TierAngst

I've got a stock LQ9 in my DD jeep and I was going to do a cam and tune to get the best possible fuel economy out of it but was wondering if it would be worth the extra money since I won't really be needing more than 350HP in it now. It currently gets 18mpg hwy (very rarely city driven) with a stock LS1 pcm running it. I've heard people go both ways as to which helps mileage more, so basically wanted to hear the tuners opinion on this.

I'd be more than happy to supply any additional details if needed.

jimmyblue

iTrader: (11)

I doubt any cam is going to improve mileage over
the stocker.

macca_779

You would be surprised what you can do with a nicely speced cam. something like a 206/210 .561 .570 115LSA would certainly improve economy.

TierAngst

Two replies in and I feel like I'm already chasing my tail!

I would do both if I could get a few knowledgable/experienced people to seriously believe that I could get 22-24 hwy. But if I'm only going to get 20 mpg with both a tune and cam, I think I'd just take my chances on doing a tune only and getting a very nice running 19 or so mpg.

TierAngst

Apparently no one does anything geared towards economy on here. Can anyone at least recommend a forum that does, or possibly a cam or tuning guru that could give some honest advice on this?

LS1Z28-00

iTrader: (8)

you should just probley get a tune. i also doubt a cam will improve gas milage. Maybe you can get away with one not hurting your MPG and improving power, but i would stick to doing headers and full exhaust, those have been known to improve MPG.

TierAngst

It has shorties, which are the only thing that fit on a jeep conversion unless you plan on chopping stuff up. The exhaust is also about as good as it is going to get due to restrictions.

WeathermanShawn

iTrader: (1)

Angst:

You need to be a little more patient with people if they do not answer your question right away. Your question is asked a lot of times on this forum.

But, nevertheless it is a legitimate question. See getting a 'tune' by itself will never produce additional MPG by by itself. If your car is like many, the factory O2's are programmed to 'switch' from rich-lean in a manner that facilitates the best fuel mileage. Tuning is usually done to enhance WOT performance..so when you mash that throttle down it goes fast.

Tuning for fuel mileage would in essence require a very lean cruise AFR..there are people who know how to do it, but it takes expertise and a lot of bucks to do it.

There a lot of smaller performance cams that could give you an additional 20-30 HP over stock..and if you drove it conservatively, you would not probably see any appreciable drop in mpg over stock. But, that is very unrealistic. Who pays for 30HP, and then does not drive it hard. It is WOT that sucks gas!

Personally, I would just save money for a smaller cam, get a tune and enjoy the benefits of each. You would have to spend more to get a 'lean cruise tune', than you could ever save in gasoline costs for over two years.

Hope that helps.

..WeathermanShawn..

TierAngst

Sorry for the impatience, I guess I got a bit carried away with myself sitting at my boring 12 hour a day job with nothing to do. Maintenance is a hurry up and wait career, looking forward to getting a new job :-P

Anywho...

I'm not so much worried about the power, that is what Sandy is for. My jeep is just my daily driver and I plan on putting a lot of miles on it without doing any significant mods. And believe me, I can keep a pretty tame foot 95% of the time.

From what you said, it doesn't sound like there is any MPG to be gained going to a different cam. Only power without a loss in MPG. Or did you only say it that way because you don't trust people's ability to moderate pedal use?

I didn't realize that about the tuning, I've been trying to browse some of the other tuning sources online but most of what I've come across so far talks about general power and tuning big cams for driveability. I'll keep searching though.

Thanks for the insight and I'll try to keep my patience level higher.

-Jake

WeathermanShawn

iTrader: (1)

Jake, I think that for the most part a cam's effect on gasoline mpg is the most negligible part of the equation. You look at some of the ZO6's that make great highway mileage, and it is true that there is a great amount of Head/Cam/Valvetrain efficiency. But added to that is their light weight and unique gearing. So, it all adds up.

It is not out of the question that if a certain cam profile is picked, and your engine's efficiency is increased..you might be able to pick up at most a 1-2 mpg increase. Perhaps a cam whose greatest cylinder pressure (efficiency) is 2500 Rpm's and lower. But there are probably greater rewards in exhaust scavenging, or even to some degree your choice of heads.

For most of us, it is all told in a sentence like this.."I added Cams and Heads, and did not lose any mpg". I think in my case, (previous set-up) running a 220/220 114+4 cam and having added headers simultaneously, I picked up an additional 25 miles per tank (~1.5 mpg).

Yea, check out Lean Cruise on a search. Not sure if your vehicle's OS can be programmed that way, but it gives you some options to look at tune-wise.

Thats about all I have for you. Good luck.

..WeathermanShawn..

TierAngst

I'm not sure what year the PCM is but it's for an LS1, from what I read the lean cruise is only enabled in Aussie cars and the 2004 GTO's (since of course they were an import).

If there were more to be had from a set of high compression heads I'd go that route, but I'm sure an efficient set of those would cost more than a cam install and wouldn't make up for fuel costs even after 10's of thousands of miles. They'd have to net a solid 4mpg to pay for themselves over the six years I plan to keep it unchanged. But even then, I'm sure if I went higher compression I'd have to switch to premium vs regular which would of course increase the time it would take to pay out.

I'd love to do a gear swap to probably 3.73's or 3.42's but having to switch two sets of them really doesn't render it a cost efficient mod either. Then again, if I didn't need four wheel drive for nasty winter and occasional off road use I wouldn't have purchased such an inefficient vehicle.

Thanks,
-Jake

Nitroused383

iTrader: (10)

Open loop maf or speed density. Under light load 15.5-16.5 AFR and increased timing. GM used EGR to increase fuel economy, the exhaust gas takes up space in the combustion chamber so not as much fuel is required to maintain stoichemetric afr (14.7). So lets look at this, what can we do to provide natural EGR to our engine.... Ah yes a properly specced cam with the right amount of overlap. Inefficient down low at cruising rpm because of excessive egr, but still enough power for cruising torque.

That being said I've tuned a 04 GTO (with lean cruise ) with a Trex cam 242/248 110LSA. I worked on driveability and fuel economy for him, went from 11 mpg in town to 17 mpg. My own car has a cam with around 10 degrees of overlap and I average 20 mpg in town. Before cam my best highway mpg was 26 and after mods with cam I have seen 29 mpg. I do constantly tune with a wideband everywhere I drive while looking for the best combo of timing and afr. Use your overlap to your advantage.

TierAngst

That's right, I remember hearing about that sort of stuff when I was on thirdgen.org. One of the guys there drives a van and he was getting 20mpg hwy with his 5000lb bus of a vehicle. I think he installed an EGR system and was testing out different cams to see what gave him the best power while maintaining as high of mpg as possible.

EDIT:
Went through some of his threads and caught a bit about injectors being ran at a higher PSI...
"The finer spray pattern helps promote atomization which helps the engine deliver more power AND better fuel mileage. Cleaner emissions too, BTW."

Does this work on LSX motors the same as it does on TPI and TBI?

Mike454SS

iTrader: (4)

Rather than looking a the cam, look for a way to bump compression up on that engine (like a set of 243 heads).

Regarding tuning...more spark at part throttle will help, limiting/disabling torque management can help too.

Make getting air in and out of that engine as restriction free as possible too, it's surprising how much MPG you can gain if you pay attention to the details.

TierAngst

Even setting a proper .040" quench, with 11:1 compression ratio I'd have to run 93 octane right? From what I've read online (I know a lot of false info flying around out there) I haven't seen anyone running that high of compression without high octane. I suppose you could pull a bunch of timing out of it but wouldn't that negate the efficiency of running the 11:1?

jimmyblue

iTrader: (11)

You can get a leaner cruise by bumping the O2 voltage
switchpoint table lower, in the airflow cells where you
find yourself cruising / idling. 15-16:1 is within reach.
I've messed with this on a 6.0 truck and seen moving
from 500mV (stock truck values) to 350mV (stock F-body
values) move the AFR from ~13.5 up to ~14.5:1. Driving it
lower would lean it out further, but we were not interested
in anything more than straight-up.

You'd want some time with a wideband and whatever
your final exhaust setup is (O2 voltage vs AFR will change
with thermal conditions, some) to dial that in. Then push
timing around for minimum cruise MAP (max efficiency)
without ping.

TierAngst

I'm not familiar with this portion. Is this a timing vs MAP table, and would the timing be retarded for greater efficiency?

Thanks,
-Jake

TierAngst

After calculating the actual cost of 93 vs 87 I think 93 would be very much okay in the long run!

That being said, would it be wise to switch to a 243 or is there a more efficient stock head that will be more efficient in that price range?

Nitroused383

iTrader: (10)

When you lean out your cruising AFR beyond stoich you will be losing torque. To make up for the loss of cruising torque you need to add timing. While cruising you can play with your timing while watching your map values to see if the engine is working harder ( higher map reading ) or more efficient ( lower map ). That being said I found playing with timing while having the cruise control set did not really change the map value you at all. Ha ha go figure

When I added my cam I also added a set of 243 heads with a proper valve job and I had them milled .020" for 11:1 compression. Believe it or not but the top cut on your valve angle can effect your gas mileage. It's hard to beat a set of milled, valve job 243's for maximum fuel efficiency.

TierAngst

Almost wish I could use my EBL setup on this thing, it has auto VE learning via both wb and nb as well as lean cruise mode. Seems like most of the people just try to trick the nb's into running at a higher AFR since they're always going to try to run at stoich with out having a lean cruise mode. How hard is it to get an old PCM from one of the Aussie cars to the US?

If the 243's are basically the same thing as a 317 except with smaller cc chambers then wouldn't it be cheaper for me to just mill my heads and do the valve job on them vs spending $500 on a set of used 243's and then having them worked on? If so what would I have to watch out for? I'm guessing a different cam would cause it have less clearance to the pistons but I don't plan on running anything majorly agressive obviously so that shouldn't be a problem.


Triple checking my calculations at current gas prices and assuming 60k miles:
87 octane and getting 22 hwy vs current 18 would allow me $1700 for mods
93 octane with +4 would allow me $1100 for mods to break even
If I look at it in a performance perspective, it would be like getting a free power boost over the long run (I could settle for that). But if I look at this only in an economy stand point I would want to spend less than what I'm saving which might be very difficult. Hmmm....