Ok... we know that the peak HP on the 5th gen are useless b/c of the fact that it's so close to the redline. So say we raise the limiter oh 500-1000rpm, that should make it faster. While sitting here I had a thought... this may or may not work, I donno... but it may be worth a shot.

*disclaimer: you try this, you break stuff, I have nothing to do with it. I've never tried it, but in theory this could work*

Anyways... the idea is to make the ECU think that your RPM is lower thna it really is. There's going to a the RPM signal wire to the ECU. Say we lower the voltage going to the ECU by 10%. This means that at a 6500rpm, your ECU will only see 5900. So effectively you have raised your rev limiter to 7200rpm. If you lower it by 15%, then you have a 7500rpm rev limit.

But you say: "after 6500rpm, car doesn't map more fuel". That's where something like the SAFC comees in. You can adjust fuel after 6500rpm.

The other issue I see is that b/c your engine thinks your rev is lower than it is, at WOT(open loop), the fuel mappings may be off. Again, S-AFC can handle this as well.

The key is 1) tuning by dyno and 2) having a A/F ratio meter. I donno for sure if this would work... I think it should.

What do you think?

-Shing

 

We need a guinea pig to test on. I would volunteer but then again maybe not. Any takers out there.

 

The UCE gets a signal from the crank position sensor. Its a pulse signal based on the notches on the crank pulley. It counts the notches and interpets it as rpm's, I dont think a voltage modification would do it.

 

Ahh, but it is voltage... cause Ari checked his service manual(4 2nd gen), and atleast in my Honda it is... There are two wires coming out of crank position sensor. One is the crank position, the other is RPM. I am pretty sure that the higher the rpm, the higher the voltage, or maybe lower. I'll doubl check in my FSM today to see if this is so.

-Shing

 

all i gotta say is NOT IT..

 

is that all you gotta say?

But what are you talking about?

 

im' not gonna be the guinea pig... so no one nominate me

 

hehe ok no problem... but I did confirm it's not a voltage thing... hmm will find out what kind of signal... probably could still fudge with that... stay tuned.

AlboKalbo will add his findings shortly.

-Shing

[Edited by Shingles on 10-27-2000 at 08:37 AM]

 

I believe it to be 0 to 5v TTL, fixed pulse width, variable
frequency.

It works the same way between Honda and Nissan. You honestly don't think a tach meter is just a simple volt meter do ya? ;-)

 

here are 3 things taht could be done:

1) Use a freq multiplier (say 4x) followed by a divider (say 5x) to get
the constant factor
2) Use a freq-voltage converter, insert a potentiometer, then a v-f
converter. This will allow you to adjust that factor
3) Use a microconroller. This requires a bit of assembly but would
guarantee you the constant PW

You may be better off just trying to change the computer, rather than the
input to the computer, since it won't be a trivial thing.

Any thoughts?

-shing

 

How about a ECU that's been modified, wouldn't it up the limiter? Plus you get all the other benifits.

Or am I talking out my........

 

I agree that it would be the best solution... but I think it will be a long while before the 5th gen ECU gets cracked... plus this could be used on any car.

 

How much different is it really from the 4th gen ECU? Would the JWT and URPD chips be close to working?

 

depending on the year... cause it appears that each year is a little different... although I think the main differences are in the accesories, like sdie air bag, etc...

-Shing

 

Some interesting thoughts. It is not as simple as just voltage though. Two things are needed to try something like this:

Find out how the signal that measures rpm varies with change in rpm, ie rpm goes up -> frequency goes up.

Find out what kind of signal it is and what voltage levels to look for TTL, ECL, whatever...

I guess it might not be too hard to hook up some TTL logic to mess with that signal and see what happens. A multiplier or something that adjusts frequency could be something as simple as a DLL or PLL. Not too hard to find or build.

But, I think the easiest route is to crack the ECU and microcontroller. If it's a standard Motorola microcontroller, the assembly code should be cake, just need to find the code and hack it.

 

After reading my FSM more closely, accessories are not controlled by the ECM ( Engine Control Module ). Accessories like anti-theft, climate control and air bags are controlled by the BCM ( Body Control Module ). All 4th gen ECM are similar except for Emission control equipments and tranny type. My Cali-spec 1999 have wires for the extra emission control unit like the Swirl valve and the extra O2 sensor. So, if you have a 97 fed spec GXE 5 speed. You can swap in a 97 fed spec SE 5 speed ECM with no problems. Regradless of what options you have. The ECM can careless if you have airbags or not =) If you have a 99 Cali-spec auto, the 99 fed-spec auto won't work because the O2 sensors are at the wrong place. The voltage reading will be off.

 

remember, the ECU uses the RPM signal for cam/spark timing.

 

True, but for example, my a 96 ECU won't work in my 98... my electronic odo I am sure is controll by ECU.. unless that's in BCM too... then the ECU from UPRD would work....


-Shing

 

A little birdy once told me that their is a wire (or a combo of wires, depending on the car) that can be cut on the ECU harness to disable the rev limiter.

 

that is not for the amature (meaning me) to do ...need more knowledge & experience..
it is true that we lose power after certain RPM since
it is not maxizime there (the A/F ratio) thus we can use the SAFC or something like that to cure the prob...
as far as tricking the ecu on the RPM.........
that would make everything off...yes SAFC can correct that but you will need to run a longgg DYNO test ...you have to spend hours on it....
that itself is expensive...heheheh....maybe NOS (yeah...cheaters....) is cheaper...
You probably want to do the above endevoar if you already have nothing else to do / mod on your car...I kinda see it as a "I mean business" tuning......
and then if you are having other power mods installed...wouldn't that make things off again...
it is neat idea though, but definately very rigorous...

 

Yep, I saw somthing like that on one of the 300zx boards. I cant rember what or where. I duno if its aplicable to the 4th & 5th gens?

 

No it won't be way off... just tap the rpm signal wires your need before the signal is adjusted.

-Shing

 

peak hp may be high, but it's torque that matters. you want to shift at the point where you'll be at where the flat torque curve is in the next gear.

For example, say my torque curve starts climbing at 3000 rpm and is flat until 4800 rpm & my hp starts climbing at 4000 rpm, peaks at 6200 rpm, then drops down. The best point to shift would be the rpm in 1st gear that makes second gear at around 3000 rpm, and so on for the next gears.

 

I think you will just run into alot of problems! If it was that easy everyone would have been doing it by now. Look at the UPRD computer reprogramming, they are running into problems with each different year and yet they are the skilled technicians. I would rather wait for UPRD to finish testing than fry my computer or engine or the whole car trying to mess with it. All i have to say now is good luck!!