[AdamIsAdam]

(Not sure what happened this morning because I asked this question but the post is not here. I'll do it again...)

I'm wondering when is the best time to shift.

I think the ideal is that you shift out of gear at the RPM generating the max hp and (again, in theory) your next gear brings you to the RPM with the max torque. Is that true?

But what happens if your gearing and peak numbers don't allow for that perfect a match? Do you adjust the hp RPM shift point so that your next gear is still at peak torque or vice versa?

Take these dyno numbers that Cliff posted this morning. Let's use the first set of dyno numbers since the spread between hp and torque is wider, and let's assume an M21 wide ratio tranny to make it interesting (and more relevant to my car )

Do you shift out of 1st at around 5k at about peak HP even if that brings you to 2nd gear below 4k where torque is peak? Or do you hold 1st a few hundred extra RPM's to keep 2nd at 4k?

My next question is: How can I calculate RPM drop for each gear so i don't have to drive around with my nose in my tach at 5,000 RPM!

[ponyakr]

Since I raced a 4-speed car for a few years, I'll take a stab at this one.

You experiment with shift points, til you find those which produce the lowest ET. Without actual, on track testing, all you have are opinions. And, as we've seen on this and most every forum, opinions can differ WIDELY, on most any given subject.

There can be too many variables with engine & cam torque & power numbers, trans & rear gear ratios, etc.

[AdamIsAdam]

THAT'S NO FUN!

I guess I was hoping for a theoretical ideal as a starting point. I live too far from the closest track to test regularly. I'm planning to hit the track this year, maybe later in the season in case I break something I don't lose the entire summer. So I was looking for starting points.

I'll be taking the car to the dyno in the next few weeks once my new fuel system is in. I have a benchmark dyno report when I first bought the car, but i later discovered that I wasn't getting WOT, so that's not much of a benchmark. I've since changed carb, intake and did a valve job with new springs (the old ones were VERY weak as per the machine shop who measured them).

I know nothing beats opinions faster than a time slip, but indulge me.

PS Hey, 2,000th post!


(I've attached that old dyno run from 3 years ago as a reference point.)

[Chris65LeMans]

Did the Dino wind it up higher than 5800? Your photo at the bottom is cut off.

Based on the info shown, I'd shift it at 5,800.

[AdamIsAdam]

Originally Posted by Chris65LeMans

Did the Dino wind it up higher than 5800? Your photo at the bottom is cut off.

Based on the info shown, I'd shift it at 5,800.

The photo is Cliff's from another thread this morning. Look closely and you'll notice that there are two dyno sheets there, so I was suggesting we look at the first one since those numbers are closer to mine plus the spread between torque and HP is wider.

[ponyakr]

"...THAT'S NO FUN!..."


Oh yeah, it was LOTS of fun, not only the testing, but especially winning races.

Not too many things in this life have been more fun, to me, than yanking on the Hurst shifter, in my GTO--and especially on the track.

[Stan Weiss]

The RPM drop is easy for a manual trans but has more variables with an automatic trans.

(new trans gear ration / Old trans gear ratio) * RPM @ shift

► (1.52 / 2.52) * 5800 = 3498.4

Stan

[pastry_chef]

https://www.youtube.com/watch?v=zZBqb0ZJSwU

[JLMounce]

Typically you want to maximize average power when shifting. This typically means shifting a little past peak depending on how sharply power drops off after it's peak. Each car will be different and that's why you need to experiment your shift rpm. One thing to keep in mind also is that shift rpm may be different for each gear depending on your gear set.

As an example somebody running a low gearset TH350 is going to have a larger spread from 1-2 than somebody running a standard gearset. But the spread from 2-3 should be roughly the same. As a result the person with the low gearset may need to shift later in 1st gear than the person with a standard set. Otherwise they risk dropping out of the power band in 2nd gear. This is crude however because your converter and how much slip it has plays a role. That's why as mentioned earlier doing this work on a manual is easier.

If you know which gears are in your tranmissions and the spread between them, you can take that information and cross-reference it against your dyno sheet to calculate where your shift points for best average power "should" be. That gets you a starting point, but because your engine will behave differently in the real world vs when it was on a dyno, you'll have to make adjustments based on your ET and trap speed to really dial that in.

[AdamIsAdam]

I love him! Car nut and engineer combined. And I saw this video way back when but now I used my numbers and calculated this all out for the 1-2 shift from 4000 RPM all the way to 5500. And wouldn't you know it, shifting at 5300 RPM nets the same torque in 1st as it does in 2nd gear. Which is where most people find their best times at with big Pontiac engines.

I LOVE IT!

Now I just need to put it in excel!

[A.W.Dille]

When I was still racing my GTO it took awhile to find the optimum shift point. I was all over the rpm range till I found what the engine liked. Even though the advertised range of the Lunati BMII cam is 1800-5800 the engine liked a shift point of 5200. Above that and the engine pull felt flat and netted no better times or mph. This was with a Saginaw four speed with a 3.11 first gear, 3.55 rear end gears and slicks. The old engine I ran years ago with a RAIV cam liked a shift point of 5800. So different combinations vary. In my opinion it's what the engine likes.
Like ponyakr the four speed can be more challenging but a good driver can run consistent times.

[Goatracer1]

My opinion. I've drag raced since 1966 and I've always found that I got the best results shifting at the point when the engine stopped pulling hard. If you lose a lot of rpm on the shift you could go another 100 rpm before shifting.

[ta man]

Experiment and have fun.Ideally you want a smooth transition into the next gear.Linear power as some would say..years ago when I used to use a G tech for testing..you could see the G's..You should start with a hard pull and slowly the G's drop off..if you shift and you feel a surge of power you have shifted too high,if it lags you have shifted too low,time slip increments are the best.Its the fun part of the hobby!

[Blued and Painted]

Don't get carried away on the 1-2 shift. You'll be past your peek numbers and stuck on the rev limiter before you know it. I don't like getting twisted all that tight in first gear. JMO.

[vitamin c]

When the optimum rpm is found, how do those of you with a four speed shift? Ill use a the term a friend keeps asking me about.
"Are you power shifting"? Keeping the accelerator to the floor and stabbing the clutch for the gear change. I don't, to me it just seems unnatural, I cant keep my foot planted while trying to shift. Now if you have a "smooth" shifting transmission, and possibly a rev limiter it may be worth trying, but I still cant bring myself to try it. I have seen a you tube video of a guy doing it in an old dodge or Plymouth.

[A.W.Dille]

Since I started racing four speeds in 1977, once I put the gas pedal to the floor I don't lift and I use the clutch, but you have to have near perfect reflexes and coordination. If you let off during shifts then you lose as much as 2-4 tenths. Guys like Ronnie Sox and Dave Strickler were the best on four speeds that ever was.

[Formulajones]

Originally Posted by vitamin c

When the optimum rpm is found, how do those of you with a four speed shift? Ill use a the term a friend keeps asking me about.
"Are you power shifting"? Keeping the accelerator to the floor and stabbing the clutch for the gear change. I don't, to me it just seems unnatural, I cant keep my foot planted while trying to shift. Now if you have a "smooth" shifting transmission, and possibly a rev limiter it may be worth trying, but I still cant bring myself to try it. I have seen a you tube video of a guy doing it in an old dodge or Plymouth.

Like this Mark gettin' it done with a little 302 and a Nash 5 speed with 1:1 5th and 5.38 gears, using a clutch and standard "H" pattern type shifter. Nothing fancy.

https://youtu.be/-emhm4hw3Kc

[PontGuy]

Originally Posted by AdamIsAdam

I saw this video way back when but now I used my numbers and calculated this all out for the 1-2 shift from 4000 RPM all the way to 5500. And wouldn't you know it, shifting at 5300 RPM nets the same torque in 1st as it does in 2nd gear.

You mean the same HP, right Adam? Engine torque is force as measured at the crank. But torque at the wheels varies by the gear ratio. So HP better represents what is getting to the ground through the gears. (Yes, another engineer here.)

I don't drag race, only test and tune nights for me and those are very infrequent, as in years in between. But I find shifting beyond peak power to give best results. How much beyond depends on the curve. If it drops off fast then not far beyond and if the curve is flat then a good ways past it. I think your math exercise is a good starting point but test passes at the track will tell all.

As for power shifting I pull back with my right foot but not all the way out. I've done the foot on the floor thing but without practice its shaky, and I never wanted to break a car practicing it. Launching a stick car with lots of power is another whole topic, and much more critical to results. I always just accept some wheel spin when playing around on the road, but that's a big no-no to getting good times at the track. For some reason my self control with a stick is not as good as with an auto trans, haha...

[AdamIsAdam]

No, I did mean torque based on the video's recommendation. Without an engine only dyno session, what else could I do? The chassis dyno is measuring in 4th gear, which is 1:1 ratio.

And yes, absolutely, launching a stick will add more variability than anything else. I started a thread on this a few years ago of you want to search on my user name. There were some good posts in it.

[Stan Weiss]

Originally Posted by PontGuy

You mean the same HP, right Adam? Engine torque is force as measured at the crank. But torque at the wheels varies by the gear ratio. So HP better represents what is getting to the ground through the gears. (Yes, another engineer here.)

I don't drag race, only test and tune nights for me and those are very infrequent, as in years in between. But I find shifting beyond peak power to give best results. How much beyond depends on the curve. If it drops off fast then not far beyond and if the curve is flat then a good ways past it. I think your math exercise is a good starting point but test passes at the track will tell all.

As for power shifting I pull back with my right foot but not all the way out. I've done the foot on the floor thing but without practice its shaky, and I never wanted to break a car practicing it. Launching a stick car with lots of power is another whole topic, and much more critical to results. I always just accept some wheel spin when playing around on the road, but that's a big no-no to getting good times at the track. For some reason my self control with a stick is not as good as with an auto trans, haha...

To me that is what counts. These were done about 5 years ago for a thread on a different forum.

Stan