Gas Mileage

[KP99]

I have an 05 Coupe with the Z51 Package. I just put on Corsa Exhaust and kept my original "H" pipe. I also installed a Air-Aid Cold Air Intake.
We just got back from the Effingham show and I only got 25 MPG. I would have thought it would have done better. I have been using 93 oc. or better gas.
Any thoughts or things I might possibly do to help get better MPG.

 

[KP99]

I have an 05 Coupe with the Z51 Package. I recently installed a Air-Aid
Cold Air Intake and Corsa Extreme Exhaust. Coming back from the Effingham show, highway driving around 72 MPH, using 93 Octane,
Tach was around 2000 RPM, I only got 25 MPH.
Is this common or is there something I should be looking at doing
without going into a lot of expense.
Your thoughts & ideas.

 

[gmjunkie]

I have an 05 Coupe with the Z51 Package. I recently installed a Air-Aid
Cold Air Intake and Corsa Extreme Exhaust. Coming back from the Effingham show, highway driving around 72 MPH, using 93 Octane,
Tach was around 2000 RPM, I only got 25 MPH.
Is this common or is there something I should be looking at doing
without going into a lot of expense.
Your thoughts & ideas.

Not Normal to me,I have a 03 Z-51 6sp coupe Bone Stock I always get 30+ most the time 34-35 on the road with 87 Regular Chevron!!

 

[Patrick]

KP99,
You didn't mention if you have a manual or automatic transmission. Manuals tend to get a little bit better gas mileage.

My '06 coupe is stock- no major performance mods. On a trip to Washington State back in July, I averaged 31 MPG largely doing the trip in sixth gear. Note that my driving style was not overly aggressive, either. I generally kept it to no more than 10 miles per hour over the posted speed limit.

 

[vett boy]

I found that my 03 had it's best mileage at 70-75 mph .On flat runs 30 + was normal.
My 08 gets less but the best cruise range is 60-70 mph and the norm is around 28 mpg .

I'll tell ya what the other 100 hp is worth 2mpg.

My opinion only ,I think your wasting money on 93 octane .

 

[twiget]

I run 91 octane in my '08 coupe, it's a 6-speed manual. I usually average 28 - 30 mpg on road trips. I even hit 32mpg on one cruse.

2000rpm at 72mph seems high to me. My car runs at 1500 rpm in 6th at 70mph. 2000rpm in 6th is north of 80mph if I remember correctly. With the mod's you mentioned, I would kind of expect your MPG to increase a little since the engine is breathing easier. As VetteBoy mentioned, 70 seems to be the sweet spot for cruising MPG.

Jason

 

[darkstar]

I was a bit disappointed on a 400 mile trip here in WA state. I have the Corsa exhaust and the Callaway cold air induction system. I averaged 65 mph, cruise mostly, and still only got 26 mpg with 92 octane. I hesitate to use a lower octane, but I guess on a trip it really does't matter as performance is not a concern. Any thoughts??

 

[Hib Halverson]

I have an 05 Coupe with the Z51 Package. I just put on Corsa Exhaust and kept my original "H" pipe. I also installed a Air-Aid Cold Air Intake.
We just got back from the Effingham show and I only got 25 MPG. I would have thought it would have done better. I have been using 93 oc. or better gas.
Any thoughts or things I might possibly do to help get better MPG.

Neither of the aftermarket parts you've installed will make a significant improvement in fuel mileage and their impact on fuel economy might not even be easy to measure.

There are very few, if any, bolt on modifications which will make any significant increase in fuel mileage.

If you are looking for a significant increase in gas mileage, install the base tire package, run your pressure at the maximum rated by GM and alter your driving habits.

 

[napacruzerC5]

How about this for mileage? On my road trip to the Black Hills Corvette Classic this July. My wife and I along with our 2 doxies, travel kennel and a full cargo hold. Dash photo taken on Hwy 50 in Nevada - long straights and empty blacktop.

'07 Coupe F55 A6 very stock except for K&N air filters

 

[65-to-00]

Trip to Maine and back was about 1,000 miles on the nose. I think I used the "GM Junkie" formula for tire pressures ... kinda' like 34 PSI or something just a "tick" high.

Speeds were about 74'ish (like religion) .... and in light traffic on the "I-States" .... it was all 30+ .... with the six speed.

I honestly don't think that a few octane points on relatively flat land and low (tourist travel), speeds will make any difference.

And ..... oh ..... "going to the mountains" ...... from New Jersey to Vermont, New Hampshire or Maine ..... you never get above 900' on the whole trip and that is one dopey spot in New York ... so the octane isn't IMHO much of an issue there. My "base elevation in NJ is like 200' and up in NH ... it's like 400' "up in the hills". I guess my point is that I used to run premium in the Volvo on those trips. Once I took a look at my altimeter numbers I run the Volvo (light turbo) on regular all the time now. The C5 .... does get premium all the time.

I don't believe for a second that 91 versus 93 would make any diff at light cruise speeds on the open road.

If you hear a loud :bash kinda' sound going up hill or when you speed up .... up the octane.

 

[vett boy]

I really don't remember what I use to get around town with the C5 but the C6 at 24-26 seems like it's better.With 20,000 miles in nine months maybe it'll get a little better with age.

 

[NORTY]

I have an 05 Coupe with the Z51 Package. I just put on Corsa Exhaust and kept my original "H" pipe. I also installed a Air-Aid Cold Air Intake.
We just got back from the Effingham show and I only got 25 MPG. I would have thought it would have done better. I have been using 93 oc. or better gas.
Any thoughts or things I might possibly do to help get better MPG.

Could have been that you "enjoyed" the sound of your Corsa exhaust system. This will drop your mileage. You also may have done something during the CAI install. Of course, the BTU value may have changed in the gasoline too. Summer blend to winter blend. Alcohol ratio will have an effect of energy content (BTU).

 

[darkstar]

Specifically, does octane really matter when you are on a roadtrip and performance is not an issue? What would be the long term affect on the engine if any.

 

[Patrick]

Specifically, does octane really matter when you are on a roadtrip and performance is not an issue? What would be the long term affect on the engine if any.

Every so often, we get questions about Octane ratings as it pertains to what kind of gas to buy. Hib posted this in a thread back in 2007:

Here's the deal on gas for C5/C6.

For some of the C5 years, GM calibrated for 91-oct. For the rest of the C5 period and all of the C6, so far, GM has calibrated for 93-oct.

This means that best performance on days with normal temperatures (ie: not a real hot day) will come with 93-octane gasoline.

Use anything less than that and you loose performance due to the engine controls' knock retard ("KR") feature retarding spark to keep the engine out of detonation. KR causes reduced performance, reduced fuel economy and increased coolant temperature.

Nonetheless, the stock calibration has enough knock retard to allow the engine to safely run on 87-oct. gas but when you do that, know that you take a significant performance "hit", your gas mileage will be worse and the engine will run warmer.

Now, on real hot days, to get the engine's ultimate performance you may need more octane than 93, perhaps as much as 95-96 to keep the engine out of detonation.

There are a lot of myths about gasoline, one of which was posted earlier:

Unfortunately, that is not correct. Octane has nothing to do with flash point or the temperature of combustion. Octane is a measure of the fuel's resistance to detonation. Generally, higher octane gasolines have a slower burn-rate but that's not universally true. Some racing gasolines have very rapid burn rates.

For more information about gasoline for Corvettes see:
http://www.idavette.net/hib/fuel/index.htm

Admittedly, this article is a bit dated with respect to some technical issues relating to oxygenated fuels but the rest of it is still quite pertinent.

The link to his article is no longer active, but perhaps we can request Hib dig that information up again.

 

[darkstar]

Thanks for the info Patrick. Just reading where a guy gets 30-35 mpg on chevron regular had me revisit the issue. I suspect most go by their gauges instead of actual averaging over till the next actual fill-up. My gauges always tell a better story than when I actually do the math myself.

 

[gmjunkie]

Thanks for the info Patrick. Just reading where a guy gets 30-35 mpg on chevron regular had me revisit the issue.

I'm sure my driving habits have something to do with it,But I've been known at times to make the average take a severe drop!!!
This photo was taken at the end of a 2800+ mile trip about a year and a half ago,I did not run Chevron the whole trip,but I did use name brands,one fill up I did use 89 because the regular pump was posted with 10% ethanol!!
I've made that mistake a couple times,the car runs like crap and the gas gauge will quit in a day or two!! Techron to the rescue!!:L:L:L
Yeah,I checked the mileage with pencil and paper sometimes too, never was more than a tenth or two off from each other!!

This was taken 3 weeks ago creeping back in the holler home after a trip to Charlotte to pick up parts,Little over 200 miles!!No I didn't run over the speed limit anywhere because Johnny was everywhere!!

But then again,I've got purdy good at economy no matter what I drive!!
Some people listen to the stereo,I listen to the engine and watch the road ahead!!

94 LT1 6 sp!

Look in the owners Manuel,If it says 87 octane or above,you shouldn't have any problems!
If you drop it to Regular 87 from 93 you will probly notice some difference in performance!
If you drop it to 89 a couple tanks and then to 87 you probly won't notice much at all!

 

[midyearroadster427]

Well to be honest I have yet to take a long roadtrip with the 08,A6,F55,273's. So I cant really say to much here as far as advice. I hope I would average somewhere around the 27-28 mpg avg, with non agressive highway driving. That would be fine with me as I get about 16 if I am lucky traveling with the BB, and less when I tow the trailer...never even bother to check when towing. But to be frank and honest...I did not buy the car for gas mileage...so whatever I get I get. Now I am not going to turn my back on any tips to get better mileage...duh. hahahahahahahahaha I like the over inflate the tires tip ...did you suggest 4 lbs more than stock????

 

[NORTY]

Specifically, does octane really matter when you are on a roadtrip and performance is not an issue?

Only if you have an engine tuned to take advantage of a higher octane's slower burn speed.

What would be the long term affect on the engine if any.

No problem as long as you don't create a situation where "pre-detonation" occurs. If you do get it to pre-detonate, then you will shorten the engine's life.

 

[darkstar]

Again thanks Norty. I won't lug the engine any to cause pre-detonation. With all this info I doubt I will even run the lower octanes. Why chance it and I believe my owners manual even says use 92 octane or better for my 08. I was not aware that the C5 was built to run on 87 as the norm.

 

[leftyvette]

Hey, Junkie, you are running a 6sp -- right? My automatic will not turn under 2,000rpm at 80mph.