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GLHS592
07-04-2008, 08:47 AM
Skip the 1st paragraph if you don't want to read a rant...

It looks like high gas prices may be "parking" my state vehicle that I was promised when I took the promotion 3 years ago. :mad: They use that promise to get people like me to drive 50+ miles to Nashville to take these jobs because the salary increase isn't that great, but that's another story...

The good news is my sister-in-law graduated, got her first job as a registered nurse, and has money burning a hole in her pocket. When she gets her new car, she will be giving me her 1994 Dodge Spirit. What kind of gas mileage should this car get? I'm guessing around 30 mpg. Would gutting the cat and bigger exhaust help with the mpg's? Is there anything else I can do for better mileage?

2.216VTurbo
07-04-2008, 10:58 AM
WooHoo, 94 Spirit Kevin:eyebrows: You're gonna be rolling hard in the thing;)

Anything that improves volumetric efficientcy of the motor will improve milage, free(er) flowing exhaust-yep. Freer flowing intake/air filter -yep. Ported and polished head-yep. The 'first' TM motor I built was in my GLHS in 1989. I worked a deal with a local speed shop ( Hughes Machine in Searcy Arakansas:) Builders of Bill Mavericks "Little Red Wagon' Wheelstander's motors) that if I swept the floor and did other meanial tasks, they would provide tools and experience to help me build up the motor. These guys were kinda old school and had never messed with any turbo 4 stuff. We tore the motor all the way down and Max showed my how to port the head/manifolds, we put larger exhaust valves in (nearly as big as the intakes:eek:) we took nearly 90 grams off each rod by grinding/polishing the casting flash off the beams (stock lightweight rods:wow1:), opened the exhaust and airbox up and reassembled the motor with STOCK turbo, STOCK injectors (back then, no one knew anything about upgrading the things that are second nature today:() Whole build took about 4 months as I was learning how to build 2.2's. We were trying for power, but it suprised the heck outta me that the milage went from about 27MPG to 32MPG:clap: I did get the car from 9.40's to 8.99. Rocketship fast I know:rolleyes: but it was 1989-90 after all;)

tryingbe
07-04-2008, 12:29 PM
Auto? Not much.

WickedShelby88
07-04-2008, 12:41 PM
depends with the auto if the lock up TC works. If its stick your golden and can easily average 25-30. Oh and with an auto though in town will suck, but on the highway won't be bad. My 89 reliant sucked fuel and was a turd and I never could figure out why being as it was a TBI car but it had the auto and at the time we had to do more in town driving than not.

overlordsshadow
07-04-2008, 01:15 PM
Will a clogged cat cause bad gas mileage or rich running? Just got a 90 shadow TBI and it's a real dog. Codes say I'm running lean, but black soot smoke says no?

moparzrule
07-05-2008, 05:08 PM
Will a clogged cat cause bad gas mileage or rich running? Just got a 90 shadow TBI and it's a real dog. Codes say I'm running lean, but black soot smoke says no?

Probably have a dead O2 sensor.


As for better mileage with the TBI, I'd go for a good tune-up first with new plugs/cap/rotor/wires, KN air filter, 2.25'' mandrel or 2.5'' crush bent exhaust with a high flow cat and whatever muffler, throttle body spacer, underdrive pulley, and whatever you can do to loose weight from the car will help too.

raccoon
07-05-2008, 05:49 PM
http://www.auto123.com/97photo/pontiac/firefly3dr3dr-base.jpg

problem solved, and others created... like your now non existent social life. lol

GLHS592
07-05-2008, 07:58 PM
It's an automatic. Mom and dad had a 1989 2.5 TBI Spirit with a 5 speed. It consistently got a touch over 30 mpg on the highway.

Vigo
07-07-2008, 11:06 AM
my 2.5/auto tbis have gotten 25+ city and right around 30 like 31 highway. best thing you can do for mileage is 5 spd swap and drive it easy, but with auto i would contentrate on making sure the airflow in and out is ok (only to the point where the tbi tb and manifold become the choke point, and then give up!) make sure the lockup converter is working, and the tires are aired up high. past that its just how you drive it. you should be able to do 30+ on the highway easily.

contraption22
07-07-2008, 11:11 AM
I have a 93 TBI Acclaim. I get about 16-18mpg in my abnormally heavy city traffic commute. But its a bit better on the highway... I wouldn't expect better than 25mpg on the highway tho.
I can maybe eek out 30mpg if I stay around 60mph. The thing really sucks gas when you go faster.

I'm thinking about chucking the cat and seeing if that helps. I do not want to make the car loud at all.

tvanlant
07-07-2008, 02:11 PM
I was complaining about my 92 Spirit's mileage this winter, but has gotten much better now that it has warmed up.
My last six tanks have been between 27.2 and 29.7. The lower one was around 50/50 city/highway, and the best tank was around 20/80. I do 75 mph on all my highway driving.

I have the stock cat with 145,00 miles on it, and a bone stock 2.5L automatic

I have also been tossing around the gutted cat and ported head idea, but I figured 29.7 mpg in a somewhat heavy, large 4 cylinder with 145K on it is pretty good.

85shelbycharger
07-08-2008, 01:39 PM
My '89 Omni with a TBI/auto is getting 33 mpg highway going back and forth to work everyday.

moparzrule
07-08-2008, 02:01 PM
An Omni will definately get better mileage as you aren't moving as much weight around. A spirit weighs atleast 500 more pounds, atleast.

contraption22
07-08-2008, 02:33 PM
Agreed. I drove a carbed '87 Omni in college and that got over 35pmg.

Vigo
07-09-2008, 05:12 PM
my 86 lebaron convert 2.5 tbi/auto got 26-27 avg with mixed driving.. i usually drove it between 75-80 on the highway though and could still get 30 and that was an 86 without a lockup converter.. breaking 30 on the highway should just be a matter of making sure the thing is actually running right..

contraption22
07-10-2008, 10:37 AM
Just filled up this morning. Just a hair under 22mpg, and that includes a 260 mile round trip to the beach and back last weekend. Something ain't right. I still need to put in that new 02 sensor.

Vigo
07-10-2008, 12:44 PM
one time my mileage went from 29 to 22 cuz of a bad connection at the speed sensor :/

RoadWarrior222
07-10-2008, 02:01 PM
If it's the A413 shift kit it. Tighten up the line pressure a touch, fill with UTF

The aerodynamics suck, but folks on allpar report a 2-3mpg increase with a 2inch drop on the front.

Air the tires up to the max on the sidewall.

Drive between 2000 and 3000 RPM as much as possible, engine is in it's best torque band there and tranny hasn't got so much slip. i.e. give it 2000 rpm when setting off and hold it until you get up to speed, lift right off then ease the pedal down until you're just maintaining. Unless you're on the highway with the TC locked, in which case ease back real slow until your feel the speed drop slightly then just touch it back again.

Fit new PCV valve. If it's using oil, use a 5W30 "high mileage" oil, if it isn't use Walmart/Supertech 0W30

Tony Hanna
07-10-2008, 02:50 PM
Skinny tires and keep 'em over inflated, swap to a 5 spd if it's an auto, and/or swap transfer gears for a higher (numerically lower) final drive ratio, use the nb output on a wideband to fool the ecu into running the engine a little leaner, advance the ignition timing to the point where it spark knocks slightly then back it off 2*, rework the intake plumbing so that it's drawing hot underhood air, lighter wt. synthetic oil, and anything else you can do to reduce friction (loosen rear wheel bearings slightly, etc).

overlordsshadow
07-11-2008, 12:19 PM
How can you tell if it is spark knocking?

RoadWarrior222
07-11-2008, 02:52 PM
It "pings" which is like "tink tink tink" as opposed to detonation which is like someone smashing at your pistons with a BFH

Tony Hanna
07-12-2008, 05:15 AM
^ That's it exactly. I wouldn't ever suggest the ping point minus 2* method for a forced induction car but it does ok for a naturally aspirated engine. The extra timing advance helps the engine make a little more low rpm torque which translates to slightly less throttle to hold a given speed. It's good for a slight increase in mileage.

TurboJerry
07-13-2008, 02:51 AM
I removed the cat, 2 1/4" exhaust, advanced the cam timing 4 deg, used a higher stall neon LU converter, and also put an L-body TBI air filter on it with heat blocked (but left the coolant to the intake though) when I had the TBI auto setup. It got 22 on the street and got 29 on the highway. I could go to SD and back on a little more then a half tank.

RoadWarrior222
07-13-2008, 11:07 AM
I don't see how a higher stall TC did anything for mileage.

moparzrule
07-13-2008, 01:28 PM
Higher stall would hurt mileage not gain mileage.

contraption22
07-13-2008, 01:33 PM
Higher stall would probably help to put the engine in it's torque band so less throttle input is needed for acceleration. Stall speed won't matter once at cruise because we are talking about lockup converters.

moparzrule
07-13-2008, 01:41 PM
It won't make it lockup at a higher RPM?

We had this discussion before anyway in a different thread. Better to have more throttle but less RPM's than higher RPM's and less throttle.

RoadWarrior222
07-13-2008, 02:43 PM
As far as I understand it, on a 2000 stall convertor, you've gotta give it 2000 RPM before you're getting 90% of your power to the road, and on a 3000 stall convertor, you've gotta get it to 3000 RPM, before you're getting as much as 90% to the road. Otherwise you're just toasting fluid and getting fractions of the motors output at the wheels.

contraption22
07-13-2008, 05:53 PM
It won't make it lockup at a higher RPM?

We had this discussion before anyway in a different thread. Better to have more throttle but less RPM's than higher RPM's and less throttle.

At cruise or when you are trying to accelerate a heavy load?

TurboJerry
07-13-2008, 08:09 PM
As far as I understand it, on a 2000 stall convertor, you've gotta give it 2000 RPM before you're getting 90% of your power to the road, and on a 3000 stall convertor, you've gotta get it to 3000 RPM, before you're getting as much as 90% to the road. Otherwise you're just toasting fluid and getting fractions of the motors output at the wheels.

Yeah, but it requires little throttle to get 3000 rpm. With 1900 stall, it seemed to require a fair amount more throttle like running the 2.60 final drive. you're actually lugging the engine less with more stall *sometimes*. The car felt lighter with more stall even though it revved higher before moving.

Vigo
07-18-2008, 11:08 PM
lower stall will give better mileage if you drive soft enough. however, if you are mostly looking for highway mileage, higher stall may improve your driveability in town with no loss of highway mileage due to the lockup. i have two vehicle with higher stalls in them right now (3.5 intrepid and 3.0/670 caravan) and i wouldnt recommend them for mileage.. they definitely come off the line harder tho, if you have low power and not much traction problems.. the intrepid would go up in smoke but the caravan is definitely stronger off the line without traction problems cuz its still WAY heavy and tall gears.

Tony Hanna
07-19-2008, 01:58 AM
It won't make it lockup at a higher RPM?


Nope. Think of it like this: When it's unlocked, it's slipping. Quite a bit for a high stall converter, but when it locks up, it's 1:1 through the converter. With a stock converter, you've about gotta be looking for it to notice the drop in rpm from the converter locking up, but with a high stall, I bet it seems like catching another gear due to the larger rpm drop between unlocked and locked.
The point that the converter locks up at is usually controlled by the computer so it will be the same regardless of converter stall.

moparzrule
07-19-2008, 06:16 AM
OK I see. Sounds like Vigo has the experience with high stall and mileage.