final =	Total
MY8	0.73	3.32	2.42
MT2 	0.74 	3.35	2.48
MG2 	0.72 	3.61	2.56

The AT cars can get better, about same or far worse MPG because have several gear sets in them. See same cave page and AOD.
Is Why some V6 wants 4T60 to get better MPG and still launch out of a hole because TH125c used w/ them often will launch but crap MPG.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

ls3mach JUN 08, 09:22 PM
I don't know if I've ever had an MY8, but as OGRE pointed out their final drive ratio is extremely close. 50MPG seems stellar

Regarding EPA numbers, I almost always exceed them with my driving, unless the vehicle is in mechanical disrepair.

If I could get a 50MPG Fiero I would certainly consider buying another. My commute is nothing, but that'd be an okay extra vehicle.
hyperv6 JUN 08, 11:01 PM
Here is the deal as I understood it from back in the day.

To get the car built they promised GM a 50 mpg commuter car. The Fiero was approved by GM based on this concept. But as we know Pontiac had no real intention.

As for the 50 mpg car it was spoken of around intro but to this day I have never seen one or known anyone who had one.. they spoke of gearing and transmission but it any were built there were few if any.

There were so skip gear shifters in the Fiero.

Once past the Fiero intro the car was never spoken of again.

I have never even seen a magazine story on it. If there was a 50 mpg car I would suspect there would be a road test.
hyperv6 JUN 08, 11:04 PM
Here is the deal as I understood it from back in the day.

To get the car built they promised GM a 50 mpg commuter car. The Fiero was approved by GM based on this concept. But as we know Pontiac had no real intention.

As for the 50 mpg car it was spoken of around intro but to this day I have never seen one or known anyone who had one.. they spoke of gearing and transmission but it any were built there were few if any.

There were so skip gear shifters in the Fiero.

Once past the Fiero intro the car was never spoken of again.

I have never even seen a magazine story on it. If there was a 50 mpg car I would suspect there would be a road test.
skywurz JUN 08, 11:05 PM
About 15 years ago i was in my 87 Duke 5spd driving back from Ukiah to the Bay area down 101. I filled up in Ukiah and once i got home (about 120 miles) i was just above 3/4 of a tank. I went to the gas station the next day just to see what mpg i had gotten because it seemed stellar and only put 2.5 gallons in the car. Never have I ever gotten that good of mileage out of that car before or since. Best i figure is it was a fluke of how i filled it perhaps the back water gas station had a faulty shutoff and i filled the expansion tank. I still have it not the same engine or trans or wheels or tires as that trip.
theogre JUN 08, 11:47 PM
The only time I get close or exceed EPA numbers w/ Auto Duke is total highway for a long trip. Got 30+ a few times on Flat Roads.
Otherwise the ECM won't keep TCC locked long enough so only get ~ 25 MPG at best.

Stick cars have similar problems... Not just in the city but often have to shift a lot in "hill county" etc. too. Is no fun dealing w/ heavy traffic or worse stop/go traffic. That later eats many clutch sets, more so w/ diaphragm spring pressure plates like many small cars have not just Fiero.

Can go to www.fueleconomy.gov to look up actual EPA numbers for 1984 and later. Cropped Image for 4 87 Fiero...

But EPA change the "Rules" how the Estimated MPG numbers are made for 2008 and again in 2017. Not just Hybrid or E-cars. So Old numbers for Fiero in 80's won't match if "retested" or "adjusted" under current rules or match cars under them too.

So Click the "button" says "View Original EPA MPG"
Examples:
87 Duke Auto New MPG is 24 combined 21 city 29 hwy but was 27 combined 24 city 32 hwy and what many doc's and posts still say.
One 84 Duke Stick New MPG is 25 combined 21 city 33 hwy but was 33 combined 27 city 47 hwy

[This message has been edited by theogre (edited 06-09-2022).]