Rev Limiter

RWKHausSupply

RWKHausSupply

NAXJA Forum User
Location
yorba linda, Cali
How to remove or Up the Rev Limiter on a OBD1 (92-95) ECU?

I have a 4.8 that with the nice amount of head porting, 2.0int/1.6exh, long rod, 10.5:1comp, etc... Would really benifit from going up to over the 5250 or what ever it really is RPM, It is limited to.

How do I remove or go up to say 6200-6500 RPM with the OBD1 system?

I have been searching and called a few that either said they cant do it and it likely cant be done on this setup, or "will look into it" and yet to call me back...

The early Viper was on this system and I would be very surprised if it hasent been done for at least that application.

help.
 
Talyn said:
Have you heard of the cam harmonic issue with these engine between s 5400 and 5700 RPM?
Click to expand...

No, I have not. I will search. I know that John Currie and Gerald from Savvy had the OBD2 system and just used a programmer to raise thier RPM to 6100 or 6200 I forget which, and they ran their hesco 4.6 with alot of happiness in the higher RPM range.

But with some electrical issues they had to swap the ECU with another spare before KOH and the race, and they were on a stock tune and stock ecu everything. They still loved the way it ran, and beat everyone, even mod class.

SO I dont know if its needed, but I know my engine has a disire to go higher, if its good for it or not, I dont know?
 
Yes, its the point where the cam begins to snake around in the block. If you don't hold it there for too long it won't likely cause much damage. However, I don't know what too long is nor do I know if there would be any long term damage caused if even not held there for too long.

Also, if you have an auto transmission the TCM would need to have its shift point raised. I doubt you have an auto though. You can try [email protected] to see if he can raise the limited on the OBD I PCM. If he can there should be a whole list of other mods he can do on the PCM. I just don't know if he handles OBD I.
 
Talyn said:
Yes, its the point where the cam begins to snake around in the block. If you don't hold it there for too long it won't likely cause much damage. However, I don't know what too long is nor do I know if there would be any long term damage caused if even not held there for too long.

Also, if you have an auto transmission the TCM would need to have its shift point raised. I doubt you have an auto though. You can try [email protected] to see if he can raise the limited on the OBD I PCM. If he can there should be a whole list of other mods he can do on the PCM. I just don't know if he handles OBD I.
Click to expand...

I started to read on it. I do have the 12wt crank so that is kinda help full I am reading (not for cam but for stress).

We are using RADesigns stand alone shifters for the AW4.

it is likely that same Chris, I just got a call back from.

He is very confident he can "socket" the ecu and adjust alot in it. Now to find a cost friendly Dyno in OC, and set up a meeting of Chris, the Dyno, and the XJ.
 
Talyn said:
The Chris I know is Los Angeles. If its the same one (last name starts with a J) he is very knowledgeable and does good work.
Click to expand...

Well this chris is close enough to LA to be the same one I think. He said he was actually in Culver City, so yeah LA basically.

He is looking to get in to the Stroker scene and wants to see what he can do for me. SO I will for sure report back with any experiences.
 
The cam harmonic that can break the timing chain or throw the distributor out of the block at 5600-5700rpm isn't the only problem. The crank journals also have a tendency to crack at 5500+rpm unless you have them nitrided or cryo treated.
My advice is don't mess with the stock rev limiter.
 
I know this has been brought up some where before, but just for the sake of argument, if say you wanted to destroke the engine, to the late sixties 199 ci crank, so that you could make displacement requirements for certain racing brackets, wouldn't you want to mess with the rev limiter to push power higher in the RPM band. Not sure if anyone has destroked their 4.0l before and what effect it would have on the cam at higher revs, just a thought.
 
Last edited:
How many people on here have suffered from the harmonic? I have heard about the crank harmonic but, not the camshaft...

Sorry about the hijack. LMK if I need to open my own thread.

dave b
 
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