After being with the Pontiac GTP Forums, I noted one thread that kept popping up. Gas Mileage.
I figured I would start a thread and ask all of you your average MPG in the lovely 2 seater we have all come to love.
For me:
I've been able to get up to 31 MPG in my 86 GT with a 4 speed muncie at 70MPH. It's the stock 2.8 with over 121,000 miles. I got this kind of gas mileage by using 91 non ethanol fuel and was cruising at a constant speed.
What about you? What engine are you running, and what year/what transmission are you using?
BTW, Happy New Year!
------------------ Every fiero has a story, It's our job to keep that story alive.
88 Formula 5-speed. I typically average about 20mpg in mixed driving, mostly in town. The best I've ever acheived was 33mpg on a trip to Florida. It was literally tank up at a station just off the Interstate, pull onto I-95 and cruise for the entire tank. A/C off, windows up, running cruise control around 70-75mph. That's virtually flat striaght road for the entire tank, so that's about as true a "best case" as I'll find. No hyper-miling tricks, etc.
@zzzhuh the big reason you get great MPG, is your altitude. Air density is lower, so your engine needs less fuel. But it also makes less power than it would at sea level.
For me, when my 87 GT was running and on the road, I got 19-20 MPG on local roads, and about 28-31 on all highway. A/C compressor was removed, as it had locked up.
Once I get it running again with the built LS4, I will hopefully be getting better than that.
My 87 GT five speed will get 29-31 mpg on the highway with cruise on. When new, (the speed limit was 55), it would get in the mid 30s using non ethanol gas back then. It isn't used for much around town driving but it drops to 25 mpg or so.
@zzzhuh the big reason you get great MPG, is your altitude. Air density is lower, so your engine needs less fuel. But it also makes less power than it would at sea level.
My altitude probably has a lot to do with my MPG, I've read that the average for the 2.8L is around 26-28.
[This message has been edited by zzzhuh (edited 01-02-2015).]
Originally posted by zzzhuh: Wow, I wouldn't expect an LS4 pushing that much power to get almost 30. That's pretty impressive considering the specs of the LS4.
It's not that surprising really, considering the GP GXP was rated at 25 highway with the 4t65. I was hoping fieroguru would see a bit more than that with the F40 and all aluminum flywheel, but I suspect his cam might have taken a few MPG from what a stock LS4 would get with that trans/clutch. I'm hoping to do more than that with my build, but at this point I think my engine build is going a bit off the deep end with all I want to do with it.
Originally posted by zzzhuh: Wow, I wouldn't expect an LS4 pushing that much power to get almost 30. That's pretty impressive considering the specs of the LS4.
quote
Originally posted by dobey: It's not that surprising really, considering the GP GXP was rated at 25 highway with the 4t65. I was hoping fieroguru would see a bit more than that with the F40 and all aluminum flywheel, but I suspect his cam might have taken a few MPG from what a stock LS4 would get with that trans/clutch. I'm hoping to do more than that with my build, but at this point I think my engine build is going a bit off the deep end with all I want to do with it.
Good cruise fuel economy on a large displacement engine is all about the trade off of reducing pumping losses vs. needing more fuel per cycle to cruise. At steady state cruise, the displacement is pulling against the manifold vacuum at 1/2 the RPM of the engine... so this is significant wasted energy. If you drop the cruise RPM, the engine will have to work harder to maintain speed, will open the throttle blade further, will use more fuel per cycle, but fewer cycles per mile, and also have lower manifold vacuum and less pumping losses...
So if you can drop your cruise RPM by say 10% and only need 8% more fuel to maintain speed at this lower RPM, you could improve fuel economy by cruising at a lower RPM. However, if you drop RPM by 10% and have to add 12% more fuel, you are worse off and MPG will suffer. Also, if you increase your cruise RPM by 20% (like using the F40 vs a T56), if you don't reduce the fuel by at least 20% you will be worse off... (and pumping losses increase with RPM)
The OEMs keep the pumping losses in check by keeping the cruise RPM in the 1600-1800 RPM range on large cube engines (or by using DoD/AFM and shutting off 1/2 of the cylinders, effectively dropping displacement, seeing a higher load per cylinder, and lowering intake manifold vacuum). The V8's have plenty of torque to pull at that RPM, plus it requires more engine torque, so the throttle blade is open further, so there is less engine manifold vacuum, so the pumping losses are less.
Now on my car, with the F40 my cruise RPM at 75 MPH is around 2100 RPM. This is about 20% higher than GM would have it run, but is what it is. The other way to reduce pumping losses is with an EGR or a camshaft with some overlap. Both will lower intake manifold vacuum at cruise. On a carbed car or older fuel injected application, overlap kills fuel economy as some of the fuel is pulled right out the exhaust port. However, later model ecms allow you to adjust the injector spray timing so it starts to spray after your exhaust valve is shut. So you get all the benefits of the overlap (lower intake manifold vacuum), but w/o the wasted fuel and poor economy. The camshaft and the EOIT (End Of Injector Timing) tuning is why my car gets very good fuel economy.
Given the cruise RPM range of the F40, I think running a stock camshaft will hurt fuel economy by 1-2 MPG (not help it), because it will have higher intake manifold vacuum, but I also don't think running a camshaft with more overlap than my current setup will help it either. There might be a camshaft with overlap between stock and my current setup that would improve economy by 1-2 MPG...
At higher elevation, there is less oxygen per volume of air and less atmospheric pressure... both require the throttle blade to be open further, which lowers intake manifold vacuum, and reduces pumping losses. There is also less air density which should reduce the power needs for steady state cruise as well.
[This message has been edited by fieroguru (edited 01-02-2015).]
I get right around 30mpg on the highway with the LS3 w/hot cam and 6 speed with larger diameter tires - no idea what the body mods and chop do to the drag coefficient
Purple 87 GT with 1998 3800na / 4T65E. I drive 32 miles round trip on 55mph back roads with 6 stop signs. I get 25-27mpg on my drive to work and use 87 octane... and I'm usually romping on it to pass people... When I drive 75 mph on the highway I get 28-30mph... My car is also running rich...
Isn't it strange that after a bombing, everyone blames the bomber, his upbringing, his environment, his culture, his mental state but … after a shooting, the problem is the gun?
Purple 87 GT with 1998 3800na / 4T65E. I drive 32 miles round trip on 55mph back roads with 6 stop signs. I get 25-27mpg on my drive to work and use 87 octane... and I'm usually romping on it to pass people... When I drive 75 mph on the highway I get 28-30mph... My car is also running rich...
That's pretty good considering your getting on it. If you stayed consistent I'd imagine you could get up to 35mpg.
Any one know about the 4 cylinder Iron Duke? I've heard people get up to 40 but I'd love to hear what you personally get.
[This message has been edited by zzzhuh (edited 01-02-2015).]
In 1995 I drove a new Saturn SW2 station wagon on vacation from Florida to Colorado and averaged 44 mpg at 70 to 75 on the Interstate with two adults and a teenager and lots of luggage.
My Avalanche has gotten 22 MPG from STL to Rolla, but the return trip wasn't so good--usually 18-20. The HP is 295, and torque about the same. Yeah, for a 5730 lbs. vehicle, not bad, considering its 600+ mile range. If only my Fiero went as far on a tank.
Originally posted by Csjag: In 1995 I drove a new Saturn SW2 station wagon on vacation from Florida to Colorado and averaged 44 mpg at 70 to 75 on the Interstate with two adults and a teenager and lots of luggage.
Ok. That was using non-ethanol fuel, surely! I used to have a Saturn SL2 with a 5-speed. My MPGs were in the 30s, but I didn't really care with gas at $1.19/gal.
I wonder what my Fiero would get with non-ethanol fuel?
This is the worse time of year to be comparing MPG. Until an engine warms up, its efficiency will suck.
For a lot of people in colder climates, their engines will not have yet reached proper operating temperatures by the time they reach their destinations... especially with short trips.
------------------
[This message has been edited by Patrick (edited 01-03-2015).]
We used to wrap our radiators in AK. It's 43 degrees F here. My engine is showing full temp in about 5 minutes. The interior may take a bit to warm up.
Here I expected Canada to be cold!
Here, the winter blend fuel seems to give better MPG.
[This message has been edited by tshark (edited 01-03-2015).]
my 88 duke with a 5 speed no A/C gets 34 in the summer. now it gets around 30-31 with the winter blend up here. my friends are all jealous it takes less than 30 bucks to fill it up for a week of driving to work.
Ok. That was using non-ethanol fuel, surely! I used to have a Saturn SL2 with a 5-speed. My MPGs were in the 30s, but I didn't really care with gas at $1.19/gal.
I wonder what my Fiero would get with non-ethanol fuel?
I am sure it was non-ethanol but the car had the 4 speed automatic transmission. I see some Race Track stations around here offering ethanol free gas now, it would be interesting to test gas mileage differrence.
I am sure it was non-ethanol but the car had the 4 speed automatic transmission. I see some Race Track stations around here offering ethanol free gas now, it would be interesting to test gas mileage differrence.
The difference between pure petrol and 10% ethanol mix is going to be very small for MPG. You might see 1-2 MPG more with pure petrol. The Saturn wagon would get better highway mileage than the coupe though, due to aerodynamics, assuming tire sizes and gear ratios are the same.
'88 Formula 2.8 5-spd - I averaged 28mpg. My main commutes were 30 minutes to and from work of which 20 were mainly open freeway and then around 10 minutes of stop and go city driving.
'84 SE 2.5 Automatic - I average 34mpg. Same commute as mentioned above. I'm considering swapping to a manual but it's a lot of work and the car has zero issues so I still haven't done it.
'12 Avenger 3.6 Auto - I average 30mpg. Same commuteas the other two. Just thought i would throw it in there since I keep very good MPG records of each car and drive them on identical routes.
Stock 86 GT 2.8 auto did around 24 on average. Up to 27 on a long highway trip. Stock 2.8 GT 2.8 5 speed did around 27 mixed driving. Up to 30 on a long highway trip. Modified 3.4, 4 speed does around 27 mixed. 30 highway. Just swapped to a 7730/DIS setup before I put it away for the winter. We'll see what that does for MPG. Also just picked up a new 5 speed, so that should help when I get that in too.
But for MPG, I've got a '12 Cruze Eco 1.4 manual. Best tank was 47 mpg. Worst tanks around this time of year. Cold temps, idling to defrost, short trips over a mountain, wheelspin in the snow. ~35 mpg.
Originally posted by tshark: In several vehicles, I have noticed several MPG difference between ethanol and non-ethanol fuels. As much as 4 MPG!
The SL was a sedan. The SC was the coupe.
The MPG difference with 10% blend depends on the vehicle. Some cars will have almost no discernible difference in MPG (like my 87 GT, which I've had for a long time, driven it through many states, and which has always got the same MPG regardless of which fuel went in it, except for when it had a fuel leak or when one of the calipers froze up). Some will have a much larger difference in MPG. More efficient engines will have a much lower difference, and less efficient engines will have a higher difference. It also depends on how much ethanol is actually getting into the mix. Simply fueling at the same pump can result in some difference in the mixture. I've only seen any difference as large as 4 MPG documented when going from regular fuel to E85 though. The 07+ Avalanche with LC9 flex-fuel is EPA rated about 4 MPG lower for E85, for example.
Right on the SL being a sedan and SC coupe. They have the same basic body compared to the wagon though, and roughly the same aerodynamics. The wagon's hatch improves aerodynamics in the rear of the car, which improves fuel economy on the highway.
I have an '03 Tahoe, and an '03 Avalanche. Both have the 5.3V8. Different trannies, true. The Tahoe is 4WD, but is much lighter. The Tahoe is for sure a flex-fuel vehicle. The Avalanche gets consistently better MPG. 16MPG is good for the Tahoe, but I've gotten 22 on the Avalanche. Of course, the Tahoe has a lower grade of tires.
I've driven the Volt. I've also followed it. Oddly, I have a hard time merging into highway traffic with it. It has the same 0-60 as my Fiero (supposedly), but no top end (max 85 MPH, I think), and nothing off the line. I expected more torque. It seems peppy when following it, but not from a stop.
Anyway, the Volt couldn't hang with my Fiero getting onto the highway from a standing start. It had a brief burst where it gained on me, but then it fell behind. We started from 2 staggered turn lanes, with me more than a car length behind on the inside. We swapped cars, kept positions, same result. If they'd add some go to it, it wouldn't be a bad car.
My vehicles are listed as follows and all use 10% ethanol high test pump gas in conjunction with the Getrag 282 and conservative tunes (richer side). The cruise is generally at around 73-74 with the A/C running since a lot of my trips are during hot weather.
87 Mera with turbo 3.4 pushrod (25-26 MPG with a 272 cam)
87 Mera with stock 3800 SC Series II engine and 3.4 pulley (around 25 mpg but I really cannot tell much until it stops eating fuel pumps)
88 Mera with 3800 SC Series III with IC, N* tv, VS cam, TOG Headders, and 3.4 pulley (25-26 mpg)
88 Mera with fuel injected 383 (have not driven it enough to establish a road trip mpg but I am hoping for 17 or so mpg)
As a comparison my 2010 Expedition with an auto transmission and 5.7 L V8 gets 20-21 mpg with regular 10% ethanol fuel.
Nelson
[This message has been edited by hnthomps (edited 01-04-2015).]
