How do they...
Discussion
Right, I know a bit about engines, ask me to take one apart and I'll give it a shot before politely telling you were to shove it!
I know how the power is produced by a 4 pot, Aero engines and the such. 4 Stroke cycle is like candy from a baby!
Can someone (either by posting here or e-mailing me) please explain the technical bits of V8's and V12's, like, how the hell do they produce so much power and torque?!?!?! A V8 is basically 2 4 pots joined at the crank, obviously not quite as simple! The same goes for a V12, 2 6 pots (TVR did exactly that with their V12)! I'm a tad confused by the machanics of V engines.
Help!!!
I know how the power is produced by a 4 pot, Aero engines and the such. 4 Stroke cycle is like candy from a baby!
Can someone (either by posting here or e-mailing me) please explain the technical bits of V8's and V12's, like, how the hell do they produce so much power and torque?!?!?! A V8 is basically 2 4 pots joined at the crank, obviously not quite as simple! The same goes for a V12, 2 6 pots (TVR did exactly that with their V12)! I'm a tad confused by the machanics of V engines.
Help!!!
You'll usally find that a big engine has a lot of cylinders as it's much easier to get a small combustion chamber to burn fast and well, you can make a 5 ltr 4 pot but you'd have trouble getting it to run at a decent speed eg. 6000RPm.
As engine power is dictated partly by how fast you can run it, then it tends to be a more efficent solution to have lots of small pistons (to get the capacity) running fast (to get the power). The downsides are the complexity of the engine and the potential for extra friction but they do sound great!
Matt
As engine power is dictated partly by how fast you can run it, then it tends to be a more efficent solution to have lots of small pistons (to get the capacity) running fast (to get the power). The downsides are the complexity of the engine and the potential for extra friction but they do sound great!
Matt
quote:I'm no expert, but I suspect the cylinder configuration doesn't have much effect on power or torque output. It's more a question of producing a more compact engine (V6 is shorter than a straight six, V8 shorter than a straight eight etc).
Ok, now I know that more pistons = more power/torque! But, which is more powerfull, a 4litre InLine 6 or a 4 litre V6???
How much effect on the power/torque does the Vee angle make (before you ask, i'm not going to design/build/run my own V8!!)
Actually engine/cylinder configuration does have an effect on a motors output. Vee engines by their design are more compact, but you must look a little further. Vee engines don't have: a long crankshaft, which saves weight, long connecting rods, which saves weight and has an effect on connecting rod angularity. Saving weight not only makes it easier to balance an engine, but it allows the engine to RPM faster through its entire power range. So more compact, less weight, ability to RPM faster allow the engine to be more powerful and efficient, in addition to requiring less space. Theres more, but you must dig even deeper, to find/understand it.
quote:
Somebody may well correct me but I believe that in general a straight six will be more torquey than a V6 of the same capacity, again something to do with the packaging.
I *think* the explanation is that a V6 is more compact than a straight six, hence the innards are lighter and stronger and the engine can tolerate higher revs. This means if you fit a longer cam you can take advantage of the extra revs to get more power - at the expense of mid range torque. Hence the straight six typically has more torque but less power. I think.
Yes Green you are correct, the straight engine is more torquey, due to its tall height. Most straight engines are small bore/long strokes,again high weights internally, small valves (due to bore size), inability to rpm higher. Vee engines are usually large bores/short strokes, good rpm ability,good valve sizes. Most engine torque/horsepower curves will cross around 5250rpm (read be equal ). You must remember, if an engine does not produce torque (the work producer ), there will not be any horsepower, as horsepower is only an equation of torque measured over a period of time. All engines are only air pumps, the more air pumped through it the more power it will develope. Like I said, all depends how deep you want to investigate engines, and what improves them.
Cheeers Guys! Now I'm starting to get a clearer picture!
Right, so there is no benefit to Vee engines other than space?!?! They give less torque but more power!! So why then, is the Griff 500 so god damn fast?? Engine specs of the Rover V8 (as supplied by TVR. Vat of Salt anyone??) 90 Degree Vee. Bore/Stroke(mm) 94x90. Somebody Please explain Bore/Stroke. Max RPM 6000. I thought Vee engine couild tolerate Higher RPMs. My 4 pot revs higher than that!!! Max Power 320bhp. Max Torque 320lb/ft! This doesn't make sense to me! Why does this engine have the Same amount of Torque as it does power. And Acceleration figures to confirm it?!?!?! Am I right in thinking that the Rover V8 uses a cam which can make use of torque at (maybe) the expense of power???
I think I am starting to get this now! If I re-read this thread a few times, I think I will understand a bit better!!!
Right, so there is no benefit to Vee engines other than space?!?! They give less torque but more power!! So why then, is the Griff 500 so god damn fast?? Engine specs of the Rover V8 (as supplied by TVR. Vat of Salt anyone??) 90 Degree Vee. Bore/Stroke(mm) 94x90. Somebody Please explain Bore/Stroke. Max RPM 6000. I thought Vee engine couild tolerate Higher RPMs. My 4 pot revs higher than that!!! Max Power 320bhp. Max Torque 320lb/ft! This doesn't make sense to me! Why does this engine have the Same amount of Torque as it does power. And Acceleration figures to confirm it?!?!?! Am I right in thinking that the Rover V8 uses a cam which can make use of torque at (maybe) the expense of power???
quote:that has got to be the best explaination of an engine, any engine, I have ever ever heard!!!!
All engines are only air pumps, the more air pumped through it the more power it will develope
I think I am starting to get this now! If I re-read this thread a few times, I think I will understand a bit better!!!
The main reason the Rover V8 is Rpm limited to 6000Rpm has more to do with the design of the valvegear than the bottom end. As it's a pushrod, rocker arm arrangement the valvetrain mass is quite high especially compared to a overhead cam design. Consequently you need a pretty hefty valve spring to try and keep the valve under control, so there's quite a lot of force required to open the valve, so this means you're limited by how agressively / fast you can open the valve while maintaining valve control. This in turn limits the tuning of the engine so peak power speeds are also limited.
Of course once you've lightened the valve gear and are revving to 7 grand then you'll snap con-rod bolts but then fit a set of SPS bolts and etc etc..... until you end up with an F1 engine and are replacing pistons at the weekly rebuild.
How much torque / low speed power an engine generates is largley dependent on how it is tuned, if we were all happy with a 2000Rpm idle speed we could have more power and engines that rev to 10,000RPm without too much effort.
Matt
Of course once you've lightened the valve gear and are revving to 7 grand then you'll snap con-rod bolts but then fit a set of SPS bolts and etc etc..... until you end up with an F1 engine and are replacing pistons at the weekly rebuild.
How much torque / low speed power an engine generates is largley dependent on how it is tuned, if we were all happy with a 2000Rpm idle speed we could have more power and engines that rev to 10,000RPm without too much effort.
Matt
tvradict: Bore, the area in the block that the piston occupies. Stroke, the total distance the piston travels up/down in the bore. So your piston is 94mm wide, and it move up/down 90mm. By virtue of their larger size, large displacement engines develope more torque than a smaller engine, so therefore have more low/bottom end power. Remember torque moves shit, horsepower is a byproduct of this,so to speak. You also have to take into consideration the weight being moved (horsepower to weight ). Will your engine be as fast if in a truck ? See it's not the engine that is fast, it's the "total" package that is fast. Whoever can package the best selection of parts, usually ends up out front. It's the "total collection of parts, that are COMPATABLE " that counts. With an engine that developes lots of torque, you can use a larger spec camshaft, because the extra torque makes up for the flat spot normally associated with larger camshafts, until the engine is in its higher rpm band. With torquey engines you can sort off have your cake & eat it also. 350 matt;You are correct in stating valvetrain design has an effect on an engines ability to rpm. Whether it has solid/hydralic/roller tappets all have a bearing on operating range. Actually "valve float" is a misnomer, because it's not the valve that is floating it's the lifters. Opening/closing rates/ramps of camshafts are determined by how well you can keep the lifters/tappets in CONTACT with the lobe. Roller lifters by their virtue of being constantly in contact with the lobe are at present the best, although expensive, type....excluding the OHC engines. Don't ever forget that the factories also play a part in redlines. They have warrenties/durability factors, as well as trying to keep a tight leash on some of the "Goofy" drivers, that just have to hear it sing ! Also keep in mind that just because you can rpm higher, does not mean you are going faster. If the engines ability to breathe is impared, all you are doing is wearing out the engine,making noise (see above-Goofy), and operating the engine in the wrong power band. You are much better off short shifting at a lower rpm, where the power really is. Does not sound as cool I admit, but sure goes a hell of a lot faster, and that's what we are all after !
quote:
Most engine torque/horsepower curves will cross around 5250rpm (read be equal).
This isn't anything to do with the engine characteristics, it is a fundamental result of the relationship between power in bhp and torque in lb-ft. If your power/torque curves don't cross at 5250 rpm, somebody has been tampering with them.
GreenV8S....actually I didn't say it had any relationship with configuration, I was only trying to explain torque/Horsepower relationships, in an engines powerband. It is obvious that he is trying to grasp the basics of this subject, which may seem trivial to the folks who have already learned this, but is rather confounding to him. My hat goes off to him, and anyone who is willing to learn anything about this subject or any other for that matter. Someone explained it to me, either in a written book or verbally. Does me no good to be knowledgeable on a subject, if I keep it all to myself (speed secrets maybe ?). It just proves how dumb I can be, by withholding knowledge from others. I do not know everything, but I sure have fun trying to find it out & share it with others.
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