I know this has gone around a few times (like maybe 1000) and I've read a coupe of recent versions. This time I want to participate and ask a couple of questions....

When romping my 6-spd L98, I'm happy thru 2nd gear. It pulls well and seems relatively fast. But, when I shift to 3rd, the fun goes away. It doesn't pull that well anymore.

Conventional wisdom would say HP is to blame, but when you first shift, the rpms aren't that high yet. I don't remember for sure (cause I haven't driven it since last summer), but I'm thinking the shift to 3rd falls back around 3K-3,500rpm. I know the TPI is supposed to be done around 4,200 and I guess that's about right. So, if it were nearing 4.2K soon after the shift, I kindof get it....

-- BUT --

1) The L98 is supposed to be the "torque" motor. Does the LT1 feel better when you shift to 3rd? If so, I'm a little confused because the LT1 and the L98 have the same torque rating (though I'm thinking the LT1's occurs at a higher RPM)? Does that make it feel better in higher gears? And, in lower gears, does the LT1 remain "fun" because any low-end torque it lacks is made up for by the gearing?

2) When you want a car to pull better up high, is it more HP you want or just raising the torque curve to occur at a higher point? (Obviously both couldn't hurt).

3) Does this help me determine how an intake swap might feel? For example, if I switched to large tube runners, I would anticipate the HP and torque to increase from 3K to 4.5K rpms. I could assume the shift to 3rd gear would be more fun with the additional torque. OTOH, if I switched to a short-runner intake, the torque would shift upward and I'd see an increase in upper end HP. The car could be revved higher and shifted later. That means the motor would have more leverage (at a higher speed) when shifting to 3rd. Again, the result might be more "fun" -- even though the max torque may stay the same -- or even decrease....

I'm not sure it's ever been said this way, but here's my unscientific perspective on torque vs HP....

Torque seems like the leverage the motor can exert on the car at any given moment in time. HP seems more like the rate that the leverage is changing. So torque is a measure of how much leverage can be applied to a car. But once a car moves faster and faster, something else has to take over since the leverage drops off. And that "something" is HP. And, I assume the HP is a measure of other things like the motor's ability to rapidly move air vs apply leverage?

This view helps me understand how torque drops and HP climbs -- when viewing a dyno. I don't have any idea if this is close/accurate but it seems logical.

Any experts wanna "set me straight"?


gp

 

HP is only a number computed from torque anyway. The faster you go, the more torque is required to overcome the many physical forces you're fighting to maintain the same rate of acceleration.
As I like to say, good HP numbers sound impressive, but good torque numbers make it impressive!

 

If you shift the torque curve up you will also increase power. 345 lb-ft at 3,200 rpm is 210hp. 345 lb-ft at 4,200 rpm is 275hp.

To give you a general answer to what I think you are asking. The power you move the car through is what matters. In 1st gear you go through the whole rpm range from about 1,000 to 4,500 or so. So you get the full area under the power curve. From 1,000 to maybe 3,000 the L98 makes as much or more power than most other motors in the same rpm range (fairly similar to the LT1, LT4, and LT5). So there, with similar gearing and vehicles, the L98 isn't too shabby.

However, it gets worse as the revs go up. And once you get going, you will never see 1,000-3,000 rpm again. As you noted, the shift points just don't drop you that low.

So that is about the only advantage the L98 has. A motor more like the LT1 will be putting more power down once it is rolling. In addition it also has more rpm range, meaning it can go further in a gear (given the same gearing) and also will be higher in the rpm range after a shift (shifting at 6,000 vs 4,500 for example, drops rpm after the shift to maybe 4,500 vs 3,400 or something) where the higher revving motor further enhances its power advantage.

When talking L98 vs LT1 though they really aren't hugely different. The power peak on the LT1 isn't all that high either.

That I believe more or less explains the power advantage. There are other advantages to more rpm.

Personally I think it is easier to explain when the difference is more pronounced. So I'll take the LT5 vs the L98. Both have similar torque down low (actually the LT5 has more everywhere stock). But the LT5 builds as the revs build, the L98 doesn't.

If you took both of them with the same gearing, the LT5 could run 1st gear out to about 62mph or so. The L98 runs out at like 38mph. So if you wanted to take away the low-end advantage of the L98, it is very easy. Put more gear in the LT5. Since it runs to 7,000 rpm you can use way more gear. Put in 4.56:1's or something. 1st gear would still run out higher than the L98 with stock 3.33:1's. In fact you'd need something like a 5.18:1 in the LT5 to have the same speeds in gear assuming the L98 has to shift at 4,500 rpm.

Now imagine 1st gear with an LT5 with 5.18:1 gears behind it. You wouldn't think the L98 was a low-end torque-monster anymore.

So in my opinion, you can't go wrong getting more top end and more rpm range. Of course it's total power that matters, so if the car is a dog in the 1,000-4,000rpm range, you'd really need to be accelerating for a while (to a high speed) to offset the lack of low end with a large top end. If you were only accelerating to the speed limit, or to the next intersection, the car would really seem like a dog. But as said, to a decent degree you can vary gears to compensate.

 

Just to be clear, I am not suggesting that torque isn't necessary. Torque and horsepower are mathmatically linked. You can't have one without the other in a gasoline engine.

However, I think the whole "low end torque" thing is fantasy so some people can feel better about their car. Not that the L98 is something to feel bad about. It is what it is, and goes as fast as it goes regardless of any of these discussions.

But on these more recent motors, GM has never made a Corvette faster by targetting low-end torque. The LT1 has less low-end than the L98, yet stock for stock it is faster. The LT4 I believe has a pretty similar low end to the LT1, yet is faster. The LS6 had less low-end than the LS1, yet it's faster. Now when you talk LS2, LS3, LS7, etc, of course the torque went up on the low end, but only because the motor displaced more.

 

1. What is wrong with low-end torque? What good is a super-peaky torque curve? How are you going to utilize that high-rpm power when it takes ages to pull your way up to the high rpms?

2. The LT4 in fact has a ton more low-end torque than the LT1. Maybe someone will post the picture from the owner's manual that has side-by-side dyno graphs of the two; the LT1's peaks severely up high while the LT4's looks totally flat in comparison.

3. You "forgot" to mention how much low end torque the LS1 makes. Rumor has it that when the GM engineers were planning their next engine, they did a blind comparison with one car that had the flat-torque-curved LT4, and another car that had the high-revving LT5. Without knowing which was which, all agreed that the LT4 felt like it had more kick, which makes sense because the average corvette driver is not going to be hanging out at 6,000 RPM constantly and would like some torque in the range that they're actually using. This little experiment supposedly influenced the LS series by giving them more low-end grunt and a more favorable flatter torque curve.

Remember, the number that's at the peak of a power curve isn't what's important; it's the area under the curve (the integral, if you're familiar with math) that actually moves the car over time. Flat torque curves provide more area under them than spikey peaky curves.

 

 

Torque is a force. If you weigh 200 pounds and you stand at the end of a one foot long breaker bar, you are exerting 200 ft.lbs. of force (torque) to the socket on the other end of the breaker bar. It doesn't matter if the socket turns or not, the force is there.

Horse power is the measure of the ability to do work. Work is defined as "force through a distance". Therefore, horsepower measures the distance a weight can be moved on a given amount of time. Through obsevation, James Watt defined a "horsepower" as the movement of 550 pounds one foot in one second. If you care to do the math (I have) that makes horsepower equal to torque times rpms, divided by 5252. HP = [Tq X RPMs] ÷ 5252.

If you consider the relationship between torque and horsepower you soon realize as Aurora40 said in the first paragrah of post #3, that the either/or question you ask in #2 are the same thing.

RACE ON!!!

 

There is one and only one thing that makes a car accelerate forward and that is the force the rear (drive) tires exert on the pavement!!!!!!

Basically that force is torque!!!!! To convert this to horsepower you multiply the torque by wheel rpm.

One really neat concept is that wheel horsepower equals motor horsepower!! So the more horsepower a motor is producing at any instant the more rear wheel torque you have and the more acceleration you have.

What is really needed is maximum horsepower with proper gearing to keep the motor at or near the horsepower peak, which keeps the rear wheels near horsepower peak, which maximizes rear wheel torque which maximizes acceleration!!!

So horsepower is king.......lower horsepower but higher torque motors are neat for the street because we have such poor transmissions....what is really needed is a CVT able to handle the power of our V8 engines...then horsepower would be king..

More to the story, but a part of my two cents...

 

And that CVT had better have a manual adjustment. I hate how CVTs now are all automatic, when it would be trivial to make a manual control. An auto CVT is worthless to anyone who cares to manage their throttle and RPMs independently.

 

THANKS!!! I did not understand this. In fact, I had mistakenly thought torque lowered as HP rose (at least in some circumstances). This was a result of some (apparently) erroneous dyno graphs in the super rodder article to which I originally referred.

For example, here's one....


Note that the beginning of the Holley torque curve is above the stock TPI torque curve. It shouldn't be (right?) When I reviewed the stock TPI dyno, I see they labeled the WRONG line! Here is the link to the entire article: http://www.compcams.com/Community/Ar...?ID=1737510521

For comparison, I added dots to show where the large tube runner intake would fall. Because the HSR is a little lower (than stock) until 4K rpm -- while the LT setup is above stock in that range -- the LT setup would have a big margin in the first part of a race. On the streets, this might even be the better setup.

And, it's my reason for trying to understand the torque vs HP relationship.

 

An efficient CVT that keeps the engine RPM at the maximum horspower rpm is the ideal transmission for acceleration as in drag racing...

No throtte management or rpm management required!!!

 

The ZF6 in my 92 pulls hard through 4th gear.

 

Great, so what about when you're not drag racing?

 

except I thought this thread was focused on achieving maximum acceleration as in drag racing...

 

I looked at the intake article again. (see link in my previous post above). I can't friggin' believe it, they screwed up the labeling the torque curve for the miniram, superram, the single-plane, and the HSR!!! EVERYONE of the short-runner intakes has the torque curve mis-labeled. (In each case, they labeled the factory intake's curve as the short runner intake). )(*&#$_(*&#_& IT!!!!!!!

That led my to a false conclusion about the relationship between torque and HP. One, quite frankly that seemed plain wrong. Now I fell MUCH better!!!!

I'm pretty sure I know which intake is the correct one for my application now....



gp

 

I cant really add much to the above since it has been covered well.
I can only add my experience and opinion.
I had a modded 6 speed L98, a 90 model that went 13.50s at 105mph and put down 36x rwtrq and 26x rwhp
That car was a blast to drive in 1st and 2nd gear but as you said it ran out of steam on top. My mods moved my tq/hp curve further up the rpm ladder and it helped some. The dyno results showed it to peak about 500rpm higher than stock. It had the stock 3.31 gears too.

Switch to my present car. A 96 LT4. I am the 2nd owner and it was %100 stock down to the paper filter when I got it. It didn't have near the low end and the first couple months I had it I was a bit disappointed in its performance (based on seat of the pants) but I got it to the track and it ran 2 tenths faster and 2 mph faster. I've added a couple mods since then and it feels about like my 90 did down low now. The 4.10 gears made the most SOTP improvement down low. Where as my 90 dropped off at around 5k rpm my 96 is just getting interesting.

 

Someone made it real simple for me once.

HP is torque over time.

Let's say you have 500 FTLBS of torque, you can move X amount of weight.

If you have low horsepower with that torque, it will take longer to move the same weight compared to a higher HP motor. The higher the HP with the torque being the same the faster the work gets done. Either way, it gets done.

 

http://en.wikipedia.org/wiki/Straw_man_argument

Where did I say low-end torque had something wrong with it? And where did I say a super peaky torque curve was good?

The graphs are in the owners manual. Define a "ton". Regardless, I doubt the engineers goal was to make the car faster via more bottom end, and then the top end was just an accident.

Actually, I specifically mentioned the LS1. As I said, it makes more torque in the lower rpms than the LS6. Yet stock for stock, the LS6 powered Corvette is faster.

As for my understanding of math, yes I've heard of an integral. In fact if you read my post I said basically the same exact thing. Total power, or power under the curve is what is important. Low-end torque with no top end is not the way to achieve that.

 

Well, hmmm, no, that's not what your post said at all. It might have been what you "thought" but it isn't what you "posted." Also:

 

Torque vs. RPM has everything to do with RPM and nothing to do with what gear your in or what speed you're going.

"torque" simply means your car makes its power lower in the rpm band.

That's it.

Once you're in the powerband, the horsepower/weight ratio between shift points tells all. Nothing else matters. Don't think of tq/hp as different things, they're not. In fact, ignore torque entirely.

HP wins races, TQ gets people to brag on the internet about their slow V8s.