This is really windy, so hit the delete key now if you are easily
tech spooked.
Lou wrote,
>Jarrid,
>Is a gain of that much horsepower worth the loss of a similar amount of
>torque? And is that torque lost in relationship with stock or in
>relationship with the new cam? I am going to replace my cam as well in my
>daily driver and would like to keep the streetability of the car intact,
but
>would like some power to go up hills. You did not sepcify the lift of the
>cam. Is it the same as stock? Have you compared it to the isky cam that
Rick
>is marketing? what is your opinion. Lou
Horsepower vs torque tradeoffs are subjective.
Horsepower is the engines potential to do work.
Perhaps best described as the force produced at a given rate.
Torque is force, and is clearly the bottom line to accelerartion,
but there is one really big catch, and that is if you spin the engine
faster, and still make the same level of torque, you make more horsepower,
becuase you are doing more work.
The simlified equation for HP is...
HP = Torque(lb*ft) * (RPM/5250)
This basicaly says that if you make 1 lf ft of torque at 5250 RPM, you are
producing 1 HP of power.
Engines dont have a flat torque curve though.
An alpine engine torque curve might look like this.
RPM TQ HP
---------------
1000 45 9
2000 65 25
3000 90 51
4000 105 80
5000 95 91
6000 70 80
What the above curve shows you is that you get the best acceleration
in a given gear at 4000 RPM, but it gives you the most horsepower at 5000.
You might say, but if I get the best acceleration at 4000 RPM, why not shift
then, and avoid the lower torque area at 5000 RPM?
The answer is that by jumping into the next gear up, you are not only
penalised the shift time, but the added ratio increase decreases your
acceleration too.
You want to spend as much time in the gear as possible, so as to
stay in the lower gear longer, generate mor acceleration for longer
and maximize the area under the curve.
The gain in horsepower comes at significant cost.
Cost in that to get at the horsepower, you push the peak
torque RPM up in the band, where the engine will age faster.
Also it means that you lose valuable torque in the range more
fitting toward normal driving.
This means that pickup will be slower if the car is not driven
in the aggressive mannor, where the engine produces the most power.
It also means that in order to take full advantage of the new
horsepower, the final drive ratio should be altered to suit the
RPMs that the engine needs to run to make the power.
The lost low end torque that I am speaking of is as a result of equalizing
the cam lobe split, on a regrind from a stock SV cam core.
Additional low end torque can and would be lost from additional overlap
from the regrind process too.
Because of I am talking about changing both the grind, as well as
base timing, any comparison to stock cam performance would need to
be taken with a grain of salt, however in general, advancing the cam
will yield more low end torque at the expence of top end torque, and
horsepower. This only applies to the first 6 or so crank degrees.
Anything beyond that cant be generalized so easily, as seen on the H120
cam, and its performance figures.
In answering the "power up the hills" question, you could have enormous
power up a hill, provided you are in the appropriate gear for your engine.
Putting a full race cam in and alpine and lugging it around all day at
2500 RPM, would yield little performance satisfaction, and result in
a very rapid engine failure.
In answering Lou's question on my cam lift, it was .460.
Later examination of the lift vs flow profile of the cylinder heads
showed that stock valves in stock ports didnt flow substancialy better
at .460 lift versus .300 lift. This being said, dont go overboard on
a high lift cam, it just doesnt help that much on the alpine.
Didnt know that Rick was selling Isky grinds.
What does he get for them, and whats the spec (SB1,SB2 or SB3)?
jarrid gross
This archive was generated by hypermail 2b30 : Tue Sep 05 2000 - 10:45:24 CDT