Air Flow: This is where I get a bit lost. Calculations > me!. Can anyone help me with this? I just need to know the air flow for a stock 6g72 in say 75 degree f. weather. I did some calculations from a site but they don't feel right to me. But here they are:

181 / 3456 x 5800 rpm x .85 VE. x pressure ratio = 784.9 cfm or ~54 lbs/minute


does this seem right? Does a stock 3 liter flow 54 lbs? This formula seems weird to me. Where did the 3456 number come from? does a stock 3.0 really flow 54 lbs/min?

The math is fine. The 3456 converts the cubic inches to cubic feet. Can a 3.0 litre flow this much air? At some point the heads will be a restriction and would require possibley more boost than your desired pressure ratio to flow 785 cfm.

Are you planning to run a single?

 

The math is fine. The 3456 converts the cubic inches to cubic feet.

Agreed, but it does more than that... It takes the 1728 CI in a cubic foot and doubles it, to compensate in the formula for the fact that a 4 stroke engine only takes in 1/2 volume each revolution.

 

more important why only 5800rpm. i would go to 8k with springs.

 

Yes, I am going to be running a single.

Mark: I was just playing around with numbers. This car will be a full street car though. Do I really need to rev higher than 6000rpm? I am not planning to build a beast! I am aiming for ~550 whp. I know, I can make that with 16g's but everyone has 16g's /

 

you want to stay in the hp as long as possible, 5800 is only going to be about for 2k rpm. that is not going to make very fast. you will be for one shifting to fast. you will atleast need to go to the stock rev limiter of 7300, i would personally get springs in the head and go to 8k and 8k is safe, some go to 9k but 8k is very do-able with springs.

that will leave you in your peak power band for about 4k or more depending on the turbo. that will make you fast. and shift less.

 

Here is a pretty good calculator that plots the turbo's flow at various RPM points (it's best to know the flow requirements at different points through the RPM range).

Squirrel Performance - Turbo Calculator Version 4

 

ok, so in this calculator i fill in the numbers and look at the different maps and see if line which represents my engine meshes with the turbos characteristics?

 

The Squirrel Performance Turbo Calculator havok91 mentioned above works well for me (example here). Jeff's calculators are also very useful:
Stealth 316 - Air/Fuel Flow Calculators
Stealth 316 - Injector Duty Cycle Calculation

 

*one thing you may want to note, the bsfc should be set to 0.5155
http://www.3si.org/forum/f35/tech-my-take-injectors-vs-timing-control-vs-hp-stock-ecu-262353/

havok91 is right on about the real world testing though. all these calculators are great for getting you in the ballpark for where you need to be, but in the end it'll all come down to what works for your car where you live.

 

do changes in turbine A/R affect compressor maps? ie would the map change if you went from an a/r of .81 to say .91 or whatever?

I am basically just looking for a turbo to make in the neighbourhood of 550 awhp but with minimal lag... I would be happier with a turbo that has a healthier low end and falls off in the high end, and from my readings I assume that means I would want something with a lower turbine a/r?

 

do changes in turbine A/R affect compressor maps? ie would the map change if you went from an a/r of .81 to say .91 or whatever?

The compressor map wouldn't change, but your engine's demand lines might (VE).

I am basically just looking for a turbo to make in the neighbourhood of 550 awhp but with minimal lag... I would be happier with a turbo that has a healthier low end and falls off in the high end, and from my readings I assume that means I would want something with a lower turbine a/r?

Correct, but turbos capable of doubling the stock configuration's power output will exhibit considerable lag regardless (i.e.- "minimal" will be significantly more than stock).

 

im currently running a t76 on a P trim turbine, divided exhuast housing .84 a/r. it spools right about 3500 but doesnt really pull hard till 4k. so when i install springs ill shift at 8k. and that will give me a car cable of 700whp and 4000 rpm of straight pulling and hauling ass. ( and its only journal bearing not ball bearing ) well for now

you ofcourse dont need anyhing that big so about a 66mm turbo will do your job.

 

sound performance has a "billit" t-71 that hits full spool (+30psi) before 4k rpm. that same turbo has put down well over 800whp on supras. with the turbos that have come out in the last few years lag isn't really an issue with our motors unless your trying to get a car over 900whp.

 

just as a reference, does this look like a good match?

http://www.squirrelpf.com/turbocalc...airflow3=38.4&airflow4=50.7&airflow5=60&airflow6=71&airflow7=79.4&product_id=49