What kind of performance gains could I see from advancing the timing only? Is it worth it?
The exact answer would obviously depend on the nature of your setup and how aggressive the tune is.
A halfway decent way to have an idea of the gains is how much you think you could increase the timing. Do you know what your max timing is?
Most intercooled cars that I've seen run 17-18 degrees of timing max. Warmer ACTs would likely back that off a couple or few degrees depending on how much boost and compression the car is running. My car, on 8-9ish pounds of non-intercooled boost, is able to run 24 degrees of timing with no detonation
with the water/meth spraying (I've actually gone up to 26 at the track, but no gain was found as that was likely over maximum brake torque timing; going from 23-24 only showed slight, inconsistent gains). That is on my 'race' tune (slightly more aggressive ramp-in timing, and less timing pulled in the 140-160 ACT range). My street tune is almost identical, except the timing is backed down to around 18 degrees of timing. There is a HUGE, very noticeable difference. I've actually never raced on the street tune, but I'd guess it's an easy 30-40 rwhp and even more torque low in the RPM range.
Bottom line: if your max timing is in the 18ish degree range and you were able to bump that up to say 23 degrees with water/meth, you should see a nice gain. The gain should be bigger in the summer when the hot ACTs might pull the timing back even further, to maybe 15 or 16 degrees.
How safely and accurately you'll be able to bump that timing using the ACTs on an intercooled car, I honestly don't know, I don't have direct experience with that. The idea is to add in a lot of timing when the water/meth brings the temperatures way down. On my non-intercooled setup, that's super easy to do. With no water/meth, the temps skyrocket to 200+ almost instantaneously. But with the water meth, temps will extremely quickly drop sub-140. So pretty much, when the air charge temps are less than 140, we are 100% sure that the methanol system is working properly, and thus throw the timing to its arse. This way, we are increasing the timing from the lower ACTs, but we are also taking advantage of the octane from the methanol because the cool ACTs tell us that there's definitely methanol there. That's why I'm able to run 24 degrees of timing on the same ACTs that you're only able to run 18.
But, with an intercooled setup that is only seeing ACTs in the 120 range, it may be harder to distinguish if the meth system is working by only looking at the ACTs. I honestly don't know how much the meth will bring the temps down. That's why I said (in one thread or another) to not be afraid to experiment and really throw some volume at it. Obviously you don't want the car to go super rich or bog down from all the extra fuel and water, but you still want the largest temperature difference possible so you can be more confident in the meth system working correctly, and thus more confidently (and safely) add in the extra timing.
