ok, im bored and want to flex my brain, and this is a topic that many people do not agree on, some say that you cannot run turbo cars on a high compression motor, some say you can and it actually will run better, well heres my facts on the matter, lets say you have a stock b18c1 with 10:1 compression, now, atmospheric pressure is 14.7psi at sea level, so where gonna use that, so when your motor intakes a stroke of air and fuel an comresses it it has turned that 14.7 and multiplyed it by 10, to 147psi.
so that was an easy one, now, lets say you stick a turbo on that motor and run 8psi of boost, now at peak boost you will have the 14.7 plus the 8psi of boost, making 22.7 psi going into your motor on the intake stroke, now compress that by 10 and u have 227psi
ok, so now we change pistons and lower the compression to 9:1 we run the same boost of 8psi so we have the 22.7psi going in but only comressing it by 9 wich gives us 204.3psi, wich is less than with stock comression, wich means we will make less power, this is where the common missconception comes in that you can run more boost with a lower compression motor, well it is true, but your making more boost to compensate for the lack of compression that your motor has. you see, to get the same power out of the lower compression motor you would have to run 10.5psi(10.522 to be exact) of boost, add the 14.7 wich makes 25.22 and multiply that by 9 giving us the 227 wich is the same amount of compression at TDC as the stock compression motor.
now, running 10.5psi of boost to get the same power is going to have drawbacks you will not spool up as quickly becuase you have to spool to 10.5 psi rather than 8 wich isnt much but were talking 10th and hundreths of seconds in racing.
it comes down to tuning, properly tuning a higher compression motor will actually run better than a lower compression motor, you have more power in off-boost situations and with the higher compression your turbo will actually spool up quicker because of the force the exhaust is being released, now you may think that it would be more work tuning the higher compression motor, but in reality if your looking for the same amount of horsepower your going to have to increase the boost in the lower compression motor to make up for it, and in doing so the compression levels and detonation possiblity will be equal in both motors, so tuning is everything.
so that was an easy one, now, lets say you stick a turbo on that motor and run 8psi of boost, now at peak boost you will have the 14.7 plus the 8psi of boost, making 22.7 psi going into your motor on the intake stroke, now compress that by 10 and u have 227psi
ok, so now we change pistons and lower the compression to 9:1 we run the same boost of 8psi so we have the 22.7psi going in but only comressing it by 9 wich gives us 204.3psi, wich is less than with stock comression, wich means we will make less power, this is where the common missconception comes in that you can run more boost with a lower compression motor, well it is true, but your making more boost to compensate for the lack of compression that your motor has. you see, to get the same power out of the lower compression motor you would have to run 10.5psi(10.522 to be exact) of boost, add the 14.7 wich makes 25.22 and multiply that by 9 giving us the 227 wich is the same amount of compression at TDC as the stock compression motor.
now, running 10.5psi of boost to get the same power is going to have drawbacks you will not spool up as quickly becuase you have to spool to 10.5 psi rather than 8 wich isnt much but were talking 10th and hundreths of seconds in racing.
it comes down to tuning, properly tuning a higher compression motor will actually run better than a lower compression motor, you have more power in off-boost situations and with the higher compression your turbo will actually spool up quicker because of the force the exhaust is being released, now you may think that it would be more work tuning the higher compression motor, but in reality if your looking for the same amount of horsepower your going to have to increase the boost in the lower compression motor to make up for it, and in doing so the compression levels and detonation possiblity will be equal in both motors, so tuning is everything.
). It's just one hell of a lot safer to lower the compression. Even with the best tuning, problems will still occur, and it's nice to have that little bit of breathing room.