Camshaft timing/tinkering (2001 Civic LX)
 

What a great website...so much info.
I have a 2001 Civic LX, non-VTEC, automatic (for the wife). It's my wife's car...my vehicle is a bicycle 1/2 the time, and a Yamaha scooter the other 1/2. I'm currently building a hydrogen generator for the Civic in my spare time just to see what happens.

I have a thought. Toyota's basic VVT-i system changes the timing of the intake camshaft. For low rpm it advances it, for high rpm it retards it. BMW's Vanos system (of the mid 90's to very recently, if not currently) changes the timing of both exhaust and intake cams and even uses this system to allow some in cylinder EGR action.

My question is: why not put an adjustable cam pulley on my engine and advance it incrementally until I get the best mileage possible. I've heard that this will work, but has anyone on this forum tried it?

Another thought: decreasing valve overlap/int&exh duration/lift with promote a power band much lower in the rpm range. On an engine with mechanical valve lash adjustment like mine, why not back the lash adjusters off to get the desired effect of a more economical camshaft? Like instead of my current 0.008"/0.010 lash (int/exh), try 0.015/0.017 or 0.020/0.022 or 0.025/0.027? You could even vary between pairs on a single cylinder to achieve a "dual cam pattern" effect. Yeah, I know my valve train would make a racket, but with some slick 50 (or whatever) and keeping the rpms down, maybe it would be tolerable.

The problem we (car users) have is that the engines have too much power. What I mean is that my Civic does NOT need 115HP to get the job done. 50 HP would probably do. So if i can change the engine to make it's peak volumetric efficiency at 2500 RPM instead of 5000 RPM, which in turn will lower my horsepower considerably, will not ridiculously better economy be a nice side effect?

One more idea: How about removing one intake and one exhaust rocker from each cylinder to make it an 8-valve engine instead of 16? It is possible, I checked it out when doing my valve lash adjustment. Or just the intake ones to make it a 12-valve? That would cause a major reduction in volumetric efficiency, and as a result, exponentially higher intake charge speeds. Besides, that's what a VTEC is doing at low rpm anyway.

I should stop thinking out loud now. I'm starting to scare even myself.

James

Certainly some interesting ideas.

Might look into aftermarket cam shafts that will also lower the RPM range for peak power. Not sure about the Honda motors (considering most cams for them are probably gunning for peak power at high rpm), but cam selections for the Small Block Chevy for instance, come in a huge variety for where you want the power. Anywhere from a cam that gives a range of 2500-4500, to one that sings at 3000-6000 rpm.

Sometimes that power is needed to carry along the extra weight of today's bloated cars. A Civic 20 years ago can get away with that lack of power, and be a fun car to drive. I wouldn't toss a 40hp 4-banger into the current Civic. Less the engine has to work, the less fuel it needs to consume..

I don't agree. The Prius has a smaller engine than most that works WAY harder than most, which makes the car efficient. The idea is that if you use a smaller engine that is working at its peak (moving the car, charging batteries, or whatever), it will be more efficient than a larger engine not working at its peak. An engine is most efficient at WOT at peak torque RPM, in terms of energy produced compared to fuel burned. Unfortunately, at WOT peak torque, any car currently produced will be accelerating vigorously producing way too much energy.
I just came back from a road trip where I drove the steepest, hilliest highway known to man, the Coquihalla (BC, Canada). Lots of time is spent going up 8-9% grades (to 2 summits) and coasting down the backside. Fuel economy always ends up being the best in this situation because the engine is working at peak torque uphill, and coasting down (using zero fuel). My normal 44 mpg (imp) went to over 50 mpg during this segment. Anyway, that's off topic. Back to my questions please.

James

I think you will find that if you advance the camshaft you will hurt your fuel economy. I've tried changing valve timing on four different engines and every time the more retarded setting gave better fuel economy. Normally retarding the camshaft increases fuel economy, reduces low end torque and increases high RPM horsepower. It also makes the idle quieter. If you retard it a lot, you will lose power at all engine speeds. The four engines I used were a Ford 351C, a Porsche 2.2 flat six, a VW 1.7 four cylinder and a Chevrolet 1.8 four cylinder in a Pontiac version of the Cavalier. On the Ford and Porsche engines, I retarded the valve timing and gained fuel economy. On the VW and Chevrolet engines, I advanced the timing and lost fuel economy but gained low end torque. On the Porsche, the engine felt a little weak at low speed but it became very powerful above 4000 RPM. Its fuel economy went up from 24 to 27 MPG on the highway. The VW engine was in a Plymouth Horizon with manual transmission. Its highway mileage went down about 9 MPG when the camshaft was advanced by one tooth. It could get 44 MPG in the more retarded position. I decided to change it back. The Ford actually doubled its mileage from 9 MPG to 18 MPG after I retarded its performance camshaft by 12 degrees. It also lost power at all engine speeds. I later set it to 8 degrees retarded for some extra power when I deactivated four of the cylinders. The highway mileage with that setting was 24 MPG. I would like to have a way of adjusting the camshaft while driving. It could run retarded most of the time but go to a more advanced position for fast acceleration at low engine speeds. The Pontiac was too sluggish with the original timing. I think I advanced it by 4 degrees and reduced fuel economy about ten percent.

I tried asking a mechanic in a garage about the effect of valve timing on fuel economy and his answer was that advancing the camshaft increases torque and fuel economy. That seems to be the prevailing belief of people who want to modify engines. Experiments show that they are wrong.

If you can find a camshaft with less duration it may help you get better economy. I would not recommend increasing the valve lash by more than a couple thousanths of an inch. That causes more stress on camshaft lobes, rocker arms, valves and valve seats. They may wear out fast, especially if you use high engine speeds. If you break a valve, the damage is even worse. You could destroy a cylinder head, piston and cylinder wall.

I agree that car engines are too powerful for best fuel economy. Car engines are most efficient at about 1/3 of maximum power. If you normally use 15 HP to drive 55 MPH, a 45 HP engine would be the right choice. The displacement would be about 750 cc. Of course you would have to accept slow acceleration and hill climbing. Normal car engines usually are most efficient at about 2500 RPM and about 2/3 throttle (not WOT). Some vacuum improves fuel vaporization. If your engine runs on natural gas then it might be most efficient at wide open throttle.

It is possible to remove rocker arms from Honda engines. I tried it in my Accord to see how it runs on two cylinders. Be sure to block any oil holes in the rocker shafts where rocker arms were removed with hose clamps so you keep up the oil pressure to the other rocker arms. Deactivating half the intake valves may increase your fuel economy but deactivating exhaust valves will probably reduce power without helping fuel economy.

Andyman, I think that you will find if you can advance just the intake cam (on a DOHC engine) you will improve low-end torque and fuel economy. The engines you mentioned IIRC, being too lazy to check, are all single-cam engines. You are only advancing/retarding the timing of the entire valvetrain events relative to the crankshaft. By advancing/retarding the cams independently in a DOHC engine you are effectively changing the LSA. The 2008 (or maybe 2009) Dodge Hemi does this using a cam-within-cam arrangement to adjust intake timing by shifting the lobe separation angle, and improved both power output and fuel economy.

I've actually experienced what mechman600 is describing in a Honda v-twin air-cooled industrial engine. Those engines have to have the valve lash adjusted rather frequently upon initial break-in. So much so that out of the box they are often ZERO to .002" both intake/exhaust so that they wear in to their specification. If they get wider than spec by more than .004 or so the idle speed of the engine will begin to creep up dramatically because the engine runs more efficiently at the low (<2k rpm on a 3600 rpm governor) speed range. You're then left to adjust the carb's idle stop but even then sometimes the air bleed through the pilot circuit is enough to run elevated idle until you clamp back down on the valve lash.

I talked to an old-timer drag racer who used to adjust valve lash depending on how the car launched. If the car bogged off the line, he would loosen valve lash to get more torque. If it spun off the line, he would tighten it down to reduce low-end torque.

It's a trade-off between low speed torque and high speed power, but for fuel efficiency the high speed power situations are rarely experienced. The reduced valve lift at lower speeds should help improve combustion by increasing port velocity. If you're going to do a 12-valver I'm not sure if you're better off dropping 4 intakes or 4 exhausts...most 3 valve engines have 2 intakes and 1 exhaust. Ferrari once had a 40-valve V8 with 3 intakes and 2 exhausts. If i were to try anything that adventurous I'd probably drop from 16 to 8 and see if that was too much of a loss, and if I needed a mid-point I'd add the intakes back in. Reduced exhaust flow will increase retained EGR, but choked intake flow could really hurt your pumping losses.

Sorry, but minimal BSFC is almost always found at lower engine speeds than torque peak and at about 80% of peak load. At WOT you'll have power enrichment and, in some cases, spark retard if knock limited.
If that was the case then we'd all tow boat anchors when accelerating just to increase loads as much as possible and get better FE. We don't because higher power demands from an engine won't get us better fuel economy.

Fuel use increases with power, so the more power you were making climbing those hills the more fuel, pounds per hour, gallons per mile, you were burning. It's true that brake secific fuel (pounds of fuel used per horsepower produced) will be better at high loads, but that's kind of a red herring. The first thing you want to do is reduce the power demand as much as possible, THEN you want to go for more volumetric efficiency (reduced throttle/pumping losses) at that power.

Sorry my bad. Everytime I drive this stretch of road and my mileage is over 10% higher than normal "flat" highway driving, my calculator is clearly making a mistake. I'll be sure to buy a new one.
Right.

James

You're right that none of the engines I mentioned had DOHC. I'm not convinced that advancing only the intake camshaft will increase fuel economy. This would increase valve overlap and reduce reversion of gas flow (from cylinder to intake manifold) at the beginning of the compression stroke. The reversion helps to lower intake manifold vacuum when the engine runs at low speeds and low loads. This causes a reduction in pumping losses. Advancing the camshaft increases the vacuum at a given power level and therefore causes increased pumping losses. Increasing the valve overlap is also likely to reduce fuel economy by increasing the amount of exhaust gases mixing with the intake mixture. Too much EGR slows down combustion.

Do you know how the intake valve timing is controlled in the new Dodge Hemi? Does it depend only on engine speed or is it also affected by the throttle position? What is it at idle? I would think that the most efficient way to control it to leave it retarded except at low speed and high load.

That's interesting about how the valve lash affects the industrial engines. Part of the idle speed change may be caused by the engine pulling in more fuel by increasing manifold vacuum. I can believe that they also more efficient at low RPM with more valve lash.

You reminded me of an experiment I did on a lawnmower engine. I removed the engine's thick head gasket and put back the cylinder head with some sealant. This raised the compression ratio. The engine ran faster than normal even though the throttle was at the minimum. I didn't get to use it very long. It broke a connecting rod. I guess it was running faster than the redline. If it didn't break I would have had a very fuel efficient lawn mower.

I've read that the Honda VTEC-e engine keeps half of the intake valves shut during low speed operation. I think this increases turbulence in the combustion chamber and speeds up combustion. Both of the exhaust valves work all the time. I agree that choked intake flow could increase pumping losses but that would only happen at high RPM.

To garys_1k: a lot of what you're saying is true but I believe mechman600 when he says he can get better fuel economy in the hills then he can get normally. His engine is more efficient at high loads than low loads so it is better to use a high load part of the time and no load the rest of the time than to use a low load all of the time. It's basically the same as pulse and glide (or burn and coast) except that hills let the speed remain relatively constant. If the engine was small enough to run at maximum efficiency at highway speed then the hills would probably reduce fuel economy by causing the engine to run at higher power than the level that gives greatest efficiency.
In general it's true that lower power demands help fuel economy. Keep in mind that mechman600's car still has about the same average power demand in the hills as on a level road.

Thanks for the insight, especially Andyman and MechEngVT.
I would be hesitant to go more than a few thou on the lash over spec, as you've said. A cam profile slowly lifts the valve off its seat, and rapidly opens and closes it before gently setting it back down. Throwing a 0.030" clearance in there would probably prevent the "gentle" beginning and end from taking place, thus increasing the stress on all parts in the process. I really do think more economy is possible through drastically reduced duration & lift, and this would be the easiest way. But I can buy a lot of gas for the price a new valve-train.
And I never thought of manifold vacuum helping with atomization (2/3 throttle vs. WOT). Interesting.
Ideally, I'd like my 1.7 to make peak horsepower at 4000 rpm and peak torque at 2500, but that's asking a lot, as it's around 5800/4000 as is. torque would remain the same, horsepower would obviously be much lower, like 75 or so. I need someone who has the machine to grind camshafts to my spec. Yikes...that would be a cool machine to have.

Andyman is right..."advancing" the intake cam WILL reduce lobe separation angle, not widen it. You want to retard the intake and/or advance the exhaust to widen lobe separation, which is the net effect of increasing valve lash (ignoring the change in lift). That lawnmower probably didn't overspeed as most small engines are rev limited in the valve train, but probably started to warm up and the connecting rod and crank throw expanded faster than the block until you smacked the piston into the head. If the connecting rod was the weaker link, there she blows. You probably would have been fine if you kept the (probably about .040" thick) gasket but milled the deck by .010 or so.

garys_1k: you ignore the law of conservation of energy. Climbing a mountain uses more fuel per mile driven but that fuel isn't just pissed into the wind. The energy from burning it is converted into potential energy due to the change in elevation of the vehicle. As mechman600 stated, if he EOC's down the back side of the mountain he's burning ZERO lbs per mile and recovering the potential energy. Dragging a boat anchor to run at peak BSFC *is* pissing fuel into the wind because you've got nothing to show for it in the end. Climbing a mountain is different. BSFC is not and won't be a red herring as you use and/or tweak your BSFC (more accurately iso-efficiency islands) to determine if you are indeed better off running at high load at lower speed or lower load at higher speed. There's often overlap or times when the unintuitive is better.

There was a guy on GS who lives in the rockies and gets phenominal mpg (with a vtec ford stick shift). I have a few hilly spots on my route that I get terrific mileage through also so I suspect there is something to it.

The anchor analogy is interesting, but the engine stops having to work so hard once up to speed, unlike when climbing, so not exactly the same scenario, but might be an interesting test :) I have had some of my best runs with passengers in the car (EOC style of course).

When you think about it, a hybrid car is sort of like a hill. The engine works harder than normal (because it's smaller than normal and is charging batteries) so it can turn off when running in EV mode when it uses no energy. Also, the newer multi-displacement engines are another example of "working harder = more efficient", having half the cylinders working twice as hard as normal during cruising speeds, saving fuel. A little bit, anyway.

The Prius has a variant of the engine in found in the Yaris/Echo/xA/xB1. However, instead of 105-108hp, it makes 76hp (IIRC). This is achieved through a valve cycle scheme that maximizes efficiency at the expense of power. As such, what mechman600 wants to achieve isn't completely insane. 50hp in a non-80s Civic would probably verge on undriveable, but changing the cams to keep the peak power at a low RPM would probably help a lot.

The Prius uses the Atkinson cycle, as opposed to the normal Otto cycle.
Atkinson cycle - Wikipedia, the free encyclopedia

In effect, it lowers the compression ratio by keeping the intake valve open longer than an Otto cycle engine.

So does anyone have a SOHC Honda where retarding the cam increased FE? I advanced the cam on my SOHC Honda engine (Acura Vigor) and low end torque is definitely up, and FE seems to be up...but that could be a placebo effect.

I dont think its a placebo Rower, retarding the cam reduces the dynamic compression ratio wihich is not good for efficiency.

That was what I figured. The torque from 800-2000 rpm is noticeably improved also...I can lug along in 5th ~5mph lower than I could before. Shift earlier also....accelerating on the flat I can shift at 1500rpm.

If you advance the camshaft you might be advancing the ignition timing at the same time because the distributor is usually connected to the camshaft. Advancing the ignition timing can make the engine more efficient and may have a greater effect than the change in valve timing. If the engine has a crankshaft position sensor then the ignition timing probably depends on the crankshaft instead of the camshaft. In this case it might not be a good idea to retard the camshaft because the lower cylinder pressure requires a more advanced spark for optimum efficiency and there is no adjustment to change it. Possibly you could increase intake air temperature instead to speed up combustion.

If the camshaft is set more retarded then the engine can tolerate a little more advanced ignition timing without knocking. This combination is likely to give the best fuel economy. If you retard the camshaft and it retards the ignition timing at the same time, I would expect lower fuel economy.

I have another Honda with a SOHC engine, a '94 Civic with a 1.5 liter 8 valve engine and 5 speed transmission. It has an old worn timing belt. I tightened the belt tensioner pulley so it wasn't as loose. That has a side effect of retarding the camshaft a little. Then I advanced the ignition timing a little. I took a long trip and the car averaged 50 MPG when I used about 10 gallons to go a little over 500 miles. I don't know what it would do with a new timing belt which would probably advance the valve timing a little.

I think that there are two reasons that retarded valve timing should help efficiency, at least at low RPM. One is that a later closing intake valve reduces vacuum during the intake stroke, reducing pumping power loss. The other is that a later opening exhaust valve increases the expansion ratio during the power stroke, recovering more energy from the burned gases before they are released to the exhaust system.

An ideal engine would have a completely vaporized fuel mixture, have no vacuum during the intake stroke (open throttle), compress the mixture as much as possible without preignition or detonation (about 8:1), burn all the fuel before the piston moves down, keep the heat in the gas instead of heating the engine, expand the hot gas until it reaches atmospheric pressure (which would probably require an expansion ratio of at least 16:1), and then release the exhaust at atmospheric pressure during the exhaust stroke (no exhaust restriction). The Atkinson cycle gets closer to this than a normal Otto Cycle. A retarded camshaft makes an engine more like an Atkinson cycle engine. Ideally the engine should have longer duration on the intake valve so the middle of the valve overlap period can be near TDC (piston at top dead center).

The reason the engine is tollerating more ignition advance is that the dynamic compression is down. If the engine likes more advance but you cant accomplish this without lower compression then you need more octane.

The vacuum that is at the throttle means diddly, its the vacuum at the top of the piston that is creating drag. Ideally the piston top sees atmospheric pressure for the whole intake stroke instead of near the end of the stroke. You need max valve lift early to minimize pumping loss throughout the whole stroke instead of just the end.

A late exhaust event makes for a lazy flow. This could be advantageous in that you may get more EGR which reduces your pumping losses.

A very interesting topic...still. To better visualize it in my head, I paintbrushed a crude diagram. Hopefully the attachment at the bottom works for you.

From what I see, Andyman is right. In theory. Retarded = lower dynamic compression and lower pumping losses like the Atkinson cycle, and also a larger expansion ratio. Advanced = higher dynamic compression and higher pumping losses but lower expansion ratio. 1/2 dozen one, 6 the other. All theories, so I appreciate the stories of people actually testing the results. In reality, how big of a difference will it make if I retard/advance (depending on who's right) the cam timing? 5%? Who knows.

Does anyone know of a manufacturer who makes "economy" cams for a Honda D17A1? I really doubt it as all I can find is high performance ones.
Super low duration and little valve overlap would be good. Wait a minute...how about high-perf cams made for forced induction....they have very little valve overlap and less duration than typical high perf cams, but lots of lift. Would one of those work in an economy minded engine?

[edit] Nevermind. I just looked at some specs for forced induction race cams and they have waaaay more duration than stock ones. I should have known.

James

Ok, I agree about the vacuum on the piston but a late closing intake valve does lower the vacuum in the intake manifold and that should be about the same as the vacuum on the piston when the intake valve is open. The late valve closing causes some of the air to return to the manifold at the end of each intake event. That lowers the average air flow. To regain the lost air flow so you still make the same power, you will have to open the throttle more. That lowers the restriction and the vacuum. The reduced vacuum would be applied to the piston during the whole intake stroke.

I also agree about the lazy exhaust flow when the exhaust valve is opened late. That would increase the pressure during the exhaust stroke which is another factor in the pumping loss. There is an optimum opening point depending on engine speed. For low speed, the valve should open later and for high speed the valve should open earlier. When I'm driving I only rarely let the engine get over 3000 RPM so I prefer to have the timing efficient for lower speed operation. It would be best if all the valve events could be adjusted while the engine is running. It's not an easy or cheap thing to do.

I like those valve timing diagrams.

This is making me think that disabling 1/2 of the intake valves would be a stupid idea. It would make the vacuum on the piston much higher and more efficiency would be lost than gained. What we need is a very good breathing engine with an extremely short duration camshaft....like 200/200 degrees seat duration or less, as opposed to the 280/290 or so as is. Peak torque @ <2500. That would rule. Would my engine management system know the difference? Or would the CEL come on, throwing this whole thing into an open loop nightmare?

I really don't think retarding the valves (open later) would move peak torque down lower in the rpm range....it may reduce pumping losses and provide for a larger throttle opening for the same power. Advancing the cams moves peak torque lower...in fact I think I moved mine below 2000rpm by advancing the cam 9-degrees...this was probably too much. If I cut that advance in half and make a cam key that allows for a 4-5 degrre advance I think it would be much more optimal....boosting low end torque, but moving peak torque closer to cruising rpm range, not below it. Too much advance most likely hurts pumping losses too much at cruise rpms.

Honda seems to think it's a good idea to close half the intake valves. Their VTEC-E engine uses one intake valve for low speed operation and both intake valves for high speed operation. I'm not sure what RPM activates the second valve. I would think it might be about 4000 RPM. This engine is very fuel efficient and I think the closed intake valves give it an economy boost. The faster air flow into the cylinders helps to speed up combustion and that will cause more of the energy in the gasoline to make mechanical work instead of exhaust heat. The extra restriction doesn't do much to change the vacuum on the piston except at full throttle and high RPM. A little extra restriction at the intake valves can be compensated for by opening the throttle a little more. Then you don't have a higher vacuum at the pistons. At high RPM you need the other intake valves working to get maximum power.

A short exhaust duration will help low RPM torque and fuel economy but a long intake valve duration combined with an increased compression ratio can give a big improvement in fuel economy, especially with a large engine. The late closing intake valve reduces low RPM torque but may increase high RPM torque if it isn't very much later than normal.

I remember reading a story in Hot Rod magazine about this concept about 1982 or so. They built a Chevrorolet 350 engine with a very high compression ratio by using taller domed 327 pistons and then grinding the heads so there would be enough room for them. I think the compression ratio was about 14.5:1. They also got a custom camshaft with very late intake closing events. That allowed a normal cranking compression pressure. They used the engine in a tow truck pulling a heavy trailer. The result was a big gain in miles per gallon. I think it went from about 9 to about 16. In another issue they installed the Crower Mileage System in a Chevy V8 engine and put it in an old Hot Rod, something like a 1929 Chevy. The axle ratio was high, maybe 4.11, and they used extra fat rear tires. That seems like a big mistake if they were interested in fuel economy. They reported that the car would often achieve over 25 MPG. That's a very high number for a car with a V8 and an automatic transmission without lockup torque converter or overdrive.

I think I still have those magazines and could probably dig them out. I remember that they did a dynomometer test and reported some amazing BSFC (engine efficiency) numbers at low RPM. The power was lower than normal, probably a little over 200 HP. Torque was pretty low but increased at higher engine speeds.

Changing camshaft timing, especially the intake valve closing event much will disturb the fuel injection calibration if your engine uses a MAP (manifold absolute pressure) sensor. It probably will turn on the check engine light. On my Honda Civic with the worn timing belt I needed to connect a resistor to the MAP sensor output and ground to avoid a rich fuel mixture. If you have fuel injection with an air flow sensor (like Bosche systems on european cars) then it will be more compatible with altered valve timing. All the engines I used for camshaft timing adjustments had carburetors. Carburetors may run a little rich at low RPM when the intake valves close late because of a more pulsating air flow.

It would be possible to reduce compression pressure by having intake valves close very early instead of very late but then the power would be reduced severely. This would only be practical for an engine running with a limited speed range or an engine with variable valve timing.

The closed valve at low rpm keeps the velocity across the valve up at low speeds. Not sure where I saw it but aparently as the flow approaches sonic it does amazing things for atomizing the air fuel mix.

I partially see your point about low engine load, but I dont agree that retarding the intake event will reduce pumping loss. Widening the LDA will reduce the overlap and internal EGR which will increase pumping losses.

The camshaft retarder
 

I just found something that shows that Cam Dynamics experimented with valve timing and found that retarding the camshaft improved fuel economy. They apparently were thinking about selling something called the "camshaft retarder". My guess is that it would retard the camshaft during light load operation. Check this link:

Energy Citations Database (ECD) - - Document #5538464

This is the important part from that page:

Recognizing that camshaft design in the modern automotive engine is at best a compromise for overall performance, Mark Heffington of Cam Dynamics, Inc. set out to maximize gas economy through the utilization of variable cam timing.^The initial question was whether gasoline economy could be improved upon through varying the value timing over the operational range of an automotive engine.^The testing procedure duplicated the load conditions that the automobile would be experiencing during operation.^We tested gasoline consumption from IDLE up through 60 mph in 10 mph increments.^Without question, variable valve timing is a realistic means for improving fuel economy in today`s automobile.^Further testing and development need to be done to work with the pollution controls which have an effect on the results.^The camshaft retarder is an excellent device to alter the valve timing of the standard camshaft in order to achieve better fuel economy.

FYI, in addition to lower lift & duration, the Metro XFi cam is also reportedly advanced, compared to the non-XFi cam (this from the guy who does economy cam grinds):

Note the Metro is SOHC.

Everyone who has done the XFi cam swap, myself included, has reported improved low-end torque / driveability, which should contribute to reduced fuel consumption. Impossible to say how much of this is due to valve timing vs. the lift/duration changes.

Coyote X did an (admittedly not perfect) cam retard/advance experiment and noted these results. He also re-adjusted his ignition advance to maximize it (without ping) after each cam adjustment.

http://rthompson.us/wp-content/uploa...2/camvsmpg.gif

If you are gonna monkey with the camshafts, why not get a grind that make it Atkinson cycle. Why monkey with halfway measres when you know of something that works?

I wouldn't argue with that - going Atkinson.

Though I don't think there's anyone debating whether or not the XFi cam works better for FE compared to the garden variety cam.

It's an old but very interesting thread. I was wondering if I could change a bit camshaft setting in Berta, to get better FE. The good thing is that camshaft sprocket in TDS engine is mounted the way that you can freely adjust it's angle. It's completely analog :)
I've read this topic but it's gasser related. So maybe someone has experience with adjusting diesel engine's cam? I know I need to be very careful, because once piston will meet valve and I'll have second engine restoration in Berta. I'd love to avoid that :)

So anyone? It's just a thought for now, but results can be interesting. So maybe that's worth a try. Don't you think so?