Your compression ratio may be a concern for turbo duty. Unless you are running race gas or alcohol, compression should be under 9.0 to 1 for even minor boost. With a small cam and poor flowing head, I was able to run 12 psi on 9.0 compression before ping set in on 93 octane pump gas. Once I ported the head and went to a bigger cam though, I could not run over 9 psi of boost in the same motor. Of course it was making just as much power. In both cases, I was ping limited. Same max cylinder pressure resulted in ping due to the poor head design in that motor (a 1983 Toyota 22RE). What I am getting at here is that your cam(S) don't sound bad for boost, as long as you know what you are going to get. A couple years later I splurged for 8.4 to 1 compression J&E forged pistons and contoured the chambers a bit to reduce hot spots. With a cam pretty close to the set you have, I was ablke to run 13 psi of boost before ping, and it made around 300 lb ft of torque from 3200 to 5000 rpm and about 300 hp at 5500 or so. I revved it all the way to 7250, it was falling off a bit past 6000, but still pulling hard. This was out of 2.4 litres, or 144 cu in. Without the turbo, that motor would make about 170 hp.
For comparison sake, the cam I ran was a 268S from CompCams. The ADV. DUR. was 268 on both intake and exhaust, with 110 degree lobe centers. I ran it 4 crank degrees adv. I know this sounds small compared to yours, but CompCams uses VERY FAST lift ramps as the .050 duration was 223 degrees. That is actually bigger than your chart shows. Here are the opening and closing points at .050 lift.
exhaust opens 45.5 BBDC
intake opens 5.5 BTDC
exhaust closes 2.5 BTDC 3 degrees of overlap at .050
intake closes 37.5 ABDC
Written the same way, your cams look like this.
Exhaust opens 38 BBDC
Exhaust closes 8 BTDC
Intake opens 5 ATDC 13 degrees with both valves under .050 lift.
Intake closes 31 ABDC
This is certainly not too much duration for a turbo. The lower compression needed to make a turbo useful, and the loss of the great exhaust system will cost you some of you excellent off boost power, but once the turbo comes on, you will need a crow bar to get the smile off of your face. If your motor truely does breathe like those dyno charts show, I figure your exhaust is going to cost you 40 hp once you restrict it inota turbo, and the lowered compression will probably rob another 40 or so taking you back to just (kidding a bit) 320 hp before boost, and then adding 50% at 8 psi (very realistic for a proper turbo setup) nets you 320 + 160 = 480 hp. If you can shove enough fuel into it, and not ping, you could run a tick more boost and make an even 500 hp without too much trouble. Sized right, it could also make 400 to 500 lb ft of torque down around 3500 rpm as well.
It is true that 8 psi ( more than 50% over atmospheric pressure) will not yield 50% more air flow, BUT... all of the frictional losses have already beeen taken care of. There is a small increase in losses, but the extra cylinder pressure is not going to make the oil pump, rings, cams, and accessories, 50% harder to turn. In fact, 14 psi is usually enough to double the power.
Gary M.
