opek

Braineack

iTrader: (62)

you mean like the god damn ******* FAQ in my sig?

Braineack

iTrader: (62)

what are you laughing at, the fact that you are now labeled in my mind as a complete moron?

opek

so we have 110 CI. That stays constant.

7000rpm, for this sake it can stay constant.

3456 our wonderful constant

We can assume temp is constant for this example, but 14.47 will not remain.

In the conversion from volume/time to weight/time we need to account for density. I will not be pushing the limits of the .48 t3 turbine with a stage 3 wheel anytime soon without a nice big compressor attached to it pressurizing my intake stream.

While I appreciate the fact that a 110CID motor theoretically flows 15lb/min @ 7000RPM at sea level at 120F, I think the amount of air I'll be flowing at 7000RPM is going to be mostly dependent on my compressor.

patsmx5

iTrader: (16)

^^^ Agreed. I was wondering if Brain's numbers account for the boost, as everything that goes in has to come out. Watching...

Braineack

iTrader: (62)

14.47 is simply converting CFM to Lb./min

it doesn't matter how much airflow is coming into it. your engine can only displace so much airflow. The volume is always the same (97.7 C.I. per every cycle / VE), the poundage varies.

opek

Right, but in your math 14.7 represents a conversion from a volume/time to a weight/time using atmopsheric pressure at 120*F at sea level. My intake manifold will rarely see such conditions at 7000RPM.

Braineack

iTrader: (62)

then apply the damned Ideal Gas Law and change the multiplier....is still doesn't change the fact that you can only displace so much air, regardless of how much boost. so while i may see 14 lb/min through my exhaust, you may see 12, who the **** cares, what are you arguing again?


so to sum up:

**** ton of boost in the intake = 15 lb/min through the exhaust
no boost in the intake = 15 lb/min through the exhaust

patsmx5

iTrader: (16)

What? That doesn't make sense. Why would the amount of air going through the exhaust not change? You just said 15 lb/min boosted or not, that's wrong. If your pushing in say 30 lb/min, doesn't that have to come back out? Where else would it go?

opek

No, you are wrong. One cfm at sea level weighs more than one cfm at altitude. You are converting from volume/time to weight/time. density/volume = mass, mass * gravity = weight.

The miata motor at sea level with 120* air in the intake manifold, based on only it's CID, flows 15lb/min. Once you pressurize that air, it is heavier. You are flowing more dense air through the same volume over time, which results in more corrected CFM or more corrected lb/min.

There is more air.


Arguing about what?? I politely responded to your lame point, made using some fancy mathematics most people probably don't bother to understand, and you called me a moron. Nice. Your point is lame because the airflow of the stock motor at sea level in 120* air is not nearly as relevant to turbine selection as power goals or the compressor. IMO it's not worth a damn to say, "this turbine is OK because during these completely arbitrary conditions you will never encounter that aren't even related to making power (who puts a turbo on and runs atmospheric pressure in the intake manifold?) you will be flowing less air than the turbine is rated to."

What's a t04e 50 trim flow compressor flow? 40lb/min?

patsmx5

iTrader: (16)

You displace the same VOLUME of air all the time. To change that, boost increases density so that the same volume has more pounds of air in it. You could move an infinite amount amount of air in lbs/min by increasing boost until something breaks.

opek

Just so we are clear my reply was directed at the Brain.

Arkmage

iTrader: (3)

I agree. Personally I think .63 AR turbine is ideal for 250-350 whp. Anymore power than that and you should port it unless you are wanting 500+ and don't care in the least about spool... then go to the .8X AR.

The .48 doesn't seem to breath for **** in the top end and I'm only at 214 whp. I may change my mind on this after the new downpipe and exhaust arrive.

cueball1

iTrader: (13)

Just to throw in my extremely uneducated 2 cents...

For 300 whp don't the internals have to be beefed up? Rods and Pistons? Pissing match aside it's one thing to make 300+ whp, it's another to make it hold together. Am I wrong about this?

Braineack

iTrader: (62)

more boost doesn't mean that you'll displace more air. It's a simple equation to determine a good size A/R turbine based on your displacement and airflow volume.

the more pounds of air you move, the more power you will make. pounds = mass. not volume; the volume will always stay the same. you're not increase the displacement of the motor.

you know damn well you can easily factor in your atmospheric conditions and temps, stop being a ******* douche.

Braineack

iTrader: (62)

There's something wrong on your setup then, even with my extremely restrictive exhaust i never saw boost or torque drop.


yes, the rods wont hold up. We typically start to thinking about beefing them up at 200-220rwtq.

patsmx5

iTrader: (16)

So, is this right or wrong? More like the same volume, not mass?

opek

I guess I just don't understand how this equation tells us anything about the turbine to suit my goals vs. someone who is looking for 200whp. Right, volume and weight are different. The more air you move, the more power you make; MAP is a function of the turbine as much as it is of the exhaust, head, cams, and manifold itself.

Why do you keep saying pounds = mass and not volume, clearly I understand that. My first post addresses the relevancy of using a simple cfm -> lb/min conversion to a turbocharged motor.

"You know damn well you can easily factor in your atmospheric conditions and temps, stop being a ******* douche."

Ok, let me try again. I don't think I am explaining myself very well. The conversion you used factors in pressure and temperature, but the pressure you use in your calculations is 0lb. I don't care if the turbine can flow 0lb of boost, I care if it can flow 24lb of boost. An equation to determine ideal turbine size must take into account desired airflow.

opek

That is absolutely and totally incorrect. It is so massively wrong I figured someone was going to reply with the FAIL pic he posted earlier.

lb/min is weight/min; and since we know what gravity is all about we know what is the mass of the air we are using. 15lb/min is 15lb/min always, but 300cfm can be 15lb/min or 30lb/min depending on it's density. A pressurized intake manifold does change the lb/min out of the tailpipe, and will also change the corrected CFM. (corrected for density).

opek

Can we talk about my turbo kit again?