starshifter

Me I know.
And please don't tell me to buy a Prius. I can't stand automatic cars.

I have a 99 FRC which I've owned since 2005. Soon after acquiring it, I had the rear axle ratio changed from 3.42 to 4.10. I've enjoyed my FRC on the track and have had my deal of fun on the open road. My objectives have now changed. I want to do everything top maximize fuel economy. Probably, the first thing I'll have to do will be to reverse the differential gear to 3.42. I'm also considering a 3.15 gear which, although it would hurt my 0-60 times (by being roughly equivalent to starting in 2nd with my current 4.10 setup) would have the engine turning at 1500rpm at 75mph.

I'm also ready to either get in touch with a knowledgeable tuner or buy the required software and start learning about tuning myself. I wonder whether the following changes could be implemented with either HP tuners, EIFlive or some other tuning software that I am unaware off. As of now, I am completely ignorant about tuning. So, I don't know whether the changes I thought about make any sense or whether there are more important tunes that I should consider.

- cut off fuel to injectors when coasting.
- enable 4 cyclinder mode when effortlessly cruising at constant speed and when idling (I currently shut down the engine when I get to a red light that I know will stay red for 30 seconds or more).
- modifying the air fuel ratios to always be on the super-lean side (I know that could be harmful but I intend to be very gentle with the throttle).
- force the PCM to always operate in closed loop mode.

Can someone provide useful information that could help me achieve my goal?

CTD

You will need to purchase tuning software as you will need to spend many hours trying different calibrations. Myself I've never focused mileage, it's a very good by product of working towards a good tune.

I'm not aware of any 4cyl mode, everything else you mentioned is doable or already in place. Fuel cut-off during decal is there, you can lean your part throttle cruise conditions, starting in CL is not an issue if your climate is such. Then of course idle speed, finding best timing, shift speeds, slowing down & driving habits.

A friend of mine whom is a non active member really focused on his C5 mileage with excellent results. You will need to have HPT software for him to help you.

Myself the very last thing I would do is go to the gear ratio you mentioned. Besides being one of the best bang for buck modification's, would you live long enough for the pay back?

starshifter

Thanks. Yes, I know I wouldn't live long enough for the payback. Going back to the original 3.42 gear or even lower would just be for the intellectual satisfaction of achieving perhaps 35mpg when cruising on the highway. I'd estimate I lost about 2-3mpg after switching to 4.10.

Interestingly, when I take into account the gear ratios, swapping the 4.10 differential gear for a 3.15 would be roughly equivalent to loosing my 1st gear but getting a new 7th gear.

Gear ratios - final ratio (3.15) - final ratio (3.42) final ratio (4.10)
First: 2.66 ---- 8.38 ---- 9.09 ---- 10.91
Second: 1.78 ---- 5.61 ---- 6.09 ---- 7.30
Third: 1.30 ---- 4.1 ---- 4.45 ---- 5.33
Fourth: 1.00 ---- 3.15 ---- 3.42 ---- 4.1
Fifth: 0.74 ---- 2.33 ---- 2.53 ---- 3.03
Sixth: 0.50 ---- 1.58 ---- 1.71 ---- 2.05
6th gear: 50mph/1000rpm 45mph/1000pm 38mph/1000rpm



As far as leaning my part throttle conditions, what minimum software setup would allow me to do that? Could that be achieved with a simple mail in tune? (I just noticed the $149 ECS price). Do you know what kind of fuel economy your friend was able to achieve on his C5?

CTD

I'm assuming you live somewhere with flat level roads & near sea level. I found where I'm located 6th to be useless, elevation changes, lugging etc.

Your not going to get a mail order tune that nails what you are trying to accomplish. To go deep into the tuning which is what you will have to do, your going to require software like I mentioned. Consider it a far more rewarding, learning experience than a gear change.

I will send a link to the member I'm referring to & maybe he will chime in.

starshifter

You're right. I'm in MD and I take a 1-2 trips to South Florida every year.

Thanks. I assume HPT = HP Tuners.

CTD

The member I'm referring to is not going to post.

His last trip to visit me which is a 300 mile journey thru the mountains was 46.9 mpg that is Canadian MPG. Our gallons are bigger than yours.

I asked for a copy of his tune file for that trip, there are many details. Those details are most likely hundreds of hours experiments that worked & failed.

No one silver bullet in the world of tuning should it be mileage, drive ability or power.

starshifter

Wow!!! I have a hard time believing it unless you live at sea level and he came down from the top of mount Logan!
I so much wish he would make his tune available.
Can you tell us what model year and transmission he drives?

CTD

You do understand there is quite a difference in the size of our gallon? Maybe search that out prior to believing it or not. My location is 1000' his is 3500' with plenty of higher & lower elevation changes in between. He did mention average so I'm assuming that included his return trip.

I believe it is a 2004 MY & it is a 6spd.

You just cannot copy over the 2004 tune into a 99. You would have to copy the compatible tables over, re tune a couple....very straight forward.

The devil is in the details

starshifter

No, I thought you were joking. (Pardon my ignorance. I'm originally from Belgium and still think in metric terms). I now see 1 US gallon = 3.79L = 0.834 imperial gallon. So, since 1 Canadian mile = 1 US mile ,
46.9 Canadian MPG = 39.1 US MPG. Still a remarkable average!!!

If your friend ever decides to share his setup. I'll begin experimenting with it.

CTD

How would you begin to experiment with that tune file?

starshifter

I mean, if your friend provides us with information as to what he changed from the stock setup to improve fuel economy, I will either ask the tuner I have started to talk to to work with me to get corresponding changes into my PCM or, if I'm able to get the retail version of EFIlive or HP tuners to work with Linux or max OSX, learn to do it myself (hence, my question in this thread http://forums.corvetteforum.com/c5-s...x-mac-osx.html). I just installed the demo versions of EFIlive and HP tuners under Redhat Linux and am able to run the demo EFIlive, but not the VCM editor yet.

Macleod52

I just bought a 2001 6-spd with 83,xxx miles. I averaged 31.8 mpg on the trip home (90-100 miles). The biggest way to get a significant increase in fuel economy is to change the way you drive.

I've only had the car for 1.5wks so I am experimenting with in town driving. I'm trying to keep the RPMs under 1500 when I shift and when I'm at crusing speed (cruise control set) I'm in a gear that keeps the RPMs around 1100. Right now I'm averaging 17mpg but I have a lot of stop lights and stop and go traffic. If I had a nice stretch of open city roads I could easily get 20mpg in town, maybe better. The problem is I have a lot of short trips with several stop lights/signs.

Do some research on hypermiling and start there. You shouldn't need to worry about tuning or anything at this point. Once you get a base line of what you can do by just changing driving habits, then you can look at tuning the car to achieve even better fuel economy.

starshifter

Congratulations on your purchase.
After 3 months of trying to keep my RPM near 1000 and managing to average 25mpg on a tank of gas even though 70% of my driving has been my 4.7-mile commute to work, I am not surprised by the numbers you quote. Yet, I want to do much better still and am prepared to face a few hiccups along the way...

A word of caution, I don't know about yours, but when I first got my C5, the DIC mileage was about 2-3 MPG better than actual. I got that corrected by having someone adjust the tire diameter inside the PCM. DIC MPG is now spot on.

tblu92

I agree wether a A4 or a 6 speed driver input is huge in getting optimum fuel mileage
more so on a 6 speed
My opinions---
If is scientifically proven that the most efficient use of gasoline requires an AFR of
14.68-1 so leaning it down for better mileage isn't an improver---all you are doing is adding throttle position-- Your ECM is programmed in closed loop to always try to achieve 14.68-1 to alter that you would have to run it in "open loop" all the time but even that is just a guess --If you ask for a 15.00 in open loop it doesn't necessarily mean that is what you are going to end up with The only way to verify actual AFR's in open loop is by using a wideband AND most of all in open loop the ECM is NOT making corrections via the fuel trims to correct the AFR to 15.00 in this case
DFCO I have experimented with deceleration fuel cut-off by altering the stock settings
after months of experimenting----I gave in to the GM engineers and put everything back to stock----the stock settings were the most efficient
DOD I don't believe this option was avail until 2013
My experience with Camaro's and Silverado's with DOD--- ?? 95% of my customers have me turn it OFF and report better mileage or always at least the same
PLUS If you know how DOD works and you are simply trying to save $$$ your best bet is to NOT go there or use it---- I have had over 15 silverdo customers who have had lifter failures due to DOD and had to have their engines replaced-true under warranty but if your car is not under warranty everytime your eng goes into DOD you are shortening your engines life----Again this is my opinion from my experience--just remember that every time the engine goes to 4 cylinders on a GM engine the oiling of the lifters is only by slash-as the oil pressure is solenoided OFF to disable the lifters--there is still some oiling but obviously not enough due to all the failures I've seen
Hate to say it--- A Corvette is an amazing work of Yankee engineering------0-60 in 4 seconds--capable of going 175 mph + amazing handling and still while cruising on the freeway capable of 25-30 MPH---If you wanted something with better mileage you should buy a different car----
PS: tuning is NOT the save all cure all for all your needs--Yes it may help mileage abit maybe 1-3 MPG- yes it may add HP 10-17 RWHP at the most on a stockish engine-- but tuning will not beat science or Newtons laws of Physics---

starshifter

Thank you for the education.
It all makes perfect sense, unless the thermodynamic efficiency is such that better gas mileage can be achieved under certain conditions by leaning out the AFR. Isn't this what GM tried to achieve in Australia with the PCM "lean cruise" settings?

Good to know.

Interesting.

Sure. But when I bought my car in 2005:
- gas prices were about half what they are today.
- I wanted it to be both a daily driver and a track car and it has served this dual purpose very well.
- the price differential between premium and regular unleaded was 20-30 cents per gallon, not the 60-80 cents I've seen lately.
- I was in love with it and still am.

Besides, I don't want to spend $20K on a new car that I won't enjoy driving because very few 2013 cars that are available with a manual transmission (an absolute must for me) get better gas mileage than the same car equipped with a 6-7 speed automatic.


Thank you for sharing your knowledge.
I think I'll still want to try the tuning for my own education, if only to optimize DFCO to my liking and make sure the spark timing in optimized for 86-87 octane.

I'll also go back to ECS Corvette to reverse the 3.42->4.10 differential gear change they made for me 7 years ago. I think I'll go for a 3.15 this time to have a super long 50mph/1000RPM highway gear. Maybe Doug can also optimize my tune settings at the same time.

Doug, if you happen to read this, will you please email me that quote as agreed upon by PM? I'm still waiting for your response to set up my appointment.

starshifter

Here's an update after a few months of hard work and a lot of money spent

I got hp tuners vcm suite and managed to get it to work under virtualbox on mac os x. Since then, I've changed and reflashed my PCM calibration a few hundred times and have made countless changes including:
settting target idle speed to 400 rpm
making sure DFCO is started as soon as my foot is off the gas pedal
optimizing VE table and spark tables (I'm now running exclusively 87 octane).
setting 02 sensors to switch at 100mv in closed loop (got new NGK sensors to replace the 14-year old stock ones )
And a lot more stuff...

I also got myself a new 3.15 rear end to replace my 4.10 so that my 6th gear now gets me 49mph/1000rpm

I also trained myself to become a skilled hypermiler.

It's still a work in progress but the results so far are that I've raised my city MPG from the 17-19 range to the 26-28 range. My highway MPG has improved from the 25-27 range (with the 4.10 rear end) to the 35-40MPG range.

Of course, all this has cost me much more than it will ever save me, but it's a fun obsession. Nearly everybody around me at work got themselves a new "fuel efficient" car in the last 2-3 years or so. I'm sticking with my C5 until death do us part.

WilliamSven

Sometimes I never understand some things, like folks that buy organic cigarettes, or buy hybrid gmc yukons.

Mach .25

You may want to install a Vararam VR-B2 system, gives you 40 hp and 3 mpg on the highway. Really made difference on my 2001 C5!

Sidewayz6.0

I think my Vararam probably picked up some MPG as well...But I beat it like a rented mule. So I'll likely never know.

Sox-Fan

You need to be looking into rolling resistance too.