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Old 06-10-2019, 10:54 AM   #1
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American Coach Owners Club
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Increase Horsepower

I have 370 HP 8.9L ISL engine that I understand can be reprogramed to increase the HP to 400 at a Cummins Service Center.

Question; Has anyone performed this upgrade and have comments to offer on PROS/CONS on making this change? Also, what was the cost?

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Old 06-10-2019, 12:24 PM   #2
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As far as the cost Cummins charges more if you are still under warranty. One person paid 1700$ for a 450 ISM up graded to 500 while still under warranty. Owner said a noticeable difference in performance and no change in fuel usage.

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Old 06-10-2019, 03:09 PM   #3
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I did the Cummins authorized "360hp tune" on my 6.7. Took if from 300hp/640tq to 360hp/800tq which made it just right (able to maintain 55-60 up 6% grade) and no reduction in mpg or any other issues.
RV was only 3 mo. old, still under warranty and cost ~$450 parts (the program) & labor
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Old 06-11-2019, 06:19 AM   #4
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Take the coach to a Cummins dealer. They will connect their computer to your ECU and tell you if an upgrade is possible. I had my 400 upgraded to a 450 last year by a Cunnins dealer at a rally I was attending. With the warranty the cost was right at 1K. If the unit is out of warranty it's about 400.00 for a reflash. Make sure you join the Cummins owners club as that will get you a 10% discount.
To be upgraded the transmission and radiator system will have to be compatible with the proposed upgrade. Last year at the rally I attended the 380 ISL's were not able to be upgraded to the 400 spec. Only way to know for sure is to take the coach to a Cummins dealer and have them connect the computer to your coach.
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Old 06-11-2019, 03:43 PM   #5
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Just be sure your Transmission is rated for the increase in torque
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Old 06-12-2019, 05:20 PM   #6
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What year is your engine?

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Old 06-13-2019, 04:25 AM   #7
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