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Discussion Starter #1
At the June meetup in Frederick, @PTA2PTB mentioned something about someone who replaced the gauge on their compression tester with a pressure sensor so they could see the entire stroke, not just the peaks. So I ordered a pressure transducer on Amazon, hooked it up to an Arduino, and below is roughly two revolutions of one of the cylinders:

compression-data-annotated.png

While I might be able to measure this, I know absolutely nothing about what to do with it. So for those who may have experience with tuning for racing (cough @jime cough), is there any way this data could help us in tuning the valve lash for MPG?

For example, can tweaking the intake lash for maximum compression give us better mileage?

Could tuning so that the exhaust valve appears to open at the very bottom of the cylinder help? Given this plot, it looks like the valve is opening shortly after reaching bottom - should the lash be a little tighter so it opens sooner?

Or do we not know enough about the engine, and need some dyno time to help us identify the optimum valve opening and closing positions first?

Specific to this plot, note the little bit of negative pressure at the bottom of the cycle. What are the possible reasons for this? Can this inform a procedure for setting up the valve lash?

Finally, might we also use this to tweak VTEC valve timing? Would we want to first reset the regular valves such that we can best observe our tweaks to the VTEC valves, set the VTEC valves with the VTEC mechanism engaged (how, if it is driven by oil pressure), mark the VTEC settings with a pen, then reset the VTEC valves so we can best observe the regular valves, set the regular valves, then return the VTEC valves to the marked positions?
 

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Discussion Starter #3
Cool! I misunderstood you! When you said that this person was capturing compression readings in a different way, I automatically assumed they were using a pressure sensor. Detecting a shot cylinder using cranking current is a pretty neat idea. If you did this with the IMA motor and the injector connectors pulled, you could crank for quite a while while measuring the current, overlap the readings every six revolutions, and average out the noise to do something similar to what this person has done but with more sensitivity.
 

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At the June meetup in Frederick, @PTA2PTB mentioned something about someone who replaced the gauge on their compression tester with a pressure sensor so they could see the entire stroke, not just the peaks. So I ordered a pressure transducer on Amazon, hooked it up to an Arduino, and below is roughly two revolutions of one of the cylinders:
Sean with all due respect, with all these questions about valve timing you have some reading to do on the web.

It's pretty well known what various changes in valve timing does. But you'll need a cam grinding machine to experiment (oh and a dyno too).

If there was a simple way to increase the mpg I would think that the Honda engineers would have tested it out (and we have the results now).
 

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Discussion Starter #5
Sean with all due respect, with all these questions about valve timing you have some reading to do on the web.

It's pretty well known what various changes in valve timing does. But you'll need a cam grinding machine to experiment (oh and a dyno too).

If there was a simple way to increase the mpg I would think that the Honda engineers would have tested it out (and we have the results now).
Hi @olrowdy,

I forgot that you'd be a great source of this info too.

I actually have no intention of modding the valves. The pressure sensor, though, seemed to show promise of optimizing intake and exhaust adjustments. I know first hand that I originally found mine too tight, and setting them to spec increased my mileage by about 10%.

Later,

Sean
 

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Hi @olrowdy,

I forgot that you'd be a great source of this info too.

[Blush]

I actually have no intention of modding the valves. The pressure sensor, though, seemed to show promise of optimizing intake and exhaust adjustments. I know first hand that I originally found mine too tight, and setting them to spec increased my mileage by about 10%.

Later,

Sean
Of course setting the clearance to the recommended settings just restored the engine to the correct state [base line].

But increasing mpg by tweaking the clearance further will probably not gain enough to notice with all the variations while driving.

Probably just keeping the tires inflated to somewhat higher pressure (55/50) would keep the mpg more consistent.
 

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Discussion Starter #8 (Edited)
I'm stupidly pressing forward with this idea because I can.

I finally got my pressure sensor code fixed and can read 16 bits now at 840 samples per second. The Arduino library for the ADS1115 did not support interrupts so I modded it. I think I have at least two bits of noise and I think the pressure sensor itself is doing an internal A-D-A conversion at a lower sample rate and probably lower resolution but I intend to reuse this for IMA battery voltage measurements. The 10-bit Arduino AD was probably good enough for this application.

I was fooling around with matplot and now I want to plot this in real time (something I need to do for the EGR tester.) It would be nice to know where TDC is. Anyone know if the camshaft position sensor outputs an analog or digital (on/off) signal?

<edit> looks like the sensor is coil with 2K resistance. easy enough except now I wish I had a parts car to pull connectors from.</edit>
 

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No, valve timing is not something you can tweak

That's the short answer.

The long answer is very few people do engine tuning better than Honda when they put their mind to it.

The reason for my opinion is my 100,000 miles experience with my Insight and other Honda vehicles as well, plus having co-authored an SAE technical paper on ways to simulate engine combustion chamber performance improvements.

This IS rocket science requiring lots of time, money and equipment. And making changes by adjusting valve lash is (in my opinion) unlikely to result in anything measurable. Changing valve timing with new camshafts, or indexing the lobes on the cams vs the crank, etc takes lots of effort and is more likely to have negative results than positive.

Sorry, but it's only my opinion

Mike
 
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