Shift Points

[RangerJoe]

I'm headed back to the track next week and trying to run some low 8's, and whittle down my 60ft. Just installed my shift light last night, and its amazing how off these stock tachs are.

My old 302 motor made 268/304 at the wheels, and the HP peaked pretty flat from about 5100-5300 rpms. TQ peaked around 4100 rpms. I have not dynoed my new motor, but all I did was gain a point of compression, port the heads and valve job, and larger cubes (331). Everything else is the same (GT40, Eddy Performer and TFS 1).

My top end is matched pretty well, with everything making power from idlish to 5500 rpms, which showed with the old dyno. I'm sure that with the larger displacement, I brought the power range down some, given that the heads and intake probably don't feed the stroker as well.

QUESTION: With that said, how low do you think I am making peak power? I think I am going to try shifting around 5500 RPMS. I was shifting around 5800 on stock tach, but after seeing the shift light, I think I was probably 6000+.

Thanks in advance!

Joe

 

[Bullitt347]

Just a note, the MSD rpm "pills" are not necessarily correct either. I have seen the rpm "pills" be off a couple of hundred rpm from what is printed on the pill. It is always best to have a secondary way of confirming actual engine rpm's. The factory tach's are notorious for being off actual. And the higher the rpm of the engine the further off the factory tach is.

 

[RangerJoe]

Just a note, the MSD rpm "pills" are not necessarily correct either. I have seen the rpm "pills" be off a couple of hundred rpm from what is printed on the pill. It is always best to have a secondary way of confirming actual engine rpm's. The factory tach's are notorious for being off actual. And the higher the rpm of the engine the further off the factory tach is.

Yeah, this crossed my mind. But, I had noticed that sometimes I could hit the rev limiter right at 6000 rpms, and other times it would pull past the 6000 rpm marker. So, I know the factory tach is all over the place. The shift light should, hopefully, be more accurate and consistent. My multi-meter actually reads rpms as well, I may hook it up and compare.

Any ideas on where my power band may be? My logic is that it falls lower in the rpm range, but I'm not totally sure.

Anyone?

Joe

 

[tca7291]

The only way to really tell is to throw her on a dyno.

 

[85_SS_302_Coupe]

I've personally never had any luck by shifting at max tq/hp numbers from a dyno reading. Unless you're running 4.10s or better, all you'll get is bogged down in the next gear and you'll lose ET. That said, i usually shift at about 6250 or the rev limiter, whichever one happens first.

 

[Gearbanger 101]

I've personally never had any luck by shifting at max tq/hp numbers from a dyno reading. Unless you're running 4.10s or better, all you'll get is bogged down in the next gear and you'll lose ET. That said, i usually shift at about 6250 or the rev limiter, whichever one happens first.

That's waaaay too high for most combo's. You'd need a lot of top end component to justify those shift points.

Personally, I don't think his horsepower curve is going to change a lot. His torque curve on the other hand is going to come on noticable sooner and stronger, but with those heads and that cam....

I'd still guess you'll need to shift around the 5,500RPM mark for best results.

 

[RangerJoe]

That's waaaay too high for most combo's. You'd need a lot of top end component to justify those shift points.

Personally, I don't think his horsepower curve is going to change a lot. His torque curve on the other hand is going to come on noticable sooner and stronger, but with those heads and that cam....

I'd still guess you'll need to shift around the 5,500RPM mark for best results.

Yeah, the heads and cam were left overs. I had to have a new shortblock, so I figured the stroker would give me a good foundation to grow on. AFR's will reside there one day...I hope. Thanks for the replies, think I will start at 5500 and go from there.

Joe

 

[FastDriver]

To optimize shift points, calculate the RPM in the next gear by taking the tranny gear ratio you're going to, and divide it by the gear ratio you're in then multiply that by the shift point. For example, if you're shifting at 6000 rpm from a 2.95 1st into a 1.99 2nd, it's 1.99/2.95*6000 = 4047 rpm.

Next, take your dyno, preferably a loading chassis dyno, and compare the power at your shift point with the power at the new RPM. If the power drops, your shift point should be raised unless you're at your engine's limits (electronic, mechanical, etc...). If your power increases, you should drop the shift point. Ideally, the power produced at the rear wheels is the same in the next gear. Rarely does this happen, because as it turns out, if you have the ability to spin the motor higher, you should shift your power band to the right and end up with more power. So, most built motors require spinning them as high as possible.

Your power peaked through 5300 RPM, so you probably saw an optimum shift point north of 6000 RPM, and possibly near the limiter. That's hard for some to accept, but it's just math and physics. The torque really has a long way to fall before it becomes worthwhile to shift. Consider this, the stock 5.0's optimum shift points are around 5500 from 1st, 5300 from second, and 5100 from 3rd. It's power peaks at only 4300-4400 RPM. Shifting the power peak right by 1000 RPM gives you an indication that the optimum shift point will be at least that much higher. The stock cam and the stock intake were double trouble for the torque band at high RPM, though. With both gone, the 5.0 peaks higher and also holds on for longer beyond the power peak.

The extra cubes you added should shift the powerband back to the left by a 300-400 RPM. So, I'm going to guess a shift point of greater than 5700 RPM. How much? not sure.... that's just where I'd start out at the track. Good luck.

Powershifting would cause you to lower your optimum shift point because you are essentially dragging the next gear's RPM up a bit and have to compensate by shifting a bit earlier.

 

[RangerJoe]

To optimize shift points, calculate the RPM in the next gear by taking the tranny gear ratio you're going to, and divide it by the gear ratio you're in then multiply that by the shift point. For example, if you're shifting at 6000 rpm from a 2.95 1st into a 1.99 2nd, it's 1.99/2.95*6000 = 4047 rpm.

Next, take your dyno, preferably a loading chassis dyno, and compare the power at your shift point with the power at the new RPM. If the power drops, your shift point should be raised unless you're at your engine's limits (electronic, mechanical, etc...). If your power increases, you should drop the shift point. Ideally, the power produced at the rear wheels is the same in the next gear. Rarely does this happen, because as it turns out, if you have the ability to spin the motor higher, you should shift your power band to the right and end up with more power. So, most built motors require spinning them as high as possible.

Your power peaked through 5300 RPM, so you probably saw an optimum shift point north of 6000 RPM, and possibly near the limiter. That's hard for some to accept, but it's just math and physics. The torque really has a long way to fall before it becomes worthwhile to shift. Consider this, the stock 5.0's optimum shift points are around 5500 from 1st, 5300 from second, and 5100 from 3rd. It's power peaks at only 4300-4400 RPM. Shifting the power peak right by 1000 RPM gives you an indication that the optimum shift point will be at least that much higher. The stock cam and the stock intake were double trouble for the torque band at high RPM, though. With both gone, the 5.0 peaks higher and also holds on for longer beyond the power peak.

The extra cubes you added should shift the powerband back to the left by a 300-400 RPM. So, I'm going to guess a shift point of greater than 5700 RPM. How much? not sure.... that's just where I'd start out at the track. Good luck.

Powershifting would cause you to lower your optimum shift point because you are essentially dragging the next gear's RPM up a bit and have to compensate by shifting a bit earlier.

Good info. I had tried some of the online calculators before, and they suggested 6000+rpm shifts, but I just couldn't think that was right. I guess it makes sense though. Thanks again.

Joe

 

[FastDriver]

No problem, bro. Hope it helps you achieve what you're after. As a side note, you'd be surprised at how much skepticism there is about using the HP curve instead of the torque curve, but the short answer is: trust me... I've been through the physics.... I've calculated and overlaid graphs representing torque applied at the rear wheels, which is proportional to the accelerative force applice to the car. It works out to exactly the same result as using the hp curve to start with.

If anyone gets argumentative, though, I'm happy to break out the long mathematical explanation when I'm not so busy.