Electronic RPM limiter

[Matt Timion]

On another thread, Nortonpro asked the following question:

But I would really like to know if anyone *thinks* that an electronic RPM limiter would be of any benefit or would not be a benefit to mpg testing?

I think it would be beneficial in that it would help you keep one of the most important factors constant (speed). That being said, a cruise control would accomplish the exact same thing.

[Compaq888]

not really. Even with the cruise control you can add speed and still stay on the cruise control. I think he means for daily driving without using the cruise control he wants to limit his rpm. Personally I want to do the same. I want my car to shift at 1500rpm instead of 1700-2000rpm.

[Matt Timion]

Originally Posted by Compaq888

not really. Even with the cruise control you can add speed and still stay on the cruise control. I think he means for daily driving without using the cruise control he wants to limit his rpm. Personally I want to do the same. I want my car to shift at 1500rpm instead of 1700-2000rpm.

Okay... with cruise control you CAN add speed, but if your entire point is to limit your speed (or RPMs) then why WOULD you add speed?

I'm unsure how a rev limiter would make your car shift at a lower RPM, but admittedly I don't know everything about rev limiters.

The more I read about the rev limiter I think it would be great for city driving, especially for people with VTEC or other RPM activated switches. On my future engine, the vtec-e will engage at 3000rpm. IOW, as long as I drive below 3000 RPM I will be running ultra lean and on 12 valves. Perhaps setting up a rev limiter to around 2900RPM would be good, and I could disengage it whenever I needed to use 16 valves.

Then again, how often am I going to be above 3000rpm? I don't find myself doing that NOW, and I can't imagine doing it when I have a taller geared transmission.

[rh77]

I agree with the concept -- for manuals, the engine cuts out at 3000 RPM or so -- if you needed extra power for emergencies, maybe a toggle switch or WOT switch under the pedal or on the throttle body. I wish there was a way I could keep my car in 3rd or 4th gear with more than 1/2 pedal pressure.

I'm sure automatic owners can agree -- we'd love for the car to shift at a lower RPM. I mentioned before that I lift the throttle at the desired RPM, the car shifts, then I use whatever pedal is available - but not too much, or we're back where we started. I'd love to have a "gear hold" switch or something -- 1st and 2nd are that way -- no matter what, if you're in 2nd, you start out there, and it stays there. D3 and D4 it does what it wants based on pedal pressure.

Programming an auto trans. to shift a certain RPM is sure to kill it over time. Say your going up a hill at full, or near-full throttle with a lot of weight in the car (extra passengers/cargo). The transmission is set to shift at 3000, so it does. The pressure on the transmission is tremendous because the extra torque it has on it has to be converted while the gear change takes place. It sometimes results in a hard shift. Winding out the engine or lifting takes that pressure off and the ECU knows to shift.

One more concern -- is bumping off of the rev limiter an open-loop condition?

RH77

[SVOboy]

Chipping will allow you to change your rev limit to whatev you please, go honda.

[diamondlarry]

Originally Posted by rh77

I agree with the concept -- for manuals, the engine cuts out at 3000 RPM or so -- if you needed extra power for emergencies, maybe a toggle switch or WOT switch under the pedal or on the throttle body. I wish there was a way I could keep my car in 3rd or 4th gear with more than 1/2 pedal pressure.

I'm sure automatic owners can agree -- we'd love for the car to shift at a lower RPM. I mentioned before that I lift the throttle at the desired RPM, the car shifts, then I use whatever pedal is available - but not too much, or we're back where we started. I'd love to have a "gear hold" switch or something -- 1st and 2nd are that way -- no matter what, if you're in 2nd, you start out there, and it stays there. D3 and D4 it does what it wants based on pedal pressure.

Programming an auto trans. to shift a certain RPM is sure to kill it over time. Say your going up a hill at full, or near-full throttle with a lot of weight in the car (extra passengers/cargo). The transmission is set to shift at 3000, so it does. The pressure on the transmission is tremendous because the extra torque it has on it has to be converted while the gear change takes place. It sometimes results in a hard shift. Winding out the engine or lifting takes that pressure off and the ECU knows to shift.

One more concern -- is bumping off of the rev limiter an open-loop condition?

RH77

I don't know a lot about automatic transmissions so this is hearsay on my part. I have heard from people that understand automatics that it's actually quite easy to modify the transmission to go into what ever gear you want when you shift it there. I think that as for the auto shifting, everything works the same. It only effects the manual shifting of the trasmission when it's modded.

[SVOboy]

I totally skipped this post earlier!

I agree with the concept -- for manuals, the engine cuts out at 3000 RPM or so -- if you needed extra power for emergencies, maybe a toggle switch or WOT switch under the pedal or on the throttle body. I wish there was a way I could keep my car in 3rd or 4th gear with more than 1/2 pedal pressure.

If you can figure out where your kickdown cable is (it kicks down the gear with lots of throttle) you can adjust it to get it to do more of what you want.

I'm sure automatic owners can agree -- we'd love for the car to shift at a lower RPM. I mentioned before that I lift the throttle at the desired RPM, the car shifts, then I use whatever pedal is available - but not too much, or we're back where we started. I'd love to have a "gear hold" switch or something -- 1st and 2nd are that way -- no matter what, if you're in 2nd, you start out there, and it stays there. D3 and D4 it does what it wants based on pedal pressure.

Some of this can be done with the kickdown cable too, especially the first junk.

One more concern -- is bumping off of the rev limiter an open-loop condition?

Just don't do it, , not too good for the car.

[n0rt0npr0]

Compaq and Matt,

Yep I was meaning without cruise on the limiter. It's complex when it comes to shifting automatics, so when my engine has a good day (cool dry air) it makes a lot of power and I can safely navigate traffic without revving too high. On a bed day, it makes less power(torque) so it supplements by using higher RPM's. Most the time we have bad days 'round here. My engine has no rev governor and I think installing one would level out my tank to tank mpg point spreads(by a little) ...so yah the rev limiter would cut power and my tranny will shift without me over thinking the situation. For those like krousdb, its not gonna do much. I'm still *in training* for mpg conscious driving and admittedly, this is a small short cut.

About shifting at lower rpms...well honestly its not gonna be easy on the Altima. The only option you have is to chip it. You have an electronic tranny that has programmed shift points.

Then there are the older OBD0 and OBD1 cars. Most of these shift points are controlled via a detent cable. (what SVO calls a kick-down...can also be called a throttle valve cable...)
On a cruise vehicle you'll have three cables coming off throttle body. The accel pedal, the cruise control and detent cables. Detent goes to the tranny. My main vehicle has it and it DOES allow adjustment for different shift points. Loosening the cable will allow for a lower RPM shift. Sometimes its as easy as loosening two nuts and a twist.
However then there are the vehicles that use a vacuum line pressure to determine shift points. These, of course are harder to modify. I'm not very familiar with them. (maybe the vacuum operates an electronic pressure solenoid inside the tranny, meh...)

RH77,

One more concern -- is bumping off of the rev limiter an open-loop condition?

Huh?? If you are asking whether a rev limiter would operate in closed or open loop the answer is both if your ECU is controlling it and also if the limiter is mechanically controlled. (?)

SVO,

Chipping will allow you to change your rev limit to whatev you please, go honda

Go any vehicle using OBD1 and OBD2! They all can be chipped. Not sure about these so called OBD0's, as gassavers is the first I've ever heard of them. But this is the exact method I mean when I brought up rev limiting.

[Compaq888]

It's actually really easy to limit the rpm. You see most cars limit your rpm by taking out fuel at redline. While MSD control boxes take out the spark. I used to have a MSD box and you can adjust what rpm you want the redline to be. I put it at 6200rpm because at 6250 I had fuel cut off. But I had total control of my ignition with the MSD box, I had a box, a coil and some other accesories. The problem was that the Nissan ignition system is a lot more reliable. So I sold the complete MSD system and got a new distributor cap, distributor rotor, spark plug wires, and spark plugs. It seems very reliable.

Now if you want to control your shifts then It's another thing. You can buy a $800 computer that hooks up to your tranny computer and you can tune it for fuel economy, power, or whatever you want. You can even get pedal shifters with it so you can control it anytime. The problem with that is if I had $800 to blow I'd pay somebody to convert my car to a manual. A manual car simplifies so much.

[SVOboy]

OBD0 is the what 88-91 honda pre-OBD is nicknamed because it's so similar to OBD1 and 2 in physical construction and all that.

OBD2 blows though because it can't be chipped (at least for honda), it needs to be reflashed. Most stuff besides obd0 and obd1 honda is non DIYable unless you have an assload of money, which blows. But Honda is also cool in that obd2 can be converted to obd1 without changing anything but ECU wiring.