Peak power VS. Shift points
10-21-2006, 09:21 PM
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Car: 1989 GTA
Engine: 350TPI w/ Speed Density
Transmission: 700r4
Axle/Gears: Borg warner 3.27
Peak power VS. Shift points
This might be a stupid question to some of you, but it has bothered me since I've been learning about engines. If you slap heads and a camshaft on that make peak power at 7000rpm, what is the point if you shift at say 5500 and don't even make it to the peak? Or even if you redline at 6K.
10-21-2006, 09:36 PM
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Car: 84 Z28
Engine: 357
Transmission: TH-350C
Axle/Gears: 3.43
Well, how about this...
You shift just after you drop off of the peak curve and not at 5500 if your peak is at 7k!
Make sense?
You shift just after you drop off of the peak curve and not at 5500 if your peak is at 7k!
Make sense?
10-21-2006, 09:52 PM
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Car: 1987 IROC
Engine: 350 vortec
Transmission: TH350 3500 stall
Axle/Gears: 3.73 10 bolt grenade
If you redline at 6K, but dont make the peak power until 7, its time to invest in a bottom end.
10-21-2006, 09:54 PM
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Car: 1989 GTA
Engine: 350TPI w/ Speed Density
Transmission: 700r4
Axle/Gears: Borg warner 3.27
Aha, so there wasn't some kind of puzzle. Just make the car reach the peak power. Thank you for explaining that.
10-21-2006, 10:38 PM
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Car: 87 IROC L98
Engine: 588 Alcohol BBC
Transmission: Powerglide
Axle/Gears: Ford 9"/31 spline spool/4.86
I guess the easiest way to explain it is the powerband under the curve.
Building an engine that has a very high rpm/power range also means you will have a lot of power in the mid and sometimes low rpm range because the entire powerband has been increased. Just because an engine makes peak power at 7000 rpm doesn't mean you'll be operating at that rpm all the time. Peak power should always be where the engine is doing most of it's work. In a street car that means staying below 6000 rpm however torque is what does work and for a street car, that means torque is best under 3000 rpm where the engine normally operates. A street engine can build peak torque at 4000 rpm also. That's just means it will also have more torque in that lower operating range where it normally operates. RV cams are good examples. They produce a lot of torque at low rpms but don't produce high rpm HP. They're designed to make a lot of torque to get a heavy vehicle moving quicker.
For optimal performance, You shift at or just above the peak HP so when you go into the next gear, the rpms drop down into the start of the high hp curve.
Red line is not shift point. Red line is normally at or just below where the valves float. You don't want to go that high. My camshaft/springs are set up so that there's a theoretical redline of 7800. I shift at 7000 and cross the finish line around 7400 rpm. My converter stalls at 6000 so going down the 1/4 mile track, the rpms never drop below that.
Since my camshaft makes it's best power from 5000-7500, I'm always operating in the best rpm range. Even at low speeds, my engine produces a lot of power but since it's not driven on the street, I'm not too worried about low to mid range power.
Building an engine that has a very high rpm/power range also means you will have a lot of power in the mid and sometimes low rpm range because the entire powerband has been increased. Just because an engine makes peak power at 7000 rpm doesn't mean you'll be operating at that rpm all the time. Peak power should always be where the engine is doing most of it's work. In a street car that means staying below 6000 rpm however torque is what does work and for a street car, that means torque is best under 3000 rpm where the engine normally operates. A street engine can build peak torque at 4000 rpm also. That's just means it will also have more torque in that lower operating range where it normally operates. RV cams are good examples. They produce a lot of torque at low rpms but don't produce high rpm HP. They're designed to make a lot of torque to get a heavy vehicle moving quicker.
For optimal performance, You shift at or just above the peak HP so when you go into the next gear, the rpms drop down into the start of the high hp curve.
Red line is not shift point. Red line is normally at or just below where the valves float. You don't want to go that high. My camshaft/springs are set up so that there's a theoretical redline of 7800. I shift at 7000 and cross the finish line around 7400 rpm. My converter stalls at 6000 so going down the 1/4 mile track, the rpms never drop below that.
Since my camshaft makes it's best power from 5000-7500, I'm always operating in the best rpm range. Even at low speeds, my engine produces a lot of power but since it's not driven on the street, I'm not too worried about low to mid range power.
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