Ok... lets see here. I recently was looking on eBay for 3rd gens (I just do it from time to time, just like to look) and noticed that one of them was a 1990 Camaro RS with the L03. It had the window sticker and on the EPA Fuel Mileage estimate for the highway, it said 27 MPG.

Now, I know my car is over 15 years old now, but what can I do to acheive this? I have already replaced my Rotor, cap, spark plugs, PCV valve, fuel filter, and my air cleaner and breather element.

What else can I do to get better mileage? I have the stock intake back on and driving pretty much 80% Highway I usually get about 22 MPG. I do drive at about 80 MPH though. I doubt taking it down to 65 will yield 5 MPG better though. What else can I replace to get as close to 27 MPG as I can?

 

Actualy it will yeild a totaly different gas milage. Speed has less to do with your gas milage then engine RPMS. Lower RPM @ high speed is best scenario. I would go T5 or T56 if you want wicked good gas milage.

 

I understand what you're saying but just a 250 RPM difference will make my car go 5 less miles per gallon? Because with 2.73s I notice at 80 MPH i'm right at about 2000, maybe 2050 RPMs, and at around 65 i'm at about 1800-1900.

I don't doubt you but just making sure what I think you're saying is correct.

 

If you ever drive an instant MPG reading car like the newer corvettes or...well actualy most new cars... Its actualy very surpising what 500RPM will do. Changed my driving habbits right away.

 

Well there's no way I could drive 65 here in Southern California... i'd get killed.

Would a new O2 sensor and/or spark plug wires do anything? I haven't changed either in the life of the car but a visual inspection shows that both components aren't in dire need to be replaced.

 

Using my fuel mileage calculator (old ICE homework) for a stock LO3 car with 2.73's I get 27.5mpg at 60mph. This is assuming a flat smooth road surface with no head wind. Ambeint conditions will affect this greatly. However, this seems about right given GM's rating. The best thing that you can do to maximise your mileage is to keep your car in a good state of tune. Keep your tires properly inflated and go easy on the loud pedal. Use your cruise (if you have it) to prevent short surges at cruising speeds. When my T5 LO3 was stock I would get 31/32mpg on all highway trips. Simple intake and exhaust mods can also increase your mileage.

 

go easy on the loud pedal

 

I have a 2004r tranny, in a malibu wagon, BBC TBI, cammed vortec 330/350 and 3.73's, just drove to virginia, 250 miles, @ 75 MPH, I got 17 MPG. Just for reference, the engine has 5000 miles on it.

 

Yep. I had a few screenshots showing MPG vs. TPS vs. RPM vs. VSS in my Van with the EBL, but Rbob requested that I hold off posting them due to some changes he was making.

It is amazing how bad fuel economy can get with as little as 1/2 throttle. It is directly related to engine vacuum. Less vacuum=poorer mileage. Learn to stop driving by your watch and by the vacuum gauge instead. Often times you will find that by slowing down even just a little, not accelerating quite as hard, and keeping the vacuum above 0, you will improve you mileage greatly.

My 5 mile trip to work consisting of a 30-50* cold start, 30 second warmup in neutral, a back down the driveway, 4 traffic lights in 2 miles and 3 miles of 60 mph freeway traffic was getting 12.7 on the way to work (uphill w/ 1 long light to cross the divided main road). My return trip is mostly down hill, and I get to make a right turn at the long light gets about 13.4. I was averaging about 13 so it is about right. My big cam in the 305 was not helping things at all.

The STOCK L05 should get better mileage as I will be running lean cruise as well (Big cam didn't take to kindly to it).

 

Not to be a pain. But...... Speed has *LOTS* to do with gas mileage. Assuming everything else equal (tire rolling resistance, engine efficiency, etc), the torque acting against the vehicle goes up by the square of vehicle speed. Here's a site that shows the calculations : http://www.insideracingtechnology.com/tech102drag.htm

I'm not saying keeping your vehicle in a good state of tune is a bad idea (nor is taking it easy on the throttle). But, you can quickly see how much of a potential difference there is between fuel consumption and vehicle speed from the math......

 

Torque curve has alot to do with fuel mileage as well. I used to get better mileage doing 75 than 65 with 3.08 gears. The engine did not make enough torque at the lower revs to pull the load, at the higher rpms I was into the throttle less.

 

any time you make an engine more effiecient you will get better gas miliage. Think of this; a motor is esentially an air pump, and the easier it can get this air in and out will yeild better gas miliage, not to mention more hp. Stuff like an open element air filter, headers, less restrictive intake, bigger exhaust, ect will give you better gas miliage.

 

In almost any vehicle, best highway mileage is obtained at 55mph.

 

well except in most of our camaros with 2.73s and 700r4s that is. It's pretty tough to keep mine in od while maintaining a steady 55mph on inclines.

I'd be willing to bet all money i'd get better milage at 65 than 55 because, i'd have to keep letting it downshift in this area without going faster.

 

i think i get exelent gas miliage at 35 mph, because around that speed its in 4th gear and locked up doin no more than 700 rpm

 

Wow..... What the #$%^ did we fall into, here? OK, I'll play, too. My car gets *identical* gas mileage regardless of tire pressure, engine size or vehicle weight when the engine is off and transmission is in neutral going downhill........ Under these conditions, my V8 is every bit as efficient as ANY 4 cylinder out there.......

Wait, there's more. Let's assume we're going in reverse. A 4 cylinder can go 20 miles backward (i.e. negative) on a gallon of gas while a V8 can only go 18 miles backwards. The 4 cylinder is getting -20 MPG while the V8 gets -18 MPG. The V8 is now more efficient than the 4 getting 2 MPG better mileage.......

OK, I'm done now.

 

Wtf did that have to do with gearing and optimal traveling speed? Dunno why you quote me out of there but, if there was a reason it's way over my head????

I was just basically trying to let the guy know that yes there is a big difference in milage between small variations in speed..... in od on the highway with a 700r4 and 2.73s you're only pulling about 1450-1500rpms in lockup.... It's tough to keep the car going that rpm at 55mph on an incline....

Anyways like others have said though the power it takes to move a brick in the wind go's up exponentially so in a perfect world the slower you go the less gas it would use.... Then again whens the last time you drove a couple hundred miles going 30mph????

g/l with your gas milage man you will probably need it considering the speed you travel at.

 

I know. I have tried to slow down coming home from work, but I either get stuck behind a semi going 45 or I move over into a lane that's doing 80. I can't win so I just do 80.

I wish I could go slower but I just can't. It's impossible where I live. With 2.73s (3.23s on the way when cash flow comes in) I get about 23 MPG doing 80 all the time. It's not bad, but that's why I started this thread... to hopefully eliminate some variables and possibly get my engine a bit more efficient by the time I switch to 3.23s.

Which yields another question. In switching to 3.23s how much of a loss in MPG should I see?

 

I went from 3.08s to 3.42s in my T5 car and actually saw my around town mileage improve by 2 mpg (15 to 17 mpg). My road mileage dropped by 1 mpg at 80 mph, but remained the same at 70.

My understanding is that most modern cars are designed and tuned to cruise most efficiently at 1800-2000 rpm. Most newer cars you see will run at pretty close to 1800 rpm at 70 mph, the highway speed limit in most states. Last year, i drove from Atlanta to Tulsa and back twice in a short period of time. The first trip, i averaged 80-85 mph on the highway, cruising at 23-2500 rpm and got 23mpg. The second trip, I averaged 65-70 mph, cruising at 1800-2000 rpm and got 28mpg, so 500 rpm does make a difference.

Cruising at less than 1500 rpm for extended periods of time can be dangerous, by the way. Extended low rpm operation can cause the cam bearings to not get sufficient lubrication.

I love my 3.42s. i just got an Aussie 9 bolt to swap in for the rear disc brakes; it's supposed to have 3.45s, but I'm kinda hoping it has 3.23s; I think I'd like them even better.

It's important, however, not to get to obsessed with improving gas mileage. The average person drives 1000 miles per month. if a car averages 20mpg, that means it uses 50 gallons of gas per month (or per 1000 miles). At 2.25 per gallon, that's a cost of 112.50 per month. If you improve your average gas mileage by 1 mpg, you spend 107.14 per 1000 miles (based on 2.25 per gallon) only saving 5.36 per month (or per 1,000 miles). Yes, keep your car in good tune. Yes, keep your tires properly inflated, maybe even install a vacuum gauge and learn to drive as efficiently as possible, as someone mentioned earlier, but overreacting and spending a ton of money trying to get better mileage can easily cost you much more than you'll save with the improved mileage.

A buddy of mine just traded his Expedition in for a Mazda 6 which literally gets twice the mileage. Good idea, yes? No. Since gas prices are high, he took a huge pounding on his SUV and paid a premium price for his new Mazda. We did the math last week and figured out it'll take him 8 years to make up for the loss in gas savings, and then only if gas prices stay well above 2.00 per gallon. He would've done a lot better to wait until the current panic dies down and the value on his SUV recovers before making a change.

I remember back in the first gas crisis back in the 70s when everyone freaked out because gas was ober 50 cents per gallon ... GASP!!!!. Hot Rod ran a story on how to convert a V8 into a V4 to improve mileage. A moron buddy of mine spent hundreds of bucks doing it and ended up with a slug that got about 20% better mileage, but had no power and sounded like a salad shooter. within 6 months, gas prices fell considerably, although it never back to their pre-gas crisis levels, and he went back to a V8.

 

Wow, I think I only get about 12 mpg. That can't be right. The car runs pretty good. And I don't gun it that much. Hmmm...

 

Something's wrong. Do a full tuneup.

 

Something is wrong with your state of tune or something else.

Don't overlook anything.

I just averaged 20.6 mpg on a 850 mile highway trip (Corpus Christi from DFW and back) in a 350 powered 5,300 lbs brick with 3.73 gears, running the A/C and the cruise set at 70-80 most of the way. It was still $120.00 in gas though.

 

Trust me the car is always tuned. I stay on top of that. I just realized that you guys are all talking about highway miles. And I hardly ever drive on the highway so that may be why I'm doing so bad.

 

Damn, I got 18.5 MPGs with the 2.73s and now that I switched to 3.42s I'm getting 16.5 MPGs. I drive a combination of city and highway. New plugs, cap, rotor, tires properly inflated. I don't understand how anybody gets mileage in the 20s

EDIT: New wires as well

 

MikeDirntRulez:

Plug wires I would do as well - they aren't expensive, or hard to do.

A biggy I don't see in the thread is tire pressures - check them every week - 5 psi wrong on the tire pressure can make 5mpg easily. Get a good guage (not the $1.99 job on the counter at KMart) - and never trust the built-in guages at the pay-4-air-pumps.

 

FWIW, my Malibu wagon, 350 tbi, vortec heads, 2004r, and 3.73's, gets about 16 MPG highway right now. (tuning with the new EBL board) I may drop to 3.42's, and I am adding electric fans, with the new 17 inch rims/tires, I hope to get to 18-19 mpg and I'll be happy.

 

This screen shot was taken at the first stop in Hillsboro.

 

what program is that? I want that!

 

The EBL

 

Fast, I'll tell you what, I have to tuning to do yet if your getting that kind of mileage. lol. My junk weighs less.

 

Where do I get that?

 

I know right! Damn, maybe I should get new wires or something.

 

Take note though, this mileage number is on the highway, taking it very light on the throttle while accelerating, and using the cruise control to hold 70-75 mph.

I am also fighting much more frontal area than you are and therefore much more wind resistance.

I have the advantage of swirl port heads and a tiny roller cam with 1.6:1 rockers though.

 

I have a derivitive of the vortec 330 horse engine, with 9.75:1 compression and more cam (and n2o). I've been driving 55 miles to work one way, using light throttle, and have the highway more set-up to come on @ 45 mph, and haven't got any better. I have to fill my tank 2 times a work week. But the wideband should be coming soon, and the electric fans going in this weekend. So my mileage should increase some.

 

Your mileage will definately come up, just not to anything like it would with a stock type cam. The 330 hp vortec 350 had a pretty good sized cam out of the box. If it is bigger, then there goes your highway mileage. The stock cam in mine pulls down to 1,000 rpm in OD with the TCC locked and will pull away smoothly with a light touch of the throttle. Doing 65 on the highway I have around 15 in/hg of vacuum and about 2,000 rpm. Doing 75 on the higway I am making about 17 in/hg of vacuum and turning about 2,200 rpm. It is scary how little throttle it takes to keep it rolling, on level ground.

The stock medium duty 350 roller cam specs are as follows

Lift: 0.431” I, 0.451” E
Duration: 196° I, 206° E @ .050”
Lift Centerline: 108° ATDC I, 116° BTDC E

In theory with 1.6:1 rockers I am at .460/ .481" lift and slightly more duration at .050" than 1.5:1s.