Modded CTS-V 27.4 MPG

[YukonCornelius]

I wanted to post this up since it's not the norm here. I have a 05 CTS-V that has a the Z06 LS6 and 6 speed. I have a larger than stock cam in it .580/.580 220/226 117lsa, full length headers, no cats, f.a.s.t intake manifold, ported 90mm tb ect ect.

Now onto what you guys care about. My current best full tank to date is 27.4 MPG. No engine off coasting or pulsing, not even much drafting trucks (rock chips). The car was loaded with stuff and a passenger doing a highway trip to New York (187 miles) a week of short trips where I was, the whole drive back and then some more driving around. I had all the tires around 50psi. My car has a setting for a live MPG display and from the testing I've done the thing is just about dead on. This isn't my daily so most of my usual driving is short distance and hard on throttle so I haven't made a effort to beat my full tank MPG record.

However, I have made two major ecomodder mods. First, Cadillac didn't use DFCO on this cars tune because a Cadillac is supposed to roll when you let off the throttle. So I have it set that DFCO will now engage in all gears except first at any speed and at any RPM and it doesn't feed fuel again until 1100 RPMs. This was about as low I could go and not have to worry about a possible stall. Next, and this is major, I found a way trick my PCM to accept the lean cruise that GM uses on some Australian cars. Going off my live MPG reader my car seemed to like a 16.3 AFR at cruise. And it gained 2-3 MPG from this when shutting it on and off while driving. I have the settings cranked up though, engaging lean cruise low at 40mph in any gear, and it will hold until I get about 1/3 down on the throttle. In good air by myself and on a flat highway I can cruise getting 41 MPG.

The one fault of this car is the stock gears are 3.73's. Oddly enough with my custom grind cam my car seems to get more efficient with higher RPMS when cruising. Doing 50-55 mph I have trouble getting my live mpg reading to stay at 30. If I bring it up to 72-75 I'm well into the 30's or even low 40's and can feel I'm using much less pedal. I'm going to make at road trip to Cape Cod next month and I'm looking forward getting a new best. I'm confident that I will break 30, 34 would make me really happy. I'm so tempted to block off my whole lower grill and brake vent ducts in the front but I'm a little self conscious about it on this particular car. I'd like to do a couple extra things before I leave though.

[2000neon]

Thats really sweet, I have always loved those cars, a business mans hotrod! Good job on the numbers. It really is incredible what these LS motors can do in even nearly stock tune. My boss just went to St. Louis and back (were in southern ontario, canada) and he averaged 32 mpg, and he said his average speed was around 70 mph.

I have heard that the headers specifically are a big part of the better efficiency at higher rpms, mainly due to the fact that it moves the peak torque up higher in rpms.

Any pics of the car?

[YukonCornelius]

Hopefully this works, its my first time using Flickr on my phone.

[2000neon]

It doesn't show up for me.

[YukonCornelius]

It didn't look like this when I bought it. I do paint correction for extra money , this is actually a no wax picture.

[2000neon]

Nice! I have always had a soft spot for these cars. They are one of the best looking four doors on the road.

[mcrews]

5 wpeed overdrive or 6?
Nice numbers.

[YukonCornelius]

6 speed. T56 .84 5th and .57 6th.

[MakitaDiesel]

This is impressive, given my old '81 Datsun 280zx w/ a 5 speed & a mild weight reduction got just 28 mpg. Of course this was 7 years ago, I didn't know how to drive for efficiency as well as I do now, and gas was $1.60. Keep it up, I love power when you need it, mpg when you don't.

[mcrews]

Given the right gearing, I think it will become more common for newer cars to get better mpgs w/ 'the adjustment of the nut behind the wheel'
Also you metioned the having the live mpg screen on. That is one of the main reasons for my initial leap into the mpg world.
My Q45 can be a beast but I was always trying to 'beat the screen'!

I wish I had the 6th gear!!!!