Black & Green modding thread (1998 Civic DX Coupe base)

[California98Civic]

Getting closer with the head gasket replacement, which also turned into a lot of cleaning. Machinist took camshaft out of the head and put it back in differently, so I have been taking my time getting it right as far as TDC on the #1 for both head and block when the timing belt is off. Have leaned a lot about the head and lifters. Finished setting valve lash today. Got her back to TDC compression stroke on the #1... here it is:

[Gasoline Fumes]

Originally Posted by California98Civic

With my head at the machinist through the weekend, I am working on two or three ecomods. Reinstalling a slightly rebuilt set of wheel skirts, removing and modestly redesigning the side skirts, and most importantly trying to learn if there is a way to do a "fuel economy" or low emmisions valve lash adjustment when I put the head back on and must adjust the valves.

I think tighter lash on both the exhaust and intake will produce longer, earlier, and later openings of the valves and increase overlap. What do you think? A reduced gap between the rocker and the valve stem means longer duration of the opening, with earlier opening and later closing, I think. Overlap is good for scavenging.

I set my lash with my biggest feeler gauge. Works well if you drive at very low RPM. Overlap and longer duration is good for high RPM power. Try both ways and see what works better.

[California98Civic]

I set it to minimum lash spec because the research I did says doing so will enhance low rpm efficiency, torque, and emissions. Smog test coming this summer. With minimum lash, I will get more internal EGR, more exhaust scavenging, and more heat transfer to the CAT.

[Gasoline Fumes]

Originally Posted by California98Civic

I set it to minimum lash spec because the research I did says doing so will enhance low rpm efficiency, torque, and emissions. Smog test coming this summer. With minimum lash, I will get more internal EGR, more exhaust scavenging, and more heat transfer to the CAT.

I'll admit I don't know the effects of lash on emissions. But increasing lash will reduce lift and duration, which is what you want for low-RPM. Most of my driving is at 1200-1500 RPM and I noticed a slight improvement in torque with excessive lash. And a lot more noise!

[California98Civic]

Originally Posted by Gasoline Fumes

I'll admit I don't know the effects of lash on emissions. But increasing lash will reduce lift and duration, which is what you want for low-RPM. Most of my driving is at 1200-1500 RPM and I noticed a slight improvement in torque with excessive lash. And a lot more noise!

I am no expert, either. Here is the main text I have been examining... it is called "THE IMPACT OF VALVE EVENTS UPON ENGINE PERFORMANCE AND EMISSIONS" and the best way to get it is probably through a google search for the title. It is a PDF. I downloaded it without trouble so it seems safe. Take a look at how it explains the effects of timing valves. Lots of subtlety but in pretty ordinary language. Really useful. See if you read it the way I did.

[Gasoline Fumes]

Valve overlap info from the PDF:

A given amount of overlap unfortunately tends to be ideal for only a portion of engine speed and load conditions. Generally, the torque at higher engine speeds and loads can benefit from increased overlap due to pressure waves in the exhaust manifold aiding the intake of fresh charge. Large amounts of overlap tend to result in poor emissions at lower speeds as fuel from the intake charge can flow directly into the exhaust. High overlap can also result in EGR which, although beneficial to part load economy, reduces full load torque and can cause poor combustion stability especially under low load conditions such as idle. Poor idle quality can therefore result from too much overlap.

Overlap isn't good for low-speed operation. Not that you can increase it much without changing the camshaft anyway.



Valve Lift info from the PDF:

Low values of valve peak lift will clearly restrict the ability of gas to flow into and out of the cylinder, effectively throttling the engine. Maximum engine power output will generally benefit from as much valve lift as possible up to the point where air flow becomes restricted by other features such as the manifold system or cylinder head porting.

It does not follow that engines should have the maximum possible valve lift as this can adversely affect low speed performance. Lower intake valve lifts result in higher gas velocity past the valve and this improves fuel mixing and combustion. For maximum torque at a given speed, lift should be kept as low as possible up to the point where the intake of fresh charge becomes restricted.

Part load economy will benefit from the intake being restricted by valve lift, as it reduces the need for throttling by the engine throttle and this will reduce intake pumping losses. Lift is not normally dictated by part load considerations, as this would severely limit the potential output of the engine.

The chosen value of peak valve lift is therefore a compromise between low speed and high speed full load requirements. A typical value for a production engine is in the range of 8-10mm.

Reduced lift is good for economy.

[California98Civic]

Thanks for looking it up and posting.

I don't care about full load operation since I never floor it. And I don't care about lost torque anywhere on the power band because it will mean opening the throttle plate more and therefore reducing pumping losses. I am interested in economy here but I am equally interested in better emissions.

I read that overlap section you quote as mainly a warning about excessive overlap. So I chose to discount the warning because I am not exceeding Honda factory specs, just maximizing overlap within specs. The peak valve lift section you quote is interesting too, but both of these sections need to be thought of in the context of the four sections of EVO, EVC, IVO, and IVC.

So I studied the document again and made some changes. Thanks. These notes below are as much for me as anyone else with my SOHC 16 valve engine. If you have further thoughts, I would love to hear 'em.

Limitation
First, my engine's limitations. Because of the design of my SOHC 16 valve cylinder head:

(1) If I set LESS clearance (lash) I must have this combination of valve movement characteristics: EARLIER opening, LATER closing, LONGER duration, and HIGHER peak valve lift values.

(2) If I set MORE clearance (lash) I must have this combination of valve movement characteristics: LATER opening, EARLIER closing, SHORTER duration, and LOWER peak valve lift values.

NEW SETTING:
I am thinking to change the setting to MORE lash on the exhaust side and LESS lash on the intake side. I had set for less all around. MORE lash on the exhaust side would be better than the LESS lash I set yesterday. So now overlap does not get bigger than stock as I was planning. Instead it moves slightly closer to the intake side. Doing so should reduce the likelihood of fuel mix going straight into the CAT. What I lose in scavenging I will gain in EGR. More internal EGR in the cylinder and the intake manifold will improve efficiency at partial load and low RPMs (how I drive this car). It should also improve emissions by more completely burning fuel before combustion gasses escape.

That's in theory. It is a really minor set of changes, actually. So I am kinda overthinking it, but I am learning about the dynamics so that is maybe good for the future.

Questions that remain for me:
If these adjustments change burn and flow, O2 sensor and MAP sensor data to the ECU will also change. How might data changes affect how the ECU sets AFR and ignition timing? Could any changes from the ECU negate the valve adjustment mod?

[California98Civic]

So this is what that gobbly-guk writing in the previous looks like on the head: 0.007" lash on the intake lifters & 0.011" on the exhaust lifters. There is visibly greater peak valve lift on the intake side. The most conventional settling would be 0.008 intake & 0.010 exhaust.

[California98Civic]

She is running! Timing is more stable than I ever remember. Temps are a little unsteady, but maybe I am paranoid. It is hotter and there is prolly still a lot of oil in the coolant system contaminating the coolant. Lifters sound loud, but oil is still prolly low even after my adds. Dip stick reads at the minimum.

But it is running! It would seem I did it. And did a little mod in my valve lash setting to boot.

[Xist]

Glad to hear it! Are you going to flush the radiator?