I thought I had read this somewhere once. After 7,000rpm to be reliable you would need an aftermarket ECU. I'm thinking of changing over to a solid roller to meet my horsepower and torque goals and I know that the big advantage of solid roller is being able to turn over 6,000rpms realibly. But I dont want to at the cost of needing an aftermarket ECU. Thanks

 

Yes, i believe you are right and the obd I computers are only good up to 7000rpms

 

The spark charts in the PCM only go to 7000 rpm. I believe some people claim they can spin it past 7000 but I think their tach was off. I guess you could always just take it out and see what happens... Id do it if I wasnt afraid of destorying my motor.

 

I believe that Joe Overton told me you can spin it past 7k with the factory computer. I asked him about this when I got my heads and cam from him
because I went with a solid roller

 

I've read a couple posts saying the PCM shuts off around 7200.

 

The pcm probably can't keep up. I doubt GM thought anyone would spin an LT1 past 7k on the stock computer back when they designed it.

 

OBD1 computers shut down at 7k, literally. Once they hit that point, the ECM shuts down and kills the engine, you need to key off and reset it. If you are seeing higher than that on a tach, your tach is wrong. Seen this happen with two OBD1 cars on the dyno (so RPM hookups) and also with mine a few times but no rpm hookup other than tach.

OBD2 lt1 computers are good past 7k, BUT they are really tricky to tune up there because how the fuel/spark tables are set up. You also have the opti issue to deal with, it doesnt live long at 7k.

 

Not true, we have a car that bumps off the limiter going down the track at 7200, you don't have to shut off the car. Than again it's Ed Wrights car and his tunining in the car. Maybe you just need a better tuner.

 

But how do you know it was actually at 7200? The only accurate way to tell is with a scanner and since most tachs are off by around 200 rpm that makes me think you were looking at the tach.

 

he said its bouncing off the rev limiter, the computer controls the rev limiter so its obvious the computer see's it as 7200. I have always heard it shuts off right there.

 

It has NOTHING to do with tuning. There are no tables past 7k on OBD1 equipted cars, period, the end of story. You cannot tune what doesnt exist.

 

He could be bouncing off the rev limiter and looking at the tach. If the tach is showing 7200 then its simply 200 rpm fast as most stock tachs are. Yes the computer controls the rev limiter... thats already been established. The problem is saying an OBD1 car will spin past 7k because the TACH says it did.

 

As brad said, tachs arent accurate. Also anyone who has logged a car in upper RPMs would also know that logging capabilities dont work past 6340rpms or something odd like that, so dont try that card.

If someone wants to show me a DYNO or AF graph with an external RPM lead hookup on an obd1 car, then we can talk. I want it to be still accelerating past 7k too, no momentum carrying the rpms

 

Ahhh good point, I just assumed he set his rev limiter at 7200 in the PCM.

 

Ok, now for the HARD FACTS. I have done this and ALTJAR is correct.

I have a 1993 LT1, 383 stroker and I have turned past 7200 on a dyno with their tach and my aftermarket tach and yes the factory tach is off by 200 rpms when you get up around 7000 rpms. I have had two different tuners and the chip is not even close to stock!

Here is what happened: I turned 7500 rpms because the tires were too short (26" and now I have 28"). The car has a soild roller with a .630" lift I wanted to make a decent pass to see how the car would go through the traps and see if I was out of the limits of the HP range (6800 to 7200) and I was. But the car still pulled, did not miss and was SCREAMING.

Now for the computer: TRUE, there is no data past 7000 rpms for SPARK OR FUEL, but the car will run with the last data it has at the end of the table/s.

This is why we designed a cam (COMP) to peak beteeen 6800 and 7000 rpms.

The sixty foot was 1.63 (Bad) I have shocks and springs on order and I let off the gas 1/2 down the track as it was swaying towards the guard rail, but still got a 11.5 at 117 mph. The car is capable of 10.8 easily.

Jim in Orlando; Questions? email me or post.