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Truckdriven · 03-03-2026, **(Subject: X15 CPL Change )**

I have a 2020 Kenworth T680 ESN 80143535 that I am doing an overhaul due to dropped liner, this is a 4342 CPL efficiency series high compression series engine and since we would like to program it to 565/1850 I'm wondering if we should rebuild it as a 4343 CPL? I found a same year and model truck with ESN 80167047 for a comparison, looks to me like everything is the same between the two except pistons, head and turbo. Is there anything else I'm missing I should know about? Also what are the turbo differences and can I use this same turbo until it wears out?

Rawze · 03-04-2026, **(Subject: X15 CPL Change )**

Its usually not worth trying to upgrade it ...

=. A mid-tier can be turned up to 525/1820 torque with no issues without any parts changes ... which is close enough to 1850 for anyone not to want to bother with all the extra risk and costs of trying to change out hardware to upgrade the engine that will have no warranty.

=. no core on any components like injectors, turbo, etc.

=. NO WARRANTY WHATSOEVER!.... if cummins finds out you put alternate parts in the enigne, then it voids all part warranties. Head, pistons,.. all of it. - Another risk to weigh.

=. The block / crankshaft themselves are often not the same tier on X15's. The efficiency series in particular has smaller tier crank and block casting.

=. Quickserv can be deceiving with its part #s vs cpl. You should not always trust it as far as it listing same part sometimes it gets it wrong.

=. Here is some old post with part #s where each tier was looked up in detail and verified...
info: https://rawze.com/forums/showthread.php?...0#pid51650

If your just trying to turn the power up a bit, its fine for mid-tier to go to 1820, etc... but if your trying to convert it so that you can heavy-haul with it.. your better off buying a tier-1 engine.. or better yet, finding a truck with heavy haul specs overall and heavy haul rears, 411's 3.90, etc.. -- The thole truck needs spec for it, and not trying to band-aide everything by just torturing the engine into an agonizing death spiral.

Lastly,.. the bulk of trucks that 'feel weak' under the hood are due to improper rear ends. All the stupid salesmans and stealers$its keep pushing trucks onto people (and fleets) with the rear ends waay too tall for the truck to not get out of its own way no matter how much power you add to the engine.

It is FAR CHEAPER long term to re-gear the rear ends to something like 3.70's (for 48-state 80k and lower freight) or 3.90's for 100k, 4.11's or 4.36's for above that and for best pulling on hills, mountains, etc. out west,.. etc.. than it is so make the most expensive thing in the drive-train (the engine) work harder to make up for it, torturing it in the process and shortening its lifespan. - Something to consider heavily if some yahoo 'wants more power' all the time,.. as their issue is most likely horrible rear ends than it being the engine.

Trucks meant for 80,000 and heavier freight with those bulls%@hit 3.36, 3.79, 2.63, and other crap garbage rear ends ALWAYS have issue hauling anything more than an empty trailer, making the whole truck weak-pulling, and at the same time, torturing the engine in lower rpm ranges, lugging it to an agonizing death, and this is the issue with a LOT of trucks these days.

Truckdriven · 03-04-2026, **(Subject: X15 CPL Change )**

Yeah makes sense, I'm not real interested in overly complicating things, we're not trying to do Heavy Haul with this truck. It just seems logical to me that if the manufacturer used those hard parts for the higher horsepower there must be some benefit to longevity.

But mostly I was hoping that going to the next tier would get my power and torque curves into higher rpms, seems to me the efficiency series is mapped to run lower RPMs, with this truck by 1750 RPM it is cutting power and completely limited at 1800 RPM. We are using a RR program on here currently. If I went to the next tier could I use that calibration as a base file for programming and would that get it perform better at generally higher rpms?

Rawze · 03-04-2026, **(Subject: X15 CPL Change )**

(03-04-2026 )Truckdriven Wrote: Yeah makes sense, I'm not real interested in overly complicating things, we're not trying to do Heavy Haul with this truck. It just seems logical to me that if the manufacturer used those hard parts for the higher horsepower there must be some benefit to longevity.

But mostly I was hoping that going to the next tier would get my power and torque curves into higher rpms, seems to me the efficiency series is mapped to run lower RPMs, with this truck by 1750 RPM it is cutting power and completely limited at 1800 RPM. We are using a RR program on here currently. If I went to the next tier could I use that calibration as a base file for programming and would that get it perform better at generally higher rpms?

The RPM range and power/trq can be adjusted via custom programming. No need to over-complicate it.

Truckdriven · 03-04-2026, **(Subject: X15 CPL Change )**

Okay good, I will probably pull a copy of the file and email it to you.

The end user is pretty set on the 565/1850 power setting so if we need to change any hard parts to get there let me know otherwise I will keep it Factory parts and get you in on the programming when I get to that point

Rawze

(03-04-2026 )Truckdriven Wrote: Okay good, I will probably pull a copy of the file and email it to you.

The end user is pretty set on the 565/1850 power setting so if we need to change any hard parts to get there let me know otherwise I will keep it Factory parts and get you in on the programming when I get to that point

Tell that person wanting to change the hard parts that it will void parts all warranties from the red engine maker for doing so .. That he will have to sign a special waver UP FRONT of no-liability and that of ALL PARTS, WARRANTIES, LABOR, etc. ARE VOID,.. and that ALL WORK IS, AS IS, so that you and your repair shop + any future part failures are NOT COVERED by you / your shop, once the truck is taken off your lot. - See how fast that customer back-tracks on their decisions.

FueledUp

I have the same question. But my engine is not rebuildable. Rod and piston joined the atmosphere. Original CPL is 5880 and I found a local, low mileage take out, 5879 that has 57,000 miles on it. What would i need to change over? After 565HP.