RPM Redline and limiter? - Harley Davidson Forums: Harley Davidson Motorcycle Forum
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post #1 of 33 (permalink) Old 09-03-2012, 12:33 PM Thread Starter
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RPM Redline and limiter?

Hi guys,

I am in the process of building an electronic tachometer for my Softail Deluxe 2005 88B. I need to know at which RPM the redline should start, and what the RPM is limited to by the EFI so I can design the RPM range of the tachometer accordingly.

The idea is also to have the redline start off low automatically while the engine is cold, gradually moving up to the normal value as engine temperature reaches normal operating value. What would be a sensible redline for RPM while the engine is still cold? BTW, by cold in South Africa I mean still well above 0 degrees, let's say around 40 degrees F or 5 degrees C.

Any technical info would be apprciated, thanks.
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post #2 of 33 (permalink) Old 09-03-2012, 01:11 PM
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Skip the "cold" rev limiter. If you're careless enought to rev the engine to redline when its cold, you deserve to replace a possible blown headgasket(s) since the engine isn't fully warmed and "grown" as it does at full temp. OEM redline is 5200. At 4800-4900, stock cammed engine is done making horsepower and torque. No need to rev farther. If you change the cams, raise the redline to 6200-6800 depending on cams, mods etc.....

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post #3 of 33 (permalink) Old 09-03-2012, 01:53 PM
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B-engine. Limit the engine to 6000-6200 RPM. The counter balancers can grenade at RPMs above that.
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post #4 of 33 (permalink) Old 09-03-2012, 02:12 PM Thread Starter
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Thanks for the feedback, guys, much appreciated. Just a note, though, I don't intent to do any limiting of the RPM myself, I thought the engine had it's own limiter seeing as its fuel injected. All I need to do is display the RPM, and I would like to indicate the redline with the RPM LEDs lighting up red above the redline RPM. From there the idea to show them as red earlier on while still cold, effectively lowering the redline purely from a visual indication point of view.

Just for additional info, imagine a strip of about 64 or so LEDs, one for each 100RPM, and each being able to light up green or red. I can have the redline indicated by all the LEDs above the given RPM illuminating red instead of green, and I have the choice as to which LED (or RPM) this should start at... from there the ability to dynamically vary the redline.

Sorry if I didn't express myself more clearly earlier. So what RPM should the engine be kept below while still cold?
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post #5 of 33 (permalink) Old 09-03-2012, 03:00 PM
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I see where you are going. Many with fuel infected bikes push the button and start running them way to hard. They don't seem to know the engine should be warmed up and oil circulated before riding hard. You are trying to electronically regulate stupidity. Running at low RPMs is hard on an engine also. How about a throttle limiter, for fly by wire bikes, that is temp regulated. Maybe half throttle till the oil reaches 120 degrees F?
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post #6 of 33 (permalink) Old 09-03-2012, 06:33 PM
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Originally Posted by OomD View Post
Thanks for the feedback, guys, much appreciated. Just a note, though, I don't intent to do any limiting of the RPM myself, I thought the engine had it's own limiter seeing as its fuel injected. All I need to do is display the RPM, and I would like to indicate the redline with the RPM LEDs lighting up red above the redline RPM. From there the idea to show them as red earlier on while still cold, effectively lowering the redline purely from a visual indication point of view.

Just for additional info, imagine a strip of about 64 or so LEDs, one for each 100RPM, and each being able to light up green or red. I can have the redline indicated by all the LEDs above the given RPM illuminating red instead of green, and I have the choice as to which LED (or RPM) this should start at... from there the ability to dynamically vary the redline.

Sorry if I didn't express myself more clearly earlier. So what RPM should the engine be kept below while still cold?
That sounds really bad ass man!!!!

And anyway, personally I would say under 3k when cold.
If I were you, I would make the 3k and up lights go red until a temperature sensor in the oil pan said the oil was at 150 degrees.

I really like this idea please post pics while you do it!!

Where you thinking of putting the lights on the bike. And in a circle or a straight line.

While your at it I would put a bigger shift light at the end of it just because it would look cool as hell.

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post #7 of 33 (permalink) Old 09-04-2012, 04:33 AM Thread Starter
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Thanks for the feedback, guys. Bigger shift light... check. Now about the oil temp, I was planning on fitting a temperature sensor to the oil dipstick, that way I measure the temperature of the oil in the reservoir. How does this compare to measuring the oil temp inside the engine, as the oil is circulated between the engine and reservoir anyway?

I'm assuming when you say "150 degrees" you are referring to fahrenheit, not celcius? Sorry for asking, I don't want to make any stupid mistakes on bad assumptions (here in SA we use celsius).

Here's the first pics I took this weekend after making the bracket that will hold the tacho in place. On the one photo you can see the tacho housing is actually an aftermarket chrome side-mirror for cars. The mirror face will be replaced with the tacho's face, when that is done.

The RPM LEDs will lie along the top curve of the housing, while the lower halve will house a LCD (for temperatures, etc) and speed display, together with the gear indicator.

Appreciate all the feedback, guys. BTW, what would normal operating temp for the oil be?
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post #8 of 33 (permalink) Old 09-04-2012, 07:14 AM
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You're gonna get a lot of opinions on that. A lot of guys think lower is better, no matter what,

I believe the more considered opinion is that 240F to 250F does not degrade a good synthetic oil,

where temps much lower than 215F do not promote the flushing of moisture that inevitably accumulates in oil,

due to engine blow-by water vapor, and this is a bigger concern in the US where alcohol added to fuel increases the

concern of corrosion in aluminum engines.

.

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post #9 of 33 (permalink) Old 09-04-2012, 12:14 PM Thread Starter
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Thanks for the info, Nathan. Interesting that alcohol gets mixed with your fuel, what would be the reason for that?
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post #10 of 33 (permalink) Old 09-04-2012, 12:17 PM
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Mostly politics, but it provides a cleaner burning fuel.

It may be that the only purpose for your life is to serve as a warning to others.

It may be that the only purpose of your life is to serve as a warning to others
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