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4960 messages, Last post on Nov 25, 2009 at 8:23 AM

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What is this discussion about? Brakes, Electrical, Engine, Exhaust

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#3275 of 4960 Re: Using engine to brake? [kiawah] by jipster Mar 15, 2007 (5:14 pm)
Replying to: kiawah (Mar 15, 2007 12:16 pm) Brakes are cheaper than a transmission, but if you lose your brakes from overheating going down a steep mountain road you're in big trouble. I'd check your owners manual. The manual on my 99 Buick Regal states not to drive in second gear for more than 25 miles or at speeds over 55mph. So, 35 mph should be safe.
#3276 of 4960 Which engine is better ? by jiamin Mar 16, 2007 (8:34 am)
Assume two engines are of the same displacement. One is V6 and the other is V8. Replies to this message: qbrozen (Mar 16, 2007 12:21 pm) Mr_Shiftright (Mar 16, 2007 1:29 pm)
#3277 of 4960 Re: Which engine is better ? [jiamin] by qbrozen Mar 16, 2007 (12:21 pm)
Replying to: jiamin (Mar 16, 2007 8:34 am) uhhh... can you give more details? Displacement isn't everything, and neither are cylinders. How is the fuel mileage in each? How much HP and torque in each? Should reliability be taken into account? What about weight?
#3278 of 4960 Re: Which engine is better ? [jiamin] by Mr_Shiftright HOST Mar 16, 2007 (1:29 pm)
Replying to: jiamin (Mar 16, 2007 8:34 am) I think the advantage of a V6 over the V8 would be (might be) fuel economy, cost to produce and weight, that's about it....and given they are of similar displacement, some of those advantages might be slight.
#3279 of 4960 Which engine is better ? by jiamin Mar 16, 2007 (5:58 pm)
Thanks for the reply. I know there are many things involved. What I'd like to know is which engine can produce more HP and torque, if I can also assume most other configuration are very similar. In addition, I guess V8 should be a little smoother than V6? Replies to this message: qbrozen (Mar 17, 2007 6:56 am) jiamin (Mar 17, 2007 7:38 am) kiawah (Mar 17, 2007 8:01 am) Mr_Shiftright (Mar 17, 2007 10:16 am) qbrozen (Mar 17, 2007 10:45 am) and 2 more...
#3280 of 4960 Re: Which engine is better ? [jiamin] by qbrozen Mar 17, 2007 (6:56 am)
Replying to: jiamin (Mar 16, 2007 5:58 pm) ok. so we're talking theoretically here. you've got 2 engines that are identical in every way except for number of cylinders. WELL, I'm going to go out on a limb here and say you may get more torque out of the V6 and more HP out of the V8. Why? Because a bigger combustion chamber makes for a bigger bang. However, more, smaller chambers typically makes for higher revving. I could be totally off base. I mean, with more chambers, you get more bangs per revolution ... but that's the problem with theories. They aren't always right. oh, and I'll also say I think the V8 could theoretically get better highway mileage because you can put in taller gearing because, again, more bangs per revolution makes it easier to maintain speed with lower revs. And, yes, the v8 COULD be a little smoother. Did I answer which is better? not really. ;b Replies to this message: jiamin (Mar 17, 2007 7:38 am) kiawah (Mar 17, 2007 8:01 am) Mr_Shiftright (Mar 17, 2007 10:16 am) qbrozen (Mar 17, 2007 10:45 am) Mr_Shiftright (Mar 17, 2007 11:00 am) and 1 more...
#3281 of 4960 Re: Which engine is better ? [qbrozen] by jiamin Mar 17, 2007 (7:38 am)
Replying to: qbrozen (Mar 17, 2007 6:56 am) Thanks gbrozen, and that's what I want to learn. I am not a DIY on cars but I like to read about car stuff. Engine configuration is one of them. By the way, due to their nature, I4 is never as smooth as V6, correct? To come back to theory, if I4 has perfectly designed counter balance (Forgot the name of the part), why can't it be as smooth? Replies to this message: kiawah (Mar 17, 2007 8:01 am)
#3282 of 4960 Re: Which engine is better ? [jiamin] by kiawah Mar 17, 2007 (8:01 am)
Replying to: jiamin (Mar 17, 2007 7:38 am) A 4-cycle engine, takes two revolutions of the crankshaft for each cylinder firing. The first downstroke sucks in combustable mixture, the first upstroke compresses it so that a spark plug can ignite it. The second downstroke is the power stroke where the lit gas is pushing the piston down turning the crank, then the next upstroke the piston is exhausting and clearing out the spent gas. Then it starts all over again. So for 1 cylinder, there is one power stroke for every 2 revolutions of the crank, or 720 degrees of revolution. If you were to add a 2nd cylinder to that engine, you would want to space it's firing at 360 degrees, to even out the power strokes. Both pistons would be going up and down at the same time (assuming they were 'in-line') alternating which cylinder fires when the pistons come up. You can also see that there is now more mass moving up and down at the same time. A 4cycle 2cylinder engine would have 1 power thrust per revolution, and they are spaced 360 degrees apart. A 4cycle, 4 cylinder engine, will have just 2 total power thrusts in a revolution, and they would be spaced 180 degrees apart. For a 4cycle, 6 cylinder engine, you will have 3 total power thrusts in a revolution, the power thrusts spaced at 120 degrees apart. For a 4 cycle, 8 cylinder engine, you will have 4 total power thrusts for each revolution, the power thrusts spaced at 90 degrees apart. Hence there are more evenly spaced power thrusts for an 8 cylinder car, and therefore smoother. Torque is usually related more to how far off center the crank arm is. The pistons attach to the end of the crank arm. If the arms are longer, the piston has more leverage or power over the crank, and it has more torque. It also means that the piston travel up and down is further. However, the longer the arms, the harder it is to spin it fast. The counter balances you reference, are weights that are built in to counter balance the other moving parts, to keep the offset weight from causing vibrations (thereby making it vibrate less and appear smoother). This is a different smoothness than I'm talking about earlier, with the amount of sparkplug firings per revolution.
#3283 of 4960 Re: Which engine is better ? [qbrozen] by Mr_Shiftright HOST Mar 17, 2007 (10:16 am)
Replying to: qbrozen (Mar 17, 2007 6:56 am) torque is related to the individual displacement of each cylinder, not to the # of cylinders. So you could have a high torque V6 or a gutless one, depending on displacement. With 4 cylinder engines, they seem to hit the wall on vibration when they reach 2.4L or so....after that, it gets dicey. Replies to this message: qbrozen (Mar 17, 2007 10:45 am) Mr_Shiftright (Mar 17, 2007 11:00 am) qbrozen (Mar 17, 2007 11:05 am)
#3284 of 4960 Re: Which engine is better ? [Mr_Shiftright] by qbrozen Mar 17, 2007 (10:45 am)
Replying to: Mr_Shiftright (Mar 17, 2007 10:16 am) right. which is why I speculated the V6 in this theory could have more torque than the v8 since the parameters given is that they are of the same total displacement, making the individual cylinder displacement in the V6 larger. Replies to this message: Mr_Shiftright (Mar 17, 2007 11:00 am) qbrozen (Mar 17, 2007 11:05 am)