I get 32 on the high way and with A/C on 29 mpg and 17 to 15 in the city go figure. The city dropped about 5 mpg. Depends on how I drive her and how much city driving i do I can go through a tank in about 2 to 3 days or a week again, I am not too worried.

 

Thats awesome, man.

So you know exactly what I'm talking about.

Why the "want good mileage, don't mod" post, then?

 

I will speak on his behalf because I think in a matter of less words he was saying: Why mod a car and expect good gas mileage? Performance parts were not ultimately intended for a daily driver that goes the speed limit and doesnt get into the throttle. So what the real statement should have been was: Why mod a car and not use the power you were so deperately searching for?

After I put H/C/I on my cars I was always shifting gears at a higher rpm and chirping 3rd any chance I got. My gear comment didnt come out the way I was intending. I meant taller gears usually means being zippy in 9 out of 10 cases. I liked running up on the limiter in my 3.73's much better than the previous 3.42. So again, it really is a question of why do 3/4 - full throttle mods and want better gas mileage? The only answer I can come up with is: 1. Its a DD that see's the track every once and a while.

OP - If you are basically stock a procharger would be the route I would take if I had it to do over again.

 

I've posted a bit on this in the past and I don't feel like typing it all again, maybe search some of my post about gas mileage. To keep it short GM uses EGR (exhaust gas recirculation) to reduce the volumetric efficiency of a cylinder at low rpm. By having spent exhaust gas inside the chamber there is less volume for full combustion of air and fuel. This means less air, which ='s less fuel. What do high overlap cams have??? Lots of natural EGR. With the proper amount of overlap, timing and afr there is no reason you cannot increase your gas mileage with a cam and a little extra compression makes things more efficient. Your standard dynotune is not going to include anything to do with increasing your gas mileage while cruising. Our cars do not require much torque at all to maintain 70 mph or so.

Oh and by the way, you guys can call me odd or stupid for worrying about gas mileage with a highly modded v8. I'm a little different than most people, I didn't want a daily driven car that got crappy gas mileage. My personality might explain why my ebay header, non ported head 224 car has $1000's less than most peoples cars but makes more power. I do it all myself, and I'm quite good at doing more for less than your average American. Cars, guns, dirtbikes, snowmobiles you name it. I'm a CNC/Manual machinist by trade, and most of us are perfectionist by nature.

Just a little FYI. I've tuned an 04 M6 GTO with a Trex cam (242-248 110 lsa) which has 25 degrees of overlap. This is a pig of a car with a monster cam. Car used to get 9-10 mpg in town, the thing now gets 17mpg in town. Now I'm not saying get a Trex cam for gas mileage at all, but big cam does not always mean bad gas mileage.

 

You know, I kinda admire Nitroused 383's point of view.

I have seen his post before, and he thoroughly explains EGR, VE, and how a high-performance cam does not always equate to less gas mileage.

Like Nitrous, I do not believe that wanting better gas mileage is contrary to owning a high-performance car. It is all about a M6 that has two overdrives. It allows you to play all you want in the first 4 gears, and have a .75, and .50 overdrive to cruise at at low RPM and lower Injector Flow Rates. Its a gift to have that kind of gear ratios in a manual transmission.

To the OP, you can have it both if you select the proper cam and CR. Then get it tuned properly. Some of the custom tuning software now allows you to create your own 'lean cruise' AFR's. Just do your research, and I think you will be happy.

 

I've got a 383LS6 with heads and cam (MS4) and 3600 stall. MPG in town is like 13, and is around 22-23 on the highway. ...once the converter locks up it does great!

 

Sorry to open an old thread but this topic is of great interest to me. I have taken my 100,000 mile old 2000 LS1 from 283rwhp to 447rwhp in stages and tuned for power under load and economy under part throttle. The car is a Holden Commodore with the 4160e auto and 3.07:1 gears. For you Americans, think 4 door GTO or an Australian G8.
I wanted to believe I could be clever and go to a bigger cam and still somehow achieve better cruise economy than the stock cam could get. It did not work!
Yes, I got much more power but economy dropped by 15% and the cruise economy I had with the stock cam is no longer possible no matter what tune you put in it. My data is more accurate than the factory ECU because I have measured actual results over 50,000 miles within a 1/10th of a liter of fuel actually used. Yes I’m a nerd.
The car runs lean burn at cruise and fuel and timing have been optimized. Over all the cam has cost a 15% economy drop.
Stock cam – car averaged 23mpg (UK gallons) which = 19.7mpg US combined city and highway. It is most often driven around the city. It made 283rwhp with minor bolt ons and a MAFless tune. If that sounds low, the dyno is conservative, another dyno measured it at 319rwhp but I go with the lower number. Highway: the family sedan got a best of 28mpg on a long trip with a good lean cruise tune. We use UK gallons so that was 32.7mpg for us (or 8.6L/100km). That is very good for a 4 door sedan and auto.
New cam: spec'd to gain power, work with boost, and maximize economy at part throttle. On the cam grinders advice, we went with a cam that was 222/226 @ 050 on 114/116 centerlines and 0.575" lift. We upgraded springs, pushrods, lifters etc. Car went from 283rwhp to 335rwhp on same dyno and picked up power everywhere. It has a noticeable idle but will pull 1000rpm in lock up at 34mph. Car will no longer get close to 28mpg (US).
Car now makes 447rwhp with custom STS turbo set up and 6lb boost, economy remains same. Verdict. Bigger cams add power but not economy. I think those claiming better economy on bigger cams went from a bad tune to a good one and drove it better. I’d love to be proven wrong, I’d love to see how I could run a 230-240 @ 050 cam and get it to equal the stock cam BSFC at part throttle and low rpms... I just do not think it is possible. Will I put the stock cam back in to get my mpg back up? Bugger off, I like the power too much lol

 

Gas is indeed a rip off right now... lol

 

The Moser 9" and 3.89 gears are hurting gas MPG more than a HC install will. You might drop 1MPG or so with a tune.

Some bolt-ons (Like LT headers and intake) that allow the engine to breath better increase MPG. I was running near 29Mpg highway with LTs, K&N FIPK, and a TR224 cam.

With a STS Turbo and Patriot 317 heads with a 228/228 .588/.588 cam I averaged 25Mpg highway on the HotRod Power Tour June 2008.

Went back to NA. Swapped to a Moser 9" with 4.11 gears. Dropped to 21Mpg instantly.

Swapped to VA Speed Ported 243 heads and a 228/230 .600/.601 cam on a 111LSA. Lost all of 1Mpg to 20 on the highway (US)

In Germany...that's where the Moser and gears cause some hurt. At 100Mph sustained, car was al 3000RPM. Still averaged 20Mpg. Kick the average speed to 120, Mpg dropped to 14 highway. By comparison, my friend with a C6 Vette and 2.73's averaged Mid-2xxxRPMs at 100Mph on the Autobahn and got 27Mpg.

FYI.... "***** out" at 170Mph. 1/4 tank of gas in 3 minutes. Not sure what kind of horrid Mpg that equates to

I know, kinda long.... but the fuel efficiency for a M6 comes more from the gearing than the cam/heads/ or power adder.

 

That's cool that we are within 6hp of each other on the STS setup. I have stock heads, so needed an extra psi to get there. lol

There's no doubt the M6 gets better mpg than the auto on the highway. I think that with the M6 I'd have gotten 31mpg (US gal) on the stock cam.

The 222/226 cam seems to cost around 2mpg at cruise but more around town.