Fuel economy & valve lash (1998 Honda Civic)
 

I am wondering how valve lash affects fuel economy and emissions. It seems like loosening (within reason) should benefit both.

In essence loosening the valve lash to max spec should slightly reduce the overlap time between intake and exhaust, resulting in at least three things: less fuel escaping unburnt into the CAT, therefore more complete burn in chamber, and more low-end torque.

As ecomodders who drive the low end rpm band all the time this seems like a good thing. Heck my car almost never crosses 2500 rpms (~65-70 mph) even on the freeway.

So on my 1998 Civic the service manual's recommended spec is 0.009-0.011 for exhaust valves and 0.007-0.009 for intake valves. I set them to max spec of 0.011 and 0.009 on advice I trust and after some corroborating reading online.

I'd be interested in a technical discussion, because much of it would still be over my head a bit and therefore give me a chance to learn something!

Thanks.

A test would be a great way to show if there is any benefit... :)

The economy cam in the Metro XFi was ground for lower lift and duration, shifting the torque peak down.

You'd be effectively doing something similar by going to maximum adjustment, no?

Max gives you less lift and duration as well as max distance to the next adjustment.

regrards
Mech

Well, I wouldn't know how to ABA test such a thing, because it would take most of a day in between runs, allowing too many conditions to change. But the engine sounds differently (I think a little louder). And my FE has not suffered, though I can't tell if the valve setting has anything to do it. My primary goal was emissions test prep. And my smog test went smoothly. A side effect seems to be that it *might* help fuel economy at the same time.

I set my intake and exhaust valves to the thickest of my feeler gauges. I don't remember the size. It rattles more and it might cause excess cam wear, but I felt a slight torque increase.

I realize that it has been months since the last post on this thread but I am curious if any results came of this experiment?

I can't tell. If there was a benefit as there might have been jn theory, it would have been very minor. No way to see such a small change through thr background data noise. Sorry.

0.020" shouldn't hurt, but I'm not sure it'll help. And you really can't go any tighter than factory spec. More lash will cause the intakes to close earlier, trapping more fresh charge in at lower RPM, wwhich should help if your cruise RPM is too low. Likewise on the exhaust, the extra lash will help low RPM torque there again.
But if your cruise RPM is too high, then the tight end of factory spec would be better.
As you improve the aero of the car, it'll like less cruise RPM, or less lash.

I have not performed a valve adjustment in my civic, most likely has not been done in 150k miles.

On the insights, it actually makes a difference. I have adjusted the valves on a couple extremely loud cars, and they got a noticeable power increase, and got a massive noise decrease. If you haven't adjusted your valves for more than 100,000 miles definitely do it!

Ah, ok. Preformed a valve lash adjustment last during my last tune up as good maintenance practice. Also to .009 & .011. No noticeable mpg inncrease that I can attribute to this which had me curious about the other end of the "within spec" spectrum. Thanks

Video or it didn't happen, Balto!

Mine has like 115k miles now and I was thinking about adjusting the valves, but I'd love watching somebody else do it first. Have you taken any pics or video yet?

Its been a while since I owned or serviced my 92'Civic CX, but that first valve adjustment at 30K miles was a modest improvement. Intake valve on cylinder 1 was way out of spec at that time. (too much gap)So once adjusted the car was perkier on hard acceleration. I don't recall ever needing much adjustment after the first 30K service. I do recall replacing the valve cover spark plug gaskets/seals a couple of times on cylinder 3 and 4. Wait was it 2 and 3. I can't remember now. I read somewhere, that you should tried to get the gap within 90%+ on all cylinders of the closest to specs on intake valves. Not sure on exhaust. Supposedly, doing so assures the vortec or swirl effect is more "efficient" The author was a California Smog 90 certification holder.... I think the title was "How to fix, repair, and maintain your Honda." It was a good read, that I gave away shortly after trading the car.

Nah, I haven't tbh. Considering I work in a shop now, I don't think my fellow co-workers would appreciate me showing people how to do the work. On top of that, it's kinda messy. I'll see what I can do, but I doubt I'll be able to take pics or right a tutorial.

Maybe next time it needs a timing belt. They are not louder than my ear expects and I'd rather leave well enough alone

Even on a 500 HP V8, lash is no more than 10 HP gain or loss, and even in a 200 HP vehicle, you can't feel 10 HP. So it was just the placebo effect. That's why chassis dynamometers are so popular. That way you can know for fact how many horses are making it to the road. Dyno sheets, before and after, on video, including videoing the lash change, or it didn't happen. It's this little thing called scientific procedure.