I was recently asked my opinion on what was the safest way to add more power to a DP. The owner has a Cummins ISL 8.9 Common Rail with VGT, from the 2006 era. But his question was more generic, as he had read via search, many of the cautions about increasing power. He wanted to know could any increase in power be done safely?
Here is my response to him, and wanted to get opinions on if I missed the mark in some of these?
In order of the best way, least risk engine wise, of adding more power:
1) Buy a coach with a bigger engine to start with
(Sort of a grinning response. But so often overlooked in purchasing a coach, to be sure you get a coach that supports your intended usage.)
2) See if Cummins has a reflash option for your ECM.
3) Improve back end pressure, via larger exhaust pipes and muffler and sometimes headers/manifolds.
4) If intake CFM is restrictive, add larger airbox and intake pipe along with a good quality stock like filter. (Non K&N or AFE, for example.)
5) One of the many different 'chips' or 'in between the ECM modules' available for different engines. MP-8, DIGI, etc.
6) Water/Methanol injection - juice...
(This is another one of those where how and when you use it, has a bearing on how safe it might be.)
(On pre posting edit, I lump propane injection into this grouping too.)
7) Air boxes with K&N, AFE type air filters.
(I made this last, but I also usually recommend against this for most coach owners. Just too much info available that these filters are usually not as protective as a stock OEM type filter. (Fleetguard, Donaldson, etc.)
Not mention are engine, and possibly specific years of engines, power options. Plates, Banks Kits, and others. Also left out of this are more custom mod's such as larger turbos, changing injectors, blue printing many components, etc.
I told him I felt that if done properly, items 1 - 4 are safe ways of adding power. Item 5, the 'chips/in between modules' is relatively safe, as long as the "tricking" of the ECM to change the position of the fuel metering rod within the injection pump (how most of these work, as I understand it) to provide more fuel - is not too aggressive. For example, if an MP-8, keeping the knob turned down to below 1/2 of the way vs towards the max of the scale. These might also require a supplemental fuel pump to augment those engines where fuel supply might become a problem. (FASS, Bulldog, etc.)
For the ISC, I always felt that the Banks Package was a good way to go. With some solid engineering and testing behind the mix of components. Not available from Banks anymore, thus why I did not mention it. (And was not ISL related either.)
All of these may be coach specific and vary between model years. Other factors such as transmission HP/Torque capability, and chassis engine specific cooling capacity work into this mix too.
Addition of more gauges, such as EGT temperatures, accurate water temps, etc. - can be utilized to reduce the risk of any of these that might be on the fence in the possibility of damaging an engine. Say the chips/modules again, if you see the current settings and specific demands on the engine are causing higher VGT and or water temps - you can either take your foot out of the pedal, and or also back off on the settings, if cockpit controlled.
My last comment to him, and it is one I consider before any changes I might make on my coach. Engines are expensive, Cummins (and CAT, Detroit) have quite a bit of coin in the engineering compromises between power, fuel mileage while meeting specific year emission control requirements. I felt that any of these manufacturers can get more power out of these engines. The question is how long they'd last, and if they would remain legal for over the road usage.
OK gang, sorry this was so long winded. And it was an 'over the campfire' discussion that I've tried to summarize down.
How about it, any major items missed? Any major disagreement on the different options in relation to relative safety to the engines?
Best to all, take care of your rig's, and they'll take care of you!