I know people are always asking about how to get better fuel mileage, just wanted to share my recent mpg's. I just drove from Norfolk, va to middle tennessee, a lil over 700 miles. I averaged 27 mpg for the whole trip in my 1990 camaro rs, 305 automatic. So good mileage is do able without buying a new car.

 

Doesnt surprise me, my 91 rs average between 20-23mpg with the 305 auto. I still have a vacuum leak, maybe I should get it fixed to achieve your 27 mpg lol. I assume it's completely stock?

 

Not completely stock, hooker headers, smog pump and cat delete, a/c delete, tbi spacer, fuel presure set to 13, hot chip from tbi chips, thats about it. I usually get 20 to 22 with mixed city and highway. I never expected to get 27 on straight highway though, and that was goin over the appalachians to.

 

Doesn't surprise me at all. Some of these 80s cars were geared/cammed/etc to get very good mileage for their size. I had one of those land barge Cadillac Fleetwood Broughams with the Oldsmobile 307 in it that would get an honest 25-27 mpg on long road trips. I kept that car in good tune and stayed out of the secondaries on the highway and it would do remarkeably well for a carbed car. The swirl port head, roller cam 307, 2.53 rear gears + 200-4R overdrives .67:1 ratio all certainly helped.

 

Steady highway speeds with good aero and tall gears = good mpg. I got 28 with my '87 Firebird 305 carb 2.73 700R4. Current '91 TBI with 5speed and 3.23 gets 25mpg hi-way with the A/C blowing.

 

I used to get 27 highway before I swapped in the 3.42 rear.

 

bigreed91 ,What Kind of spacer are you running?

 

If i remember right i bought the jegs brand spacer for the 1986-91 trucks, part #555-15400, i also bought the fuel line extensions but i didnt need them. I wish i would of bought the injector spacer, part #555-15410.

 

I have a 350 tbi from an 89 suburban in my 88 trans am. 700r4, headers, custom 2 1/2"-3" exhaust, 15psi fuel pressure, k&n air filter, aluminum drive shaft, custom tune on a 7427 PCM. i get 19-22 in town and 27-29 on highway trips from southern to northern Idaho. Stock gears, which i think are 2.73?

 

With my t5, hooker headers, 3 inch exhaust+cat delete, and 3.08s and windows down and t tops off I got 27. Now with the 3.73s im probably getting around 24, can't really tell because i haven't measured it out yet, along with fixing the speedometer to read correctly

 

Did 28.7 mpg at speed limit from Tacoma to Spokane (across snoqualmie pass) with a medium light foot and a passenger.

Did 24.8 mpg at 110-125 in od driving back halfway from Spokane to the Columbia river.

91 rs stock gearing, lockup converter, towing biased rebuilt 355, Non Cop Caprice injectors, performer intake, stock temp tstat, good cat and muffler, tuned by moates

Fresh battery gained me mpg in town fwiw

Edit: the tranny was rebuilt by my dads buddy, old pro now passed on. He installed the corvette servo, HD bands and such, an s10 converter that stalled a bit higher than stock but still locked up, and what he called a poormans cyclone style valve body, and warned to never shift from r to a forward gear without completely stopping. He also installed the near wot od mod.

Any idea what this valve body mod is? I'd love to learn more.

 

110-125 mph? You mean to say you ran your car at essentially WOT for like 2 hours? If that's the case, not only do I think your mpg claims are not accurate, but in what world would that kind of use be good for any car?

If I'm reading your post wrong then by all means clarify.

 

No where near wot man, bareley more throttle input than 80. Before I disabled the speed limiter in the chip it would hit the stock limiter near the top of third, or at about 2600 in OD.

 

Car pulled to about 145-155 at wot, used to street race in kent. The car isn't much in a drag race but on the freeway ran with s2000s m3s and nsxes. Edit: <----that's how I assume 145-155, I wouldn't go faster than the BMWs because they were all limited to 155 (which I understand to be the limit of stability on a stock height tg)

 

So we have two tbi 350 swaps claiming up to 29 mpg. Has anyone calculated 30? And what's the story if you did?

Word is swapping to a truck ecu gives additional economy options to play with if you've done this chime in!

 

LO5 swap here. I'm running it with EBL Flash, best I've got was 28mpg on backroads cruising at 60mph. City is more like 15 lol

 

I hit 31mpg with a stock LO3/auto years back. Thats 100% cruise control interstate on level ground for hours on end. Usually low 20s mixed and 25ish highway before the engine swap

A LO3 T56 and 2.73 gears would get even better mileage with the second OD

 

I calculated 30 even with an LG4 and T5 driving 80 ish with my only cruise control being my right foot. Mind you, a good hour of the 3 hour trip was through the Ozark mountains.

 

How did you go about getting around the SMOG delete in VA?
I've been nervous to register my car because of that.

Emissions people can be mean.

 

110-125 MPH can be reached by most vehicles in overdrive with not much throttle. Out in west TX I have run some of those roads at 100-110 mph for hours on end in my old 350 powered Express van. I still get about 16-17 MPG running that speed and I am running about 3,400 rpm @ 110 in overdrive. I get about 19 mpg @ 75-80 mph in the Express. At 110 mph in OD it takes about 30-40% throttle to maintain the speed.

Last night I drove home from San Antonio on I-35 and ran 80-90 mph with traffic most of the way home. I was averaging 18-19 MPG in my 5,800 lbs Nissan Titan 4x4 and usually only average 16-17 at 65-75 mph. Some engines that are in undergeared vehicles get better mileage at higher speeds. The Titan runs about 2,600-2,700 rpm @ 90 mph using about 1/4 pedal.

 

Ive hit 29mpg a number of times doing the Boise valley-Moscow trip here in Idaho, never could get 30 though. i used a 7747 ecm from a truck and used the lean cruise but didnt go all out on it. I switched to a 7427 pcm which has a commanded AFR option in it but without a wideband im too afraid(smart) to use it to its full extent. I still got 29mpg with the 7427 but ive always been a grandpa driver on the highways. Too many cops around and i dont need the attention.

That being said, ive hit 110-125mph+ a few times and it was nowhere near wide open throttle. Thats with the 2.73's. I imagine the tires would fly apart at WOT cruise pretty quickly.

 

The best mpg I've gotten with my 89 Formula 350 was 27 all hwy (iirc the gears were 3.27's).
And highest speed reached 163 mph, ran out of road, speed was still slowly climbing!
I hit 4,900 rpm in overdrive. And because the speedo ends at 140, extrapolating the speed was easy 3,000 rpm = 100 mph, so 4,900 / 30 = 163.3.
That blue Corvette that provoked a top speed run must have been surprised when I pulled so far ahead of him!
Only thing that really scared me at that speed was the look of my fiberglass hood.
It looked like if was gonna be ripped off any second.

 

For some reason, when you said the tires would fly apart, I laughed my *** off. lol

 

Why? If the tires are not speed rated for sustained high speed operation, tire failure is a very real possibility, and a reasonable concern.

 

Oh I know! I wasn't laughing cause it isn't true. I am laughing because I just pictured all 4 wheels blowing apart at once lol.

 

Gotcha.

 

I got 30 on my way to Connecticut from north Carolina new fuel pump injecters and tune up just did ignition system can't wait to see if it gets better