Geis

Alright, was just looking for guidance to make sure I'm doing all of this the correct way.
After researching how to read compressor maps and such, I'm further nearing piecing together my very first turbo kit! : D Went from very little knowledge of how the complete system works and how to choose the individual parts so bear with me here guys.
So first off I started with a hp goal as everyone states you should and worked fomr there backward to find the psi (PR) I would be at with a particular turbo. So I'll be shooting for around 250whp, which I converted to 300ish crank hp assuming 15% power loss to the wheels. 300 hp is approx 30lbs/min of airflow, or 427CFM (sea level 112 degrees). I then used an equation to find the airflow of my engine, a stock b20b. With that I got ( 122.047cid x 6500rpm x .5 x .90VE ) / 1728 = 206.6CFM. From here I plugged this into an equation to find what my psi would be to reach my desired CFM so I can acheive my hp goal (206.6 x PR = 427) and my PR (psi goal) came out to 2.0 or 2.1 PR depending on if I round. So here are my questions
A) I completely guessed my VE based on the advice of some of the guides I read, but I'm not sure how this really takes into account the amount of hp my engine is putting out currently.
B) I am unaware of what the VE would be of my engine if it was brand new, but if someone were to give me a number, the best way to find how much its tapered off (without using a dyno) is to run compression tests on the cylinders and to factor in the percentage of overall compression loss into what the VE would be if it was brand new to get a ballpark number of what my VE would be, right?
C) In order to find a turbo that will provide me a nice, wide, powerband along with supplying my hp goal I should look at compressor maps (I was thinking of T3s to start and going from there) plot a vertical line from 427 CFM to 2 or 2.1 PR and then find which compressor would have the widest horizontal line from beginning boost to my CFM goal AND which compressor would be in its most efficient island for holding 427CFM at 2-2.1 PR?
If anything needs to be clarified feel free to ask, I'm still new to turboing and learning how to put together an efficient system for my motor that will provide me a wide powerband and hopefully lots of fun : D

Schister66

Props to doing your homework

The quick and easy method of figuring out general turbo sizing is by comparing the lb/min (or CFM) flow rates to gauge the power levels they would support. For example, if a turbo claims 48lb/min, you can reasonably assume it will support 480bhp at max - cut that down for drivetrain losses, and you're looking at 420-440whp. A lot of the turbo choices made around here are based on other setups that have passed through the forum, not by plotting them on a compressor map.

I've never been great at plotting engine demand/flow across a compressor map...someone else will have to chime in for that side of things.

met

Like schister said its more realistic to go off what other have done. Thats cool about the lb/hr I didn't know that before.
I have done the calcs out like you have, even if you get it right they are a ball park. It seems like once you get the car on a dyno its not the same, however I still do the calcs to see. I use to use squirrel performance calc there site is down, I don't know why.
Try this site Performance Turbos | BorgWarner Turbo Systems.
Its for BW turbos if you know the specs of others you can enter them in. It makes comparing different turbos much quicker. Just to add this is like the theoretical values, real world results very.

dieselsmoke

I believe the VE of your engine isn't going to change much at all unless you make some very pointed changes....like swapping a cam or changing the cam timing, or making a huge improvement in the intake or exhaust tract.

VE is just how much air actually fills the cylinder for combustion, versus the theoretical maximum it could swallow based on displacement alone. Think of VE as de-rating your CID to what is actually going on. No cylinder fills perfectly.

turbohatch96y7

iTrader: (15)

F1 cylinders get above 100% ve

m4xwellmurd3r

Nascar engines do as well iirc. Tuned to achieve over 100% ve for a very narrow rpm range