Nitro725

Ok I have been trying to read up on sizing a turbo to CID,RPm ect ect
As well as trying to read maps for the best turbo size.
Anyways It says that a 346 would need about 44.67 lbs/min of air and with 7 pounds would make a pressure ratio at 1.47
I did do the math for 2000,3000,4000,5000 at the same psi. My question is that how can you tell a estimate of hp that you will make per PSI. As well if to maps are close would I lean towards the one that kept me in a higher effeciency curve longer, higher eff. average

Zombie

iTrader: (2)

if you are going off the VE tables from forced inductions, just multiply lbs/min of air * 10.5 and you will get your rough crank HP. My car has followed it pretty close. As a very general rule a motor will double it's hp at 14.5psi as long as the turbo is still within its range.

Paulz2820

iTrader: (1)

yah i did that the other day though and in the end you end up with the same lbs/min as by the VE map and you always end up with the same amount of horsepower. so imo the theory is flawed. you can only make "x" amount of horsepower at "x" amount of boost with a certain sized motor. so regardless of what turbo you use it will make the same power. all the compressor map does is shows you where the turbo is effecient.

JETmn

Remember to correct for the boost. Adding more boost will flow more air.

One thing to think about with turbo flow and HP is that a larger turbo will usually give you cooler air coming out. So 12psi on a T-88 is not equivalent to 12psi on a T-76, unless you have a killer FMIC that cools it well, but then the T-76 turbo is actually putting out more than 12 psi going into the engine because the air is more dense than when it came out of the turbo.

Paulz2820

iTrader: (1)

i've just never seen a good way to determine horsepower via turbo charging by using mathematics. there are just too many variables.

Wet 1

iTrader: (4)

A good basic rule of thumb is as follows:

Turbocharged hp = NA power * (boost / 14.7) + 1

Ws6reaper

iTrader: (16)

So how would you figure out the HP of a Twin Turbo?

JETmn

It doesn't matter if it is twin turbo or not, that equation still works and is a guesstimate at best.

Nitro725

Would it actaully be na power * ((boost/14.7)+1) = Turbo power

Reason I ask is bc with your way at 350hp I would make 16xhp
but with my corection it would be about 500 so hp

JETMM
Thats what I was thinking about. I couldnt peice it together how another turbo at same psi was making more hp. But if a larger/smaller turbo is more efficient then there would be more engergy tranfer, instead of temp raise. Thus keeping IATs down. Am I on the correct path???

My next question is how would to determine A/R size??? As how can you tell how much lag the turbo will have and when will it bring the boost on.

This is a Totally stock so I dont want to hurt the bottom end. Evindtually I would move to 6.0 heads to drop the compression. But Im looking to make about 400-500 hp streetable and relible like the factory. And I want to be educated on it. Not just drop the bills and have someone do it.

JETmn

Yes, that is correct. As for the turbine side, they offer cool maps like the compressor side. You pretty much have to look at similar setups or talk to experienced shops and see what fits your needs the best. There are enough people on here so someone will have a setup similar to what you are looking at.

Nitro725

Do you know where I could locate some of those maps.
Like I said Im trying to teach my self on this have about 5-6 pages of math that I have done and plotting. Would like to as much info as possible thanks

Skunkworks

Nitro725,

I personally prefer to look at air density ratio and use that as a multiplier for NA horsepower.

Air density ratio takes into account temperature rise by compression (and compressor efficiency) as well as intercooling efficiency. Now a factor that is hard to calculate is pressure drop from piping and intercooler losses. Also engine tune will also affect HP.

At very least you must take into account temperature rise as this has a dramatic effect on air density.

Mike

Nitro725

I have done that how can I calculate the HP from the density ratio???
I dont want to run to much boost on the stock pistons and so Im limiting to about 450-500 hp

Wet 1

iTrader: (4)

Why are you only limited to that amount???

Nitro725

BC this is for a DD, thats going to Germany for extended trips on the autobahn. Plus I dont know to much about the turbos right now and tuning so I want a limiting factor on it. I figuer limiting air instead of block or fuel.
That way I can play with tunning a bit and be a bit safer. once I learn I can alwasy upgrade. but I need to get the basic down now

Wet 1

iTrader: (4)

I just noticed that error, you are correct. For example if you are have 350 hp NA and add 10 psi of boost, you will make about 588 hp.

Wet 1

iTrader: (4)

Gotcha. You'll have NO problem making that power with a turbo!

Zombie

iTrader: (2)

Thats about right. My car on 10 psi with a t67 made 507 to the wheels, it's probably making a little more on the 76 due to being more efficient.

Skunkworks

Take your density ratio and multiply by base hp. Then give it a 15-20% + factor, this is for VE (volumetric efficiency) and torque curve increases. On a supercharger it is a little easier then turbo.

Some examples:
Stock C5 @ 6.5# LS1 Vortech kit = 490 RWHP
Stock Z06 @ 7.5# LS6 ATI Stage II kit = 530 RWHP
Stock Z06 @ 10# LS6 ESC D1SC kit = 580 RWHP (with meth)
Stock C5 @ 8.5# LS1 ??? turbo kit = 550 RWHP

A good breathing 346 LS1 will flow around 57-60 lbs/min at 9# and produce around 600 RWHP This is from memory.

If you want 450-500 FWHP then 5-6# should do it with an efficient system and good intercooler (assuming LS1).

Oh, 10.5-11.2 HP per lbs/min mass flow works pretty good as a rule of thumb. Or 24-28 RWHP per pound of boost on typical turbo.

Mike

parish8

iTrader: (6)

like it was said above for the most part you look at what other people have done and talk to shops with lots of experience.

the max hp on turbo's is prety acurate and a prety simple way to pick your turbo.

here are a few maps >> http://www.forcedinductions.com/compressormaps.htm i like to figure lb/min is really hpx10. so 95lb/min turbo is good for 950fwhp. the other side of the chart is in bar's. 1bar = 0 psi, 2 bar = 14.7 psi

it is alot easier to see how you are doing on a map after you get your motor running. i have a good example with my set up. look at the map for at the map for a t76 turbo. now look at 16psi(about 2.1bar) and 90lb's of air. you can see where i am right off the side of the efficency chart. that t76 is completely done on my 408. here is the compresor chart.



now my new set up is an 88mm turbo. look at the same 2.1 bar and 90lb's of air(probably more like 100lb's with the new huge exhaust side). i am over 70% on that chart. higher efficency means cooler denser air and more power. you can also see on that chart how there is a lot of room for me to make more power. i turned it up to about 22psi(2.5bar) and am seeing around 125lb's of air now. at this higher boost level you can see i am starting to fall off the side of that compresors efficency chart.



i think turbos are kind of like converters. you just count on what others have learned and then decide what you want to try. with turbos it is just so easy to turn them up for more power you will end up outgrowing whatever you pick anyways.