Other than valve float and the pistons going too fast for the flame front to catch up, what are some other reasons for the HP to curve back down where it does?
Detonation, too.
what are the rod ratios on like F1 cars?

 

Horsepower = Torque X RPM / 5252.........it is just a fact taht you aren't getting enough air flow for the speed you are going.

Getting more aggressive cams will increase torque.

 

I thought it's the other way around. Getting more aggressive cams will increase hp but decrease tq.

I was always told that to increase both hp and tq in NA (which means sans FI), one must increase either the compression or the displacement.

 

More agressive cams can increase torque up to a pint, their main purpose is to move the torque up yhe rev band, using the formula above shows the horse power improvement. 150 lbs. torque @ 6000 rpm's= 171 bhp, 150 lbs torque @ 8000 rpm's= 228 bhp. The limiting factor on bhp is air flow, whitch is restricted by bore size, valve size, inlet runner size and shape.

 

DonF, what are you driving?
I'm over in Jax Bch but ride around in Orange Park

 

You have to realize that when domestic type people speak of "torque", they simply speak of low-end power, not actual twisting force. I could make you a million foot-pounds with my arms and some gears, but if I was to power a car using that method, no one would be impressed.

Anyway, the reason the power band drops off at a certain rpm is becasue the torque dropped off. Getting more aggressive cams will raise the torque, resulting in more power. The torque rise is at a high rpm though, and will most likely kill the toruqe at lower rpms. Ultimately you will have more torque and power, but low-end power will suffer. A lot of people only care about low-end power (torque), and so you will hear complaints that aggressive cams decrease torque.

So, if your engine produces 1000lb-ft of torque from 5000-8000rpms (that's a lot of power and makes for a fast car), but only 100lb-ft below 5000rpms, people will in fact complain about the lack of "torque"...although some will actually specify lack of low-end torque.

 

my gsr teg a case example:

147/110 on dyno stock

163/125 on dyno now

122 whp/tq @ 5250rpm
peak VE/tq @ 7200rpm
peak whp @ 7600rpm

> stock manifolding
> stock intake box w/comptech filter and 4" CA feeder tube
stock rubber hose to tb
> some GSR manifold and TB trickery for more upper rpm power
> lifted/widened ports on stock header
> stock exhaust
> stock computer
> .5 oversized endyn ex valves
> itr intake valves, 3 angle valve job,
2 on seat, tapered guides, slightly larger valve runners
> portflow/ITR spring setup with Ti retainers
> CTR intake cam
> 00 ITR ex cam
> +4(on crank) ex cam, +2 intake cam at 20BTDC timing.

Much, much more fun to drive and I have alot more ways to
improve!! The cams were the first thing to make the power
and TQ, everything else is HIGHLY incremental...

 

more aggressive cams change the valve lift and overlap to improve more airflow.
To have good torque, you need good combustion. For good combustion you need as much air as you can take up. The torque up top dies down because not enough air is being ingested by the engine.

Also, to increase torque, you can increase compression. To gain more HP with this, you increase the compression ratio, lets say this adds 5 ft-lbs in the throughout the rev band from lets say 110 ft-lbs to 115 ft-lbs (assuming a flat torque curve). lets say at 7k rpm, using:

HP(rpm) = tq(rpm) * rpm/5252 where HP and tq is a function of rpm.

HP(7000) = 110 * 7000/5252 = 146.6 HP
HP(7000) = 115 * 7000/5252 = 153.6 HP

now, if you increase your redline to say... 9000 rpm with the same amount of torque, lets see our HP...


HP(9000) = 115 * 9000/5252 = 197 HP!! wow, you just gained ~50 HP from adding 5 ft-lbs of torque (and 2000 more revs per minute).

But that's the general idea, problem is, it takes work to get constant torque through the rev band(by letting enough air in), hence the variable valve lift/timing technologies, or there's turbo/force induction

-vic




[Modified by VicRS25, 2:42 AM 6/19/2002]