he stands correct

 

I have video of what a 3 to 2 upshift and a 4 to 1 downshift at the race track really looks like.. Its not pretty. But engine lived. It should have the link later this week. John

 

Well, I hope I'm not stealing the thread, and I suppose I should consider starting a new one, but I'd like to share my theory for discussion, in answering the shift point question.

Your maximum acceleration will be achieved by maintaining maximum achievable torque at the wheels, right? So, you need to consider how much torque is going to the wheels right before the shift, and right after the shift, to find the optimal shift point.

Gears multiply torque, right? If the engine makes 300 ft-lbs (flywheel) at a certain RPM, and a hypothetical gear is 2.0:1, then 600 ft-lbs of torque will be pumping down the driveshaft (ignoring losses at the transmission) at that RPM in that gear.

When I set out to determine my optimal shift point, I was planning to do some calculus to maximize the area under my torque curve. But then, after considering my statements above, I decided to plot my dyno curve in 4th gear (1:1), and then show the multiplication factor on the curve for the first 4 gears.

In my case, it is obvious that I should shift at the limiter, despite the fact that HP and Torque have fallen off by then. The reason is that the torque multiplication advantage of the lower gear (before shifting) is typically significantly higher than the amount of torque or power fall-off. The lower my gear (1st is lowest), the more true this statement is.

For example, if you look at my multiplication chart (TorqGear.jpg), you’ll notice that I’m showing almost 800 ft-lbs at the wheels in 1st gear near 6000 RPM (well down from a ~900 ft-lb peak), but in second gear, it can be no better than about 625 ft-lbs at ANY RPM. Of course my curves ignore any FURTHER losses outside of 4th gear (which is 1:1, which is how the dyno was run), but I’ve got to believe it’s close!

In summary, my theory is that you need to look at your chassis dyno torque curve, and consider the torque multiplication factor of your transmission gear ratios, to determine optimal shift point. Your optimal shift point MAY be different for a different gear. I suspect, however, that optimal shift point will probably always be engine redline for almost any setup (maximize that torque multiplication factor before shifter to the next higher gear…).

What do you think? Am I crazy? Should we start a new thread to discuss? I’m interested in your comments. Sorry for the long post!

 

^ Bah, just shift a few hundred past your peak and call it a day.
If you really want to cut some time, trim your 60' down.

On a serious note, I'm sure you could dig up some shift/rpm threads using search which may help you out.

As for hitting the limiter, I've hit mine more often than I care to admit, but a big *** shift light in my face has cured the problem.

 

Yes, I agree with your post. Just don't let Colonel see it cause he thinks acceleration is only proportional to horsepower.

Instead of worrying about torque and gearing, just worry about making sure the hp is the same before and after the shift and you don't have to worry about the torque multiplication.

 

I always hit mine if I miss a gear, other than that I try to stay away from it, some of the guys around here with Supras use it to shift off of for some reason. I don't think it will damage the car at all really, if fuel is cut completly then there is no burn and no heat so the lean should not hurt really as it is not a true lean since there is 0 burn.

 

No, I have the TSP 231/237. That cam makes power upstairs, trust me it pulls like a ****. The stock rev limiter is at 6,200. You can easily mechanically over rev it. This happens alot with 6 speed cars. Let's say you accidentally miss a shift and instead of shifting from 2nd to 3rd you go to 1st instead. That's going to make the engine mechanically rev way higher. That's where the damage occurs. If your lucky it will only cause a few bent pushrods.

 

I hit my rev limiter a lot since my mods. I have the tr 224 112 & I have a shift light. The problem is if I lose traction in 1st or 2nd it hits the rev limiter before I can react. I don't have access to a tuner, maybe I should mail in my puter to get the rev limiter raised.

 

very not good for stock push rods. get new ones and set ur rev limiter higher and dont worry about it.

 

I've done it once too when I was racing a mach1 ... my heart stopped beating for a good 3 or 4 seconds as soon as my foot let off the clutch and i realized i was in 2nd ... i pulled over right away and luckily everything was ok

 

I'm glad someone else brought this up. Unless your wheel torque falls off to below what it would be in the next gear, there's no need to shift as you're still achieving optimal acceleration.

Do the math and calculate your points based on a dynograph - shift as high as is mechanically safe within the above guidlines

Here's some reading on this: http://mclements.net/mrc-PowerTorque.html
He explains the concepts pretty well

 

Exactly. The problem is usually the rod bolts or valvetrain limits the rpm to a lower than optimal shift point. I think that's where the "shift 100 rpm past peak" misconception comes from, cause the higher you go the more you risk breaking something.

 

Most TR224 cam's I seen run out of steam by 6100RPM's.

 

Well, to answer your question, since everyone seemed to get , yes your computer cuts fuel to the engine when you hit the rev. The rev limiter is actually helping you, so that you don't over rev and bend a pushrod or much worse. So look at it as your friend. As far as you hitting it often....well I would work on your shifting. Also your factory tach may be off. Mine is about 100 rpm low. So when you do hit it, remember where its located as far as your needle position on your tach.

 

That's what happened to me my 1st time at the track, even shifting at 4.5k the tires would spin so hard that I would instantly hit the limiter every time

I hit the rev limiter all the time, it reminds me that I need to shift gears when I'm drunk

 

 

I'm going to echo the shift lite statement. They are cheap and easy to set up. Whenever I get in a race I don't even have to think about the revs or shifting. As soon as I see the light flash I just 'automatically' shift. Drops the risk a lot too, you only have to pay attention to the road, not watching your tach. Plus you'll do better because you'll be shifting at the right place. Hitting the rev limiter is a surefire way to lose a close race. It's like your car hits a wall.

Dope