Tuesday, April 25, 2017
× Discussions on The MAPster. Please limit the discussions to the applications and diagnostics aspects.

MAP and vacuum and stuff

08 Sep 2016 19:00 #13 by heysoundude
Further along these lines...I've been thinking about up-gapping my spark plugs.
Yup, I've grooved and am getting great results, but I still haven't made this happen for a variety of reasons. so I got to to wondering if there was a way to determine just how much wider I can make them, and I stumbled across a website that suggests there's a way to calculate breakdown voltage, where a spark can occur.


I know that my factory gap is .060"
but this is a waste spark system, so the gap when one coil fires is actually DOUBLE that, .12"
multiply that by 60000 and I get 7.2kV and that fits what I understand the coilpack can put out - 25kV

now if you scroll down that page, it gives a more in depth formula that involves pressures and densities. as these are in flux constantly in any engine, you would have to find an average for those and go with that...but what's interesting is if the pressure and density go UP (as happens with a grooved car - we ARE putting more air in each stroke, after all), that voltage drops which means the gap can widen... that's why it works, to a point; that point is time related, meaning the coil can't charge and discharge in the timeframe of the engine's rotation - to happen close enough to TDC. Maybe this is old news to some of you, so forgive me for being late to the penny drop. Anyway, I THINK I can take my gap up to about .075' which is 25% over stock...0.08" might even work with my sexy wires.

The more I learn, the cooler and smarter this is, Ron.
08 Sep 2016 23:23 #14 by Gadgetman2
Hey Greg.

The very first and foundation principle you should keep in mind is that the people that supply information on your equipment NEVER tell the whole truth. Fortunately, we, as Gadgetmen, never accept what we're told, until we confirm the data.

This applies in this instance as the specs for your voltage potential. You will ALWAYS find the system puts out more voltage than is reported. That way, no one complains if the actual number is higher.

You will love that chart, but it only tells a piece of the story. To find the actual figure takes some effort. That's why I developed the process of adjusting the spark gap as I did. It's the only way to find the true output of your system.

You will also need to consider decay into your work. All electronics are designed and built according to specs. But they calculate the output based on minimum figures by the lifespan of the product. From the first spark generated, the system begins its decay, producing less and less output, albeit in infinitesimal amounts.

Over time, and after many millions or even billions of firing cycles, the voltage drop can be substantial.

For now, I've got to go, but you keep up the good work!

09 Sep 2016 13:10 - 09 Sep 2016 13:31 #15 by TracyG
Dr. Dude, you could take the easiest to access plug, re-gap to your target gap. IF it's Ok, keep opening gap 'till it starts to miss, then back off .005".

If ya do that w/ the existing wire set, then with the Granetelli's there will be that much less resistance. That will ensure that virtually all the impedance load on the coil is the plugs and gaps. That should give some "cushion" to coil life, and guard against any potential for misfire.

If I recall, from an auto electrical class I took years ago, in a waste spark system, the cylinder firing the waste spark has less arc-over resistance than the one on power stroke. Plug gap arc-over voltage varies with engine load, and other factors. Better ignition parts just give more protection against misfire, and give a "hotter" spark.

The wider gap makes the coil saturate longer. This both increases spark intensity, and shortens the time of spark duration. Shorter, harder punch. Sort of a step in the direction of a Plasma spark ignition.

Dr. Jacobs talked about increasing plug gaps this way in his book. Ron has proven it, and pointed out this neat "Trick" to us. A cool way to bring out more of the hidden potential in our engines, and a freebie to boot! :woohoo: :evil:

Tracy G

Tracy Gallaway
Carburetor Coach
Mood Elevator
Gadgetman Reno, NV
10 Sep 2016 14:57 #16 by heysoundude
You guys are completely correct - I'm going to do as you suggest tomorrow Tracy. In fact I may just replace ALL the plugs and wires while I'm at it. I've been talking about it for so long, I might as well just get it done!

what I'm finding right now with Wendy Rendezvous is that she wants to be running just above idle running down a straight/level city street at 30mph, and the dash is reporting ~3.0L/100km (that's 75-ish MPG), but either as my foot moves on the gas (moving the throttle plate) or the road undulates or whatever, it pops back up to 5-5.5 or higher, and then it tries to come down again but can't seem to find it and stick there...the tranny isn't slipping - it's all vacuum and fuel delivery I think, so if plug gapping doesn't help, I'm willing to try a different MAP sensor to keep the fuel consumption as low as possible. This happens until the engine has been running for a while, and then I get a consistent 4-4.5L/100km, which is still fantastic, but it seems to be saying "I can do better - help me!"
It did this on occasion before I treated with the RVS-type engine and transmission additive, but the numbers bottomed out in the 4L range - remember that I've come to distrust the display because I've been able to prove it's off, and the error increases/mileage decreases as the air temp decreases, but it's a good indicator of how efficiently I'm driving...on recent fillups, I'm achieving in the high 6/low 7 range in L/100km or 35-ish MPG, which takes into account higher consumption getting the machine rolling.

I have a 120mile trip to take tomorrow...hopefully I can get my Wendy a bit more efficient for it before I go with new, upgapped plugs and ultra-low resistance wires. I'll let y'alll know!
22 Mar 2017 13:56 #17 by heysoundude
I keep hammering away at this because since I Grooved my Wendy, she's awfully temperature sensitive: yesterday afternoon, it was 60-ish degrees F and my dashboard readout was consistently reading in the 3.5-4L/100 km range as I was bopping about town. yeah, 60-ish MPG, if not slightly higher. Fast forward to last night, after a cold front came through and the temperature dropped into the mid 20s, my dashboard was reporting no lower than 6.9L/100km, still slightly greater than 30MPG, but not the greatest. So I went hunting online for more info on MAP sensors and how the computer reacts to their signals...and boy am I EVER happy I did!

This first link talks about Volumetric efficiency: (notice how it mentions tuned intakes. (the groove might be considered an intake tuning mod, so what if we get greater than 100% VE with it?)
(I've actually bookmarked this)

This one gets a little deeper into how the sensor works and touches a bit on the math of fuel delivery/injector pulse width:

Basically when it's cold air is more dense and the computer sees more air mass passing the throttle plate and delivers more fuel. Unfortunately for those of us who drive vehicles with these sensors, to get gains, it looks to me like the stock sensor has to be upgraded to one with a wider/bigger calibration range due to the amount of vacuum we're making in a grooved vehicle's manifold.

I've long suspected this to be necessary, and the more research I do, the more my suspicion seems to be correct. I bought a 3-bar sensor for Wendy a while ago. now I've got to take the 5 minutes to swap it in for the stock 1-bar sensor, do the re-learn and report back with results.
If I'm right, it'll take longer to warm up in the cold so I may have to swap in a higher temp T-stat, but fuel consumption should even out as I drive, regardless of the season.
22 Mar 2017 15:21 #18 by NateM
if you swap the 1bar sensor for a 3 bar sensor the ECU will think it's always in vacuum, the sensor will probably only output between 0 to 1.6V instead of 0-5v. IIRC this will cause a serious lean condition unless you have something doing signal modification between the 3bar sensor and the ecu
22 Mar 2017 16:40 #19 by heysoundude
Ive not found anything in my research to indicate what the ECU will do with a sensor that sees increased vacuum. Plenty with results from simply swapping the sensor out unboosted, plenty more for turbo or supercharged engines, but nothing in the other direction. Follow all the links I've posted. (There's one that compares voltages between 1-bar, 2-bar and 3-bar sensors - look at the corresponding throttle angles and you'll see where my head is at)
I'm betting on the computer adjusting to sensor input that indicates increased vacuum by reducing fuel injector pulse duration. I'm fully prepared to be incorrect - but there are plenty of electronic solutions that adjust voltage presented to the ECU, why not just go with a sensor that's built to do it?
Like I've said, I'll report back, one way or another.
Remember, we're TRYING to lean the engine for efficiency and economy.
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