I have an 89 with a 6 speed. What is the optimum RPM to shift at for drag racing? Do I look at the torque curve and shift at the rpm for maximum torque or isn't it all that simple?

 

Its not that simple. You have to experiment.

If your going off the stock tach...good luck, they are usually way off. And if they are not off, then they are slow...

The best way is a shift light. But there is time it takes when you see the light to when you actually make the shift. I have seen as much as 600-800 RPMs higher than the shift light, so on a manual I would think its even more.

You have to experiment with your car. If you know you have to shift at 5000RPM and you wait to 5000 RPM to show on your tach, you will WAY overshift it most likely.

On my car I am shifting at 6200 for a 6800 on average RPM actual shift.

 

Without getting technical... a stock L98 stick shift typically gets its best results aiming for a 4400 RPM shift point.

 

I try to shift at 4500 therabouts. But.. I'm probably overrunning first gear because of tach delay. It's not as big a problem in 2nd or 3rd, since the revs don't come up as fast.

4000.. 4150... 4330.. 4390.. 4680.. doh! shift..

 

I think the best way to determine when to shift is to practice and listen to your motor. I have a 94 LT1, when I drag I launch, go up through first, then look down at the tach. At around 4500 my left foot and right hand should already be moving. Shift....look down the track....look at the tach...4500 start moving. I am in 4th by the line. When I take my CBR 929 to a track day (a road course, not a drag strip) I RARELY look at my guages I can just "feel" when to shift. At around 10,500 RPM power starts to drop off. The rev limiter is around 11,600. I just know that when the power starts to drop off, I shift. Every motor is different...you just have to practice. You also have to think about where the tach will land after the shift...shift too soon you might be out of the power band. PRACTICE, PRACTICE, PRACTICE!!!!!

 

I have always used the rule of thumb: about 500 rpms past maximum horsepower.

You are still making good HP and after the shift you want the next gear to hit as close to maximum torque as you can.

 

I found that the LT1 is a pain becase the torque (to the ground) at the rev limiter in any gear is greater than the torque at the same speed in the next higher gear, so shifting before the rev limiter is losing time in the 1/4.

Your results may vary since you have the L98.

 

I agree completely, if you shift at you maximum peak hp or torque, you will be farther away from the power band when you hit the next gear.

Rev it to the max......and power shift, when you hit the next gear, you are right back in your power band. One advantage of small blocks is RPM, so use it !

 

a couple weeks ago when I was running at bowling green I was trying to shift around 6k but my problem was that at the end of the quarter I was hitting the rev limiter (6500) in third gear around 110 mph and didn't want to shift because I was so close to the traps I thought I would screw myself. So I left it in third and let it bounce off the rev limiter for a second or so ended up running fairly consistant high 12's around 112 or 113 mph I might have hit a 12.5 the run where I snapped the spindle .... talk about hooking up off the line

 

The theoretical optimum shift point is when you will have more RWTQ in the next gear vs. the current one.

Here's an example:
http://www.datsuns.com/Tech/whentoshift.htm

 

Do not wait for the rev limiter to shift. On a L98 listen to Scorp, he has drag raced his many times and knows when to shift.

Pretty much you just have to keep making passes in your car till you find your spot. In my car I don't even watch the tach, at least not directly, I just use my ears. Some will say it's not as accurate and I would tend to agree, but the numbers don't lie.

Here I am shifting my LT1

http://temp.corvetteforum.net/c4/mrmojo2//shiftvid1.wmv

 

Mr.Mojo...a couple of dumb questions...do you have any clue what gear you have? (your shift points are almost identical to mine)...and how did you get that shift light to work? My last trap speed was around 106 and I was in fourth. ToyC4 says he is running 110 in 3rd.

 

I don't have a shift light. I do have 3.45 gears. Note that even though the tach is reading above 6000, it's more likely around 5800.

Also remember that the speedo can't keep up with the car either.

I was already slowing down before the speedo could register the top speed I had hit(usually 106-108 depending on the weather).

 

Ski would likely argue with me until he's blue in the face but it, doesn't matter I'm not going there. I didn't even read what he posted because I don't want to start and argument. Here are my $.02 on it, take it or leave it.

If you know the power characteristics of the engine you need to do what is mentioned above and figure out what your effective torque to the ground will be in any given gear at any given RPM. If your HP starts to fall off dramatically with RPM's like the L98 there will be a point where you will put more power to the ground in the next higher gear than if you continue in the current gear. On an engine with a much different power curve, like the LT1 there is no point where this is true. You ALWAYS make more power in the lower gear, in a situation like this it is in your best interest to shift as close to the rev limiter as possible. IE if your redline is 5850, ideally you would shift gears at 5849. The problem is that when you combine the tachometer lag which is different for every gear as well as your own reaction time you can have shift points that are very erratic at best.

If you wait until you see 5800 you will hit the rev limiter every time. You can install a shift light that will help some because it eliminates the tachometer lag but you still have to factor your own reaction time. Example, my rev limiter is set to 6500 RPM's but I have to set the shift light at 6200, maybe even as low as 6100 (I don't remember exactly) or I'll hit the rev limiter every time. Even at that it differs from one gear to the next. Ideally I could have a shift light for every gear. In first gear I'd wait for one light, in second I'd wait for two, in third I'd wait for three, etc. OR I could just get an automatic trans and have it do it for me. IMHO though that takes all the fun out of it.

 

Okay, if your tach says 6200, how do you know it's actually 6800rpm?


Larry
code5coupe

 

Dumb question....how do you hook a shift light up to stock ignition?

 

i shift around 4700 with my mods....

 

Well I use an MSD digital 6, one of the key reasons being that it provides an easy place to connect a shift light. When you run one of these boxes though you have to bypass the tach filter, I believe the same wire that has the tach filter can simply be tapped to run a shift light but I could be wrong.

 

I cant speak for Ski but when I datalog my car, the lag in the tach is obvious. For instance, if I shift at 5200 on the dash, Datamaster will show the shiftpoint at 55 or 5600 RPM. My 87 has older and slower electronics than the computor I datalog with.

 

Slamming into the rev limiter is also usually a pretty good indicator too . For instance my limiter is set to 6500 but it'll hit the rev limiter when it reads around 6000. In the other gears it will blow well past 6000 before it ever hits the limiter.