A stock GSR displaces: .06346046 cf/revolution. assuming that there is NO loss due to restriction or whatever, that will equate to 481.9 cf/m @ 7600 rpm on the stock GS-R engine.
A 84 mm GSR displaces .06826325 cf/revolution. assuming there is no loss due to restriction, that is 593.9 cf/m @ 8700 rpm. Inorder to actually have the power peak at 8700 you will need some seriously bad ass cams/valvesprings.
That all equals out to the bored gsr approximately 1.23 x the hp at the peak. That number there is not including the benefits of port/polishing and things like that. Lets add an additional 10 percent for better flow rates due to a nice polished head. That brings the bored out one to 1.353 x as good as the regular GSR @ their power peaks. Lets go ahead and add another 5% for good tuning. Its now at 1.42 x170 equalling 241 hp to the crank. Now put a turbo on there that is able to push all of the cf/m @ 10psi and you have you *very estimated* 410 crank hp, which will leave you at about 375 whp.
Now lets go and do this a slightly different way.
1933/1797 = 1.08 ...the bored gsr has a minimum of 1.08x the torque of the regular GSR based solely on displacemement. Multiply that by 127 and you get 137 ft/lbs. Lets add another 10 on there for good measure/good tuning/whatever, which brings us to a fairly normaly torque number for a heavily modified GSR....145 ft/lbs. Multiply 145 x 1.7 (10psi) and you get 250 ft/lbs. 250 x 8700/5252
(assuming no loss after torque peak) and you get 412 crank HP.
Yes you are actually getting very close to 400 whp, and its even going by my "flawed" and linear standards.
Okay now for the turbo part. I know you've told me that I am wrong like 6 times, but I still haven't heard a good reason as to why I am.
I was actually wrong in previous posts (it was very late) about my numbers of cf/m...but here are the revised ones.
Assuming those cf/m numbers for the engines are above, with your GSR setup, you will need a turbo that can push a little more than 600 cf/m @ 10 psi...which should be the same amount of oxygen as 1000 cubic feet of uncompressed air (provided its the same temp). If you get a turbo that can only push 500 cf/m @ 10 psi you will only be putting the equivalent of 833 cf of air into the engine,.
Okay, so seeing all that, you have 2 diff turbos. a t66 and a t88. we'll pretend that the t66 can push 500 cf/m @ 10 psi and the t88 can push 600 cf/m @ 10 psi.
On the bored GSR running 10 psi the t88 would be ideal, because the amount of air it can move is almost exactly what the bored out engine uses at 8700 rpm.
The t66 would be ideal for the stock gsr engine @ 10 psi because the stock GSR will be able to accept almost exactly how much air the turbo can pump into it.
Now, if you put the t88 on the stock gsr, you would be creating extra drag and lag which is un-necessary for that engine running at 10 psi. The t88 would only do any better on the stock GSR if you set the wastegate to 13 psi or something.
Now when you go over to the bored GSR will be getting more power with the t88, and the t66 will only be producing something like 8 psi at full throttle at the power peak (even though the waste gate is set to 10). However, if you set the waste gate down to 7 psi for both turbos, the t66 would be faster again.....
So.... with 10 psi reading at the map sensor at full throttle at a given rpm at a given temperature, the power output will actually be greater with the smaller turbo