quote:

Originally posted by Marshall Grice:
in my opinion the real difference is they're using an engine dyno to measure their hp so the drivetrain losses aren't taken into account. if you put an NA motor on an engine dyno i'm quite certain there are many teams that would make 95hp too. I mean look what happened when they chassis dyno'd their car at detroit in 04, they made 75ish hp. I'm not trying to start any pissing contests here. i'm sure they make a lot of power, i'm just reiterating the fact that dyno numbers aren't the end all be all.

The last two years we made around 77 hp peak on the dyno in Detroit. Both tests were purely inertial, so it's hard to compare them to other teams' runs, which I think were mostly steady-state. To my knowledge, though, we had the highest-power inertial run both years. Correct me if I'm wrong. But regardless, there is far more to an engine package than the peak power read off a dyno curve.

quote:

Originally posted by DaveC:
Got me, I wasnt thinking about that. But, the torque numbers are directly related to airflow, 65 vs 45 ft lb is more drivetrain loss than might be expected.

At the risk of having you go on another tirade about me being 12 years old or something, that's just not true.

Torque is not directly related to airflow, power is (generally). Same airflow at a lower RPM means more torque. You are applying a linear solution to a non-linear problem. You are simplifying and coming up with bunk conclusions.

Any forced induction after the restrictor (required by rules) still has the same problem as NA engines. You only have ambient pressure on the outside. So in the end the total max airflow cannot change. You can get more airflow at low RPMs, meaning more horsepower and torque at lower RPM ranges. This is the benefit of forced induction in FSAE.

We have made over 80hp NA for a few years. To reiterate what has been said, the turbo is just moving more air into the cylinders at lower rpm, but no more air than a choked restrictor will allow. A turbo will increase the low end of the torque curve but the peak numbers theoretically should be close between NA and forced induction with a well executed powertrain. I would think that the losses for the alternator would far outway the gains, even though it wasn't constantly on.

As for turbo lag, these turbos are so small that the spool time should not be an issue if properly executed. A big and heavy car with lots of power may be able to go fast in a straight line, but FSAE is not a drag race.

quote:

What were your torque numbers with the electric?

it's been a couple years and i can't find a dyno plot off hand but 67ftlbs @ 6000 sticks in my head.

the difference between 65 ftlbs and 45 ftlbs is the rpm. like everyone is saying you make more power down low. so if you're making the same power at a lower rpm...you're making more torque.

and the issue with lag isn't dealing with it, it's having more power under the curve.

quote:

the difference between 65 ftlbs and 45 ftlbs is the rpm. like everyone is saying you make more power down low. so if you're making the same power at a lower rpm...you're making more torque.

OK, I see. I do remember torque tapering off at higher rpms on turbo cars curves.

quote:

Originally posted by Charlie:
Torque is not directly related to airflow, power is (generally). Same airflow at a lower RPM means more torque
...
You can get more airflow at low RPMs, meaning more horsepower and torque at lower RPM ranges. This is the benefit of forced induction in FSAE.

Maybe a clarification is in order?
Torque is proportional to cylinder mass charge. (Hence you modulate Torque by modulating cylinder charge with a Throttle).
Power is proportional to Torque and Speed.
The restrictor limits mass flow, hence it limits cylinder mass charge above a certain rpm for an NA configuration.
Simplifying to a 'perfect' engine and no losses, you could theoretically get a constant power engine with an inlet compressor after the restrictor, and therefore the torque curve would be asymptotic to the x and y axes of a graph.
Ian

Sure that was a bit oversimplified but the point it was trying to counter was pretty basic too.

I guess you would say power is directly and mostly linearly proportional to mass air flow rate. Torque is not.

Sure torque changes with mass airflow, but over a range of RPM if you kept mass air flow constant, HP would be constant too but torque would change. Assuming as you say an engine with no losses.

The restrictor limits ultimate mass flow but it's not a light switch, it gradually decreases efficiency as it approaches that point.

As RPM increases, with constant mass flow, torque should degrade. I doubt it would become asymptotic with either axis, though I didn't try and plot the limits, seems unlikely to me. Probably, my lazines will mean I'm wrong.

The point was that if someone says '65 ft-lbs means you have more airflow than 45 ft-lbs' that's not true; however power is a good inidcator of that.

Like most details of an engine or vehicle for that matter, you can continue to delve into more detail and find ways to repeat statements with more accuracy if you use more words.

quote:

The point was that if someone says '65 ft-lbs means you have more airflow than 45 ft-lbs' that's not true; however power is a good inidcator of that.

It would be true if measured at the same rpm point. As murpia said, torque is directly related to VE, or mass charge, or airflow... Power (HP), again, is also a product of speed. At higher rpms, turbo cars curves do lose their huge advantage, although I'd like to see how Cornell's ewastegate system extended the powerband.

I'm going to have to disagree, Charlie, As I understand it, torque is more closely related to how much air is in the cylinder than HP. However, you are right I came up with a bad conclusion, because I wasnt thinking about behavior across the rpm range, and considering the whole picture. Marshall made that clear. And, no, I dont have to go on a tirade and compare you to a 12 yr old because youre not behaving badly .

I'm going to have to disagree with dave disagreeing with charlie. charlie said torque doesn't depend on mass flow rate, which is true. not to be confused with VE, which torque does depend on.

quote:

although I'd like to see how Cornell's ewastegate system extended the powerband.

search, they've posted dyno plots before iirc.

we're pretty much covering old ground now so i'm done. the auction ended, for WAY more money then any of us were expecting btw, and it didn't go to an fsaer so all this disscussion isn't of much use considering nobody has any electric superchargers here...

Bet somebody bought it for their street car and is gonna have a biotch of a time trying to instal it, and then summarily blow their engine. lolz.

OK, sorry. I was relating torque to VE, which doesnt have much to do with total mass flow rates, my mistake not communicating legibly...

Two points:

1. Murpia summed up the torque/power/air-flow-rate stuff quite well. A turbo/supercharged + restricted IC engine is similar to an electric motor - ie. a flat power curve and torque that drops asymptotically to the X-axis - which is a good thing for FSAE conditions.

2. Since a T/S/C'd engine can make more torque at lower rpm (achieving the same max power allowed by the restrictor) it will likely have less frictional losses than a high revving N/A engine. Frictional power loss is mostly function of rpm^1, 2 & 3. Hence the T/S/C'd engine, "all other things being equal", will likely show more power on the dyno (output power = combustion chamber power - frictional losses).

Z