Cam for fuel economy

[scrounger]

I am more interested in getting better fuel economy than performance. I drive below 60 mph 95% of the time and accelerate mildly, usually taking a mile to get to 60.

I have traced through some threads about camshafts and almost all topics are based on getting more performance. I saw the spread sheet graphs that theman posted discussing overlap.

Any idea on what camshaft would improve fuel economy.  I am thinking less overlap and lift. but am unsure as to timing and lobe centers.  Is there a special marine cam? I don't think I could afford a custom cam.

[CrazyAndy]

The AAZs  were available as an industrial motor that had a cam with shorter lift durations and very little overlap that were made to run at a fixed RPM.  I don't know where you'd find one, but that might be the way to go if you plan on goinf for maximum, rev-holding highway economy.  But the downside would be poor high rev performance and less power, but you are going for economy, so that won't matter to you.

[theman53]

Being a diesel I think you want the most air in as possible per stroke. The cam in a gasser will increase vacuum and open more, but there it is a fuel and air mix at approx 14.7:1 ratio. In that the bigger the cam the more fuel you use. In our diesels the more cam the more air, in turn the cleaner the burn. The only thing that will use more fuel is if you set your pump to inject more or press harder on the go pedal. I would think if you got the most performance cam you could get and not touch your fuel settings would yeild the best milage.

[scrounger]

Thanks for the responses.
I got an industrial AAZ cam on ebay for 40.

I agree that these engines need lots of air but I thought that having lots of overlap would tend to reduce cylinder pressure at lower rpms.

I plan on changing the timing belt this spring. Will install cam at the same time. If it proves not to work I will put  the stock cam back in. I wonder if I will have  to change the injector timing?

[TylerDurden]

I skimmed a couple of those cam threads and IMO camshaft tweeking seems like the most difficult and complicated way to improve efficiency, with the highest potential for the opposite result. Just my .02...

[scrounger]

I am not going to get it converted real soon but am acquiring the materials.

The powerband will be more like a TDI,  Peak torque about 2000 rpm and done by 4000. My best cruise speed will be a bit lower, just thinking can a TDI transmission be fitted? I have a 2.95 top gear now with 25" tires.

[bbob203]

I am not going to get it converted real soon but am acquiring the materials.

The powerband will be more like a TDI,  Peak torque about 2000 rpm and done by 4000. My best cruise speed will be a bit lower, just thinking can a TDI transmission be fitted? I have a 2.95 top gear now with 25" tires.

Yes it can i thought about doing it but was told that tall of a ring and pinion wouldnt work out to well.

You would need pedal cluster for hydro clutch or manual cable for the 02a transmission. cable operated shifterbox. a gearbox obviously and new clutch kit. Some holes here and there and maybe a few cut outs and your good to go.

[R.O.R-2.0]

Thanks for the responses.
I got an industrial AAZ cam on ebay for 40.

I agree that these engines need lots of air but I thought that having lots of overlap would tend to reduce cylinder pressure at lower rpms.

I plan on changing the timing belt this spring. Will install cam at the same time. If it proves not to work I will put  the stock cam back in. I wonder if I will have  to change the injector timing?

smaller cam will net you less power, and in the end, less economy, because you will have to push the throttle further to get the same power..

valve overlap is at a minimum on diesels, because there simply isnt enough room @ TDC for the valves to be open at ALL.. valve overlap is for gassers, diesels really dont need any valve overlap..

i would think that a Dr. Diesel cam would be a way better bet than a low lift, low duration industrial cam..

[Blownoiler]

I wouldn't advise copying the petrol engine guidelines when looking for economy, as mentioned above shorter duration will make the engine work harder because of the lower volumetric efficiency (more power wasted trying to inhale and exhale air/exhaust gas). Increasing V.E. will give better results. A well designed inlet manifold tuned to your cruising revs could lower pumping losses. Experimenting with the camshafts timing can improve V.E. in a particular rev range too if your engine has sufficient piston to valve clearance, advance the cam for more low end (at the expense of top end), retard for more top end (at the expense of low end)

[scrounger]

I am looking for running the engine up to 2800 maybe 3000 max.

Industrial engines are rated for max power from 3600-4200 rpm.

I am figuring that by closing the intake earlier I might be able to keep some air from bleeding out the exhaust valve while there is overlap, increasing the charge in the combustion chamber at lower rpm. More O2 should equal more torque (aka efficency) I'll let you guys roll by me at 70-80 mph.

If it was more efficient for having a bigger cam on the lower speed engine then surly the VW engineers would have specified a road cam in their industrial engines.

Maybe you guys are right. I think I owe it to myself to find out. A used cam was the only way for me to go. No regrinds or new cam money is in the budget.
Appreciate everyones comments.

[Blownoiler]

I did a cam timing experiment on a Toyota 2lt engine a few years back,  I got 2 extra keyways milled into the cam gear for about $60. by a local machine shop, that gave me 5 degree and 7 degree slots to play with. First up I advanced the cam 7 deg., and was expecting better power everywhere because of supposedly better (earlier opening exhaust valve) exhaust blowdown leading to more energy available to spin the turbine plus less pumping loss, what I got wasn't quite what I expected- the engine started much easier on a cold (0deg.C) morning, power was great up to about 3000 revs then nothing much at all to the 4000 redline. I found it difficult to keep up with normal hyway traffic with no top end power, 60 mph was it, where previously the 4runner would pull 75 mph. Around town i noticed a good gain in low end torque, I hardly had to touch the gearstick at all, it would just plug along happily down to 750ish revs in top gear.  Sorry but I didn't do any mileage tests with that adjustment. After a week I couldn't stand the lack of top end power so switched the camshaft to 7 degrees retarded, cold starts took a tad longer than the standard setup, low end power was slightly down, but 3000 to 4000 revs was much better. I advanced the injector pump a few degrees to get back the low end loss, so wound up with a good power gain overall. The standard 2lt used 12 litres/100 k. after a few mods to improve power, sensible driving netted 10 litres/100k (remember these 4runners are big windsocks on the hyway, so guzzle a bit of fuel). Edit: 7 degrees is a rather large adjustment to make, but the 2lt engine has a lot of valve to piston clearance, maybe 3 or 4 degrees is doable on your engine-you will have to check the clearance before running the engine with any adjustments!

[shorttimer]

I don't want to sound trite, but mileage STARTS with aerodynamics. Other things help.

[scrounger]

Thanks for the insight blown oiler.
My tach isn't working so I can't say exactly what my shift points but I am shifting if the next gear will pull smoothly, Typically I am into 5th at 30-40mph. If someone wants to pass me then so be it. It will cruise at 60 at 2-3psi. The car will run 95 mph now. I would be happy with 70-75 max speed if the fuel economy is improved some. Like you said. it is reversible if I don't like it.  Maybe a few degrees of stock cam timing advance would be a good thing to try.

Except for you, no one has said anything about personal experience with this subject. My first test will be running stock industrial cam timing.When I read your two recent posts I got two messages. One was to improve efficiency by building a new intake. Your next note was more positive to try the industrial cam. Perhaps you gained insight as to what I was trying to do.

Yep you have it there with aerodynamics short timer. The easy stuff has been done. I drive like a turtle.  My tires are rock hard. The car will coast a mile in neutral I have changed the shape of the back end, had  grill covers. The car has been mired at 55 mpg for the last year using aero mods.  Am looking to put it past 60, 64 to be precise, that is 2oz/mile. I had a post a while ago about some changes that I have made to aerodynamics. It was not well received.

[TylerDurden]

I wouldn't give much gravity to the feedback on aesthetics.

60mpg @ 55mph is probably achievable with the current aero mods and fine tuning of timing and break pressures.

65mpg will take a bit more effort (laws of diminishing returns, yadda...).

[bbob203]

scrounger you need to cruise on over to vwdieselparts.com forum aka the hillbilly forum and read haggars thread on tuning for smileage. I think it was called old man old rabbit both happy.