Took the truck for a drive a few weekends back. First time on a long haul; 360 miles round trip towing a trailer the whole way.
I'll consider this the first real shakedown run since the swap was finished. I wanted to see how it would do, what works and what doesn't.
This was my view for most of the trip:
As with any project, some things go according to plan and others try to leave you stranded on the side of the road...
Having never towed with a gas engine with turbos - I'm in uncharted territory. With lighter trailers (empty) it seems like it cruises along just fine, aside from some issues caused by the TCC control strategy that needs to be completely changed. I'm just stoked that the lockup is finally working on the TCC (had to drop the pan and re-trace all the wires to figure out why, trans was from a '90-ish truck with PCM controls). Running out to the west side of the state, towing a 2000# car trailer, it got 17.2mpg. Towing a 3000# ish boat it was about 16.5-16.8
First thing I found was that I don't like the EPS setup anymore. It just has a completely dead feeling, and I'm having inconsistent assist from it. It's hit or miss while maneuvering around parking lots - it would cut out randomly. Most likely I'm going to end up with a hydraulic over electric system, going back to the stock gearbox and finding a standalone pump from like an MR2, what other options do you guys know of? No, belt driven pump is not an option, I need power steering assist when the engine is off.
Next is the TCC strategy. The series 2 PCM can't control the on/off TCC in the 700-r4 from what I'm told. Is there a way to make the (98 grand prix) PCM control the TCC, which needs an on/off +12v control? If not, I'll have to use a proximity switch on the throttle body to only let it lock in the 5-20% throttle range, no matter what gear it's in, or change the trans to something that bolts in that the PCM can control shift points and TCC (I don't know what trans that would be... 4L65e? Something that won't freak out about up-shifting lol) I don't want to open the transfer case can of worms if I don't have to.
Otherwise I made the first leg of the trip fine, and after fighting with the thing I went out there for, we eventually ended up with this:
4500# of van, 2500# of trailer, give or take. And yes, it pulled it just fine! For a little while, but that wasn't the engine's fault (not relevant to this discussion)
My hydraulically activated (increases brake signal to the trailer with increased brake effort) brake controller from 1979 still works. I had never had a chance to test it out until now, so I'm stoked about that too.
Anyhow...
To people that tow with turbo gas engines - and by tow I mean a loaded car hauler, 38' travel trailer, etc. Does the motor cruise under boost? 1-2 PSI, or more? I would think that monitoring EGT is going to be an issue if it's constantly under boost, as well as heat management. I have a 4-core big block radiator on this, it's over 2" thick and takes up the whole front end of the truck. I didn't notice any issues with coolant temperature, it never exceeded the thermostat set point. Also has a big trans cooler and big (thermostatically diverted) oil cooler. I'm not worried about it getting into boost while climbing hills or whatever, just concerned that prolonged periods under boost (is 1psi ok? 2? 5?...) might drive too high of a combustion temperature and cause piston damage.
This would be just one factor in determining the ideal cruise-while-towing RPM. That is, with the TCC locked. I feel like it's really really close as it is now. 4.10/4.11 gears with a 265-70r17 tire puts 4th + lockup at about 2150rpm. Towing 3000# or so (light) this was on the borderline of making positive pressure while cruising. A few hundred more RPM would have kept it out of boost in 4th + lockup. The endgame for this truck is going to be a 4.56 full float rear (and matching front). That would put 70 @ 2500 RPM which seems like it would be a good balance for cruising and light towing - but it pushes 3rd @ 65 up to 3200 rpm (heavy towing) and that means the turbskies are on a hair trigger because they are all in - 6psi @ 2700rpm - from what I've seen. And it's going to hurt the gas mileage.
I need to get tires for this, my thought was to get a smaller tire (used) to bump the cruise RPM up and test it out, rinse and repeat, to find the ideal ratio before taking the plunge on the full-float and new LT tires. But I'm not sure if I'm overlooking any other issues from running constantly in low boost or if that's really a problem. If it's just a question of thermal management, and the EGT says it's ok, then I don't need to make any changes.