What are the best shifing points for an LS? The torque peak is 5200 rpm and the h.p peak is 6300 rpm.

 

I will give you the short answer. If you want to go as fast as possible, it is best to shift at redline. The reason is that if you shift sooner, the RPM's in the next gear are too low to develop optimum power. It is true that peak HP is usually gained a bit below redline, but you must consider where you end up in the next gear. Also remember that horsepower is a funciton of torque * engine speed. The torque peak is not where the engine is making the most "go fast power".

I am assuming you didn't want to know how to get the best fuel economy.

 

Basically what he said, the idea is that in most hondas you make more EFFECTIVE torque (at wheels) at redline in a given gear than after the shift into the next gear. Hondas usually have a basically flat torque curve (aka line), and due to gearing in the tranny lots of effective torque is lost with each shift to a higher gear.

Mustangs and V type engines have lots of torque in a very specific powerband, and the torque typically plummets as the revs get past 4k. In these cars, it is possible to accelerate faster by shifting well before redline because even after the torque lost via gearing in the transmission, there is more effective torque at the bottom of the next gear.

HTH.

Dustin

 

Thanks for the info. I've also been trying to figure out the relationship between torque and h.p. I know that torque moves mass. That's why V-8's get some nasty quarter mile times, but why is it that peak whp is obsessed over in the import scene and torque is not? Like I said, I have a pretty good idea about both, but I still need a simple explanation. Excuse the ignorance.....

 

Torque is twisting force. Horsepower is twisting force relative to time. You need ample amounts of both for good acceleration. If you have a motor that can put out only 100ft-lb of torque, but it can rev to 16k RPM, it will have about 300hp. The reason this is useful is because of gearing. Since our motors cannot rev to say 50,000 rpm (although that would be nice), we have to use transmissions to exchange torque for speed. So if a motor can accelerate LONGER in a specific gear before upshifting, more effective torque can be put to the wheels for longer, and the car will be faster. It will not PULL any harder (no extra torque), but it will be faster because it pulls longer in each gear and can use gearing.

If you had a motor with 500ft-lb of torque that could only rev to 2k rpm, it would only have 190 hp. Yes it would PULL hard, but almost instantly it would have to shift to the next gear, and it would lose tons of effective torque AT the wheels because of the gearing. That, and it would be shifting every 1.5 seconds or something.

So basically, torque is what accelerates your car. But the longer you can use torque in a given gear, the higher the horsepower and the faster the car.

For the fastest car, you would have ONE gear, and an infinitely high redline. No shifting, no torque lost through gearing. Unfortunately, we currently are unable to build motors that can 1) produce stable torque through really wide RPM bands or 2) withstand the heat and force of unspeakably high RPMs.

Piston motors are not very efficient because they accelerate pistons and then decelerate them to stopped (for an instant) constantly. Rotary engines are much better and that is why they produce less vibration, but they have their own set of issues

Dustin

 

for a related, long, technical thread (with arguing) read this: https://honda-tech.com/zerothread?id=61559

 

Thanks for the info! That link was extremely useful. So, theoretically, if my redline could be raised to say 10,000 rpm, I would run the quarter mile much faster because I can pull longer in every gear?

 

Yep, if you had a reasonable amount of torque all the way up to 10k rpm you would

Dustin

 

Nice explanation Dustin !

Just remember, for and Internally un-modified LS engines, with only as much mods as say I/HE, using the stock LS tranny, the torque curve kicks in at very low RPM and is very fat (for a 4cyl) and it peaks out at about 6200 to 6600 rpm** (depending of engine's condition), even tho there is some more useable HP up to the 7200rpm gas limiter in stock form...........

in the 1st and even 2nd gears, it is best to shift in the mid 6000 rpm range to avoid the torque drop off and drag in speed advancement. By 4th gear, this is useless and you need to shift at redline to use all of your available HP up there, (you can be in the 120's easy....)

If you redline 4th and make it to 5th, you should be living in Germany, have a full racing suspension, 225+ tires and a helmet.....

 

I had a hunch that the LS would benefit from shifting at that point being that it is not as peaky as the GSR. The only way to find out is at the track....I'll let you know...