Well, I've got a soon to be DD GTO, that is stock. Right now I am rockin' my other DD honda accord but it is tired....very tired.

Looking to extract the maximum fuel mileage possible and be able to run 87oct.

First of all I don't care about HP with this car at all it'll be enough. It's going to be a 'going to work' car. If I could get 30mpg on 87, it would be perfect for that as long as getting it to that point would be cost effective. I drive about 75 miles round trip all highway. The reason I think the GTO would work instead of selling it and getting a smaller car is that I don't want a car that isn't comfortable. The car is an excellent GT car. I already own the car. It is already 'close' in goals. Right now I get about 23mpg avg on premium and 25-27 on lean cruise enabled.

Now for the technical side:
I could either entertain the 87 through just tuning or 6.0 heads. Which would be more efficient and why?

What about a custom cam ground for gas mileage?

What other mods would be cost effective to increase mileage? It's got an LS6 intake, I could switch to an LS1 intake that would net $250+ and possibly increase mileage? or would that negatively affect mileage?

Most importantly all this has to be cost effective to achieve.

I have HPtuners for the car already. No cost there.

This is a different approach to LS1 "performance" and I am interested in it as well as interested in your thoughts on it.

 

gear change out back will help with milage on the freeway and full eghaust including headers would help as well.

 

Gears for the GTO cost ~$500 not including install and headers are around $800-$1000.

Neither would be cost effective for about 4 years an maybe not even then.

 

How much do you assume that 6.0 heads or a custom cam is going to cost??

The only thing that you can do that's "cost effective" would involve not changing anything, and doing a tune. Changing parts is going to cost money, and if $500 is too much, there really isn't anything you can do anyways.

 

Muscle car and good gas mileage dont work well in the same sentence....good luck, just tune it up and do some little stuff to help the engine breath better.

 

I can pick up a set of 317 heads for ~$150 or less. That would probably be cost effective if I could get the same mileage with 87 and 9:1 as I do with premium and 10:1 Right? Or would reducing timing to a point I can run 87 net better results?

Custom cams run about $400 or so. They would only be cost effective if I could pull 4mpg+ out of a cam. I am asking if that is even possible? The stock GTO cam is basically an '02 fbody cam as it is.

Gears won't net me 4mpg+ I don't think. The GTO's have 3.42s and I believe 3.08s are available. Labor costs are moot on engine work. I do my own work.

 

Why not? The engine from the factory is a blend of performance and economy. Most of the time people here look to increase performance at the expense of economy. I am wanting to shift it the other way..... I will take a performance hit for better economy.

Is breathing better on the intake side good for economy? I would think better breathing exhaust would help, i.e. remove cats (basically free) But what about LS6 vs LS1 intake? Which will net better mileage? Maximizing torque in my drive range is the key I think. That is right around 1,800-2,000 or 80mph or so. So anything that helps breathing up top will usually sacrifice low end. Not what I want.

Maybe this is blasphemy or something and that's why the answers are defensive and short instead of in depth?

 

Weight reduction, aerodynamics, pump up the tires a couple of pounds, a good dyno tune that will maximize torque production in the lower RPM range, reducing your highway speeds, synthetic gear lube/motor oil/ wheel bearing grease, all these help a little. Together, it may add up to a considerable amount.

 

What is your normal cruise speed? Reduce it by 5mph....that alone is worth 1.5mpg on my vette.

 

My point was you dont buy a muscle car to get good economy, youve got your priorities mixed up a bit, not saying it cant be done, its just an uphill battle is all. Breathing better will help, stock airboxes have plenty of room for improvement. Take some weight out as Gearhead said as well, look around, there is plenty you can remove. I drive 50 miles a day round trip in stop and go traffic, so i feel your pain, i just knew i wasnt gonna get 30mpg when i got the car, but its a sacrifice i am plenty willing to make,

 

Stoichiometric ratio @ approx. 14:1 under 2000rpm will net sizeable mpg gains since a dd spends the vast majority of time and miles under 2000rpm.

 

I was going to say something very similar to what Eric just did. Well put.

Ben T.

 

.....you got that right...

 

I remember when Car Craft used to do street car challenges back in the early 90s. They would get 4 guys with differemt muscle cars and put them through their paces. This included 1/4 mile, handling, street driving and crafsmanship in building the car. In the street driving segment gas milage was logged. One of the cars they tested was a Buick GN which through the use of a custom tuned chip was able to get close to 40 MPG on the highway.

So tuning can make a huge impact on gas milage. They ran the car way leaner than stoich. Upside is improved milage, downside is the risk of rattling the pistons. When you have a very lean tune you have to be gentle when accelerating to crusing speed or you might get detonation and hurt the motor.

One of the factors that is greatly affecting the milage you're going to get is the gas being sold today. Two years ago I was able to get 360 miles to a tankful on the highway in my M6 Z28 at 75-85 MPH cruise speed. Under the same driving conditions I'm only able to get 320 miles to a tankful nowadays. All the ethanol they're adding to gas is killing milage. Another brilliant idea by the government for us to get worse milage and burn more fuel at a time when gas prices are the highest they've ever been.

I say go and buy some kind of tuning software and lower the timing a bit and you should be able to run 87 octane. You can also play with the tuning and lean the car out at crusing speed. You'll know when the car is too lean at cruise speed because it will start to buck/surge a little bit. When you reach that point just add a little fuel and the bucking/surging will stop. Just don't floor the gas when you have the lean tune in it and monitor KR for a couple of trips. If you're not getting any KR or surging the tune should be good and milage will increase.

 

Eh, nope thats actually going to DECREASE mileage. The PCM already controls for 14.7:1 AFR at part throttle....and hes already running lean cruise which is a tad leaner than that.

 

I realize that. I didn't initially buy it for economy. I've already had a 408 in it at one point. But after car shopping for 4mo now, there is nothing out there that fits what I want/need. The only thing that comes close is a v6 accord coupe.

But since I have this car already and would probably take a hit trading/selling. I might as well keep it. It has all the qualities I want except it takes premium and I could use about 7-10 more mpg.

Now. Back when I first got the car, before H/C, before 408. I had HPtuners and did play around with lean cruise that was enabled in the software (hush hush ) It helped quite a bit. I will re-enable that, I've got some weight reduction here and there.

Anybody shed light on the 6.0 heads and lowering compression? If I can run 87 but lose 5mpg with the heads.... net loss probably. IF that is the case?

CAN a cam be ground for significant mileage gains over the stock cam?

Would not a free flowing intake side demand more fuel and lower low end torque?

 

Yeah ~15.6:1 and about +6 more timing netted best results while keeping EGT in check.

 

Hey Boss.....

I can't say for certain (because I'm no expert), but I'd expect the 6.0L heads would be a good move. You should be able to run 87 without pulling timing way back. And that $.20+ a gallon difference in fuel cost should pay off the heads and gaskets pretty quick. I would't expect a drop in fuel economy, but I don't think there'd be much gain there either. Ports on the 317 heads are basically the same as the LS6 heads, so they're pretty good, which should mean easy breathing.

Optimum fuel economy ratio is actually closer to 17:1 AFR (for straight gasoline) just like optimum power occurs at about 12:1 AFR. I'm not sure how the 10% methanol blend that we now must suffer with affects those ratios. At that lean a ratio, it'll run kinda warm, so you got to make sure your cooling system is up to snuf. I'd be concerned about cylinder #7 (no crossover / vent tubes on the rear).

Aero drag at 80 mph is pretty significant. Slowing down 5 mph will save you $$$, but may not be practical (depending upon the area you drive in). I'm not sure that there are any easy aero changes you can make to reduce drag.

There aren't many things you can do to reduce rolling drag. Certainly airing your tires up will help, but probaby at the cost of reduced tire life (wearing out the centers before the edges). Narrower, harder compound tires should have reduced drag, so when it comes time for new tires, you might think seriously about a non-performance oriented set of tires (or maybe just a 2nd set).

If you're running at 80mph all the time, a gear ratio change might actually pay for itself. I don't think you'd get 4 mpg, but I would think you'd pick up 1 or 2 by going from 3.42 to 3.08. You said there are 2 ratios available, maybe you could swap with somebody who has the other ratio and wants more performance? Might not cost you anything but labor / gaskets / fluid. Worth looking into.

Better breathing in and out should help fuel economy, if you can keep your foot out of the throttle. Free flowing exhaust, maybe headers, and intake (K & N or equivalent) would probably all help. Headers would probably be tough to justify on a fuel economy basis, however.

Sadly, there probably is no magic 5mpg silver bullet (if there was, I'd bet GM would have listed it as a $5,000 option). All of these changes might get you there, but it'll be alot more work than changing one thing.

'JustDreamin'

 

Thanks man for the in depth response!

I also think the 6.0 heads might be a good start. The motor is out of the car right now so a swap would be pretty easy.

 

Have you considered or do you know about ECO Fuel Systems Fuel Catalist?

PM me for details.