#### SnailOnARampage

##### Senior Member

The rule is this: 8psi is 8psi coming from any turbo (big or small), as long as there is no pressure drop at the high end due to your engine being able to suck in more air than the turbo can blow.

If you had a guage in your h22a prelude that showed how many psi the turbo system was running at, and you were running 7 psi on a t3 ( or some small turbo) the guage/rpm would look something like this:

remember I am just using these as a visual...these are not actual numbers from a dyno..they are just out of my brain.

1000 rpms: 0 psi

2000 rpms: 0 psi

2500 rpms: 4 psi (+ 25 percent more tq theoretically)

3000 rpms: 7 psi (+47% more tq..theoretically)

3500 rpms: 7 psi (+47% more tq..theoretically)

4000 rpms: 6 psi (+40 % more tq..theoretically)

4500 rpms: 5.5 psi (+ 37% more tq..theoretically)

5000 rpms: 4.5 psi (+30% more tq..theoretically)

5500 rpms: 3 psi (+20 % more tq)

6000 rpms: 3 psi ( +20 percent more tq)

6500 rpms: 2 psi (+13% more power)

7000 rpms: 2 psi (+13% more power)

so...if the power peak for the h22a engine was at 7000 rpm, you would have 170 ft/lbs instead of 150 ft/lbs...but your average torque from 2500 to 6000 rpms would be something like 35 percent higher.

that same small turbo on a d15b7 at 7 psi might look like this:

2000 rpms - 0 psi

3000 rpms - 0 psi

3500 rpms - 3psi

4000 rpms - 6 psi

4500 rpms - 7 psi

5000 rpms - 7 psi

5500 rpms - 7 psi (47 percent increase in torque from 4500 rpms to red line)

6000 rpms - 7 psi

what if you put a big ass turbo on a d15b7?

2000 rpms - 0 psi

3000 rpms - 0 psi

4000 rpms - 0 psi

4500 rpms - 0 psi

5000 rpms - 3 psi 20 percent more tq

5500 rpms - 5 psi 35 percent more tq

6000 rpms - 7 psi 47 percent increase in tq

notice how the average torque gain is a lot lower than the smaller turbo, and the peak torque gain is the same?

that same large turbo on a h22a might look like this:

2000 rpms 0 psi

2500 rpms 0 psi

3000 rpms 2 psi

3500 rpms 5 psi

4000 rpms 7 psi

4500 rpms 7 psi

5000 rpms 7 psi 47 percent increase in tq

5500 rpms 7 psi

6000 rpms 6.5 psi 44 percent increase in tq

6500 rpms 6 psi 40 percent increase in tq

Horsepower = torque x rpm/5252

If the h22a had 150 ft/lbs of torque w/o boost, with 7 lbs, it would have close to 220 ft/lbs of tq.

the h22a @ 7k rpms w/o boost would have 199 hp/ 150 ft/lbs

the h22a @ 7k rpms w/big turbo would have 293 hp/ 220 ft/lbs

the h22a @ 7k rpms w/small turbo would have 226 hp/ 170 ft/lbs

the d15b7 @ 6k rpms w/o boost has 102 hp / 98 ft/lbs

the d15b7 @ 6k rpms w/big turbo would have 150 hp and 140 ft/lbs

the d15b7 @ 6k rpms w/small turbo would have 150 hp/ 140 ft/lbs, but it would have one hell of a lot more power throughout the whole power band...making it a much better daily drivable car

A b16/b18 would be somewhere inbetween the d15/h22a

this is my 2 cents on turbos...hope it helps someone