Cam + tuning vs tuning only

[tierangst]

I asked a question about this on the performance forums but of course they're not the least bit interested in fuel economy. Hopefully I'll have better luck here but since I've got a 6.0L V8 I'm not sure anyone will take me seriously. Anyways...

I was wondering if a camshaft (properly tuned) can add enough fuel economy to make it worth while vs just an economy oriented tune.

Background info: Jeep wrangler, LQ9 conversion, 4.11's with 30" tires. Currently gets 16-18mpg city/hwy, I'm not expecting something like 30mpg but 22-24 hwy would make it worthwhile to do both. Otherwise I wouldn't make up for it over the 100k I'm hoping to get out of this setup.

I know I could do gears but mind you this is very expensive when you're talking about doing two sets for a 4x4.

[moonmonkey]

a cam can change the rpm range where your engine operates most effectively, some milage cams with low lift and shorter duration were effective at increasing some older v-8,s milage master, was one of them, you would have to research the avalible cams for your engine and see if it will pay you back,, you should also look at partial grill blocks,underpans,mirror delete/reduction,and other aerodynamic changes and consider a 149.00 scangauge that will tell you avarge mpg/instant mpg,rpm,tps position,air inlet temp,water temp and much more info that you can use to drive more efficently it also scans and clears trouble codes( its for obd2 cars/trucks).

[metroschultz]

You can change the cam timing, without changing the cam itself for a boost in economy. There are cam gear kits available for virtually every car made. (I got a +10* gear from 3tech.com)
Advance the cam timing by 10* and this will effectively lower the RPM of the power band. Allowing you to use less pedal for more torque.

Much of your fuel is used to move your truck from standing to rolling. By lowering the torque curve, you make it easier for the motor to move the truck and use less fuel to get there.

You will also lower your peak RPM. This means no more rolling thunder at 90MPH on the highway.

You will notice your truck pulls easier but doesn't have as much a$$ in the top speed area.

I don't roll past 60MPH anyway, so I didn't see any problem with my +10* cam gear.
Hope this helps.

[womprat]

Engines usually have a wide range of camshafts to fit. Some may be lazier than stock. Study the aftermarket options.

I'm not too familiar with your engine (V8s in general heh), but you may be able to find a variation of the engine with factory cam tuned for lower rpm towing/pulling etc. If it's a factory new/or common second hand part your possibly saving enough $$ over a bespoke item to make it worthwhile. Low end torque improvements are going to improve driveability for 95% of your driving. You should be able to keep the RPM down when climbing hills etc.

Go for the low end torque. Nobody needs more than ~200hp on the road anyway, even in some pretty big vehicles.

A lazy camshaft will reduce load on your valve/springs, you'll save some wear and tear and recoup a little energy lost to friction. You could even find the springs and rockers that go with the lazier cam, they may be lighter!

Also, it's been talked about on this forum and others but it may be possible to do a bit of DIY atkinson cycle. I've often thought a Atkinson cycle camshaft profile sounds alot like a high duration performance camshaft (at least when talking about the intake duration) that's been heavily retarded. Maybe there's something in that.

[tierangst]

I've never heard of the atkinson cycle, I'll have to look into that. I'd say overall you guys have confirmed my suspicion.

[tierangst]

From what I saw it was basically that no one was willing to try doing the Atkinson style cam swap due to suspicions of reliability an actual effectiveness. I think for my application I would be better off with a normal style cam designed to run in my specific rpm range. Reason being, I saw a few stated claims that the Atkinson design was only 10-15% more efficient which would put me from 18hwy to 20hwy and reduce power output very noticeably. That seems like an absolutely terrible trade-off for the amount of FE gained. I would still like to see some actual hard evidence from someone that has tried it though, I'm just not willing to be the guinea pig in this situation.

[some_other_dave]

How much gas do you think you can save with the cam swap? My guess is that it would be rather less than 10%, probably more like 2-3% overall. Multiply that by how much gas you use per year, and by the price per gallon you want to use as your comparison. Then compare that to the cost of the cam swap, plus the cost of any tuning you have to do in order to accommodate that swap.

Unless you use a whole lot of gas every year, it will likely be many many years before you break even on the $$ spent.

-soD

[tierangst]

I would be plenty satisfied breaking even on the swap after 60k. I think it would improve the overall drive-ability and whether it saved any money over the long run it would still be cool to say I get an average 5mpg over EPA and with 250hp over stock.

[womprat]

I have a feeling with a big lazy torquey V8 the gains from an economy camshaft won't be as profound as some of the busy little engines out there. But if your doing big mileage on your vehicle it'll definatley pay for itself.

[tierangst]

From what I read online, the cam for the LQ9 is actually the same as for the LS1 cars. Seems to me like it would do a lot better to have a cam designed to operate in a lower range designed for my application, the LS1 cars aren't known for their low end torque.