PDA

View Full Version : Same Engine/Displacement/Design, But One's A V6 & the other'


eightballsidepocket
03-24-2005, 01:45 PM
Whats the difference if you had a V6 or a V8 that was the same displacement, and design? <p>Each is DOHC, 4 valves per cylinder, fuel injected, same cam profile(V.V.T.), compression, metallurgy of the major components such as crank and rods...i.e. forged steel.....etc. <p>Can anyone comment on disadvantages or advantages between the two engine designs? <p>The one thought I had was that the V8 would have more frictional area with the additional pistons/rods/valves(24 vs. 32), and that might take away some efficiency. <p>How about inherent balance of the two engines too? Actually, what if you threw in a V4 with the same valve train, and camming? What about an inline 8 or 6? <p>Let's first start with the V6/V8 comparison. Comments please. <IMG NAME="icon" SRC="http://images.zeroforum.com/smile/emwink.gif" BORDER="0">

CalinG7
03-24-2005, 02:01 PM
I wish I could help you, but I've wondered about this too; also about the difference between a 4 cylinder and a 6 cylinder of the same displacement, as we have with the Nissan 2.5L I4 and the BMW 2.5L I6.<p>The only thing I can think of is, as you said, a loss of efficiency due to increased frictional area, but also the added weight of 2 cylinders. If the engines are otherwise similar except for cylinder count, then I would guess the 6 would be more efficient than the 8 because it has less weight to lug around.<p>That seems to be true, logically, but then wouldn't all engines be 4 cylinders, or 3? From the few sources that I've read, there seems to be a HVH area to think about, at least when speaking of 4 cylinder engines, because the larger the displacement the more inherently imbalanced they seem to get. I'm not sure, but this might apply to other engine configurations as well.

KebabGud
03-24-2005, 02:02 PM
the V8 has more torque..<br>

eightballsidepocket
03-24-2005, 02:05 PM
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD><i>Quote, originally posted by <b>KebabGud</b> &raquo;</i></TD></TR><TR><TD CLASS="quote">the V8 has more torque..<br></TD></TR></TABLE><p><B>Why?</B>

Santeno
03-24-2005, 02:06 PM
If there are so many similarities between the two engines the first assumption I would make is that the 6 is likely to be a cut-down version of the eight (or the opposite). If so I would assume that cylinder angles would probably be optimum for the bigger selling of the two configurations. since there is a greater variety of applications for the 6 instead of the 8 (in sheer volumes of cars and trucks), let's assume it's the optimum angle for a v6 (90 degrees). All else being equal, you would likely have a lighter engine with greter overall horsepower per cylinder then the 8 cylinder. Possible benefits would most likely be amortization of development and production costs over two engine families; higher output powerplants in smaller packaging; greater range of vehicle applications.

CalinG7
03-24-2005, 02:54 PM
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD><i>Quote, originally posted by <b>Santeno</b> &raquo;</i></TD></TR><TR><TD CLASS="quote">If there are so many similarities between the two engines the first assumption I would make is that the 6 is likely to be a cut-down version of the eight (or the opposite). .</TD></TR></TABLE><p>The way I understood his question is that the engines are almost completely the same, including displacement, engine "size." In that case, one couldn't be a cut-down version of the other, as the added cylinders would increase the displacement. <p>KebabGud, torque is mainly dependent on engine size, or displacement, meaning that a 2.5L engine will have more torque than a 2.4L engine, all things being equal. I'd be curious to know the torque figures on the Nissan 2.5L 4 cylinder engine and Audi's 2.4L V6, if someone wants to take the time to look that up.

Santeno
03-24-2005, 03:02 PM
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD><i>Quote, originally posted by <b>CalinG7</b> &raquo;</i></TD></TR><TR><TD CLASS="quote">The way I understood his question is that the engines are almost completely the same, including displacement, engine "size." In that case, one couldn't be a cut-down version of the other, as the added cylinders would increase the displacement.</TD></TR></TABLE><br>Not if the 6 has been bored out to equal the 8's displacement, which is the assumption I made.

eightballsidepocket
03-24-2005, 05:51 PM
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD><i>Quote, originally posted by <b>Santeno</b> &raquo;</i></TD></TR><TR><TD CLASS="quote"><br>Not if the 6 has been bored out to equal the 8's displacement, which is the assumption I made.</TD></TR></TABLE><p>That's what I was thinking. Could be two-less cylinders chopped off, but you would have to increase bore or stroke or both to match the V8 displacement. I guess Ford is big into the Modular engine concept.<p>Actually, I understand that my 4.3 Chevy Astro V6 is the 5.7 GM V8 with two-less cylinders. In fact, some engine swap books and weblinks mention that fact in replacing the Astro/Safari 4.3 V6 with the GM 5.7 as almost a straight drop-in, because the engines are related in no small way. Of course there are some pretty major issues with that swap, but the engine-block design i.e. engine mounts is supposed to be very close.<p>

Mindless T
03-24-2005, 07:15 PM
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD><i>Quote, originally posted by <b>KebabGud</b> &raquo;</i></TD></TR><TR><TD CLASS="quote">the V8 has more torque..<br></TD></TR></TABLE><br>and cylinders!

Nick
03-24-2005, 09:50 PM
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD><i>Quote, originally posted by <b>eightballsidepocket</b> &raquo;</i></TD></TR><TR><TD CLASS="quote">That's what I was thinking. Could be two-less cylinders chopped off, but you would have to increase bore or stroke or both to match the V8 displacement. I guess Ford is big into the Modular engine concept.<p>Actually, I understand that my 4.3 Chevy Astro V6 is the 5.7 GM V8 with two-less cylinders. In fact, some engine swap books and weblinks mention that fact in replacing the Astro/Safari 4.3 V6 with the GM 5.7 as almost a straight drop-in, because the engines are related in no small way. Of course there are some pretty major issues with that swap, but the engine-block design i.e. engine mounts is supposed to be very close.</TD></TR></TABLE><br>Actually you're right, the 4.3 is exactly the same engine as the 5.7 minus 2 cylinders...atleast the 90 degree block is...I believe the one used in the S-10 is a bit different, but when doing a 4.3 to 5.7 swap all you basically have to do is change around the engine mounts, reprogram the ECU to account for the extra cylinders, and I believe that's about it...not much to the swap...the 4.3 is a cool engine because it has a lot of potential...it's a really good sleeper engine because most people wont take you seriously with it because a V6, but they don't realize that this V6 is just as big as some V8's and being that it is virtually a 5.7, it is easy to find performance parts for...look at the engine bay of a 5.7, then look at the engine bay of a 4.3..exactly the same parts except the fan shroud is a little longer in the 4.3 due to the fact that the engine is shorter so the fan is farther in...but yea...it's a really easy swap...bolts right up to the 4L60E tranny no problem

MontrealMustang
03-25-2005, 07:55 AM
I would think that the difference between a V6 and V8 of identical displacement would be that the V6's torque would be slightly higher (bigger pistons and stroke) and the horsepower would come in low in the powerband. While the V8 would have slightly less torque and would rev much higher (Smaller pistons, shorter stroke).<p>Just look at those big Hino type trucks. They have 4.7 liter diesel 4 cylinder engines and they make like 175hp@2,700rpm and 347lbs/feet of torque at 1,600RPM. Compare that to a 4.6 liter Triton V8 and it's 231hp@4,750rpm and 293lbs/feet at around 3,500rpm. Okay, I'll admit that the Turbodiesel part of the engine kind of stacks the odds towards the 4 banger, but it still illustrates what I mean.

Cozz
03-25-2005, 08:07 AM
<br>The thermal efficiency of the V8 is lower than the V6 and because it has more moving parts.<p>On paper, the V6 will make more power because it is more efficient. Though, I expect the V8 to be a smoother motor because the overall displacment in power spread out more evenly.<p>

Santeno
03-25-2005, 08:10 AM
As I understand it, as far as balance is concerned, a pretty good rule of thumb to go buy is: the more cylinders and engine has the smoother it will appear to run. while the packaging benefits of a four cylinder engine is desireable, in order to get high horsepower numbers out of one, you need to get relatively high displacement and compression ratios out of it. doing that increases the engine's naturally occurring resonance, giving you a powerful but very rough engine. There is nothing you can do from an angine point of view to cure this. Porsche and mitsubishi have both found a way to diminish much of the harshness caused by these types of engines, by using counter-rotating balance shafts. However, I don't think that that is the type of thechnology you can easily swap from what vehicle to another without some major modifications of the engine compartment. Perhaps someone who knows a bit more about how countr-rotating balance shafts work can explain the technology further.

Cozz
03-25-2005, 08:37 AM
The Mitsu 4 cyl motor uses a counter balance shaft that spins twice as fast as the motor or at least the speed of the heads. MB uses 2 balance shafts at twice the speed at the back bottom of the motor, below the crank.

eightballsidepocket
03-25-2005, 10:02 AM
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD><i>Quote, originally posted by <b>Santeno</b> &raquo;</i></TD></TR><TR><TD CLASS="quote">As I understand it, as far as balance is concerned, a pretty good rule of thumb to go buy is: the more cylinders and engine has the smoother it will appear to run. while the packaging benefits of a four cylinder engine is desireable, in order to get high horsepower numbers out of one, you need to get relatively high displacement and compression ratios out of it. doing that increases the engine's naturally occurring resonance, giving you a powerful but very rough engine. There is nothing you can do from an angine point of view to cure this. Porsche and mitsubishi have both found a way to diminish much of the harshness caused by these types of engines, by using counter-rotating balance shafts. However, I don't think that that is the type of thechnology you can easily swap from what vehicle to another without some major modifications of the engine compartment. Perhaps someone who knows a bit more about how countr-rotating balance shafts work can explain the technology further.</TD></TR></TABLE><p>Interesting that you mention that.<p>I owned a 93 Porsche 968, with a 3.0 Liter, DOHC, inline 4 cylinder, that put out 236 H.p., and had 11:1 Compression! It was definitely counter-balanced! It definitely put out power. It was developed from Halving the Porsche 928 V8 engine. <B>By the way.......that was 236 Non-Turboed H.P.!</B><p>It was extremely smooth-running, but I'm sure without the counter balances it would have been as rough as a tractor engine.<p>I thought that the V-design eliminated the need for counter balancing.<p>Does anyone remember that Saab even build a V4 and it was in the Sonnet, I believe. This is many years back.<p>.......................<p>By the way I'd still have the Porsche if it didn't bankrupt me everytime it needed maintenance or repair(and that was often). I don't think reliability is Porsche's trade mark. I lusted for a Porche, and sure learned my lesson. I scrambled right back to Asian cars. I had the Porsche experience, but I'll take the Asian reliability.lol<BR><BR>
<i>Modified by eightballsidepocket at 9:09 AM 3/25/2005</i>

Verdegrrl
03-25-2005, 11:01 AM
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD><i>Quote, originally posted by <b>eightballsidepocket</b> &raquo;</i></TD></TR><TR><TD CLASS="quote">Whats the difference if you had a V6 or a V8 that was the same displacement, and design? <p>Each is DOHC, 4 valves per cylinder, fuel injected, same cam profile(V.V.T.), compression, metallurgy of the major components such as crank and rods...i.e. forged steel.....etc. <p>Can anyone comment on disadvantages or advantages between the two engine designs? <p>The one thought I had was that the V8 would have more frictional area with the additional pistons/rods/valves(24 vs. 32), and that might take away some efficiency. <p>How about inherent balance of the two engines too? Actually, what if you threw in a V4 with the same valve train, and camming? What about an inline 8 or 6? <p>Let's first start with the V6/V8 comparison. Comments please. <IMG NAME="icon" SRC="http://images.zeroforum.com/smile/emwink.gif" BORDER="0"> </TD></TR></TABLE><p>You get more power strokes with more cylinders for any given rpm. That usually offsets the extra friction and inertia. It also makes for a smoother running engine because there are more smaller pulses rather than a few large ones.<p>Fewer cylinders usually means less fuel used, not because the displacement is less of course, but just because there are usually fewer power strokes. They are usually lighter, smaller, and less complex.<p>Vincenzo Lancia and Fred Marmom both experimented with V4 engines early in the last century, but gave up due to vibration. Lancia went on to make the first mass production (if you want to call it that) V6. Up until then, inline engines were the obvious choice, since they were easy to build and usually very smooth. <p>Basic info <A HREF="http://www.answers.com/topic/straight-engine" TARGET="_blank">http://www.answers.com/topic/straight-engine</A> <p>Read about piston firing order <A HREF="http://www.epi-eng.com/ET-PistonExcit.htm" TARGET="_blank">http://www.epi-eng.com/ET-PistonExcit.htm</A> <p>

eightballsidepocket
03-25-2005, 03:16 PM
I wonder why Saab went with a V4 in the Sonnet years back?

Naga Royal Guard
03-25-2005, 03:22 PM
outboard engines on boats have V4s

Nick
03-26-2005, 12:08 AM
my uncle's flat bottom speed boat has an in-board blown, ported and polished 454 running dry stacks and roller cams hooked up to a v-drive...needless to say it's a beast...not that that has to do with anything in this topic...

Verdegrrl
03-28-2005, 11:23 AM
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD><i>Quote, originally posted by <b>eightballsidepocket</b> &raquo;</i></TD></TR><TR><TD CLASS="quote">I wonder why Saab went with a V4 in the Sonnet years back?</TD></TR></TABLE><p>Small, light, and cheaply sourced from Ford. Looming emissions requirements meant the 2 stroke 3 cylinder used by Saab up to then, wasn't going to cut it. The new motor was known as the FoMoCo engine, and used in industrial as well as automotive applications:<p> <A HREF="http://encyclopedia.thefreedictionary.com/Ford%20Taunus%20V4%20engine" TARGET="_blank">http://encyclopedia.thefreedic...ngine</A>

knicks125
03-28-2005, 11:24 AM
ummm...interesting, v4 engines existed...i always wondered...thanks <IMG NAME="icon" SRC="http://www.germancarfans.com/images/forums/beigesmilewinkgrin.gif" BORDER="0">