projekt

after reading the flame fest that was the 'how much horepower does your n/a make' thread i was wondering...

with all these 150whp and 160whp cars, how much is that over stock? Miata's consistenly dyno 23hp below stock so it's generally accepted. I know our drivelines are similar to their's, so i was curious. This goes for both S4s and S5s.

if i could afford a dyno, i'd go check myself, but well....

Tofuball

Yeh, a decent number on what people think our drivetrain loss is, would be useful.

hIGGI

iTrader: (7)

anything between 10 to 25%

20% is pretty normal even for new cars

SureShot

Other variables:
which gear (4th bypasses the countershaft)
tire pressure
Ambient air temp
barometric pressure
altitude
intercooler heat soak
dyno calibration
mineral or synthetic gear oil

dorifc3s

considering all that whats the average hp loss?

projekt

thank you, since loss isn't measured in percentage, care to give me an actual number?

projekt

and i'm asking about N/As

1987RX7guy

iTrader: (3)

Its impossible to tell you the number. All cars will have a different number. even a few degrees in temp can change the results. The only stock dynosheet I can remember seeing is the one from mazdatrix and that was like 110whp or something similar which is a huge loss from 146bhp. I had seen a thread here with a large scan of that sheet but I think it may have been deleted.

Slacker7

iTrader: (2)

drivetrain losses is actually measured in %. It is a form of mechanical efficiency.

A 1000 hp car will lose about 200 hp through the drivetrain and a 100hp car about 20hp.. percentages might not be "the" number but it's far more accurate than any "actual" numbers.

13bpower

After wasting the better half of my life browsing this site I have come to the conclusion that a health stock rx7 N/A will dyno, on average of corse, 115-125 s4 ; 125-135 s5

The highest N/A dyno sheet I have ever seen on this site was a highly modded s4 making 168 at the wheels.

1987RX7guy

iTrader: (3)

Didn't Icemark do something like 170 to the wheels the other day And he still has a cat on that thing. Man I need to get him to do my Sport's porting


Santiago

projekt

thank you for being extremely helpful, this is exactly what i wanted to know

and as far as a percentage, explain to me, using science/math how a 300hp supra dynos 260 at the wheels. but then once it's modified and dynos 860 at the wheels it really makes 1000hp by your logic? the drivetrain hasn't changed significantly, it still produces the same amount of drag.

nonameo

We have drivetrain loss because of friction.

Friction is normally measured as a coefficient. its a multiplier(or divider whichever way you want to look at it....)

take your hands and start rubbing them against some cloth. getting warm eh? rub em HARDER. More heat? same principle.

Tsunami

he is correct, but to add another variable to this equation: Not all cars are rated at their exact factory rating, first there exists a difference fromthe factory, quality control can be an issue and in some cases differen horsepower and torque by a significant amount. (ive seen as much as ~20whp on LT1 camaros, but that quality control isnt as good as foreign cars.) second, often cars are underrated, I believe the supra TT was rated at 320 stock, yes? LS1 camaros are underrated by around 10 hp or so. SO basically, unless you take your engine out and dyno it, then dyno it through driverain under same conditions, youll never know.

projekt

but people have done that, specifically with miatas, and turbo/supercharger/na they still give a 23-25 hp difference.

and if you wanna talk drivetrain loss, the 350z in this months super street dyno'd 235 whp. down 50, pretty sad. the nitrous kit they installed bumped it to 350 though

so by my method it makes 400 now, by yours it makes ~430. i don't believe in free HP so i'll stick with mine.
and there's no increase in friction, so the hand warming idea, although suitable for the wintertime, is invalid.

Icemark

Those numbers seem pretty close to what I have seen as well.

I normally figure 25 to 30 HP loss on a FC or NA/NB drivetrain.

Icemark

yeah, but I personally (despite several other people suggestions) that the dyno I was on was probably reading about 10 HP high, since the first run I only did 163.

nonameo

you're right... its dependant on engine speed. And the speed of the rest of the components. The FASTER they move the more loss there will be. Do I have this right? loss @ X rpm will be the same regardless of hp, but @ different rpm's it changes? its been a while since ive had physics so hrm... can ya tell?

Slacker7

iTrader: (2)

The drivetrain as you know it rotates. This rotation causes the drivetrain's rotational inertia or "effective" mass to increase as it spins faster.

F=ma

since you have more power on the flywheel we know that "a" will definitely increase therefore "F" must also increase in order to achieve that particular "a". Keep in mind that you have to be accelerating to measure the peak Hp. You can't have constant speed to measure peak hp.

Also you Clutch efficiencies are given in percentages. Normal street clutches are rated at about 85%-90%?? while performance clutches 90%-95%??

Slacker7

iTrader: (2)

yeah the hp loss will be the same for the same acceleration. However, hp losses will be different at different acceleration rates.

rx-7s rock

I knew I was pretty much correct when I factored drivetrain loss on my car. Since people always ask me how much hp it has. I say, "146hp to the flywheel, which gives me about 120hp to the wheels."

SureShot

FWIW my G-tech shows 170 net HP.
Net HP = flywheel HP - driveline loss - air drag on the body.

projekt

umm F=ma isn't a good comparison. the force will increase(power/torque), and the mass will stay the same so the acceleration will increase. you've just shown how more power makes your car accelerate faster.
and there's no power on the flywheel. only torque and rpm are any mechanical parts' concerns.

Slacker7

iTrader: (2)

Sorry I couldn't explain it better.

But F=ma is the easiest way to explain it. In order for the engine to accelerate the car, it must first accelerate the drivetrain. Which takes up hp (which is proportional to torque). The faster you accelerate the drivetrain, the more hp(or torque) it takes.

Whatever power(torque) is not used is what you have to the wheels and that is what determines the car's acceleration.

Tsunami

no, f=ma works, it just depends on what F you are calculating. If you are calculating F as the force exerted by the engine, then yes it is bad,however;
if you are calculating F as the force required to twist a drivetrain then it works.

F=M(constant)A(increases as engine produces more power). As the drivetrain accelerates faster, more force is required to do so. Thus as long as the mass is constant, more force is required to accellerate the drivetrain.

its proven, the more power you make, the more power you lose to drivetrain loss.

perhaps its not as noticeable between a 125fwhp miata and a 170hp turbo miata, but between a 275fwhp lt1 and a 450fwhp S/C Lt1 its quite noticeable.