[onesillynotch]

i cant for the life of me remeber what a carrot means? :dunno:

[GREG O'Brien]

67King: If you go to the Garrett home page they have turbine maps for all the GT series turbos. They look alot different than a compressor map... and it is alot harder to match to an engine IMHO because of the multiple variables.

I am sure that they exist for the T3 and T4 turbines - but I don't think they were ever made public.


onesillynotch: a "carrot" means "raised to the power of".... for example 3^7 = 3x3x3 = 27

[Jeff K]

A little typo there Greg.... 3^7 = 3x3x3x3x3x3x3 = 2187, 7^3 = 7x7x7 = 343. :pat:

[onesillynotch]

so how do you do 1.68^.283???

nm i figured it out..thanks

[Jeff K]

Originally posted by onesillynotch:
so how do you do 1.68^.283???

You need a calculator with a y^x (y to the x power) button. To do 1.68^.283, you would enter 1.68, press the y^x key, enter .283, and then press the "=" key to see the result. Can also do it on a spreadsheet by picking a cell, and typing =1.68^.283, and pressing the ENTER key.

[onesillynotch]

thanks jeff..i ended up typing it into my drafting program (Acad 2000) and it reconized it

[JLoveNC]

I'm confused as to how much air flow in lbs/min a mostly stockish 2.3L @ 7000 RPM will consume. All my math @ 85% VE says around 17lb/min, but if so none of these maps make sense, even the 60 trim T-3. So I am missing something...

(CID × RPM) ÷3456 = CFM
140 x 7000 = 283.56 * .85 ve = 241 CFM
241 * .069 = 16.63 lb/min

looking at the maps, this doesn't sound right...

[GREG O'Brien]

sorry about the math typo - fingers thinking for themselves

I DO NOT recommend using the CFM calculations... I haven't found them to be very accurate. In your particular case - you are calculating air flow for a NATURALLY ASPIRATED MOTOR - no where in there does it factor in positive intake pressure.... in which case - 16#/min starts to make sense... a worked N/A 2.3L will make about 160hp based on the 1#/min = 10hp rule of thumb

go back to my post and follow how I got my #/.min numbers... I think it is easier to follow and gets better results in the real work application.

[Jeff K]

I agree with Greg about that equation CFM=CIDxRPM/3456 not being reliable at all. All that equation calculates is the total volume displaced per minute during the intake stroke. Here is where it comes from:

CID/2 = volume filled (assuming 100% VE... WRONG!)per crank revolution x RPM = total cubic inches of volume displaced per minute. To convert that to CFM, divide that result by 1728 cu in per cu ft. Note the constant of 3456 in the original equation is just the factors of 2 and 1728 multiplied together. So that equation DOES NOT take into account VE, or forced induction!!

[Rara]

The CFM calcs can be used to get a decent ballpark figure for a turbo (hardly something to rely on, but close enough for an educated WAG ) but only if you include the factors of the VE and the pressure ratio (PR=(boost psi/ambient psi) or basically absolute manifold pressure in Bars)

so you get CFM=VExPRx(CIDxRPM)/3456 (note I didn't recheck the constant