Obviously you can already tell I'm far from a mechanic by asking this question. :D

Okay, why does the L98 have more torque than the LT1? Is it because of runner length and/or cam profile?

Reason is, my friend has a Mustang and just bought a new engine for it. His brother-in-law just bought a new engine as well. One is rated at 400 hp, and the other is rated at 365. I told him that between the L98 and Lt1, there was like 50 hp difference and really only like a 0.3 second difference in the 1/4 which could really come down to who is the better driver.

I asked him who had more torque, he said his was supposed to have 390 and not sure about the brother-in-laws. He then asked me what will give me more torque, and what increases torque?

So, here it is , corvette brothers, what increases torque?

 

Torque is the real power the engine makes, HP is just a function of it that keeps the party going at speed and helps you accelerate to really high speeds.

The reason why the L98 makes torque and little HP is mainly the runner length, theyre too long to adequately feed the motor at high rpms and so the HP numbers fall off dramatically. They feed air at low rpms very well and at a high port velocity, so the L98 screams off the line. The LT1 has short runners, and so the air doesnt come in at high velocity off the line (there isnt that much difference in cam duration) but because they are short they can feed the motor very well at high rpms and the HP numbers go way up.

Anything that lets the engine breathe better will increase torque, but if you make the distance that the air travels increase, the HP numbers drop or drop at a higher rpm.

 

Very well said !!!
I'd like to add in the case of the difference in cars .... I think we're talking two engines and two cars ... Mustang and a Vette??
If this is Correct ... don't forget to add in the Equation along with the driving skill you mentioned .. Weight!!
A fox body mustang can weigh as little as 2700 pounds ... and a vette well Shoot ... uhmm lets just say more than that. :D

Mark A.

 

torque, is basically the twisting power of your engine, theres 9 basic ways to increase torque
(1) increase the efficiency of your cylinders fill rate, things like longer runners that add ram inertia to the intake or headers that help scavage the cylinders are in this area
(2)increase the stroke length,(stroker crank) increases the leverage the piston has and in most case adds displacement allowing a greater amount of fuel/air mix to be burnt
(3)increase the compression ratio, this allows a more efficient burn and a greater percentage of the fuels energy to be used (UP TO THE DETONATION POINT of THE FUEL)
(4)increase displacement,, more fuel/air mix burnt per power stroke adds more force on the piston
(5)increase the transmission and/or rear gearing ratio, (example change from,3.08 to 3.73 allows about 20% more power strokes for a given distance traveled) this allows more power strokes for the distance traveled due to the engines increase in rpms over a given distance
(6) super charging, increases the volume of fuel/air mix that is stuffed mechanically into the cylinder, allowing a effective increase in displacement
(7)ADD a high stall converter, this allows both more power strokes per minute and a torque multiplication in the converter
(8)nitrous, allows a far greater amount of fuel air mix to be effectively burnt per power stroke
(9) reduce mechanical losses, things like synthetic oil, windage trays,larger oil pans , air foil design crankshaft counter weights,lighter rotateing assemblys, allow a greater amount of the power produced to reach the transmission by moveing the spinning assembly away from the oil sump.
here read this also http://www.69mustang.com/hp_torque.htm











[Modified by grumpyvette, 10:12 PM 5/12/2003]

 

Thanks for the info guys. I know the 400 hp/390 tq Mustang will be shooting for me, but he just really wants to beat his brother-in-law bad, haha. They're both Mustangs, one is 87 and other is like 91 I think. Both same body style.

I just told him about the torque differences between the L98 and LT1 along with the hp differences. Now he said, he has to make sure he has more torque than his brother-in-law now. Haha, they're pretty competetive.

When that Mustang comes shooting for me, I'm pretty sure I'll take him, but if not, a little spray will make sure I'll kill him.

 

This was the explanation in Charles Probst's book on Corvette Fuel Injection

The long runners are "tuned" for low(er) RPM operation. What happens is that the air comes rushing down the runner at a certain velocity. As the valves open and close, the air either passes through the valve or "bounces" back. You end up with a wave of air that's resonating back and forth through the runner. The velocity of the wave and the length of the runner determine the wavelength (the time it takes the pressure front to to the round trip). At certain RPMs (happens to be the low RPM range for the L98) the opening of the valve coincides with the peak pressure of wave and you get a mini "ram air" effect, enabling more air to get into the cylinder. At higher rpms the air pulse is out of sync with the valve timing and the engine power suffers.

 

Another way to look at is HP is determined by what RPM your torque peak occurs at. For short bursts torque is king, but if you have room to build rpms, the L98 falls on its face. The best way to differentiate between HP and torque is to comparison drive. I've always known what torque feels like because of the Vette. 2 weeks ago I drove a '99 Porsche 996. Over 340 HP, but only something like 230 lb/ft of torque. Couldn't even spin the tires off the line but it turned into an absolute rocket above about 3000rpm's. Now I know EXACTLY what the difference between HP and TQ is! :D I know this is a little different than what you originally asked, but it seems to be the way this thread is going.
Steve

 

Torque is a measurement of an engines ability to do work.
Horsepower tells you how fast it can do that work.

 

I'm not going to go into a long explanation, becaust it feels like I have several times in the last month or so, but I do need to make one clarification to the above posts:

Torque is NOT a measure of power. Torque is work, and Horsepower is power. Work is a force multiplied by a distance (cylinder pressure x piston area x EFFECTIVE stroke length...not the 3.48" of a 350 SBC) whereas power is work / unit time. Very different meanings, but horsepower is a function of torque...plain and simple. Changing to a higher stall torque converter will not improve torque, but may allow the engine to get into it's power band faster. Rear gearing does the same thing (though it does change the road torque, but it all washes out when you look at horsepower numbers).

The short and simple answer is to not worry about how much torque the motor is making, but rather the power to weight ratio of the two cars and how long they can each spend in their respective powerbands. Without looking at driver effects, the above two things will tell you who will win a race. Torque is nice for conversation and bragging rights, but horsepower wins races.

 

real torque answer - torque is the application of force on a lever arm.

The force pushes the piston down. simple isn't it?

Increasing, or determining for that matter, force is not so simple. To increase the force on the piston you must increase the pressure:
1) increase temperature
2) increase mass
3) increase heat coeficient (okay this star trek so don't ask unless you really want to know).

1) You can increase temperature on the power stroke by a) increasing timing, b) changing fuel type, c) Allow the air charge to heat up (cast iron heads over Al heads), or d) optimize the air fuel ratio for temperature.
2) You can increase mass by just putting more of it in there. This is where having great flowing intake, heads, and exhuast come into play. Oh and don't forget forced induction here (turbos and superchargers)
3) As stated before this ain't star trek so there's no changing the laws of physics...or at least on the fly.

Finally, Horse power (energy) is the integral of force applied over a unit of time (Rev per MINUTE)

basic engineering my friend :U

 

Let me add to that......Effectively using your HP wins races and makes a car fast.

That is why I think so many guys do not run anywhere near what they should. They stick big gears in the cars and can't effectively put the power to the road. There is no way Corky and I would be pulling the 60' times we are with bigger gears. At least not without major mods to the rears.

Gears and overrevving engines are probably the two biggest offenders of slow ETs, just my .02 :cheers:

 

Nah, you cant call it work either, its torque, thats the only thing you can call it. The units are the same yes, but its not the same thing.

For the layman though, you can call it work or power (since power is just work/time).

 

I always think the simple way to look at this is that torque is the horse power of the engine for 1 revolution of that engine. So if you want more power you either do more revs, or you increase the power per rev(ie torque) at the revs you are doing.

Easy!

 

Well, you're right except for the fact that torque and horsepower are equal at 5252 rpm.

 

I haven't seen any of you get it right yet. Here's a link that will give you all the answers to torque and horsepower.
http://vettenet.org/torquehp.html

 

Of course they are. but this is only a matter of the units used to measure torque and horsepower."Except for" is not an issue.

I repeat torque is the horsepower for 1 revolution of the engine. (5250 comes into it when you convert the units these things are measured in)

My point is that if you understand that simple fact., all this torque /horsepower argument becomes irrelevant.

If you cant do many revs, you need a lot of torque.

If you can do lots of revs, you dont need so much power per rev (torque!!!)

Think about this, it really works

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:) :)

 

Don't forget; you can have measured torque with zero rpm, hence zero "work".
A steam engine develops its max torque at zero rpm (so I've read).
So, it is not the horsepower of one revolution, either.
It is simply the 'twisting' force acting on a mechanical member.

Larry
code5coupe
:seeya

 

Disagree.

Torque is the potential to do work.

Power (horsepower) is the amount of work performed over time.

Peak Torque and Peak HP have no meaning except braggin rights.

It is the power curve of the engine that matters - across the usable rpm range. Then the power curve must be mated to the correct drivetrain, gearing and traction for the application. After that it's up to the driver.


Pete

 

Power is just work/time yes. P=F.v
You can call it a potential to do work in the same way that a regular linear Force is the potential to do work on an object, this is a real misconception/misnomer among laypeople.
F=dV/dx, N=dV/d(theta)

Im guilty of it as well, but only because I'm trying not to confuse people on the forum about the real physics. I realize that they dont want a lecture on the subject so I dont break out my Mechanics books on the subject.


[Modified by vader86, 11:31 PM 5/13/2003]

 

Well, by now your friend has a few ways to increase the "torque" (i.e. build more low end torque) of his engine.

However, as mentioned, he still has to put it to the ground, so it may benefit him to idealize his power band to his car's drive train. That is, tune overall perforamnce for the best 1/4mi ET.

At the strip he can see his "torque" at work by reduced 60' times. But he still needs enough top end torque (known as HP) to take the win stripe.