This is in regards to my '89 IROC (see sig).

I'm not very experienced when it comes to gas mileage--I've just been happy to only need to fill up once a week under normal driving conditions. However, I've just recently started taking my IROC on some trips lately between College Station and Dallas.

I've calculated my mileage on this trip several times, and I keep getting about 20.5 MPG with an average speed of 75 MPH to 80 MPH.

I know that might not seem that disappointing to some of you guys running different setups. However, I'm running a "stock" L98 engine--it has been rebuilt, but it wasn't a "performance" rebuild. Plus, I've got a 2.77 rearend, which means that I'm not even pulling 2,500 RPM the whole time (according to the stock tach).

I could be wrong, but doesn't <21 MPG seem pretty sad for a mild, fuel-injected V8 with an overdrive transmission and 2.77 rearend?

Feel free to correct me if I'm wrong, but if this is bad mileage, what could be the cause?

Thanks!

 

TPI isn't as fuel efficient as some other injection systems... That doesn't seem bad to me, though I'm sure some other people will be able to give a better answer than that.

 

if you cruise around at really light throttle for a short while and then lift all the way off, does the engine speed surge?

if it does, try replacing your EGR valve.... that helped me a good amount with my gas miliage... i already had the car in a great state of tune... but the valve still helped alot..


i would start with a regular tuneup, and go on from there.

 

That's not really all that bad; TPI may not be as fuel-efficient as some of the newer control systems, but it's alot better than some others.... you're not too far off of its OE specs which IIRC were about 23 mpg.

Now if you were getting 11 mpg on the road, you'd have something to complain about.

Correctly functioning EGR will alow the maximum possible timing advance, which (along with correct misture) is where highway mileage comes from.

 

Your right on target new they claimed about 15-17 city and 20-24 hgy depending on year and exact setup so your not far off, One of the pains of living with this car in California.

 

just another confirmation, I have a stock L98 and get 21-23mpg on highway..

 

I guess this is the only time a TBI Camaro will win, in the MPG contest, I get 28-31 Mpg on the Hwy!!!

 

Wanna sell your IROC then?

 

hey i have tpi and net 28-29 MPG highway so no sniff here on the tpi.

 

I have a 86 L69 Iroc with 4 speed auto and 3.23s, Its TPI and I got 33 MPG with it on the highway.

Digger

 

lmao! yup... i got a tank of 33mpg on my road trip from dallas to charleston, SC

 

10 mpg here....

 

Mileage has alot to do how hard you have your foot into it. The harder you drive your car the more gas you will use.

 

ha think you got it bad try this ****... 91 LO3 TBI camaro, stock rear with like 2.23 or somethin i believe, automatic with OD... i was getting 8 or so in town, 12 on highway... i mean i tried my damndest to get the best mileage i could and thats it.... i switched it all to carburetored, and believe it or not i gained gas mileage... about 15-17 on highway... go figure.. but don't feel bad for gettin that with stock setup

 

Yeah, I got 17-18 mpg highway when I had my red bird (355 E-tec, Performer RPM, 800cfm Edelbrock carb, 3.08 rear gears)... That was with the lockup switch on the whole way!

Oh, I think your TBI was broken then..

 

If you cruised at more like 65-70 MPH you'd likely see a better number.

 

Driving 2 miles round trip a day(w/ 5 stop signs) gets me 7.5MPG but I get 21-23MPG on the highway like I said in this post 5 months ago

You make it sound like lockup hurts gas mileage, if you have a 700r4 that locks up and you dont lock it up, itll burn up quickly

 

damn... with normal driving conditions (hitting it once and a while) i get about 12 mpg in the city... im sure if i baby it i'd get 15. highway gives me about 16-17 i think but im always flying... hopefully i get better milage on my rebuild, lol

 

my neighbor's moped gets like 80 MPG!! OMG but it only holds a gallon....but still...pretty cool

 

I didn't mean to make it sound like that.. I meant for it to read as thats why I achieved such high numbers!!

 

A 700r4 will not burn up without lockup if it has a good cooler. I just hooked the lockup back up no my 1983 G20 van after it had been disconnected for who knows how long. Wired a 2 way switch so that it will lock off the vac switch or just locks after 2-3rd shift and stays locked. The point is I have never heard of a 700r4 burn up by not locking up unless it is on the verge of failing anyway.

 

 

Over 60k on my previous 700r4 without lockup and a stock converter. Never worked at all. Transmission never burned fluid or slipped, or had any shifting problems at all. Problem was inside the transmission, probably lockup solenoid. Drove it until the case split 3/4 around the bell and vibration got so bad at high RPM's I was afraid it was going to fall out.

It had a LARGE aftermarket cooler and didn't use the radiator cooler at all.

The present 700r4 doesn't even have lockup in it but neither does the Vigilante converter.

Oops, I think I just inavertently helped hijack this thread. Sorry.

BTW, I got about 15 in town and 20 hwy in a '89 GMC with compeltely factory '88 TPI, (except that lockup never worked). Now I'm back in the thread!