On my last highway trip I got 46mpg with my 85 2.5L. I was tempted to post it before but I thought many people wouldnt beleive it. I averaged about 120km/h over 525km with over 1/8th of a tank to spare. I dont get near that milage in town though.
Had an 85 Coupe, 4 Cyl, 5 speed that would get 38 mpg cruising at 80 mph on trips and 32 in local driving. Also had an 85 SE V6, auto that would vary between 27 and 31 on trips and 23 to 26 local. The V6, auto was more sensitive to what kind of terrain I was driving on, but the 4 cyl, 5 speed didn't seem to matter. It got the same milage consistently. ( Wish I had it now... )
Dave
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09:19 AM
computer_engineer Member
Posts: 335 From: South Dakota Registered: Aug 2005
On my last highway trip I got 46mpg with my 85 2.5L. I was tempted to post it before but I thought many people wouldnt beleive it. I averaged about 120km/h over 525km with over 1/8th of a tank to spare. I dont get near that milage in town though.
This kills me, how does an old Iron Duke get econamy like that but the most modern GM's dont?
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11:42 AM
deceler8 Member
Posts: 2139 From: Sioux City, Iowa USA Registered: Sep 1999
On my last highway trip I got 46mpg with my 85 2.5L. I was tempted to post it before but I thought many people wouldnt beleive it. I averaged about 120km/h over 525km with over 1/8th of a tank to spare. I dont get near that milage in town though.
I gotta go with Rickady88GT on this one. So I'll claim on 46mpg.
------------------ Tim Red 88 Formula Auto 2.8 100K+ Miles
I don't care how much money you have, free stuff is always a good thing.
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04:45 PM
D B Cooper Member
Posts: 3141 From: East Detroit, MI Registered: Jul 2005
'86GT auto, stock with mild manifold gasket leak. 23.2 combined (80% freeway @ 20-80mph, 20% city). She's burnt 173.7 gallons since aug 17th going 4030 miles. Would probably do a little better though if I replace the manifold gasket. I just aluminum foiled the heck out of it and tied it off with a stainless hose clamp to take most of the noise out.
wish I had the 5 speed
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05:31 PM
Nextel dude Member
Posts: 446 From: Fenwick Island, Delaware Registered: Jun 2005
Hey guys what do you do to get these kind of mpg numbers out of your cars? I have a stock 87 GT 2.8 auto thats barely breaks 20 on the road, averages about 18 combined and that is moderate driving, not hotdoggin, and after a full tune up. I can understand a 5 speed getting a few more mpg's but....30-35 wow and how about a duke breaking 40 mpg. On my GT I assume the cat is original so anyone think changing the cat and installing a K & N air filter and pipe might help? Or should I go buy a fiero with a duke and a 5 speed and see if I can get me some of that 40+ mpg?
Chuck
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05:57 PM
cooguyfish Member
Posts: 2658 From: Hamilton, OH, USA Registered: Mar 2002
This kills me, how does an old Iron Duke get econamy like that but the most modern GM's dont?
I've been saying it for a while now. Saturn S-series cars. I got 40.2 MPG on my first tank with my 96 SL1 5 spd. that's mild combined driving, I wonder since the motor is mostly rebuilt if I'll get better as I break it in. I think it will because I've already gone further on the same amount of tank than the last one, and have done less highway driving.
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06:06 PM
Blacktree Member
Posts: 20770 From: Central Florida Registered: Dec 2001
I get about 27-28 MPG (combined city/hwy) with my '87 Duke / auto.
I wish I still had the '86 coupe (Duke / 5spd). It got high 20s in stop-n-go traffic and high 30s on the freeway. It also had a K&N air filter, deleted catalyst, and a couple degrees of timing advance.
85 5 speed duke the best tank was 36 MPG the worst tank was 21 MPG It will not stay very true but the Average per tank is 30 MPG Still most new cars do not get but around 30 MPG. I had a Honda CRX that got 50MPG and got 46MPG most of the time wish I had it back.
I found this 1985 Pontiac Fiero
Sorted by MPG (city), Click on column headings to resort MPG Annual Fuel Cost* Greenhouse Gas Emissions (tons/yr)* EPA Air Pollution Score From 0 to 10 (best)
* Based on 45% highway driving, 55% city driving, 15000 annual miles and the price of fuel used by the vehicle. You may customize these values to reflect the price of fuel in your area and your own driving patterns.
GHG-Greenhouse gas emissions expressed in CO2 equivalents. Estimates include the full fuel cycle and exclude vehicle manufacture. (U.S. Department of Energy, GREET Model, Argonne National Laboratory)
[This message has been edited by F355spider (edited 10-03-2005).]
I get 24.5 plus or minus a tad with mixed highway and stop-n-go rush hour driving. On long trips on flat ground I get 28-29 at 75+, and on occasion have gotten as high as 31 (but that was on a load of bad gas that had me running too lean, setting several codes in the process).
I've got a 2.8/Getrag that's bored and stroked to 3.2L and the Crane 2030H cam, otherwise stock. Oh, and I removed the tube joint obstruction in the manifolds but did not touch the flange port weld.
JazzMan
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07:54 PM
30+mpg Member
Posts: 4061 From: Russellville, AR Registered: Feb 2002
My old 87 Duke got 42 mpg, now my Formula is a different story, driven on the highway for long drives it gets around 30 mpg, however recently since I am doing a motor swap and don't care if the old girl blows I have been getting around 22 with it to the floor for the majority of the time.
hehe shall I post a picture of my gas receipt and the track file from my GPS?
yes, please do. my '84 duke with 4 speed manual gets 30mpg average. it's in good shape, and im no leadfoot, so 50% improvement is, frankly, a little hard to believe.
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11:16 PM
GTFiero1 Member
Posts: 6508 From: Camden County NJ Registered: Sep 2001
My '87 GT with automatic is like Nextel dude's - I get 18-20mpg city/highway. When I finish my 4.9L swap in my '86, I hope to get more with the 4T60E though. Any 4.9L with auto mileage results (3.33 final drive)?
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02:44 AM
FieroLinks Member
Posts: 397 From: Spring Hill, FL, USA Registered: May 2002
The Finale with the 4.9 and 4T60E will get abotu 31 on Interstate if I keep it at 70mph or less. If I run with traffic at between 75 and 80 I get about 27. Overall, mixed highway city, I get about 24.
John Stricker
quote
Originally posted by EngineerBill:
My '87 GT with automatic is like Nextel dude's - I get 18-20mpg city/highway. When I finish my 4.9L swap in my '86, I hope to get more with the 4T60E though. Any 4.9L with auto mileage results (3.33 final drive)?
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01:07 PM
befarrer Member
Posts: 1962 From: Westlock, Alberta, CANADA Registered: Aug 2002
yes, please do. my '84 duke with 4 speed manual gets 30mpg average. it's in good shape, and im no leadfoot, so 50% improvement is, frankly, a little hard to believe.
He has an 85, which will have the Isuzu 5 speed in it, which makes the Duke turn about 2400RPM at 60MPH I think, plus I think he is measuring in Canadian gallons, which are larger, I would guess about 38MPG American. But I can see his mileage figures, I got 42MPG canadian with my 84 Duke, auto driving in the mountains at 80-100KM/h.
My Quad 4 HO 5-speed got 38MPG Canadian on the highway doing 130KM/h+ and not driving easy, downshifting to 3rd to pass while doing 130KM/h probably lowered my gas mileage somewhat. Any the engine has 336,000KM on it and has a bad fuel pressure regulator.
------------------ [IMG] 84 Fiero Sport Coupe #1192 :: 86 Fiero Base Coupe Quad 4 :: 84 Chevette CS 4 Door
Originally posted by lurker: yes, please do. my '84 duke with 4 speed manual gets 30mpg average. it's in good shape, and im no leadfoot, so 50% improvement is, frankly, a little hard to believe.
Hehe I find this a little funny. The bigger engine guys post pics for their 1/4 mile time slips. And the duke people post pics of gas receipts
And here is the GPS data for that day. Trip Data in Magellan Mapsend Format. - Trip Data in XLS. Note: I cut off a few legs of the start and end off the track in the GPS files because I dont want to give directions right to my house
[This message has been edited by Caladin (edited 10-05-2005).]
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03:37 PM
PFF
System Bot
jstricker Member
Posts: 12956 From: Russell, KS USA Registered: Apr 2002
Your GPS track has an end time of 23:31:36 on 9/7/2005 and your receipt shows you filled up at 16:38:24 on 9/7/2005. GPS relies on extremely accurate time to function and I've yet to see a self serve pump that was more than a few minutes off. How did you manage that or am I missing something?
John Stricker
Edited to add that this looks like the wrong receipt, I think it's the one you got when you filled up before you left on that trip as your beginning time is 17:52:46 on 9/7/2005. You didn't average 120 km/hr either, it was 102 km/hr.
Even if this slip is correct (which it can't be by the times), you didn't make anywhere near 40 mpg. If we use your distance of 525 km then that's 326 miles. You used (on the slip) 33.746 Liters and that's 8.91 gallons. That makes a mileage figure of 36.6 mpg.
quote
Originally posted by Caladin:
Hehe I find this a little funny. The bigger engine guys post pics for their 1/4 mile time slips. And the duke people post pics of gas receipts
And here is the GPS data for that day. Trip Data in Magellan Mapsend Format. - Trip Data in XLS. Note: I cut off a few legs of the start and end off the track in the GPS files because I dont want to give directions right to my house
[This message has been edited by jstricker (edited 10-05-2005).]
23mpg city, duke w. auto. After reading other's mileages, this seems WAY too low! Maybe the lead foot has something to do with it? I've never had it on the highway long enough to calculate the highway mileage.
Originally posted by jstricker: Your GPS track has an end time of 23:31:36 on 9/7/2005 and your receipt shows you filled up at 16:38:24 on 9/7/2005.
The GPS logs use the UTC (+7 hours ahead of PST) to ensure accuracy since you could start in one time zone and end in another (the GPS software accounts for this automatically). The pump lists the local time. The few minutes between is the time I filled up on gas and for a few travel points that I removed.
quote
Originally posted by jstricker: You didn't average 120km/hr either, it was 102 km/hr.
Well yes I supose your correct. I count more or less the highway driving. While the GPS includes all the driving around looking for a place to eat as well. These things obviously bring avrg down. As well the GPS didnt record the top speed in the Log file either. While the unit itself showed and recorded a top speed of over 150kmh the log file simply averages speed between 2 points. This also applies to distance as the unit dosn't record every few feet. That would be far to much data for the distance traveled. I had it set to medium detail so it does cut alot of corners.
quote
Originally posted by jstricker: Even if this slip is correct (which it can't be by the times), you didn't make anywhere near 40 mpg. If we use your distance of 525 km then that's 326 miles. You used (on the slip) 33.746 Liters and that's 8.91 gallons. That makes a mileage figure of 36.6 mpg.
You are correct. And I blame the canadian government! ;p When at the Auto show they were handing out these things Its a slider that you use to figure out your MPG or L/100km. As I now see the L/100km is correct but the US MPG is WAAAY off. Oh well atleast it has the format we use correct.
Edit: Spelling and It looks like they did 33.746 liter = 7.4230823 gallon [UK] instead of US gallons.
[This message has been edited by Caladin (edited 10-05-2005).]
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06:07 PM
88gtNewb Member
Posts: 922 From: Surrey, BC, Canada Registered: Aug 2004
TBI 4.5/4t60= 22~24 mpg in town. For comparison on the same daily drive, the v8 minivan gets 16~18, the v6 Thunderbird gets 20 and my new Cavalier gets 26~28.
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08:58 PM
862m62 Member
Posts: 278 From: Ocean View, De. Registered: Jul 2005
That's the semi-official name given to the 4-cylinder engine design used in the Fiero and many other GM products. The Duke 2.5 L4 was used in millions of GM cars from the late 70's through the mid to late 90's.
JazzMan
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11:42 PM
Oct 6th, 2005
lurker Member
Posts: 12355 From: salisbury nc usa Registered: Feb 2002
Originally posted by Caladin: Hehe I find this a little funny. The bigger engine guys post pics for their 1/4 mile time slips. And the duke people post pics of gas receipts
different priorities they fret the mpHs, we fret the mpGs
quote
Originally posted by jstricker: That makes a mileage figure of 36.6 mpg.
this figure i can believe. ive been thinking of asking if anyone wants to trade a good driving 4 speed for a good driving 5 speed, for exactly this reason.
[This message has been edited by lurker (edited 10-06-2005).]
)
on 46mpg.
I've never had it on the highway long enough to calculate the highway mileage.
they fret the mpHs, we fret the mpGs
