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WesPearson · 02-17-2018, 01:04 PM

Just had a Cummins factory reman ISB5.9 engine installed. Runs great but the shift points on 1st and second gears is about 1900 rpm. This doesn't give much performance on acceleration. I can't remember for sure but it seem like it used to allow a higher RPM before shifting if I had my foot in it. It's a 3000 trans in a 37 ft. HR Endeavor 1999. Would changing the engine affect the trans programing. The engine should have the latest ECM updates. Any ideas? Performance seems good in the upper gears but it will allow higher rpm before shifting.

LJowdy · 02-17-2018, 02:41 PM

According to Cummins, your maximum torque is either at 1,400 or 1,600 RPM's depending on which year engine you have. Exceeding that won't make you go faster as the torque will start to decline the more RPM's you pull. If it's shifting at 1,900 then I'd leave it alone.

twinboat · 02-17-2018, 03:24 PM

Its not as important at what RPM it shifts at, as what RPM it drops to, after the shift.

As long as its still in the power band of the engine, it will pull fine. If it drops to low an RPM, the engine will bog down.

johnhicks · 02-17-2018, 06:48 PM

A corrolary question. I have a 6BT5.9 and MD-3060 reman. When climbing a hill the transmission appears to me to be lugging the engine; RPM will drop to 1200 or lower before downshifting to fourth. Puts me in a psuedo coffin corner; out of speed and out of RPM.

It works fine when I shift it. So I think I'd like to get it reprogrammed to shift down to fourth at 1300-1400.

I have a fairly new-to-me toad and uphill takes a bit more hp/torque.

Does this make sense?

Piker · 02-23-2018, 03:55 AM

Contrary to popular belief, it's at peak HP that will result in the fastest acceleration. This is why when guys mod their cummins pickup trucks into street racers, they increase the usable RPM up to 4000 and beyond. More RPM = More HP = faster acceleration.

The torque of a diesel engine is great, but to say a motor is torquey... is just to say that it produces great hp at low rpm. Something gas engines don't generally do.

-cheers

Mr_D · 03-04-2018, 06:29 PM

I think my engine is "torquey"! 1950 ft lb from 1100 to 1700 rpm according to Cummins.

Piker · 03-05-2018, 04:24 AM

Quote:

Originally Posted by Mr_D

I think my engine is "torquey"! 1950 ft lb from 1100 to 1700 rpm according to Cummins.

That, good sir, is an awful lot of torque...

That is also a lot of hp... and at a very low rpm I might add. What a beast!

Cheers

Soppy · 03-05-2018, 07:10 AM

1900 sounds a little low . The important part is the RPM the engine drops to when it shifts. The ECM programming may or may not affect the transmission shift points. Some use a separate module to control the transmission.
You could try some acceleration runs manually shifting to get the best RPM for your shift points and then have then programmed to your PCM. Have done this with fire trucks to obtain the quickest acceleration.