How do you calculate parasitic loss?

[Redfox0099]

So a low compression supercharger will make less RWHP than a high compression one...well duh no genius needed there.


So you have a 8.6:1 compression motor making for example 440 RWHP (just a # for example) and then you run a super charger off the motor and you loose HP from the power needed to run the S/C...how do you calculate how much power you lose from running the S/C?

Not terribly important just being curious.

[formerice]

I read somewhere that the blowers on topfuel dragsters require over 1000 hp to drive them. So out of 8,000 hp 12.5% parasitic loss at wot. If you have 440 hp now, you actually had around 500 before the blower sucked off 60 hp. Hey it's a wild shot in the dark. I'm sure there are articles out there as to what a given motor will gain given a fixed boost, but a lot of variables.

[Trojan]

So you have a 8.6:1 compression motor making for example 440 RWHP (just a # for example)

[Redfox0099]

What, I haven't dynoed my car yet so I made a guess on the power...why the heads into bricks Chris?

If you have 440 hp now, you actually had around 500 before the blower sucked off 60 hp. .

No I meant if you had 440 RWHP and THEN ran the blower how do you calculate it...again I haven't dynoed the car yet so I was just throwing a # out.

[Trojan]

I just thought it was funny that I fit your example to a "T". But as far as how you caculate? Not sure at all, But I will be able to have real world results next week sometime on the new total HP after the Blower is tuned. It will be posted as soon as it happens.

[Redfox0099]

You fit my example to a "T" how?...not sure of what I did?

[Trojan]

8.5:1 Comp/440 rwhp. Thats my motor specs N/A.

[hawkxp]

I would assume it would be a specification for the blower...

I know for airplanes turbos it is...

To calculate it, I would assume they use a bench turbo and use a highly calibrted driving engine and measure at the crank before and after the turbo is attached...

Then use the charts knowing when the turbo has spooled up and starts producing power as a a base line loss..

Ie if, the engine is producing 500 at the crank normally at a certain RPM.. Then a Turbo is attached and disengaged its now producing 495 or so.. just having a disengaged turbo is 5hp... (purely made up BS numbers for the example)

Then they engage it, and you should see a drop in HP while it spools up before its "functioning" that drop is more parasitic...

Just a guess... I could be full of poopie since Im just guessin ghere..

[done]

You fit my example to a "T" how?...not sure of what I did?

I think he isaying that he has 440 RWHP and is now adding a SC.

By the way, the parasitic loss number is chasing moonbeams. The HP that moves the brick is that found at the real wheels.

If you wind up with 600 HP at the wheels, why does it make a difference how much the SC uses?

[SDChargerSRT]

I would guess you would need to run the engine less supercharger, then run the engine with the supercharger but without it pushing air into the engine. If you just measure HP before and after the supercharger, the numbers with the supercharger will include the loss, if I'm understanding your question correctly.
Unless you've got a way to run the supercharger "on the bench" and measure how much power it takes, but that probably wouldn't be very realistic to actual operating conditions.

[hawkxp]

I think he isaying that he has 440 RWHP and is now adding a SC.

By the way, the parasitic loss number is chasing moonbeams. The HP that moves the brick is that found at the real wheels.

If you wind up with 600 HP at the wheels, why does it make a difference how much the SC uses?

While I agree to some point... The changes to the power curve will show that parasitic loss differently depending on the type/brand of SC used....

So knowing the power curve of the SC on its own, and when it draws more power then it can produce and when.. is important..

If a SC takes 10 hp to gen 90 hp... and the 10hp and 90hp is constant independent of all other things... it really doesnt matter.. its simply a 80 hp turbo.. but since its probably not.. and there may be times when the 10hp may be a net loss on the system, I think it would be imporatnt to know this.

[Redfox0099]

why does it make a difference how much the SC uses?

Cause I was bored and thought I would ask to see if there was an answer

[hawkxp]

I would guess you would need to run the engine less supercharger, then run the engine with the supercharger but without it pushing air into the engine. If you just measure HP before and after the supercharger, the numbers with the supercharger will include the loss, if I'm understanding your question correctly.
Unless you've got a way to run the supercharger "on the bench" and measure how much power it takes, but that probably wouldn't be very realistic to actual operating conditions.

I dont know.. but just like an engine needs an exhaust to be fully efficient, a SC needs the backpressure into the intake to be full efficiency

[Wetcoast]

I'm gonna say it depends solely on the input vs. CFM and pressure curve for the specific blower. Different vane design and volume will vary the output cfm at any given backpressure.

http://www.airkingblower.com/centrif...wers_range.htm

[HEMIDON]

I would assume it would be a specification for the blower...

..

I agree... There should be some formula that would include pressure,RPM and cfm demand to get power required to turn the blower. IAT and DA would have some influence but, not enough to influence a rough estimate