Drivability blower vs turbos
for compression I was thinking something like 8.1 I know it needs to be low
8.1 will work but you're leaving a lot on the table.
You will make more horsepower per lb of boost than you will per point of compression. An all out race car may run very low compression and a very high amount of boost because they are not worried about throttle response with everyday driving. Since you are building a street car you want to move the compression up so it's not such a dog but not so much that you can't run very much boost without adding higher octane fuel.
I've found that a nice area to stay around for a street car is close to 9 to 1 compression. You can play with calculators computing your "Dynamic" compression ratio with expected compression ratio and boost to find where you are happy running on 93 octane. You need to decide how much power you will be happy with on the street on 93 octane vs at the track on race fuel.
Horsepower with engine size and turbos. You can make way more power than you need to run 9s on a smallblock with single or twin turbos. For instance. Let's say you build a 9-1 compression 360. This is a pretty simple motor but you've put good forged parts in it. With decent heads this motor should make around 300 rwhp. Now let's add a little science. Atmospheric pressure is 14.7 lbs. So for every 14.7 lbs of "boost" you are adding one atmospheric pressure. I usually round it to 15lbs to make the numbers easy. Take your 300rwhp 360 motor and add 15lbs of boost. You have now doubled the output and are close to 600rwhp. This is enough power to push a 3200lb car into the 10.teen range at around 130mph. All on 93 octane. If you change to a higher octane fuel for racing and run the boost up to around 20lbs let's look at the numbers. Engine makes 300 rwhp. 15lbs of boost adds 300rwhp so you're adding roughly 20hp per lb of boost. With 20lbs you would be adding 400rwhp to your original 300 NA RWHP so you'd be at 700rwhp. That's easily enough for a mid 9 second pass.
If you build a 9-1 compression 360 based 408 and make around 400rwhp NA you can run the numbers and see you will be easily in the low 9s around 145mph on 15lbs of boost and pump gas.
Turbos: You're turbo sizing is completely dependent on your motor choice and horsepower goals. There are common turbos that people run but even if you pick a size each size will have several variations. Depending on what you are putting this in you may end up running a single simply to make it fit. At the end of the day what you are looking for is CFM. Your motor will require a certain CFM to run NA. You are attempting to increase that so you need a turbo that will push the required CFM at a boost level it is happy with. You need to look at compressor maps and pick a turbo that will suit your build.
Gearing - Don't run such a high gear that the car is sluggish. Turbos do like long pulls but they also like rpm. Figure out how much power you're going to make. Calculate what your trap speed will be. Pick a gear that put's you just under redline on the tire you will be running for the target trap speed. Autos and turbos are made for each other.
You have a lot of research to do but it's not rocket science. I hope I've been able to shed some light on it for you.
