Question on CR and Torque

[newage1928]

I was looking at some engine output numbers on older second gen camaros and many of the 305 and 350 v8s back then put out only 170 HP but also made like 280 some ft lbs of torque. How was this possible, was it because of the lower compression ratios of 8.0-8.2? Could someone please help me to understand how all of these things relate? Does a lower compression ratio mean more torque?

Also why is it that the 305s and 350s of the late 70's and ealry 80's only made 130-170 hp while the 305s and 350s of today make like 300+ HP? My 3.4 makes more that 130 hp.

[auto666]

Re: Question on CR and Torque

the reason power levels where so low was emmisions vs technoligy typically a lower compression ratio will net a little more torque but it was easier to get torque that hp and still comply with emission then

[Smoke Panther]

Re: Question on CR and Torque

Since horsepower is a measure of torque over distance, early engines were not as efficient as modern ones

[newage1928]

Re: Question on CR and Torque

I am not sure I understand, why was it then that a v8 back then made 140 HP yet 280 lbs of torque when I make like 140 HP with prolly 160 lbs of Torque. It seems I am less efficient and they were more efficient considering the difference in torque.

Did they get more torque because the engines usd up alot more gas?

How did they "get" more torque.

[CDNFB]

Re: Question on CR and Torque

Its all the design of the engine. A combination of these five variables in the design of an engine will determine torque (as well as HP):

1) Number of cylinders. The more cylinders the higher the torque because the power pulses are closer together and less rotational losses between the pulses.

2) Displacement. The bigger the face of the pistons, the more working forces are transmitted to the crank.

3) Cylinder pressures. The higher the pressure the higher the torque. More pressure more power

4) Stroke - the longer the piston travels (or stroke) the higher the torque. More time for the pressure to work on the piston and crank to produce power.

5) Parasitic losses (friction, geometric inefficiencies, etc…). The less you have of these, the more power gets put into the crank.

In your case of the V8 with 140 Hp/280 Torque. Because it had 8 cylinders, was of sizable displacement (300+ cu in) and a fairly decent stroke, the torque number is a bit up there, but because the cylinder pressures were not very high (to avoid detonation or knock cause of the quality of gas in those days was poor) the horse power was limited.

It’s the Torque that determines how fast a car can accelerate, and just for fun, I use the calculation HP=(torque X RPM) divided by 5252 to compare power outputs of different engines. For example,

My 72 400cu in V8 produces 325 HP and 420 ft lbs of torque at 3800 rpm. I hear guys bragging about how their Hondas make 300 HP, but they fail to mention that they only have 250 ft lbs of torque and to get that HP they have to turn 6500 RPM. Somehow they believe that they are on the same level as me. Not quite. I use the formula to determine how much more horsepower they need to match my torque.

420-250=170. So HP = (170 X 6500) divided by 5252. Which works out to 210. Adding this to the 300 HP they already have and you can say “At 6500 RPM, the Honda engine needs to produce 510 HP to match the 420 ft.lbs of Torque that I have.

Now remember that this is all theoretical, and if said Honda adjusted the wastegate controller to produce 510 HP, he would blow the doors off me cause it’s probably installed in an 1800 lb car vs my 3200 lb car and even though my peak torque occurs at a much lower RPM.

You have to remember that when you hear people brag only about their HP (especially 4 cylinder cars and short stroke engines), you are only getting half of the story. Torque is just as important as HP, and high HP engines with low torque outputs are difficult to race.

[skorpion317]

Re: Question on CR and Torque

Torque is the actual physical force that moves the car. Horsepower is an abstract measurement of torque produced over time. You cannot feel horsepower.

Older (late 70s/early 80s) V8 engines produced less horsepower because of lower compression ratios and inefficient designs. They still produced a lot of torque because of their displacement, however.

[newage1928]

Re: Question on CR and Torque

CDNFB,

Thanks alot that really helped me to understand the dynamics of an engine. Gotta love those ricers... :P

Does anyone know of any websites or reference materials that could also help me to understand the other sciences and physics behind the design of an engine? I thoroughly understand what all of the parts of an engine do and I could most likely strip and engine down and put it back together (just like legos :) ) But I would like to learn more!

I have seen all of the HowThingsWork.com pages on cars...

[skorpion317]

Re: Question on CR and Torque

CDNFB,

Thanks alot that really helped me to understand the dynamics of an engine. Gotta love those ricers... :P

Does anyone know of any websites or reference materials that could also help me to understand the other sciences and physics behind the design of an engine? I thoroughly understand what all of the parts of an engine do and I could most likely strip and engine down and put it back together (just like legos :) ) But I would like to learn more!

I have seen all of the HowThingsWork.com pages on cars...

Just look around on teh intarweb. There's plenty of websites that can explain engine design better than we ever could.

[mloaks]

Re: Question on CR and Torque

Mostly, computorized drivetrain mgt, electronics, and material improvements.

[matt3989]

Re: Question on CR and Torque

www.wikipedia.com and www.howstuffworks.com are good places to start