Power Band?

[Ericjayrol]

hey guys,

Ive been reading about power bands lately, and its apparently quite important to know your cars when it comes to racing especially in the case of a naturally aspirated car.

My question is, how do you know what your power band is? Is it just drive and feel it for yourself or does each car have a power band that any common car owner can tell you?

I've also wondered about when racing, is it best to shift out of first at say 4 rpm and then build the revs in the higher gears or is it better to rev it higher in first? I feel like when I rev high in first im not really getting as much power as if I let it rev in second, and I just feeling the wrong thing?

I've never actually looked at the speedo while testing all this as im worried about keeping my eyes off the road.

Any help is greatly appreciated, one of my friends beat me in his celica the other day and all the stats show that my car should have won if my technique was better, so im trying my best to better understand everything.

Thanks

[TwoCents]

http://www.skylinesaustralia.com/forums/20...20&start=20

covered abit of it in that topic

[Ericjayrol]

Thanks two cents, After reading that topic on page 2 its helped me understand things a lot more

[scathing]

My question is, how do you know what your power band is?

If its stock its hard to see. But if you've got an aftermarket powerband, like this one, you can see what it has been set to.

[KezR33]

Its always been my understanding that in NA applications: more revs = more power.

Although there's a bit of discussion on the Supra forums that the NA 2J gets choked at around 5500-6000rpm and its best to shift then.

[switchlanez]

The RPM where you feel your car pulling is where the power band is. Look at horsepower and torque curves (dyno graphs) on google and you will see exactly what a power band looks like. You will want to launch your car with your engine revved such that after the clutch grabs the needle drops to around the RPM where the torque curve for your car shows it is a constant level (not where it is rising steeply) so you get a strong pull at takeoff. Does that make sense?

High revving lower displacement engines such as VTECs have the peaky power (in the top end of the RPM range) but larger displacement N/A engines can have more torque in the low end too (i.e. Nissan 350z/370z).

[Ericjayrol]

Thanks heaps switchlanez.

Thats loads of useful information you packed into that response, im looking at bringing the car to one of the dyno days here in sydney so I can get some proper info to base things on.

[Briggs]

having been on track on 2 stroke road bikes i can tell you changing gears is pretty much the same no matter what your in/on. you want to shift from first into second only when doing so will result in more acceleration, for 99% of vehicles this means changing at redline. with actual 2 stroke machines with proper powerband, changing early can result in having almost no power as they often only make any real power in the top 20% of their rev range. as to a good launch, as much as it may kill your clutch, to do a perfect launch on the bike i would simply give it full throttle at take off and slip the clutch out keeping the revs at around 12k (where the bike its max power). not 100% on doing this in a car but definitely the way to go on the bike.

[MissR34]

my car launches its hardest at around 5500rpm

[Ericjayrol]

Thanks Briggs and missr34 for the extra info

[StealthX]

If its stock its hard to see. But if you've got an aftermarket powerband, like this one, you can see what it has been set to.

bahahhaha that website is focking gold!

lol @ "clear" headlights!

[sssc]

well said briggs i no what ur saying, and lol at that site was classic and havent seen it before lol

[Galois]

i've read in a couple of places that the powerband can be shifted by changing cams or using cam gears, how does this work?

when it comes to changing gears, it depends when your car falls off its power band, this may be at 6500, or (more likely) much higher, like 8000rpm.

think of the power curve of the engine, you always want to be accelerating as hard as possible, so if you change at 4000rpm you're missing out on 4000-7000rpm goodness, which is where most of the power is. theoretically, the higher the rpm, the more explosions per second, the more power, but all sorts of efficiency issues get in the way. still, higher rpm = higher power. in f1 when they want to dial back the power to save the engine/fuel, they turn it's redline down.

[zebra]

Generally - the larger the cams, the more revs are needed to get the engine to make power e.g at set of 280deg 11mm lift cams on an RB25DE would need 4500-5000rpm before it started to make power, below that the airflow through the ports is very slow and inefficiant, So you then need to rev the engine harder eg 9000rpm redline in order to have a decent power band, if the engine only revved to 7000, you would only have 2000rpm where the engine makes any grunt, so each time you changed gear you would drop out of the power and go no where.

Think of big cams like you would a big turbo...kinda

[mad082]

i've read in a couple of places that the powerband can be shifted by changing cams or using cam gears, how does this work?

when it comes to changing gears, it depends when your car falls off its power band, this may be at 6500, or (more likely) much higher, like 8000rpm.

think of the power curve of the engine, you always want to be accelerating as hard as possible, so if you change at 4000rpm you're missing out on 4000-7000rpm goodness, which is where most of the power is. theoretically, the higher the rpm, the more explosions per second, the more power, but all sorts of efficiency issues get in the way. still, higher rpm = higher power. in f1 when they want to dial back the power to save the engine/fuel, they turn it's redline down.

also you are missing out on 3000rpm of accelerating in a lower gear with an easier ratio. that is where the argument of "what rpm to change gears at" starts to get a bit more complicated. a simple view is to change gears the moment you get past the peak power output. what this doesn't take into account is that even though the power may be dropping off, it may still be higher than at the rpm you will be at in the next gear. and then as i said above, the more time you spend in the lower gear (within reason), the easier the car will accelerate, especially when you are talking about the higher gears. that is where each car needs to be evaluated individually to see what works best. i know that in the case of the missus SSS pulsar, with the stock headers it would start to choke around 5500rpm, and it was pretty much pointless to rev it past 6500rpm. put on a set of extractors and it doesn't start to choke until about 6500rpm but will still pull all the way to the 7500rpm redline.

[R34Liner]

If its stock its hard to see. But if you've got an aftermarket powerband, like this one, you can see what it has been set to.

I love that website!!! so fkn funny!

[R34 -_-]

Can they actually let ppl go through with the transaction if they try buy stuff off there?

Edited June 11, 2010 by R34 -_-