Power upgrade ideas Cummins 6.7

[bjeff77]

Thanks for the link. To add to the confusion, my 2018 Seneca HJ is actually built on a 2017 Freightliner chassis (common practice in the rv industry), so sadly, I'm 340 hp and it has the MH2500 transmission rather than the 3000.

[bjeff77]

Correct you are! I went to my local Allison distributor and he suggested a reflash on my 2500 trans (stock is a 2200 rpm max shift, the new tune is 2600). We took it for a test drive and the difference was impressive! Before, the trans was (with normal throttle input) shifting around 1500-1600, and just missing the power band. Now, it shifts about 1950-2000 rpm with normal throttle input, and the difference is startling. Not sure how that will affect fuel mileage, but the coach seems happier with this tune (as does the driver!). The other biggie is that the stock tune only has the engine brake work in 6 and 5th gears. He advised changing that down to 2nd gear. On his advice I did. It's obviously a little noisier, BUT, I had previously noticed many times when I had to stop faster than I would have wanted, I'd get a noticeable brake smell off the front brakes. This seems to be resolved now. I'm not sure if I'm going to pursue the engine uprate to 360 hp, but for now, I'm just going to live with it for a bit and see how it goes. Thanks all for the helpful input

[bjeff77]

Wanted to post an update on my progress so far. I consulted the local Allison distributor and he pretty firmly tried to discourage me from either uprating my Cummins 6.7 or adding the AG Specialties kit to boost hp and torque. He suggested we first load what he called the 2600 tune to the transmission. I did so at a very reasonable cost of about $140. The other thing he did while he was in there was change my exhaust brake setting so that it operates all the way down to 2nd gear. That alone was worth the cost, as previously, I'd get a hot brake smell if I had to stop more quickly than I otherwise wanted (sudden yellow light ahead, etc). I just took the first trip towing a dinghy (Wrangler unlimited with 37" tires and a lot of aftermarket stuff, so it's much heavier than stock). I was amazed at how much more willing the rig was to downshift into the power band when going up hills, and how much more effective the engine braking was. It FEELS like I have an extra 25-30 hp, even though the engine remains bone stock. I'm going to run with this setup for a while before deciding on any other mods, such as bumping the engine hp. For reference, I have a 2017 chassis, 6.7 with Allison 2500 and a single 'tune' in the transmission. Later ones had a switchable tune from what I understand. I think Jayco cheaped out using the 2500, which is right on the edge of its performance capability in stock trim. They later repented and started using the 3000.