road tune with a load

i've been pulling a trailer to the tip lately an had a good 900kg on the back of my wrx with trailer. Got to say the load feels so hard that its nearly got to be worth thinking that set weights on trailer and a good few pulls has to be way better then dyno tunes. I know im hitting cels i wouldnt normally use but if the weights are selected properly and the pulls done nicely you would get a fair tune off it. And the real world air flow etc would be there straight away. Anyone done anything like it or have a say?

All i can say is doing a WOT pull with a trailer on the back would make me nervous lol. Bare in mind most cars dont have a tow bar nor can you map to MBT on the road effectively either.

I think his point is that the vehicle can be loaded more which would mean it moves through the range being tuned more slowly.

On a steep hill, with vehicle loaded (and with a trailer?) it may even be possible to mimic steady(ish) speed operation at some rpm/throttle positions, not by any means a replacement for a proper dyno'- but needs must.

Might work better for EGT, etc, than an inertia type as heat soak, etc, will be fully present.

I'm having trouble understanding the question. Can you rephrase it OP?

Like Gord said, this can allow u to move through the cels slower and keep real air flow over the EGT IAT and intercooler plus engine is getting plenty of air also. Using the LTT , quick tune or data graphs to really dial in the tune.

Im not far off running my motor in then i will get it tuned on a dyno but also after that i might try the trailer with 400-500kg and see what the data shows. If the dyno is best then the LTT wont move and data pulls will show no changes .. The thing is not to use to much weight and cross over to cels that u would never use. Aim would be to load the car up without ringing its neck and been able to drive around on a public road in a safe manner. Im only new to the game and thinking out loud.

Having tuned cars on both the dyno and the road for something like 16 years now I honestly don't see the point or any real advantage. First of all you should be seeing pretty consistent AFR and boost in most of the higher gears - Certainly 4th-6th should provide little variation. Secondly we want to tune the car under the conditions it's actually operating in and hence doing pulls with a 900 kg trailer behind is not super relevant unless you're planning to actually use the car for that purpose.

The only thing I see as a potential upside here is that on a slower acceleration pull you may see higher combustion chamber temps and this can make the engine more prone to knock compared to a faster ramp through the rev range, and hence you can make sure that the ignition advance is safe under these conditions. Again it's a matter of understanding this and tuning the car under realistic conditions. What I mean is that it doesn't make much sense detuning the ignition table to avoid knock under a condition that you could never replicate in real world conditions unless you're towing a 900 kg trailer.

If you want to increase the load, a much easier and infinitely more flexible option is to left foot brake. The only caveat is that you obviously need to watch the temp you're getting into the brakes.

yeah thanks andre. Makes sense. Was just trying to steer away from using the brake. Will let tuner set it up and watch and learn..

Andre, your second paragraph is what I was getting at - heat soak can kill an engine on a longer pull if it was 'tuned' on an inertial roller where the engine didn't build similar levels of heat.