This post is just plain silly.

 

By this logic every car is disappointing in 3rd because of the loss of leverage. I think I get it...

 

This post is even more silly!!!

 

This is more fun than watching chimps attempt brain surgery.

 

Maybe you haven't driven the right cars?
If you are saying that the advantage is that it has more power in the 0-3000 rpm range than the LT1 (or more torque if you prefer), then yes. Where does the 1-2 shift put you with your L98? If you shift at 4,500 rpm with the ZF6, it will drop you to 3,025 rpm. Not to mention the LT1 won't have to shift as soon, and it's 6,000 rpm shift will drop it to 4,030 rpm, in the meat of its taller power band.

What are you really trying to get at though? What to do to your L98? If so, none of this really matters. What matters, assuming you aren't willing to throw a lot of money at R&D, is what have other people done and how did it help?

 

Unfortunately my college physics days are years behind me and my memory for things I don't use is terrible. So I can only go with my gut. However, I don't believe that is true. And here is why.

Take a car with a torque curve that goes up until ~4,500 rpm. From there it slowly falls off to about 7,000 rpm. The torque at the wheels in any particular gear will follow this torque curve then. So the torque will be the most at about 4,500 rpm and will slowly fall away as the engine speeds up to 7,000 rpm. So according to you the acceleration will be the strongest at 4,500 rpm, and slowly fall off. Then after the shift the acceleration will fall off a lot in the next gear.

However, my reality does not match that. A car with a slowly falling torque curve can still have an increasing power curve. And acceleration will match the power curve, not the torque curve.

Take a look at my dyno graph. Tell me where you think the acceleration feels the strongest:

http://members.aol.com/corvettezr11990/misc/dyno.jpg

If you were local, I'd take you for a ride and then ask you where it really feels the strongest. It accelerates harder and harder as the revs go up. It does not start to wane after 4,500 rpm like your "wheel torque" explanation would suggest.

Of course acceleration will fall off some though. 3rd gear will have more aero drag than 1st gear. And you are never in the power peak after a shift. A similar increase in speed in 3rd gear moves you less towards the peak than in 1st. I.e. speeding up 10mph in 1st gear moves you lots of rpms, in 3rd a 10mph increase doesn't move you nearly as much. So your acceleration spends more time in the non-peak areas.

According to you, acceleration in 3rd gear would be 47% of what it is in 1st gear. That's a huge drop. Does your LT4 really feel that bad in 3rd?

 

OK....you asked for more and more you shall get.....this is in reference to your dyno curve....

In each gear the strongest acceleration will be at 4500 rpm at the engine torque peak of 350 ft-lb

Now here is where it gets a little more complex to understand.....if you could downshift at this same mph where the engine torque is 350 such that the engine speed would jump to 7000 rpm, even tho the engine torque is only about 285 ft-lbs, your torque multiplication (from the lower transmission gear) would increase by a factor of 7000/4500=1.55, the net result however would be that rear wheel torque would increase by a factor of (7000/4500)*(285/350)=1.267!!!!!

Note the horsepower would also increase by this same factor or from about 302 hp at 4500 to 383hp at 7000...



Horsepower always wins if you have the gearing to use it...

 

[QUOTE=Aurora40

However, my reality does not match that. A car with a slowly falling torque curve can still have an increasing power curve. And acceleration will match the power curve, not the torque curve.
QUOTE]

Wow this is a good example of how important it is to understand concepts and to not just use words......no offense intended...as obviously these words and concepts are very difficult...

but in any given gear, acceleration will in fact match the torque curve...as in a=f/m (acceleration= force/mass)....torque is the relevant measure of force!!!!



BTW your car has got to be one strong running vehicle based on that dyno curve!!!!

 

[QUOTE=Aurora40;1563219801] And you are never in the power peak after a shift.

Again, the key. GREGGPEN, You might be at your peak torque after a shift, but you will not be at your peak power. It is the HORSEPOWER at the REAR WHEELS that you need and are lacking with a TPI. And yes, every car does feel like it acelerates slow in third gear, compared to first. Lets say my car makes power to 6500 and I'm at 5000 in 2nd gear, you have to shift your tpi car now or may already have, and I can hang on to 2nd for a while longer yet. Gearing is torque multiplication. The more torque you make, the more horsepower you make, at ANY rpm. You would have to have killer power down low to be accelerating as fast as me at this point. I'm not doing the math to prove it but you would need phenomenal power to overcome the gearing disadvantage you have when you are in 3rd and I'm in 2nd. This is figuring on similarly geared cars. Now, you could change your gearing drastically and beat me in this scenario, but then you would be out of gear before the end of the 1/4 or 1/8th or whatever.

And yes, the real advantage of the L98 FOR DRAG RACING is gone by the end of 1st gear. Ever race a near stock LT1 with a near stock L98, similarly geared? I have. I beat him till not long after I shifted to 2nd. He went on by. Then when I hit 3rd he was distancing me even worse. Now, if you are looking to cruise around at low rpm's and get great fuel mileage and stoplight race once in a while then the advantage of the L98 is pretty big.

 

One of the best posts and concepts I've read on THIS forum. GOOD THINKING!

That isn't right. it is for the scenario you mentioned above (a drag race), but if you want something else, like max fuel economy for example, you might want to run the engine at WOT at a very low RPM, rather than light throttle, and much higer RPM, as the current systems operate now.

 

What he is saying is correct, but it really matters most when you are accelerating from a stop. After that point you can generally select a gear to put your car in its powerband.

The acceleration does fall off substantially in each gear that you increase (assuming you're using the same powerband). Look at it like this: A stock LT4 takes roughly 5 seconds to hit 60 MPH and that is basically using first and second gears. If you continued to accelerate at the same average rate, you would hit 120 MPH in 10 seconds. But in reality, in about 13 seconds you're about 105 MPH. The average rate of acceleration for the last 8 seconds is about 5.6 MPH/second. The average rate of acceleration for the first 5 seconds is 12 MPH/second. I don't exactly feel like the stock LT4 is lazy in 3rd gear, but it simply cannot accelerate at the same rate that it does in first gear due to several factors, but torque multiplication of the gearbox is a major part of that reason.

 

[QUOTE=LT4BUD;1563221308]

but in any given gear, acceleration will in fact match the torque curve...as in a=f/m (acceleration= force/mass)....torque is the relevant measure of force!!!! [QUOTE]

I am by no means wanting to argue here, but I honestly THINK horsepower is the relevant measure of force. I think, I'm not sure. I do know that no work is being done if all you have is torque. I can apply force to my torque wrench on a bolt but no acceleration is taking place. Now if I apply enough force that the bolt starts moving then there is an acceleration involved....and there is horsepower involved.


Not 100% sure here so correct me if I'm wrong.....but the acceleration curve might look similar the torque curve till you hit 5252 rpm's. (of course taking out all things like wind resistance) Your torque can be falling off but if your horsepower staying dead flat after 5252, and the acceleration rate can be staying the same. It is possible for a motor to accelerate harder up high when the torque curve is falling off than when it is at it's peak torque. I am pretty sure the acceleration follows the rear wheel horsepower curve, in each gear. You would have to take the dyno sheet of the engine and factor in all the gearing for each gear, then you would have an acceleration curve for each gear. Would the curve for each gear look the same as one another, just that you are accelerating at a slower rate (ie it takes longer to make the curve)? I have no idea.

 

Let's take gears out of the equation. Say I select 2nd gear with my car, and the power graph shown above. You are saying that my acceleration will peak at around 4,500 rpm and slowly fall off from there? At 7,000 rpm my acceleration would be (280/350) 80% of the acceleration rate at 4,500?

I have to tell you, my butt dyno sure doesn't feel that way. The car keeps pulling harder to about 6,000-6,500 and then keeps pulling at about the same rate until I am forced to shift. When the car was stock, you could feel the acceleration drop off past about 6,500, and I suspect the power curve would have reflected this as well. Stock or not stock though, the torque curve has always turned down around 4,500 give or take.

And let's pretend that the engine could keep revving to 10,000 rpm. Extrapolating that graph, it would be at about 200 lb-ft @ 10,000 rpm, which is about 380hp. So from about 6,000 rpm to 10,000 rpm the power would be about the same. I would expect the car would accelerate at about the same rate through that whole range. I would not expect the acceleration to keep dropping off as the torque curve drops off. Is that incorrect?

 

[QUOTE=dan0617;1563221466][QUOTE=LT4BUD;1563221308]

but in any given gear, acceleration will in fact match the torque curve...as in a=f/m (acceleration= force/mass)....torque is the relevant measure of force!!!! [QUOTE]

I am by no means wanting to argue here, but I honestly THINK horsepower is the relevant measure of force. I think, I'm not sure.

I am sure!!!
.

Your torque can be falling off but if your horsepower staying dead flat after 5252, and the acceleration rate can be staying the same.

Acceleration will follow directly the rear wheel torque curve and unless you shift gears, wheel torque mirrors motor torque

 

Acceleration will drop off as rear wheel torque drops off..

BTW, the optimum shift point based on your dyno is 7000 rpm..

 

No, I'm not saying that I was responding to your note about the gears not increasing the torque at the wheels (at least that was my understanding of your post).

I'm sure you realize that the old butt dyno is not exactly the most scientific and reliable method of analysis. If you really want to know, datalog your MPH versus time on a few runs holding it in 4th gear (or whatever gear you choose) and you can then see where the rate of acceleration peaks and what happens when. You could even do this with one of those GTECH's. Too bad I left mine at home.

The torque at each RPM is what you would use to calculate the force that the car's tire applies to the pavement. If the torque drops, the force is going to drop. Since Force=Mass*Acceleration or Acceleration=Force/Mass, you can see that as the force goes down, so does the acceleration (unless there's a change in mass). It may still feel good and you're obviously still accelerating, but those are the laws of physics.

 

I've got numerous datalogs of my car in 3rd gear (which tops out at like 117mph, 4th would be hard to do on the street!). I will do exactly this. I'm interested to see what it shows. I realize the butt dyno is not very calibrated. And I'm certainly ready to eat crow. It just seems very odd that acceleration would map to the torque curve and not the power curve.

 

I got a good one.....

Horsepower = Honda Prelude Vtec with a Turbo....my buddy has one. The car is a turd in the lower RPM range, no low end torque. But, when she spools up, hold on to your a$$ cause your going for a ride. Its a fun little car to drive.

Torque = 1996 Corvette 383 LT4.....my car will shred the tires off with a blip of throttle in 1st and 2nd gear with the factory 3.45 rear gears. Lots of low end torque. But I guess I have the best of both worlds....

Basically what I saying is go for a ride in any smiler car as the 2 i mentioned and you can feel the difference in horsepower and torque.

 

Exactly!

Take a Formula 1 car, they produce 850 hp at roughly 18000rpm.
They don't stop accelarating at those rpm's, to the contrary if it would be possible those engines would rev till 25,000 rpm and over.
I believe that torque is what gets you moving and horsepower is what keeps you accelarating after the torque starts dropping.