Originally posted by 30+mpg: Did the 2.5 come with an auto four speed? My TH125 gives me 2700 rpm @ 60mph. With a .705 overdrive, the revs would drop to about 1900 rpm. Does the 2.5 have enough torque at that rpm? HMMMM, at 5000 rpm that would be 157 mph. Now that's really FAST!!
I had the t125 replaced on my 3.4 with a t440 and at 80 I'm running at 2000 rpm. I can get consistant 30+ on the highway at 70 mph. I don't know about the torque requirements for a t440. Mine will down shift up to about 60 mph if I give it a little gas. Really great for over the road cruising, but does a lot of shifting around town.
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10:35 PM
fierorush Member
Posts: 40 From: San Diego, Ca. USA Registered: Mar 2002
I have a 1985 GT with an Isuzu 5speed tranny swap and I get 30mpg at 80mph! at 65mph with my old muncie I would be at 3000 rpm, not I am 1800 rpm in 5th gear.!
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11:11 PM
Mar 12th, 2002
30+mpg Member
Posts: 4061 From: Russellville, AR Registered: Feb 2002
Just thought I'd throw my numbers out.My '85 V6 SE automatic has 19,000 miles on it,stock except I removed the cat,tuned,aligned,new oxygen sensor.Gets a very consistent 14 MPG City on my 3 mile daily commute.Never gets to warm up in the 5 minutes it takes to get to work.Gets 30 MPG on the highway at 65 MPH.Big difference.Love the car no matter what.Have an '86 GT that seems to do a little better (75,000 miles)
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09:44 PM
Mar 14th, 2002
30+mpg Member
Posts: 4061 From: Russellville, AR Registered: Feb 2002
304.4 miles on 9.332 gallons. An extra .005" of spark plug gap doesn't seem to have much effect. I'm purchasing a MSD blaster coil to see if throwing a hotter spark across the gap will make any difference.
Originally posted by 30+mpg: How much HP @ 60 MPH?
Guestimating Fiero Cd at 0.34...
60 mph = 100 kph = 27.7 m/s (V) Frontal area = 46" x 65" ~ 3000 sqin ~ 2 sqm (A)
F = (Cd*A*V^2)/2 F = 262 N
P = F*V = 7,277 W ~ 10 HP
10 HP @ 1750 RPM -> 30 rwtq @ 1750 RPM
Sanity check: doubling the speed to 120 yields a requirement of 80 HP. This is probably about right since the 92 HP Iron Duck was past it's power peak at its magazine listed top speed of 115.
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10:17 AM
lou_dias Member
Posts: 5369 From: Warwick, RI Registered: Jun 2000
my brand spanking new 3.4 semi-performance rebuild averaged 26mpg on a 1100 mile trip from the Fiero factory in AL to Fall River MA with NY traffic included 2 summers ago. My average speed was 80+mph...
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11:43 AM
Mar 18th, 2002
30+mpg Member
Posts: 4061 From: Russellville, AR Registered: Feb 2002
How do you know you're filling it up to the same level every time?
I dont't, that's why I've provided several fill up readings. Things should average out. Otherwise my tank would be less and less full after each fill up!
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11:09 AM
buzzin_'86 Junior Member
Posts: 8 From: Chapin, SC, USA Registered: Mar 2002
30+, It depends on what type of driving you do but here are some thoughts. 1) Remove the atlernator - if you don't drive it that far just charge when you get home. 2) Remove the A/C. Even if you don't use it there is rolling resistance there plus the engery needed to bend the belt. 3) Rollers, not even sure if they they make them for the 2.5? 4) If you don't remove the alterate switch to an electric water pump. 5) New wheel bearing and repack them with synthetic. 6) Coast more . No really I have an Aurura and sometimes when I'm really bored I'll bring up the average miles/gallon on the computer and see how high I can get it by coasting when I know a stop sign is coming up or don't brake when entering the neighborhood.
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11:40 AM
30+mpg Member
Posts: 4061 From: Russellville, AR Registered: Feb 2002
The car doesn't have an A/C compressor, but it's starting to warm up around here. 37 miles one way to work, I need the alternator! Anyone have any experience w/ roller rockers on a 2.5L. I communicated with a guy that had a used set for sale (his price was higher than new!) but had only used them for racing.
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01:32 PM
buzzin_'86 Junior Member
Posts: 8 From: Chapin, SC, USA Registered: Mar 2002
I am not sure if 80 miles a day on a battery is all that bad. So long as you don't have you headlights on the entire time, even then I am not sure.
Just to see how the battery holds up you could disconnect the positive side of the Alt. If the battery holds up OK try removing the alt.
I doubt you want to go through the trouble of charging the battery every night, but it would be interesting to see what type of improvement you see.
If it turns out you really don't mind the hassle you probably want to get a deep cycle marine battery.
I you do the experiment let me know how it goes.
FYI: When I worked with a teleco equipment manufacture I remember doing all sorts of load testing on lead acid and gell cell batteries. Most telco equipment runs off of -48V so that it can run off batteries. We were seeing a lot of problems with batteries blotting up after many deep cycle depleations and chargings. The gell cells really held up well. If I remember correctly it took quite a while for the batteries to discharge even with a stiff load.
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05:12 PM
30+mpg Member
Posts: 4061 From: Russellville, AR Registered: Feb 2002
My 86 2.5 with 5 speed cam and larger throttle body gets 32-33 mpg at 80 mph. I run from my home 70 miles south of Daytona to Daytona twice a week and it is always the same. Above 80 it starts to drop off. All four tires are P215 60R's on American wheels
The 185-70/13 tires on the front already make the car scrape in some situations. I dont't want to be like those guys in SoCal that weave thru the parking lots to avoid speed bumps!
What I really would like to know are the spot-on alignment settings that give the least rolling resistance, but know one seems to pocess that knowledge.
I have a 2.5L with an Isuzu 5sp at 109,000 miles. I try to keep it tuned, tires properly inflated, etc. etc. etc.
My route to and from work is about 12 miles, highest 'legal' limit is 55 for about a mile, most is 45 with maybe 2 miles at less than 45. There are 8 stoplights/stopsigns and with traffic NORMALLY 6 of the 8 require a stop regardless of how I drive.
* IF I am driving 'for power' and rev it above 4500 before shifting I will average 23 to 28 MPG but have a lot of fun 'battling inertia'.
IF I drive 'for economy', trying to time movement and not use brakes, 'timing' lights and shifting at max manifold vacume (shift light or my added vac gage - which works out to about 2300 rpm) I can get 35-36 mpg on this route.
Last year, I did a 120 mile round trip at 55MPH with cruise control, no air and windows closed and got 43 mpg.
Remember "Drive 55" ? That was the days this thing was made in! Given that the advertised highway milage estimates would be based on a maximum of 55mph (the law when the car was made) the design of the car and the fact that 70 mph takes 30% more fuel than 50 mph --- 32 MPG at 65 to 70 is Damn Good!
While physics makes a difference the fact remain that the driver is the greatest single variable in fuel economy.
[This message has been edited by Tryxalon (edited 05-07-2002).]
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09:33 PM
May 8th, 2002
30+mpg Member
Posts: 4061 From: Russellville, AR Registered: Feb 2002
Originally posted by 30+mpg: I do my own wheel alignments, using a spool of white thread, a tape measure, 4 jack stands, a plumb bob, a flat concrete indoor floor, masking tape, a pen, viener calipers, a level, a square, a caster gage, patience and the nut & bolt suspension tools per "How to Make Your Car Handle" book. So give me the toe, camber and caster numbers for front and rear and I can crank them in myself for $0. +{]:O) < Bless you!
I have access to AddAll at work, I will try and get the info for you, That is a hard way to do an alignment, but if that's how you do it have at it man.
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09:25 PM
2m4believer Member
Posts: 35 From: Santa Rosa, CA Registered: May 2002
Hey i drove my 84 2.5 5 speed from oklahoma to california, and got 45 mpg,it used split fire plugs and wires, resent tune up, and a complete rebuild of the tranny, it can and has been done, i wish you could have been there to see it!
3.4L V6 w/ 5speed all stop and go city driving, and im getting 9-10km/L or roughly 24-25 MPG (correct me if im wrong, im not sure on the exact conversion)
Now in my books thats not bad for a decent sized motor in the city. And its certainly better than my old (actually rebuilt, but exploded) 2.8, call me happy!
. No really I have an Aurura and sometimes when I'm really bored I'll bring up the average miles/gallon on the computer and see how high I can get it by coasting when I know a stop sign is coming up or don't brake when entering the neighborhood. 
