Okay,
First of all, thanks to all for helping to explain this to me.
I need a little explanation between torque and horsepower. I thought torque was what gave the vehicle towing power. My TV is 94 suburban (non vortec). If I am following the answers I am getting, if I am running at my peak torque rpm’s (2800), my TV should be able to maintain it’s speed easier than if I were running 4,000 RPM’s which would give it its peak horsepower. Would higher RPM’s put more stress on the tranny, or are RPM’s a non-issue in regards to heating the tranny? I talked to a guy the other day that used to work at a tranny shop. He told me OD puts the most stress on the tranny that I have and I should never tow in OD. He also told me 2nd gear would put the least stress on the transmission on long hills. When I asked if first gear would put even less stress on the tranny, he told me first gear would put more stress on the tranny than 2nd gear. Your thoughts?
Hey....dont all be so quick to slam the 4000 rpm crowd!...the reason you hear that number a lot is because the NEWER V8s have a higher rpm at peak Torque. That is what I remember from mt 5.3 GMC. Totally different that the older 5.7
A torque converter that is unlocked will contribute to heating the transmission. If the torque converter is locked the transmission will run cool at any rpm. If the torque converter is unlocked there will be heat generated in the fluid. The more it slips the more heat. The torque converter will slip more at lower rpm especially below 2000 and will get much worse below 1500. Some vehicles will lock the torque converter in second, mine does. I don't think any allow the torque converter to lock in low gear. I believe this is why the transmission guy says low is harder on the transmission. If you can scale the grade in second at 3000 rpm and you want to slow to under 25 mph to use low gear at the same rpm I think you would be fine.
My torque converter will unlock at about 2600/2750 if in second gear and speed is declining. In third my torque converter will unlock at that same rpm just before the downshift to second. You need to be tuned in to when your TC unlocks. You will see 100 to 300 rpm change as it does.
2001 F150 SuperCrew 5.4 Lariat Offroad 4x4 Tow Package 4.10 Truetrac
2006 Keystone Springdale 249FWBHLS
12K SuperGlide, KGE3000Ti 2.3kw rated 2.6kw max
Frank's voltage booster, Prosine 1800 powered by 4 GC2 batteries
mrad wrote: Okay,
First of all, thanks to all for helping to explain this to me.
I need a little explanation between torque and horsepower. I thought torque was what gave the vehicle towing power. My TV is 94 suburban (non vortec). If I am following the answers I am getting, if I am running at my peak torque rpm’s (2800), my TV should be able to maintain it’s speed easier than if I were running 4,000 RPM’s which would give it its peak horsepower. Would higher RPM’s put more stress on the tranny, or are RPM’s a non-issue in regards to heating the tranny? I talked to a guy the other day that used to work at a tranny shop. He told me OD puts the most stress on the tranny that I have and I should never tow in OD. He also told me 2nd gear would put the least stress on the transmission on long hills. When I asked if first gear would put even less stress on the tranny, he told me first gear would put more stress on the tranny than 2nd gear. Your thoughts?
Torque and horsepower are different ways of measuring the same thing (engine power). As was previously posted the relationship is: HP= Torque * RPM / 5252 in this equation you can see that horsepower is torque per period of time (rotations per minute). That is because torque is a measurement of force and horsepower is work done (ie force per unit of time). I’m not going to get into why engines produce torque or horsepower peaks at what time. I’m just going to say that the more horsepower produced the more work that can be done.
There is no such thing as overall “stress” on a transmission. Different gears and conditions stress different parts. In 3rd gear (1:1 ratio) all the planetary gears are locked together and the transmission rotates at the same speed as the engine. In addition the torque converter can be locked minimizing the heat in the transmission. In my opinion this puts the least “stress” on the transmission.
With a 94 Suburban I think you have a 4L60E transmission (I think it’s the same as my 97), which has a reputation as having a “weak” overdrive. I don’t use overdrive at all while towing.
ttstansfield wrote: Why did they stop making the 8.1?????? (I know I know...diesels have taken over!)....but WHAT a flat torque curve....beautiful!
If you could explain many decision that GM has made then you should be their CEO. GM is very good at shooting themselves in the foot and bringing out products on the down curve. They were 5-10 years late on a Diesel. GM could have been the dominate diesel if they had been on the ball. Dropped the 8.1 when it may have become a big hit. If you plot prices for gasoline and Diesel the last 5 years you should not be surprised at the current trend. The 8.1 was a great towing machine.
mrad wrote: I need a little explanation between torque and horsepower. I thought torque was what gave the vehicle towing power.
Most people do not understand the concept of power (which is often measured in HP). Power is NOT strength, rather it is strength combined with speed. Torque is strength. RPM is speed. Power is the combination of the two.
cronus wrote: Torque and horsepower are different ways of measuring the same thing (engine power).
Torque and horsepower definitely do not measure the same thing. Although they are related, they are two different things completely. Torque is applied to produce work, i.e. to cause something to move. Power is how fast that work is accomplished, just like speed is how fast a certain distance is travelled. Few people confuse distance travelled with speed, but for some reason the similar relationship between work and power is often misunderstood.
mrad wrote: if I am running at my peak torque rpm’s (2800), my TV should be able to maintain it’s speed easier than if I were running 4,000 RPM’s which would give it its peak horsepower.
It's not that simple. First of all, those torque/HP curves assume wide-open throttle. If you don't have the throttle pinned, you're not matching the curves. Second, it depends on how fast you want to go. The speed, coupled with the weight, angle of incline, and frontal area of your rig, will all determine the power (not torque) required to get the job done.
For climbing or accelerating, you want extra torque at the rear wheels, not necessarily at the crankshaft. Running a lower gear will always provide more torque at the wheels. In other words, you will get more rear-wheel torque by running a lower gear at max engine HP than you will by running a higher gear at max engine torque.
In short, run the RPMs and gear that allow you to climb the hill at the speed you want.
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