from the factory what were the '89 L98's mpg? what does everyone actually see?

also what octane is recommended for the L98?

im a 4th gen guy, don't know many details about the torque-monster known as the L98

thanks

Jon

 

I run super, I belive it has a factory 6* initial advance, so you better run at least unleaded plus, super if you live where is is really hot. As a matter of fact, I don't have a factory manual, but I thought the L98's required super unleaded. I know the vettes did.
I think the L98's should get 24-28mpg on hwy depending on speed and gears. Intown I'm not sure, bt my 305 in my camaro gets 12-14 in town.

 

thank you for the responce.

so NO ONE else here has a L98 motor and knows what kinda gas they put in it/suppose to use? and what kinda milage they get?

i was hoping for a few responces....

Thanks

Jon

 

It depends on how clean the engine is too. If you have a lot of miles and carbo build up, use super only. If you reguarly use GOOD fuel system cleaner, thenyou have less carbon deposits in your engine and it will have less of a tendancy to knock.

 

TBI works,

thank you once again for the responce.

Jon

 

My 89 Corvette gets 21mpg and I use 92

 

I have an 88 L98 and I average about 22 mpg on 89 oct.

 

I believe from the factory they recommend 89 octane and the EPA ratings were along the order of 16/26, give or take a few mpg. Corvette L98's have higher compression and some (like mine) came with manual trannies so they recommend premium for them. You will get the best gas mileage and best performance by running the lowest octance gas without running into preignition (detonation, ping, etc), so i run 87 with no problems in my gta because right now she could use both!

 

thanks guys

Jon

 

Well to be exact GM called for 91 octane.

Dave

 

89 L98, pure highway driving with regular gas, right at 25 mpg's..w/2.77's...mpg's go down to the 12-14 range in pure stop and go driving.
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Oh yea, I have the window sticker somewhere, maybe if I cme across it, I'll repost what was on it.

 

I don't know if an '87 is the same as your '89, but page 2-6 of my manual for the 5.0 (F) engine and the 5.7 (8) engine says:

Your engine is designed to operate on premium grade unleaded fuel. However, with the electronic spark control system, you may use regular unlead fuel at slightly reduced acceleration performance.

I guess that's why our engines have knock sensors.

I get 17-18 mpg city and 23 hwy MPG.

Hope this helps.

Rick

 

1990 Iroc L98 ( I think the axle gearing is 3.23 or 3.27 )and a daily 60 mile commute to work( 23 miles of freeway at 65 to 80mph and 7 miles rural/city with stop lights and stop signs) 76K miles on the car and I have been averaging between 19 and 20mpg running all 3 grades of fuel 87, 89, and 91 or 92 ( I did notice pinging a few times going up a steep grade with 87 before I changed out the plugs, wires, coil, and cap and rotor ).

 

thanks guys, if anyone cares to know why i want to know is b/c going to look at a wrecked '89 iroc w/L98, my buddy wants the engine for his fiero. should be mad fast car w/ that engine...

since we really don't know much about the L98, thought start w/ basics such as gas, and milage etc. (i do know some about the lt1 (have a '94)....)

once again thanks.

Jon

 

I used to get like 24 High way mpg or so using 93 in my 89 RS w/ a 305 TBI. it was good. Now w/ my 88 IROC lol I swear i get 19 or less on the highway. Still using 93. I use 93 out of habit, or a fool sense of reassurance thats its probably a better quality gas I think i could run 89 just fine. even 87.

 

Check the sig.. I avg 20mpg on a working commute city/hiway mix 50/50 and I haul A$$. 25 on hiway trips avg 75mph. Thats with mid or 89. With high test I do a little better (1-2mpg) but better pwr. What I use depends on price or if I want to race.

 

Mine probably does have the same recommendation as yours does, but even when I hammer on it with 87, I get no ping or knock detection.

Could be because of the "Ca. emissions"? My understanding is that the EPROM is different for Ca Emissions, might be spark tables are difference...hence the reason I don't get knock/retard...I dunno, but at a $1.55 a gallon for 87 and near $2.00 a gallon for 92...mine'll live on 87 for a long time

 

Last I checked 89 octane was recomended for for an 87 iron headed L98. The aluminum headed corvette version needed higher octane due to higher compression. I've run 89 on my car with no trouble at all. Car runs nice and clean, clean enough to pass emissions without a cat. No knocking no pinging and believe me this car takes abuse.

 

Well I don't know about 89 but my 92 manual
calls for 91 oct I get 24 mph on the beltway.

 

SHEEEET....someone should run at the strip 5 times or so on 87 then go back and run 5 more on 93. Start with 1/4 tank 87, run it down, then go with Premium.....If you need to mix the gas just be sure to fill up with Premium...that should give you something like 90, 91 or 92, depends on how far you run it down......

 

I got the L98 in my 89 IROC, but I get sh!tty 10 mpg around town and stuff, with lil highway. If I do a lil more highway I get like 16, but my car isn't exactly ''in tune''.... yet!

 

i get an average(about half in-town and half highway) of 12.5mpg with my 350TPI/th350 tranny and 3.42 gears.

 

HMM I just read my manual for 89 and it says to use 87 for both LB9 and L98. I've alwasy used 87 in my Formula 350 and get about 23-24 mpg. I find it to run better on 87

 

Hmm I don't have a manual, the prev owner said he would mail it to me, so much for that, never got it If thats honestly true I'll get 87 next time, I just don't want my engine to knock though.

 

My L98 has got 67,000 miles on it with a 700R4 and 2.77 rear end and I pull down 16-17 mpg in town and 25-28 on the freeway running 87 octane fuel. Personally I couldn't be much happier.

Ryan

 

well I got a 89 L98 Iroc, and I did my mileage awhile back, I use to go from tampa to FSU in Tallahassa, it was like a 4hour trip I could just make it to the Tallh. exit before I had to get gas, I had 2.77 gears back then, and did 75 the whole way on crusie control, with one bath room stop, and it was something like 21mpg or 22mpg, could have been a little more, its been like 3 years ago. I believe I was all stock back then well pretty sure, but anyway I had like 70 to 80,000 miles, one the motor, back then. Oh I use highest oct.

 

My '88 Vette gets 31-32mpg highway (2.59 gears) and the '86 IROC pulls 25-26mpg highway (3.45 gears).

The gears and weight will make the difference.

I run 92-93 octane in both cars because the timing is at the max for performance.

 

I get about 13mpg mostly city with 89 octane and 3.27 gears

 

I get about 4-6mpg at 150mph plus.
I also get about 22mpg if Im sane. I have gotten 27mpg a long time ago when it was just a cold air,header, heads, ported intake and cat back (mild bolt ons).
3.27 gear in 9bolt

 

I have to refuel the car about every 220 miles. like 70% of it is urban driving and 30% on highways. I use only 98 or 99 octane fuel. In finland the "worst" gasoline you can buy from gas stations is 95 octane.

thats about 16mpg on 98 octane. Not that my car is completely stock though

 

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