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I dont know what gt15 came on. But a GT17 is a fairly common turbo as it comes on a saab. It is also ballbearing i believe where as the gt15 isnt

The smaller the turbo...the sooner it'll kick in.
But..turbo's have a maximum flow,anything over that will kill it's efficiency,so you could lose power in the high rpm range for all it'd then do is blow hot air into your intake.
This is why (street) people use hybrid turbos like t25/t28 or t3/t4 on bigger displacement motors so boost will kick in at a reasonable rpm for midrange power and it won't run out of steamin the high rpm ranges.
for example Drag people would go straight to a huge T3/T4 or a T4 because they don't need a streetable powerband,punch the throttle through the floorboard at 3or 4000 rpm when running one of them big hairdryers and farkall will happen (turbo lag)
So yeah it's really down to the choice of " what is your goal"
hope this made sense

what happens if you hit boost to early or is it that it wouldnt have enough boost

i have a t25-28 on my 1400 and it is on full boost at 3000rpm. i would say it is too small

still looking at turbos. and have looked at garrett gt15, has any one used this before and if not why? according to my research t15 should be the right size (btween 1lt and 1.6lt) please correct me if im wrong. is the reason why everyone says go a t2 because there cheap or is it because they like to oversize everything. as i said correct me if im wrong

it has been done to death. mostly people saying to use ca18 turbos or wrx ones, because they're cheap. not at all suited to our engines.

read the info at the link i posted. I knew nothing, i read the tutorial and in the end i was able to understand the compressor maps, it's not that hard.

we need to get people familiar with the documentation.

hasn't this q been done to death???

S/h a turbo of a tx3 is a good size.

But why buy s?h when new turbos are so cheap??? as already said T25/28 not bad.

something off a 1.8 is going to be too big, it will "work" but not at all ideal.

Id go for the t25 off a ca18det. Simply because they are fairly common and they are generaly sold cheap due to upgrades on ca motors.

I run an Air Research M10 (same internal size as T2) but slightly smaller outside. I think T3 will be way to big. After all if it's a road car you don't want to be rev'n it's head off all day only whne you have to