I have an orange ECU , I guess they are for 6,000 RPM? the aftermarket ECU's are for what RPM? like the ones from Autozone / O'Reilly and the local parts houses , some I heard are for 4,500 RPM so how can you tell what you are buying? OHM reading to tell what RPM? I want to replace the orange unit but what one is good? thanks.

I've never seen one w an RPM rating....but all they are is a transistor switch which I would think could switch faster than the engine ever needed it to....I've never heard of anyone complain that they seem to have an RPM limit.

Chinese aftermarket ECU's can sometimes be used as a 3000rpm limiter...

I've had an orange ECU break up near 6000-6500rpm. That was, at least in the time I still used these orange junk boxes.

Yup...
I recall a Mopar Performance bulletin said the Orange box was good up to 6K RPM and the Chrome box up to 8K RPM... I always use a Chrome box, actually have an MSD 6 box with the Chrysler connector (USA made back in the 90s), to me I prefer the Chrome box..

Just my $0.02..

the MP chrome box gets good reviews here. Might be a bit pricey tho. I would also price one at your parts house. Standard Motor Products parts house ECU's were pretty good but are made overseas now. I've used em on a DD & no issues.

Hilarious!!! Ten years ago the chrome box was "junk" and the orange box was "actually better".

The only way to actually come up with an rpm max for a pa4ticular box would be in some sort of test apparatus with a variable frequency pulse generator and an oscilloscope. I believe Don at FBO has some of that information but no idea if he wants to give it out. He has his own box with guts designed by Daytona Sensors and it's more than likely better than either.

I did some math and it appears the transistor has to be capable of operating at 6khz for 6000 rpm.

R.

Let's see, 4 sparks per rpm assuming V8, remember it sparks once per cylinder every two revolutions.

That would be 24,000 sparks per minute, 4 x 6000.

KHZ means cycles per second, so 24000/60 is 400 hz. The transistor needs to turn on/off 400 times a second, not sure where you got 6000 from.

Nacho our South American electronic whiz said alot of ECU failures are the main transistor & to replace it with a Motorola "MJ10005". my notes say he said that was for the orange box but not sure if he meant exclusively or if that is what he was working on at the time but the next one I run into that goes out I'm gonna dig out the goo & solder one in & give it a shot. it'd sure be worth it if it fixes it

Supercuda, you forgot that the transistor has to switch off and on in 3 degrees of rotation in order to have 42 degrees closed time or dwell.

R.

The original factory ECU's had published RPM limits that varied from 5200 to 9500 depending on part number/heat sink color.

The info is in the old DC racing manual page 471.

the OP may also be referring to when and if timing pull may happen . he may have forgotten about this post

None of which affects how many times per second the transistor switches, just how quickly it has to do it.

I think you forgot there are 360 degrees in one revolution.

Remember each cylinder fires once for every TWO revolutions (720 degrees vice 360 degrees).

It's hopeless trying to explain things to you. We can, however, always count on you for a negative comment.

R.

I had both the orange box and the chrome box on my 1968 10 second Dart, to see if there was any difference in performance. I shifted my 395 stroker W2 small block at 7,200 rpm. Guess what? No difference in performance, and the orange box worked flawlessly to 7,200 rpm!

When my son had our orange box on his 400 Dart he pushed it to 6500 with no problems. Never missed at all up to 6500. I use it now and I shift around 6200 and it works good for me. I do remember Mopar rating the orange box at 6000 rpm and the Chrome box much higher. Ron

probably the only difference is the price and the shiny chrome.