Torque vs. Horsepower

[-Josh-]

Originally Posted by tr0ike

To keep my own ill-advised miseducated questions/statements seperate from the original post ... a few things I think I know / wonder about.

*I've heard that torque is merely some simple equation of horsepower / RPM, or something .. don't remember what the factors were.

*I've also been told that horsepower really only comes into affect in higher speeds, i.e. freeway/top gear acceleration. The Top Gear (TV) episode with the Lamborghini Murcialago (sp) vs. the Mitsubishi Lancer Evo VIII (whichever special edition it was), where they place the Mitsu and some Euro econobox in top gear and accelerate - and the econobox pulls away from the Mitsu, which has no HP in lower RPMs/speeds - seems to demonstrate this.
I suppose gearing has a lot to do with it, but is there a general speed / RPM range where HP overtakes torque in importance?

*Why is it that diesel engines put out such massive torque? VW's 1.9L TDI, for example, puts out (IIRC) 90hp but 155 lb-ft of torque

*I also notice that many factory turbo cars have equal HP/torque numbers ... example: IIRC, Subari Impreza WRX STI has 300hp/300lb-ft.

*Why do SOHC engines produce more torque than DOHCs, and have lower power curves? For example, my VW has a SOHC 2.0L producing 115 hp @ 5400(?) rpm + 122 lb-ft of torque @ 3000 rpm. My mother's Civic I drove before I bought my own car has a DOHC 1.6L (non-Vtec); it puts out the same 115hp (at a higher RPM) but I believe only 111 lb-ft torque (likely also at a higher RPM). Does it have to do with the higher compression of SOHC engines somehow?

*What is better? Which do you prefer for various daily/racing applications?
I hear torque is better for average/city driving, as most people don't operate in high RPM ranges. If I were to race against another car with a bit more hp but a bit less torque than my car (i.e. VTEC Civic), I presume my car would be ahead at first - due to quicker shifts and more low-end power - but eventually the civic would gain/pass?

*Why are most engine modifications (intake/chip/exhaust etc.) focused on HP only? Do they actually bump torque a bit as well, but only advertise HP? Is there any way to bump torque? Would it be worth it, or is increasing HP better?

I'm certainly not asking for someone to answer all of these, but any insight/expansion/correction/clarification whatsoever on these, or other topics, would be greatly appreciated

1) There is an equation, and i used to know it, however in the whole scheme of things, unless you're an engineer building engines...you dont need to know it.

2) Horsepower is not some...thing, that just comes and goes at different speeds or RPM's, horsepower is always there, it's just that engines operate at different powerbands through different RPM ranges, the reason the mitsu got pulled on is because it was waiting for the huge turbo to spool up on it, without that turbo that car is probably a high 15 ssecond car. And yes gearing does play a factor in it, a huge factor.

3) Generally Diesels produce more torque because of how they operate, you take a gas engine like the 1.8T the VW's use and look at the TDI, and how general combustion works in each. Gas engines operate with air, fuel, and spark each revolution, and combustion pressure isn't nearly as high. Diesel engines on the other hand only require fuel and air, and glow plugs to merely start the combustion process, after that diesel engines operate with high combustion pressures, and this is due to the fact that diesel gas only requires compression, the pressure is so great that it creates it's own combustion without the use of spark, there are other factors but im trying to keep this short.This is a great explanation here(and i'm not that good at explaining things)

4) When you strap a turbo on a car, it creates displacement, much like cubic inches on an engine, so not only do you get horsepower, but you also get good torque with turbo's, notice turbo's are also used on diesel engines; low compression ratio's are ideal for turbo's.

5) That statement is not necessarily true, it's all about the type of engineering that goes into an engine, and the components used. There's more factored in to an engine's horsepower and torque than whether it's SOHC or DOHC. Compression ratio is merely where combustion takes place in the cylinder, it can have an effect on horsepower and torque readings when you rebuild and engine or set timing but in your case it's just two different engines.

6) It all depends on the car really. Horsepower and torque are always there together, other than that i think the debate should be, do you want a car that gets good gas mileage, or a gas hog? And there is more that gets factored into a car besides horsepower and torque, such as gearing and horsepower and torque RPM range, also, how it gets the horsepower, N/A Turbo or S/C.

7) Once again, HP and Torque work one in the same, adding HP will at the same time add Torque, people are just more commonly associated with HP than Torque, so they advertise that. Messing with the timing, or adding a component that adjusts timing can increase horsepower and decrease torque, or vice versa...it all depends on what you add and what it does.

There's a shit load of factors that go into increasing horsepower and torque. There's also a lot of factors that go into properly tuning a vehicle, some people think you can just throw on a turbo or supercharger and be done with the car, not knowing that in the long run, or right away that there's many other things you have to do for the car to perform properly; such as fuel and ignition system, gearing, timing, new RPM powerbands(when to shift). Questions like, will i need a chip with these new injectors, fuel rail, and pressure regulator that i just put in to compensate for the huge turbo that i put on my car a few weeks ago, and what chip will i need for it? There's a lot to learn about cars, and you wont learn it all in a period of months, it takes years of experience and mistakes to know about cars and working on them/tuning them properly.

I hope this helped, cause i'm really not good at explaining things, and i hope i didn't confuse you even more. This is stuff that i know and just try to put it to words, which isn't easy.

[tr0ike]

Awesome, thanks for all that Josh! Didn't mean for someone to take so much time answering

Definately helped answer some of my curiosities though. I know a lot more about cars than I did when I got mine (when I knew nothing), but its definately a life-long learning process. Good thing for the internet, or I wouldn't know a damn thing.

I don't plan on adding any forced induction to my car, its a daily driver / my only car, so probably just intake/chip/exhaust at some point to make it a little more peppy.

[Hypsi87]

Originally Posted by TheStang00

torque is a torque arm multiplied by the force applied to that torque arm. so the reason diesel engines have such massive torque is because they have massive torque arms. as you may or may not know diesel engines do not use spark plugs, instead they compress the fuel mixture to the point of combustion. they may have a compression ratio of 23:1. a normal gasoline engine might have something like 9:1... give or take a few.

Ok first of all, there is not Air/Fuel mixture on a diesel einge. When the piston is on it's intake stroke, all the engine does is bring AIR only into the cylinder. Then when the cylinder is compressing the air on the compression stroke. When the piston reaches the correct postion, the injector is actuated and fuel is shot into the cylinder at 20k+PSI.

And common compression raitos for a diesle are in the 15-18 to 1

but since they have not Air/Fuel mixture to pre deatoniate. you can run som crazy boost

[-The Stig-]

Originally Posted by Hypsi87

Ok first of all, there is not Air/Fuel mixture on a diesel einge. When the piston is on it's intake stroke, all the engine does is bring AIR only into the cylinder. Then when the cylinder is compressing the air on the compression stroke. When the piston reaches the correct postion, the injector is actuated and fuel is shot into the cylinder at 20k+PSI.

And common compression raitos for a diesle are in the 15-18 to 1

but since they have not Air/Fuel mixture to pre deatoniate. you can run som crazy boost

And what could you possibly know about Diesel engines Mr. Andy?




Kidding, Just for those who don't know... Hypsi87 works for Catepillar and all those big ol diesels.

[TheStang00]

Originally Posted by Hypsi87

Ok first of all, there is not Air/Fuel mixture on a diesel einge. When the piston is on it's intake stroke, all the engine does is bring AIR only into the cylinder. Then when the cylinder is compressing the air on the compression stroke. When the piston reaches the correct postion, the injector is actuated and fuel is shot into the cylinder at 20k+PSI.

And common compression raitos for a diesle are in the 15-18 to 1

but since they have not Air/Fuel mixture to pre deatoniate. you can run som crazy boost

well my frickin bad... geez, im not a certified diesel mechanic sorry. but i said 23:1 or whatever... i have heard of that in diesel engines b4. atleast i was partially right... or atleast i think

[Hypsi87]

Originally Posted by TheStang00

well my frickin bad... geez, im not a certified diesel mechanic sorry. but i said 23:1 or whatever... i have heard of that in diesel engines b4. atleast i was partially right... or atleast i think

ez killer, I did not mean to be an ass about it. Remember, this is the internet.... Can't really show emoition.