Some Interesting Calculations

[Xero]

So I was bored yesterday and started doing some turbo sizing math and lfow and efficiencys and stuff.

Using some equations from my SCCs, October 2001, June 2003, and September 2001 to be exact. And I've come to these calculations,

600cc injectors = 460hp w/ .50 BSFC555cc injectors = 422hp w/ .50 BSFC

550hp = 725cc w/ .50 BSFC

1809cc @ 20psi = 455hp @ 9000rpm w/ 11.5 A/F & .55 BSFC1853cc (1mm over) @ 20psi = 470hp @ 9000rpm w/ 11.5 A/F & .55 BSFC1853cc @ 25psi = 535hp @ 9000rpm w/ 11.5 A/F & .55 BSFC

there are ALOT of variables in these equations. And it's a whole lot easier if you have the magazines 'cause it explains how to use these equations, but I'll post them here (or attempt to post them here) anyway.

Compressor matching: finding pressure ratio and compressor mass flow rate

1st: pressure ratio

PCO = Boost + Atmospheric Pressure + Intercooler Pressure Drop

Pressure Ratio = PCO /(divided by) Atmospheric Pressure--atmospheric pressure is 14.7, average pressure drop across anintercooler(aftermarket) is 1.5

2nd: Compressor Mass Flow Rate (this can get tricky)

Di = Boost + Atmospheric Pressure / 53.3 x 12 x (460 + post intercooler temp) --- I used 130 for the post intercooler temp

Mf = Di x Displacement in C.I. x RPM / 2 x Volumetric Efficiency --- 110 is the displacement of a CA18, if it's overbored 1mm it's 113 --- I used .90 (90%) for Volumetric Efficiency

CMf = Mf / 1.054

CMf is your corrected Mass Flow Rate, and you can now use your 2 numbers to plot points on a compressor map, plug in different RPMs, different boost pressures etc and find the right turbo for you.

If you have any questions, I'll try and answer them,

[Xero]

To find HP and Injector Sizes, you use these equations:

1st: HP

HP = Airflow (your CMf from above) x 60 / A/F ratio x BSFC

A/F ratio is 10.5 or so on a richly tuned engine, like stock, you can get as far out as 13 on special race gas.

BSFC is Brake Specific Fuel Consumption. Rich engine might run .60, that same race engine might run as low as .45

2nd: Fuel Injector Sizing

Injector Size (lb/hr) = expected HP x BSFC / number of injectors

You can reverse this equation to see how much power can be made by using certain injectors

[14.5drift]

wow, you guys are smart. And I'm not being wise ***. How would I calculate every thing I need for 300whp. like 370 at the crank no? How much boost, injectors etc. Now is this formula universal, or wouldn't it differ from engine to engine. Since obviously one motor can be more efficient than onother motor, it different. Or is this basically calculating what x amount of gas ignited in y amount of space creates z amount of force. And then what makes it out of the crank varies per motor. Sorry if I'm rambling

[Xero]

If you read through those equations, you'll notice that they ask for some certain statistics that are constant. air will hold so much oxygen at a certain temprature. Also, it asks for engine size and volumetric efficiency. Therefor all variables that are different from engine to engine have been covered.

Calculating for a certain hp could be tricky, but you can do it if you use thoese equations and run them backwards, and all HP levels are crank HP, and your car will NOT lose 70hp through the drivetrain, 240s generally lose 20hp or so,

[CA19DET]

Quote »1853cc (1mm over) @ 20psi = 470hp @ 9000rpm w/ 11.5 A/F & .55 BSFC[/quote]THATS ME!!

[14.5drift]

you got dyno? no dyno = Lies

[Xero]

He's still building it, you can't call him a lier when it's not even built. He does have 84mm pistons, though, therefor he would be at that engine size, and he may plan on running 20psi,

[boost_boy]

Hmmm, I wonder what we can get with 33psi of boost and 1000cc injectors on a stock bore with some serious 272 cams with a 10.5mm lift, GT3037, solid lifters and and say..9400rpm?

[Xero]

I can do 9400rpm at 33psi, and I can tell you what HP you can expect from 1000cc injectors, but injector size doesn't come into play when determining mass flow rate.

anyway, here's your stuff:

for plotting on a compressor map, you'll need this number as your pressure ratio: 3.35

CMf or Corrected Mass Flow rate: 68.89

Now for HP, I'm gonna assume your running race gas, and alot of it, so I'm gonna tune the A/F down to 12.5 ( just to be a little conservative ) and your BSFC to .50

Your HP @ 33psi @ 9400rpm is 660hp w/ race gas tuned to 12.5:1 A/F and a 50% BSFC

now for those 1000cc injectors, you can expect to pull 760hp with a 50% BSFC

Now, looking at the Garrett GT37 Compressor Map, we can see that it is not on the map, and a GT37 will not be able to spin to 33psi. Looking through my other maps, I can see that a GT42 compressor would work, but that's as small as you'd be able to go, a T66 compressor will also work well for that set-up.

[Xero]

After reading my post, I think we need a "Geek" smily.

[14.5drift]

He's still building it, you can't call him a lier when it's not even built. He does have 84mm pistons, though, therefor he would be at that engine size, and he may plan on running 20psi,

I saweee. But but no slip = lies:pface

[boost_boy]

Quote »Now, looking at the Garrett GT37 Compressor Map, we can see that it is not on the map, and a GT37 will not be able to spin to 33psi.[/quote] This was more of a toss-up,but realistically it would be in the 25-28psi range. And a T66 on this motor (unless it's really built with nitrous spooling) is a shot in the foot. Hmmm, seems like you're having fun with this:D Thanks for the info.

Dee

[Xero]

Yep, the T66 would be horrible, so would the GT42, but for 25-28psi, the GT37 will own

[gore]

where in these calculations does it have the engine exploding into a bunch of tiny pieces:pface

[14.5drift]

he he Iron block rules, but if you open her up after that all the internals prolly fall out like pencil shavings

[Xero]

if an SR can take 600-700hp, a CA can with equal building,

[boost_boy]

It can take it! I don't see a thing in my engine that's not up to the task. If the turbo holds up, so will the engine.

[gore]

boost tell me when you're getting a new engine. I want one badly, also do you take credit card :P

[boost_boy]

I'll let you know on Monday and CCs are accepted.

[gore]

boost do you have aol instant messenger or something? email is far too sluggish

[boost_boy]

turb0sentra