Is your rev counter accurate? 
What rpm for 1-2 shift?
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MilesnMiles
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, better stop fannying around 
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Dave-R
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Always worth a try. The point is that the best rpm shift point is different for every engine.
You need to shift past peak power, where HP is dropping off. When you shift you want the rpms to be at the point on the power curve before peak where you are making exactly the same power as when you shifted.
This way the area under the power curve is maximised and you get the most from the engine.
A typical mopar automatic has the following gear ratios;
2.45:1 (first)
1.45:1 (second)
1:1 (third or drive)
To work out the rpm drop we need to know the ratio between each gear.
The ratio between 1st and 2nd is 2.45 divided by 1.45.
2.45/1.45 = 1.69
So if you decide you want to shift to second at 6500rpm just divide 6500 by 1.69 and you get the rpm the engine drops to.
6500/1.69 = 3846rpm
So on this shift I went from 6500 to 3846rpm on the shift. Adjust the shift point on your power curve until you are making exactly the same power at the lower point than you were at the shift point.
Or you can draw a line between these two points on a graph of the power curve you can see if the line is norozontal or not. When it is a perfectly level line you have found the correct shift point.
Going from 2nd to 3rd the ratio is 1.45/1 = 1.45 so a different shift point is needed for the 2-3 shift.
Here are two examples of wrong shift points and one perfect shift point.
JUST REMEMBER THAT EVERY ENGINE HAS A DIFFERENT SHIFT POINT DEPENDING ON SPEC. DO NOT COPY THESE SHIFT POINTS AND EXPECT IT TO WORK.
You need to shift past peak power, where HP is dropping off. When you shift you want the rpms to be at the point on the power curve before peak where you are making exactly the same power as when you shifted.
This way the area under the power curve is maximised and you get the most from the engine.
A typical mopar automatic has the following gear ratios;
2.45:1 (first)
1.45:1 (second)
1:1 (third or drive)
To work out the rpm drop we need to know the ratio between each gear.
The ratio between 1st and 2nd is 2.45 divided by 1.45.
2.45/1.45 = 1.69
So if you decide you want to shift to second at 6500rpm just divide 6500 by 1.69 and you get the rpm the engine drops to.
6500/1.69 = 3846rpm
So on this shift I went from 6500 to 3846rpm on the shift. Adjust the shift point on your power curve until you are making exactly the same power at the lower point than you were at the shift point.
Or you can draw a line between these two points on a graph of the power curve you can see if the line is norozontal or not. When it is a perfectly level line you have found the correct shift point.
Going from 2nd to 3rd the ratio is 1.45/1 = 1.45 so a different shift point is needed for the 2-3 shift.
Here are two examples of wrong shift points and one perfect shift point.
JUST REMEMBER THAT EVERY ENGINE HAS A DIFFERENT SHIFT POINT DEPENDING ON SPEC. DO NOT COPY THESE SHIFT POINTS AND EXPECT IT TO WORK.
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Dave-R
- Posts: 24752
- Joined: Sun Apr 18, 04 11:23 pm
- Location: Dave Robson lives in Geordieland
- Contact:
Reasons for this NOT working for you.
The only reasons this method might not give you better ETs are;
1/ Your power curve is not correct. This should not happen as, although the amount of power might not be right, the cam duration dictates the shape and rpm peak of the curve.
2/ Your engine is not breathing well enough for the rpm. Is there a restriction in carb size, air filter size, intake or exhaust etc?
3/ Going lean. is the fuel system keeping up with demand at high rpms?
The only reasons this method might not give you better ETs are;
1/ Your power curve is not correct. This should not happen as, although the amount of power might not be right, the cam duration dictates the shape and rpm peak of the curve.
2/ Your engine is not breathing well enough for the rpm. Is there a restriction in carb size, air filter size, intake or exhaust etc?
3/ Going lean. is the fuel system keeping up with demand at high rpms?
