I have a 1990 pontiac formula 305 going to a 350. What is the highest rpm the stock setup can handle?
Is it a software limitation (prom programming) or a hardware limit (need a whole different ecm/computer to fix)

 

the only limitations to what rpm you can run are air and fuel, jsut like another system. teh computer can be programmed for any changes you make to the system.
several people have added mild cams such as stock LT1 and LT4 cams to their stock chipped tbi's and had greeat success by adjusting base timing and fuel pressure.

later
tim

 

I wouldn't use stock TBI ecm's on a motor that had a redline above 6000. Stock the resolution of fuel becomes pretty linear with anything above 3200 to 6400. Past 6400 and who knows (I will but test bench needs more parts). Timing is also pretty limited in resolution stock. Source code changes and you can fix that, else it's not worth it. A solid street 350 shouldn't need to rev much past 5500 anyways. Performance isn't in how many revs you can make, it's how much power you make before a shift. Many many a ricers have fallen thinking rev happy thoughts .
So I guess the final answer for most people would be RPM limitations with TBI; software limited to 255x25 which is 6375rpm. You could have no problems spinning a motor past that, just not a good idea unless you're getting into source coding and modify the code. It's really cool stuff but not for everybody. When I say software limited it's not in the eprom, it's in the built on rom. If you could be tricky and figure a way to do it with the eprom (sure there is a way) then awesome. Either that or make the ecm romless so you can edit ALL the code.

 

[QUOTE]Originally posted by Belstain
[B]I have a 1990 pontiac formula 305 going to a 350. What is the highest rpm the stock setup can handle?

I recently put in a 350 in my 90RS Camaro and the car shifts at 5500rpm. I did nothing to the tranny or programming. I used the same chip that I was using in my 305. Thermomaster for a 305. However, I do not recommend that. I desperately need to get a custom chip made. It runs lean.

 

Not really sure. I've seen the '747 used to 7,500 RPM as an ignition controller (w/carb). Within the hardware the limiting factor would be the 64KHz clock used for the timer/counters. That gives a 15.26 usec resolution.

Within the software there isn't anything that limits the RPM. The code is a real time system, however, it is run asynchronously to the engine. It is the hardware that syncs the ECM to the engine (via the DRP).

What you will hear is that the ECM is RPM limited because the tables only go to such & such an RPM. This is only a partial truth. If the VE tables max at 6375 RPM what is the effect? Well, how much will the engines VE change between 6375 RPM & 7500 RPM? If not by much then it isn't a limiting factor. You are more limited by the amount of time (or lack thereof) to get the injector to pulse enough fuel.

Same with spark advance (SA). The main SA table goes to 3600 RPM. Then an adder comes into effect that extends to 6375 RPM. Beyond that how much does the SA really need to be changed? Most of the time all of the SA is in by 3200 RPM.

What would be nice is to have a SA modifier vs transmission gear. Then as each higher gear is selected the SA may be reduced by a small amount. That is the kind of stuff that matters more.

RBob.