You might want to monitor your water temps in and out to see what's up. There's no way you should have that much heat post-IC if you're flowing enough cool water through the core (and have enough water capacity in your system). The BTU transfer ability of a core that size should be plenty so long as you've got enough temperature differential between the heat exchanger surface and the charge air. Which would require flowing enough water through the core to offset your charge temp drop with a reasonable water temp rise across the core, say 20 degrees. So if the water is 80 degrees going in, and 100 degrees coming out and your intercooler is say 80% efficiency, with charge temps of 374 degrees, your air temps post-IC would be 147 degrees. 227 degree drop. If you're flowing 53 lb/min of air that's 3007 BTU/min (edit: it's actually 4x that in BTUs...it takes .25 btu to cool a lb of air 1 degree F so I had already done the math on that but didn't initially show that step here). that needs to be removed. To maintain that 20 degree water temp rise across the core then, you'd need to flow 3007/20=150 lb/min. 150/8= 18.75 gallons per minute through the core. Flow half that and you get twice the temp rise and so on. It would turn into kind of a recursive problem to actually figure out what's going on with your system without knowing what the water temps in and out are, but I wager due to system head pressure, you're probably flowing 5gpm or less with that Meziere when you need to be flowing closer to 20gpm. And with the heat exchanger being less of a realtime process with that kind of heat load, even with adequate flow rate through the core you need a hefty system capacity, or phase change to keep water temps in check.
I have a VERY strong suspicion flow rate is the problem. But with that taken care of and you actually dumping more heat into the water, rapidly rising water temps on-boost will likely be the next bottleneck to pop up...easily fixed with ice, less so with water mass.
Could be flow possibly, but gonna doubt it for now.
I think more of the problem is speed of the air blasting through a small IC core.
We are talking about a 6x6x3 core. How much of that is going across the whole thing uniformly is probably not super great.
Here is pic of inlet side.
Outlet side
Get an idea of the core... Myself, would have liked more fin count but apparently that was
an issue of getting that maybe during the process of getting a custom core made.
Finding a better replacement core that fits the bill could boost increase of temp drop by a good percent I would think.
We have a big blower, that makes big heat, sitting on what is probably considered a
tiny intercooler.
If you look at the v8 guys running twin screws, they run a HUUUUUUGE intercooler core.
Almost rivals the front mount heat exchangers....
Ice would help, but it melts in like 10 seconds... and can't drive daily with an ice maker in the trunk... (or can we?)
I am sure there could be some pump fine tuning on flow but not fast enough to cause cavitation but i think i worst enemy is room.
There isn't much room to fit a monster core under the blower for us. Only way is to keep going up and make it tall as possible.
Remove dog bones, lower mount setup... put the blower in front of the engine like a cobalt sorta, and run a true A/W intercooler for it blow into.
Then can run a trashcan sized intercooler
Alternative is if someone would finally cast a new lower intake manifold to maximize the ability to run a monster core setup. have it drop down into the lifter valley if need be if
running no balance shaft.