Where would your shift point be?
Safety Car
Joined: Sep 2000
Posts: 3,524
Likes: 4
From: Hinckley Ohio
Originally Posted by hippy
Math works for stick shift cars, not so well on auto cars unless you know your slippage.
I datamastered a few (50) runs last year. My car shifted out of 1st at 6100 and ended up around 4500 in 2nd.
My tq conv is showing a stall of around 2700.
I datamastered a few (50) runs last year. My car shifted out of 1st at 6100 and ended up around 4500 in 2nd.
My tq conv is showing a stall of around 2700.
Looking at his dyno curve at 6100rpm you are at about 420hp and if you shift to 4500rpm you drop to 360hp......if you don't shift and wait til 6400rpm you will stay aroun 410-420hp vs th 360-370hp you would have if you shifted...
Math works for me????
At any mph what gear gives you the most horsepower....pick this gear....if you have 420hp at 6100rpm or 360hp at 4500rpm it is clear it is not time to shift unless you are running into redline considerations..
At these rpms I would think the tranny is pretty well into lockup??
Last edited by LT4BUD; Mar 2, 2006 at 01:52 PM.
Le Mans Master
Joined: May 2000
Posts: 7,033
Likes: 12
Originally Posted by LT4BUD
Why would you say math doesn't work????
Looking at his dyno curve at 6100rpm you are at about 420hp and if you shift to 4500rpm you drop to 360hp......if you don't shift and wait til 6400rpm you will stay aroun 410-410hp vs th 360-370hp you would have if you shifted...
Math works for me????
At any mph what gear gives you the most horsepower....pick this gear....if you have 420hp at 6100rpm or 360hp at 4500rpm it is clear it is not time to shift unless you are running into redline considerations..
At these rpms I would think the tranny is pretty well into lockup??
Looking at his dyno curve at 6100rpm you are at about 420hp and if you shift to 4500rpm you drop to 360hp......if you don't shift and wait til 6400rpm you will stay aroun 410-410hp vs th 360-370hp you would have if you shifted...
Math works for me????
At any mph what gear gives you the most horsepower....pick this gear....if you have 420hp at 6100rpm or 360hp at 4500rpm it is clear it is not time to shift unless you are running into redline considerations..
At these rpms I would think the tranny is pretty well into lockup??
When I say the math doesn't work I mean where the rpm is going to end up after the shift. An auto has slippage in it and isn't fully locked. From first to second should be 53% of the rpm, but it isn't going to be. My point being is if he shifts out at 6400 he isn't going to drop all the way to 3500.
Unless he changed his lockup, it probably is happening well into 3rd gear as well.
Thread Starter
Le Mans Master
Joined: Feb 1999
Posts: 9,935
Likes: 38
From: South Carolina
St. Jude Donor '03 & '05
Originally Posted by hippy
When I say the math doesn't work I mean where the rpm is going to end up after the shift. An auto has slippage in it and isn't fully locked. From first to second should be 53% of the rpm, but it isn't going to be. My point being is if he shifts out at 6400 he isn't going to drop all the way to 3500.
Unless he changed his lockup, it probably is happening well into 3rd gear as well.
Unless he changed his lockup, it probably is happening well into 3rd gear as well.
Safety Car
Joined: Sep 2000
Posts: 3,524
Likes: 4
From: Hinckley Ohio
Originally Posted by steve40th
So, I really need to pay attention to where it is when it engages second gear. I have a 2800 rpm Vigilante. It doesnt lock till like 90 mph in third. I need to see if I have any WOT runs to see, through the gears/ Otherwise I need to run it again and see..
Any shift before 6000rpm(your hp peak) will result in going to a lower horspower, no matter what the new rpm is since it will be less than 6000...
Between 6000 and 6400 the only way you could shift and not loose power would be if your rpms only dropped a few hundred rpm...look at say 6200.....the only window of rpms where the power is equal or greater is between about 5600 and 6200.....you will certainly drop way below that which will result in a significant power drop....
Your optimum shift point is 6400+, since ANY shift point below that will result in a power loss....
Le Mans Master
Joined: May 2000
Posts: 7,033
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Originally Posted by LT4BUD
Perhaps theoretically this is important, but just look at your dyno curve...
Any shift before 6000rpm(your hp peak) will result in going to a lower horspower, no matter what the new rpm is since it will be less than 6000...
Between 6000 and 6400 the only way you could shift and not loose power would be if your rpms only dropped a few hundred rpm...look at say 6200.....the only window of rpms where the power is equal or greater is between about 5600 and 6200.....you will certainly drop way below that which will result in a significant power drop....
Your optimum shift point is 6400+, since ANY shift point below that will result in a power loss....
Any shift before 6000rpm(your hp peak) will result in going to a lower horspower, no matter what the new rpm is since it will be less than 6000...
Between 6000 and 6400 the only way you could shift and not loose power would be if your rpms only dropped a few hundred rpm...look at say 6200.....the only window of rpms where the power is equal or greater is between about 5600 and 6200.....you will certainly drop way below that which will result in a significant power drop....
Your optimum shift point is 6400+, since ANY shift point below that will result in a power loss....
My motor is a stock 90 short block and I am making peak power around what rpm you are but I am a little bit scared that I will create 8 single cylinder junk piles each yielding 43ci if I push my motor to 6500.
To me it looked like you had a peak hp of around 59-6000 so that's why I originally said 6500.
Safety Car
Joined: Apr 2004
Posts: 4,532
Likes: 7
From: Lahaina Hi
You have to keep in mind ,in a perferct world all things being equal.
I would shift when my shift light comes on .If you spin the tires at launch then you will be beyond your power curve.The motor will lose power and it takes more time for it to recover.
Check the track and see what the tires will hold and fudge the shift up or down by 3 to 500 rpm's.
You can have 10,000 horse power but if you can't keep it on the ground the car will not go anywear.
I would shift when my shift light comes on .If you spin the tires at launch then you will be beyond your power curve.The motor will lose power and it takes more time for it to recover.
Check the track and see what the tires will hold and fudge the shift up or down by 3 to 500 rpm's.
You can have 10,000 horse power but if you can't keep it on the ground the car will not go anywear.
Melting Slicks
Joined: May 2004
Posts: 2,286
Likes: 2
From: Stamping Ground KY
I'm pretty sure that acceleration is a function of torque, not horsepower.
T=F*d
F=m*a
then
a=T/(m*d)
where a = acceleration
T = torque at x rpm
m = mass of car
d = effective torque multiplication ratio (requires gearing and tire size)
Of course a can't be greater than the amount of friction your tires can provide times the ratio of the vehicles weight on the rear tires.
Or I could be full of crap, I'll leave it to you to figure that out.
T=F*d
F=m*a
then
a=T/(m*d)
where a = acceleration
T = torque at x rpm
m = mass of car
d = effective torque multiplication ratio (requires gearing and tire size)
Of course a can't be greater than the amount of friction your tires can provide times the ratio of the vehicles weight on the rear tires.
Or I could be full of crap, I'll leave it to you to figure that out.
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Thread Starter
Le Mans Master
Joined: Feb 1999
Posts: 9,935
Likes: 38
From: South Carolina
St. Jude Donor '03 & '05
Originally Posted by REDC4CORVETTE
You have to keep in mind ,in a perferct world all things being equal.
I would shift when my shift light comes on .If you spin the tires at launch then you will be beyond your power curve.The motor will lose power and it takes more time for it to recover.
Check the track and see what the tires will hold and fudge the shift up or down by 3 to 500 rpm's. You can have 10,000 horse power but if you can't keep it on the ground the car will not go anywear.
I would shift when my shift light comes on .If you spin the tires at launch then you will be beyond your power curve.The motor will lose power and it takes more time for it to recover.
Check the track and see what the tires will hold and fudge the shift up or down by 3 to 500 rpm's.
You can have 10,000 horse power but if you can't keep it on the ground the car will not go anywear.
Melting Slicks
Joined: Aug 2003
Posts: 3,401
Likes: 397
From: Lakeville MI
Horsepower is independent of gearing, torque is not.
Simply put: Choose the gear that gives you the most horsepower for a given speed. In this case you will also have most torque vs speed at the wheels.
Don't shift until you will have more or equal hp in the next gear, unless you redline first.
Simply put: Choose the gear that gives you the most horsepower for a given speed. In this case you will also have most torque vs speed at the wheels.
Don't shift until you will have more or equal hp in the next gear, unless you redline first.
Melting Slicks
Joined: May 2004
Posts: 2,286
Likes: 2
From: Stamping Ground KY
Originally Posted by tequilaboy
Horsepower is independent of gearing, torque is not.
...
...
BUT
a well designed car will have the gearing matched to the output of the engine. Again, that's why the S2000 can almost keep up with an early C4, even though it has less than half the torque, it has been geared to take advantage of its ability to reach high RPMs.
Torque area under the curve is what really accelerates you, HP is the hedge to simplify the relationship between torque and RPM.
Safety Car
Joined: Sep 2000
Posts: 3,524
Likes: 4
From: Hinckley Ohio
Originally Posted by tequilaboy
Horsepower is independent of gearing, torque is not.
Simply put: Choose the gear that gives you the most horsepower for a given speed. In this case you will also have most torque vs speed at the wheels.
Don't shift until you will have more or equal hp in the next gear, unless you redline first.
Simply put: Choose the gear that gives you the most horsepower for a given speed. In this case you will also have most torque vs speed at the wheels.
Don't shift until you will have more or equal hp in the next gear, unless you redline first.
