So how do these relate. I know a high compression rate is bad for boost, but how do you know if a turbo or S/C is better

 

turbo and sc, doesnt matter when comparing boost pressure with compression. generally, people like an 8.5:1 or 9:1 when they plan to run high boost. although its not uncommon to see people run 8-10psi on a 9.5:1 compression ratio.

 

So if the ratio is too high nitrous is better? Why is it super chargers are better for stangs

 

if the compression is too high, neither forced induction nor n2o is good. you want lower compression for both.
sc are not better for mustangs or really any cars as compared to a sc. turbos are more efficient then a sc and dont produce drag on the crank like a sc does. the reason more people buy a sc is because kits for mustangs are a dime a dozen compared to a turbo kit. most turbo kits are made to order and are very expensive..... usually at least twice the price of a sc. if you can fab your own kit, you can make a turbo kit for a fraction of the price of a sc kit but more people cant make their own turbo set up. i only run a sc because of emissions. the next mustang i build will be old enough to be emissions exempt and will never know what a sc is. it will have a 408 innercooled turbo.
also, because of the ease of installing a sc, the demand is higher then that of a turbo so through competition between manufacturers, the price of a sc kit has come down. then you have the idiots that think turbos are for ricers regardless of the fact that turbos are more efficient and creat more hp per pound of boost then a sc

 

Ummm................... you might wanna shoot your sources for telling you that. Cuz they certainly are giving you false advice. I'm not saying turbo's are the best for everyone but it's a fact that a turbo will give you more power than a supercharger at the same psi rating. The reason for that is that it doesn't take power to make power in a turbo unlike in a S/C. It all depends on someones setup as well. Plus people with superchargers are people that want low end torque and don't want to have to wait for the power to kick in whereas a turbo will give you more power but you'll have to deal with the lag. It's a trade off that you have to consider.

 

superchargers are more ECONOMICALLY sound compared to a turbo....

as far as performance goes...what the guy said above me is dead on...its a trade off

 

the higher the compression rate, the easier (more likely) it is for detonation to occur (gas + air exploding due to heat and compression instead of from a spark plug), which is dangerous for motors.

 

it breaks down to this. Compression is 5 psi (roughly) is 1 point of compression. So if you are running 8:1 compression and you want to go up to 10:1 you want to run 10 psi of boost. That's how the two are related. Is that what you were askin?