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Old 07-08-2008, 01:39 AM   #1 (permalink)
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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

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Old 07-08-2008, 03:11 AM   #2 (permalink)
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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.

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The problem we (car users) have is that the engines have too much power.
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..
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Old 07-08-2008, 11:05 AM   #3 (permalink)
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Originally Posted by texanidiot25 View Post
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.

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Old 07-08-2008, 01:05 PM   #4 (permalink)
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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.

Last edited by Andyman; 07-11-2008 at 07:57 PM.. Reason: missing word
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Old 07-08-2008, 05:42 PM   #5 (permalink)
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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.
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Old 07-08-2008, 06:05 PM   #6 (permalink)
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Quote:
Originally Posted by mechman600 View Post
An engine is most efficient at WOT at peak torque RPM, in terms of energy produced compared to fuel burned.
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.
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Originally Posted by mechman600 View Post
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).
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.
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Old 07-08-2008, 09:56 PM   #7 (permalink)
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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.

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Old 07-09-2008, 12:21 AM   #8 (permalink)
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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.
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Old 07-09-2008, 01:53 AM   #9 (permalink)
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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.
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Old 07-09-2008, 07:42 AM   #10 (permalink)
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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.

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