I have a 89 Z, 305 TPI stock and calculated that I'm getting about 23 MPG on the highway. Is this good? What do you get so I can compare?

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89 IROC original owner, 3 amplifier 8 speaker Kenwood/Infinity sound system, 300,000 miles on original 305 TPI. Change your oil!!!
Jeff's IROC Restoration

 

Vike,

23 is really quite good. It would be very boring to drive in such a manner that would provide more mileage than that.

However, as the summer nears and fuel prices get closer to that $3.00 per gallon prediction, I'm guessing this will be a hot topic very soon.

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Later,
Vader
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"I know how to solve your problem, but I can't tell
you since you might use the information illegally..."
Adobe Acrobat Reader 4.0

 

300,000 miles, MY GOD.

Screw gas mileage, be glad it still runs, lol.

Anyway, assuming you have an auto tranny, 23 is sub-par from the high numbers I've heard, of course everyone exaggerates(sp?)

Make sure the car is tuned up and timed to suit your needs. My timing is bumped up probably more than it should be, but when I had it around 8* advanced, I had a best of 32 MPG in my 5-speed RS 305 TBI.

Freeing up the exhaust and intake adds HP and MPG, efficiency is the key, and engine is a big air pump, the easier it is to get air in and out, the better it works.

 

hmm....

[This message has been edited by Ovrclck350 (edited February 09, 2001).]

 

I'm gettin 17 HWY...what's wrong?

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See pics @ Billy's Firebird
92 Bird 3.1L Auto
Best $750 I ever spent....
DRIVE IT LIKE YOU STOLE IT!
Kills:
93 Mustang LX (Before Mods)
98 or 99 Dodge Stratus (tough one, edged out at 40)
92 Camaro RS 305 TPI
97+ Honda somethin or another...modded....kept at my door the entire way
Close Calls
94 Grand Am 3.1 V6
92 Cavalier 3.1 V6
01 Porsche 911 Turbo (Had em till first gear)
Mods-Jet Stage 2 Performance Chip, Accel Cap/Rotor, Accel 8.8 MM Wires, Accell Coil, AC Delco Rapidfire Plugs, Dynomax Catback, K&N
AIM name OVRCLCK350

 

The wife and I just made an 800 mile road trip in "her" '90 IROC 350, averaged 23.6MPG at 70-90MPH most of the way. It never downshifted once. Does a helluva lot better than my ZR2 Blazer, which is logging in an astonishing 16.8MPG average on the interstate.

 

I've been getting 18 combined lately but I may need a new O2. The best mileage I get is when I do the 200 mile trip to Milwaukee at about 75 mph - 29 mpg.

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Base: 89 Iroc-Z LB9 auto 2.73 posi
Exh: 3" Dynomax muffler, 3" Pipe in place of cat
Ign: GMPP 8MM wires, Accel cap&rotor, AC Plugs
Fuel: Cleaned and flow-matched injectors, afpr, !air pump&diverter valve
Sound: Clarion deck, Kicker speakers and amps
Suspension/Drivetrain: KYB Shocks, BMR Strut Tower Brace
Misc: TB Bypass, All synthetics, Flexlite Transmission cooler
On the way: flow tech headers, alum. driveshaft

"Deserve's got nuthin' to do with it..."

 

i averaged a little over 22 on my 305 tpi 5spd convertible.

my 88 truck with a 305 tbi only gets an average of 11 though, and it used to get 19 average around 3 years ago. yet it passes echeck like it was a joke..

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My `91 Z28 Convertible

 

23 mpg? That's great. My son's 83 Z (305 HO, 700R4 and probably not the original rear gears gets 11 to 12 around town. Of course, it's turning just over 3000 rpm at 55 in overdrive. We've talked about going back to the original 3.73's if indeed the previous owner had changed gears but he's hooked by the acceleration. He told be a couple months ago that he wasn't impressed by the new Mustang GTs. When asked what he meant he said they can't keep up from the stoplight to 45 mph (speed limit on the main drag here.)

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Z's r Best

 

Mac,

I thought 23 was very good for a car that's been around the globe more than a dozen times. My relatively stock TPI does around 22.something on the road, and that's with a 2.77 Borg axle and lockup.

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Later,
Vader
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"I know how to solve your problem, but I can't tell
you since you might use the information illegally..."
Adobe Acrobat Reader 4.0

 

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I was getting about 28-30 mpg on the highway in the summer. The last highway trip I made which was in 25*F weather. I drove 200 miles and put 10 gallons back in the tank. That comes out to 20 mpg. Quite a difference! Go figure .

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'88 IROC 305 TPI
Crappy 700R4 slushbox
Gutted airboxes
180 degree T-stat
Advanced base TPS voltage
Relocated IAT sensor
Momo steering wheel (gotta luv it)
Ram-air setup coming soon
Flowmaster muffler (puke)
Taylor SpiroPro wires
Accel cap and rotor
Ported plenum
Kills: '94 Z28, Olds Aurora V8, bunch of Mustangs, T-birds, ricers, and others who assumed a 12 year-old car would be too slow.

 

Thanks for all the replys. Seems like my MPG is not as bad as I thought then. It actually improved a little this winter when I switched the oil back to 10W40 instead of my usual 20W50. Since I have a heated garage I can run that weight oil in the winter and not have to worry about those cold morning starts. Lighter oil, better MPG, make sense?

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89 IROC original owner, 3 amplifier 8 speaker Kenwood/Infinity sound system, 300,000 miles on original 305 TPI. Change your oil!!!
Jeff's IROC Restoration

 

My 1992 B4C w/ 350 motor got 25.8 mpg on a trip from Denver to New Mexico and that was doing 85mph most of the time then some 90mph following a Ford Excursion. I bet he was only getting 6mpg.

 

88irocz28. It's your relocated MAT with cold weather that is causing you to run overly rich. A relocated MAT (proper GM term) is fine in the summer, but unless you re-work the code of the eprom, it'll run too rich if the ambient air temperature falls below +40*F.

If you are not prepared to learn how to program your own eprom (the only real fix), then reconnect your stock MAT in the plenum until the weather warms up above +40*F.

 

BTW, when I say "wait for +40*F weather", I am talking about the minimum ambient air temperatures.

 

Vader, I say it's not as good as it could be because of my past MPG experience in my "inefficient" TBI car. Plus, Pony Killer swears he got 27 MPG in his LG4 with a flat cam, IE no lobe left, lol..

I suppose 300K miles would hamper the MPG a bit, but I assume the ring seal is still fairly optimal if the car is still running as good as he says.

 

LOL at the excursion comment. don't the 2000 and later vettes get like 12 mpg at a constant 150 mph!!? If is was feasible (no traffic) that would be sweet to go to FL from IN in 12 hours and still get big-a$$ ferd SUV-tank soccer mom gas mileage!

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Base: 89 Iroc-Z LB9 auto 2.73 posi
Exh: 3" Dynomax muffler, 3" Pipe in place of cat
Ign: GMPP 8MM wires, Accel cap&rotor, AC Plugs
Fuel: Cleaned and flow-matched injectors, afpr, !air pump&diverter valve
Sound: Clarion deck, Kicker speakers and amps
Suspension/Drivetrain: KYB Shocks, BMR Strut Tower Brace
Misc: TB Bypass, All synthetics, Flexlite Transmission cooler
On the way: flow tech headers, alum. driveshaft

"Deserve's got nuthin' to do with it..."

 

What am I doing wrong?! I'm getting like 10-15 with an LG4! I've got about 140k and idoubt if my oxygen sensor has been changed ever. If I got a new sensor, what could I expect to get? I also seem to run really rich (I guess thats what black carbon deposits on my tailpipe and the ground when I rev up means! What can I do to fix that problem as well?

 

I get around 14-18 mpg depending on how I drive. I got modded 350tpi and it's the 4.10's that are killin' me on any road going over 55mph

 

i'm getting about 16 average...cuz i do a lot of driving on 301...its sort of like an interstate. I know i get real good mileage on the Beltway cruisin at 70. I can only go 210 miles on 13 gallons, but gas here is only 1.59 for 93 octane, i consider myself lucky

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1988 Pontiac GTA 5.0 TPI
-K&N Filter
-Hypertech Air Foil
-Hypertech Perf. Chip
-2.5in Flowmaster Muffler
-Catco Hi-flow Cat

Kills
94 Probe GT, 95 Mustang GT, 96 Impala SS, 85 Thunderbird 5.0, 95 Accord V6, 98 Integra VTEC, 70 Chevelle Malibu, CRX w/ Turbo and Intercooler (have it on tape to prove it)

 

Well, lets see, i put 7.290 gallons in my car, and traveled 111 miles (some doing 55, some doing 40 and 35). That comes out to about 15.2...sound about correct for a car with 179,9xx? Shoot, in the summer i would get around, 22 - 23... i got hit hard in the belt after the Fuel Pump install...

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89 IROC-Z 350 TPI

-Flowmaster Catback
-Performance Resource Chip
-700R4 (Rebuilt) Too much done to actually list
-K&N Airfilters
-Ported Plenum
-2.77 Gears (not much to brag about but eh, its there)
-MSD 8.5 mm plug wires
-Problems every other day with the car (probably not a mod, but to me it sure makes a difference)

 

I get about 15 on My Lg4, But Im Running a Mech Qjet from a 74 Truck.



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60 Ranchero - Project ( Money Hole )
85 Sport Coupe LG4 - Daily Driver

Just another Hot Rod kid, or thats what they all tell me.
Livin' the Stereotype

 

My 305TBI gets about 25mpg on hwy trips doing anywhere from 55-130something(hooked up the switch to the vss). I do a lot of speed changes as it gets boring going 65 for hours on end. In town, I avg........I don't know but it not good, I like to drive it like I stole it . BTW, it's got over 98k on it.

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http://albums.photopoint.com/j/View?...781&p=29492901 http://albums.photopoint.com/j/View?...781&p=29492902 http://albums.photopoint.com/j/View?...781&p=29495767
"DriveHarder"
Stock 305TBI,
Eibach Sportline Springs,
Koni Struts and Shocks,
SSPE lower control arms and Panhard bar,
Hellwig Rear Swaybar and Energy Suspension bushings.Aluminum Driveshaft. Posi-rear

 

I have a 383, 30 lb injectors, solid roller cam, 255 lph fuel pump, 4.10 gears and get 20-22 mpg on the highway. Not bad , huh? Don't ask what I get around town, though. I could show you on less than two hands. I think thats a tuning problem though. Nice job keeping your engine alive for 300,000 miles. I'm trying to break 200,000 on my 2.5 Iron Puke S10. Still runs strong and can chirp in fourth gear if the moment is right.

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1992 Camaro Z28; Engine:383 w/Edelbrock RPM ported heads. Lunati Solid Roller Cam 224/232 .502/.502, Fluidampr, 1.5 Roller rockers, 30 lb injectors. Haltech E6GM DFI, SLP 1 3/4" headers, 4" Mufflex, T56, 4.10. Super Ram.

Mo steel for Mo stremph!

 

with my nonCC carb and distributer, on top of a 350, i get 28mph on the highway doing about 70 (Manual Tranny). Now in the city, my best is 16 to the gallon, but my average is only about 9 (I like to play)..

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My 1986 Z28 and more!!
view my car (movie)

R.I.P Dale Earnhardt

 

i have 3 friends with tbi 305 camaros.. not a single one of them gets over 20 mpg ever, even when it's 100% highway miles.. all there cars are stock, and in great condition.. maybe it's the air in kentucky, or they are just redneks.. my cousin switched to tpi from tbi and gained around 4 mpg.. it's just intresting to see the gas mileage the tbi's are getting, I never thought they were that good.. might have bought one if I knew this earlier.. I saw one for sale for $1250 in great condition..


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My `91 Z28 Convertible

 

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I get an average of 15mpg from my 350 GTA. I do about 10 miles a day to and from work, about half and half rural and urban roads (with speed bumps.....arrrrrrgh!!). On a run I can get better gas mileage(or I can use my dad's car which gets me excellent mpg....even if it is a F**D!!!).
(I wish I could get 30mpg as gas is about US $4.50 a gallon here....oh the price of devotion!!).

 

I got about 25-27 when I had the 2.73s. After the switch to 3.42s that dropped to around 22-24. I guess that's pretty good with the mods I have.
bsa

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"If they do not run, Then they will die." - Stonewall Jackson
#3
'87 IROC, 355 TPI, Converted to SD, 700R4, B&M Megashifter, 3.42, Trick Flow Twisted Wedge Heads, Comp Cam, Crane Gold rockers, Lucas 23# injectors, Edelbrock headers, Flowmaster 3'' exhaust, gutted cat, Mallory coil, Mallory HyFire IV ignition box, Mallory Sidewinder 8mm wires, Autolite platinum plugs, K&N filters, Transgo Performance Shift Kit, Corvette Servo, 2,000 Stall Torque Converter