Rev Limit
- Thread starter dumbo
- Start date
IJ.;1474151 said:My point was you already have a 7k limit
LMAO, oh....haha
Ive tried getting mine to rev (drove till it hit 6300 then let off) past 6250. It wont do it. So how is it 7k??? Just curious.
It just wouldnt go anymore. Felt kind of like it was in a loop. It would drop about 100rpms then rev to 6300 again, then repeat the process. I didnt do it for to long, because I wasnt sure what might happen if I continued.
Have a look at Wes Beech's vid of his burnout that's hard cut, yours sounds a bit like valve float from your description.
Ok, will do. Im rebuilding the engine anyways, so hopefully with the parts I use Ill be fine. Thank you.
The ECU computes RPM by averaging the time between the last 4 NE signals from the CPS. Since the NE signals must be synched to crank position for the ignition to work properly, there is no way to fudge the signal like you do with a piggyback and the AFM.
With the stock 12MHz crystal the resolution of the NE delta timer is 1us. There is a check after the RPM computation to make sure it is not exceeding the max rpm allowed, which is 500rpm past redline on the dash gauge on the ECUs I've looked at.
By changing the crystal you can skew the clock timer and at least in principle change the redline. The problem is that same timer is used for a ton of other things such as the injector duration, ignition advance, AFM frequency, speed input, IGf verification, and all analog sensors running through the ADC chip (air temp, coolant temp, bat voltage, TPS). They will all be off the same amount as the redline was shifted and all the internal maps will be off as well by the same amount. For small change in clock frequency maybe it doesn't matter too much, but it won't be running like Toyota designed it and if it was my car I sure wouldn't be happy about it.
With the stock 12MHz crystal the resolution of the NE delta timer is 1us. There is a check after the RPM computation to make sure it is not exceeding the max rpm allowed, which is 500rpm past redline on the dash gauge on the ECUs I've looked at.
By changing the crystal you can skew the clock timer and at least in principle change the redline. The problem is that same timer is used for a ton of other things such as the injector duration, ignition advance, AFM frequency, speed input, IGf verification, and all analog sensors running through the ADC chip (air temp, coolant temp, bat voltage, TPS). They will all be off the same amount as the redline was shifted and all the internal maps will be off as well by the same amount. For small change in clock frequency maybe it doesn't matter too much, but it won't be running like Toyota designed it and if it was my car I sure wouldn't be happy about it.
Thanks 3P that was my understanding of the crystal mod.
Would be interesting to know how much and in which direction it skews the tables.
Would be interesting to know how much and in which direction it skews the tables.
I just checked and at least for the pre89 7M-GE the rev limit is 6800rpm. At that rpm fuel is cut, ignition continues to work normally. In practice, that keeps the rpm below about 7000rpm.
3p141592654;1474298 said:
LOL that's what I was basing the 7000 I quoted earlier on, my GE would go to 7 before hard cutting so in reality 6800 and 200 of inertia/brain lag before I pulled the next gear.
Ian, its a mess, each sensor will be scaled some upwards some downwards.
To raise the rev limit you would need to increase the clock frequency, that makes the number of clock ticks between each NE pulse increase and so the ECU thinks the crank is spinning slower.
With a faster clock, the fuel calc will computed the same as before (in clock ticks), but the injector duration in real time will be shorter, so it will run leaner. Presumably over time the internal fuel trim would catch this because the lean condition will be seen with the ox sensor. The AFM will read higher, which will lower fuel cut. and so on.
To raise the rev limit you would need to increase the clock frequency, that makes the number of clock ticks between each NE pulse increase and so the ECU thinks the crank is spinning slower.
With a faster clock, the fuel calc will computed the same as before (in clock ticks), but the injector duration in real time will be shorter, so it will run leaner. Presumably over time the internal fuel trim would catch this because the lean condition will be seen with the ox sensor. The AFM will read higher, which will lower fuel cut. and so on.
3p141592654;1474308 said:
Which places it firmly in the "use at own risk" or Your mileage may vary" bracket!
Thanks for your input on this one 3P, I always suspected it wasn't the best way to go about it but didn't realise there wouldn't be a uniform shift in parameters one way or the other.
IJ.;1474161 said:
I think his description sounds like the factory rev limiter. My guess is that his tach is just slightly off of the actual engine RPM. My AVC-R also reports a slightly different reading than my tach up at the limiter and I have seen as high as 6700 rpm on my 92(thru the AVCR peak hold function).
Why would one try so hard to raise the rev limit?
Isn't our engine's powerband pretty nice before redline anyway? Maybe you guys are trying to move the peaks further up in RPM?
I don't know a whole heck of a lot about engine tuning...
Isn't our engine's powerband pretty nice before redline anyway? Maybe you guys are trying to move the peaks further up in RPM?
I don't know a whole heck of a lot about engine tuning...
Figit090;1474335 said:
Horsepower = Work X Time / 5252. Work = torque and Time = RPM
If you make the same torque at a higher RPM you Yield More horsepower.
For example installing Cams can yield the same torque number but increase horsepower because the engine can breath better up top. It isnt actually making the engine able to do any more work (torque) But its doing the same work quicker therefore producing more power.
Its the reason Rotary, small Honda motors and motorcycle engines can make big HP numbers with no torque. They make 300ftlbs of torque, but they make it at 8000 thousand RPM meaning they make 450 horsepower.
A diesel will make 500ftlbs at 2000rpm and make 190horsepower.
If you look at a dyno chart the HP and torque always cross at ~5252RPM due to calculation.
The trick is knowing when enough RPM is enough. You want to shift when the engine will return to the beginning of the meaty part of the torque curve. Any more then that and your wasting time.
Last edited:
nosechunks;1474802 said:
if you do not take advantage of the free gear reduction from making the same torque at a higher engine rpm then you wont be any faster. gear reductions which multiply the torque output are key when working with your powerband to extract the maximum amount of acceleration
Poodles;1474902 said:
indeed
you can have an engine that spins to 18k. If the ports are reaching critical V at 8k, than no matter how much you try to spin after that, the flow will be CHOKED and won't go any faster.
My 92 with the stock ECU would hit the rev limiter right around 6200-6300 rpm's. I have hit 6600 rpms peak (shown on my AVCR), but I think the ECU just didn't catch it in time.
With the AEM, I'm now reving to 7300, which is a night and day difference. I can now use the 62mm turbo much better without bumping into the revlimiter constanty.
With the AEM, I'm now reving to 7300, which is a night and day difference. I can now use the 62mm turbo much better without bumping into the revlimiter constanty.