CRC has an aerosol called belt grip, try that. But I'd be checking that your alternator/a/c compressor/water pump/etc isn't seizing with a bad bearing first.
Also check that your adjustment bolts aren't stripped and/or coming loose.
valve guides trimmed (what does this do lol?)
for cam lift, and/or head flow, what size are the sticks?
BTW I think the turbo is a bit small for what you want, 240 sounds about right otherwise.
You are right, but the effect is split second and then everything equalises and assuming the CS Area's are the same then so is everything else, you would be hard pressed to feel any response effect in my opinion but I'll be honest and say that I have owned both systems and haven't tried to or noticed any difference. If you had an open pipe ie no cat back exhaust then the split dump could in theory be the better performer. But then you would be better off with a screamer pipe
Better than what???
A standard system yes, a bell mouth no difference. This answer is based on the split dump and bell mouth both having sufficient cross sectional area to remove restriction. And that is the main thing, you have go bigger. Where the gases come back in is less important [as long as they come back in in a typical split dump front pipe fashion], and that is why a bell mouth works just like a split dump = they are both bigger in area than a standard system.
A split dump is OK, no different to a bell mouth really. Heaps of guys are running with split dumps all over the world. The difference in performance between a split dump and a bell mouth is as close to f#ck all as to not count and honestly could go either way.
The biggest problem you may repeat may have with a split dump is the wastegate getting caught on the splitter flap or the piping, and this could happen to a bell mouth but is less likely. And careful use of a grinder will usually fix it - just means you have to remove and fix.
The only other problem you might have is cheaper thin metal poorly made units will fracture and crack around the welds over time - but this is true for both types.
Personally I wouldn't lose any sleep over the split vs bell debate, I'd just make sure that whichever one you decide on is a good qual unit that bolts up and sits right.
I'm with Terry on this, Camry is the one to get, resale, reliable, roomy, economical, safe ish, adequate power [for its type], low insurance etc etc etc.
Boring as hell, but sometimes even that is a plus. At least you are never disappointed.
I'd swap tuners, or swap cars. Owning a car like a GTR in a country town has its problems [i'm in the same jam]. You have to decide if you want to drive 2-300km and get a 'real' tune, or if you would rather live with an aussie V8???
I think that your mods should give good power and maybe more than what you already have, 280kw is OK, but a GTR with those mods should be over 300. So your tuner is the weak link in the chain.
As they say, only a poor workman blames his tools..............
What exhaust do you have? If it is a standard one then maybe that could be affecting final power?