why not a larger inline 4 instead of v6?

[Zenmervolt]

Originally posted by: ElFenix

Originally posted by: Zenmervolt

Originally posted by: ElFenix
couple of things i'm assuming here
1) I4 doesn't waste power with balance shafts, etc
2) crankshafts for I4s don't need to be any stronger than a V8 of twice the size, and probably don't need to be any stronger
3) the V6 is only superior in that its shorter in 1 direction

so if you take all that you should be able to get more power out of a 3 liter I4 than a 3 liter V6... so why doesn't it happen?

You're kidding about the balance shafts, right? An I4 will shake itself apart _right now_ without balance shafts. Especially a big I4. It's an I6 that's perfectly palanced without the need for balance shafts.

ZV

EDIT: Also, the 3.0 litre I4 from Porsche was in the 968, not the 944. The 944 had a 2.5 litre I4 initially, and it was bumpped to a 2.7 litre I4 near the end of 944 production.

i was under the impression that I4 did not need a balance shaft. also that v8 doesn't.

Someone told you wrong. The second order forces are not canceled out in an I4. First order forces are, but not the second order. Small I4's, because of their lesser mass, can get away without balance shafts, but the vibrations are amplified in large I4 engines and they will destroy themselves very quickly without balance shafts. A 90 degree V8 can be set up to cancel both First Order foces and one of the Second order forces, but only an I6 and a V12 balance all forces without balance shafts.

ZV

 

[CraigRT]

Originally posted by: Skoorb
If Nissan hasn't done it it can't be/shouldn't be done.

 

[CraigRT]

Originally posted by: ElFenix

Originally posted by: vi_edit

Larger valves yes but there is a limit (16 valves) compared to a V6 (24 valves).

Dunno if it's important or not, but Audi does 20V 4 cylinders in the 1.8T.

i thought only ferrari had a 5 valve per cylinder design

Ferrari and VW/Audi.. I know there is another too.. but I can't think of it right now...

 

[Zenmervolt]

Originally posted by: Yield

Originally posted by: ElFenix

Originally posted by: vi_edit

Larger valves yes but there is a limit (16 valves) compared to a V6 (24 valves).

Dunno if it's important or not, but Audi does 20V 4 cylinders in the 1.8T.

i thought only ferrari had a 5 valve per cylinder design

Ferrari and VW/Audi.. I know there is another too.. but I can't think of it right now...

Bugatti did it too. Honda had 3-valve heads in Accords back in the 1980's.

ZV

 

[Bulk Beef]

Back to your original question, the bottom line is more rpm=more power. A 3L V6 will spin higher than a 3L I4, b/c the 6 will have a shorter stroke. A 6 will also have more total valve area than a 4. Your statement

you should be able to get more power out of a 3 liter I4 than a 3 liter V6

is false. All else being equal, more cylinders will produce more power, to put it as simply as it can get.

 

[Bulk Beef]

Oh, and Yamaha has been doing production five valve designs since the mid-eighties.

 

[Tipnmo101]

EDIT: Also, the 3.0 litre I4 from Porsche was in the 968, not the 944. The 944 had a 2.5 litre I4 initially, and it was bumpped to a 2.7 litre I4 near the end of 944 production.

"In 1990 Porsche releases the 944 Series 2, designated 944 S2. The S2 was an extensive revision of the 944S which now included the aerodynamic bodywork of the 951. The previous three engines available were replaced by the 3.0 liter's 16 valve engine and a big turbo 2.5 liter 944 Turbo (sold in Europe). As well, a soft-top version of the 944 was introduced, the 944 S2 Cabriolet. The new cabriolet was produced jointly by Porsche and the German division of the American Sunroof Corporation. "

 

[ElFenix]

Originally posted by: Zenmervolt
Someone told you wrong. The second order forces are not canceled out in an I4. First order forces are, but not the second order. Small I4's, because of their lesser mass, can get away without balance shafts, but the vibrations are amplified in large I4 engines and they will destroy themselves very quickly without balance shafts. A 90 degree V8 can be set up to cancel both First Order foces and one of the Second order forces, but only an I6 and a V12 balance all forces without balance shafts.

ZV

ah, ok, no one has mentioned the second order forces before, thanks!

 

[ElFenix]

Originally posted by: sward666
Back to your original question, the bottom line is more rpm=more power. A 3L V6 will spin higher than a 3L I4, b/c the 6 will have a shorter stroke. A 6 will also have more total valve area than a 4. Your statement

you should be able to get more power out of a 3 liter I4 than a 3 liter V6

is false. All else being equal, more cylinders will produce more power, to put it as simply as it can get.

eh, i really mean torque. and the torque would be quite a bit higher in the I4. they should burn gas at pretty similar rates if both engines are square though, and its hard to get a different amount of energy out of the same process.

 

[Zenmervolt]

Originally posted by: Tipnmo101

EDIT: Also, the 3.0 litre I4 from Porsche was in the 968, not the 944. The 944 had a 2.5 litre I4 initially, and it was bumpped to a 2.7 litre I4 near the end of 944 production.

"In 1990 Porsche releases the 944 Series 2, designated 944 S2. The S2 was an extensive revision of the 944S which now included the aerodynamic bodywork of the 951. The previous three engines available were replaced by the 3.0 liter's 16 valve engine and a big turbo 2.5 liter 944 Turbo (sold in Europe). As well, a soft-top version of the 944 was introduced, the 944 S2 Cabriolet. The new cabriolet was produced jointly by Porsche and the German division of the American Sunroof Corporation. "

Oops. My bad.

ZV

 

[boyRacer]

Originally posted by: sward666
Oh, and Yamaha has been doing production five valve designs since the mid-eighties.

Yamaha co designed the 3S-GTE... ...not five valves per cyclinder but over engineered engine nevertheless...

 

[Zenmervolt]

Originally posted by: sward666
Back to your original question, the bottom line is more rpm=more power. A 3L V6 will spin higher than a 3L I4, b/c the 6 will have a shorter stroke. A 6 will also have more total valve area than a 4. Your statement

you should be able to get more power out of a 3 liter I4 than a 3 liter V6

is false. All else being equal, more cylinders will produce more power, to put it as simply as it can get.

Actually, all things being truly equal, (i.e. equal valve area, equal total displacement, equal redline, equal setup, etc), an engine with more cylinders will produce very slightly less power because of increased frictional losses. However, there are so many advantageous pathways opened up by having more cylinders that things are never equal and engines with more cylinders make more power because things are not equal.

ZV

 

[WinkOsmosis]

Originally posted by: ElFenix

Originally posted by: Zenmervolt

Originally posted by: ElFenix
couple of things i'm assuming here
1) I4 doesn't waste power with balance shafts, etc
2) crankshafts for I4s don't need to be any stronger than a V8 of twice the size, and probably don't need to be any stronger
3) the V6 is only superior in that its shorter in 1 direction

so if you take all that you should be able to get more power out of a 3 liter I4 than a 3 liter V6... so why doesn't it happen?

You're kidding about the balance shafts, right? An I4 will shake itself apart _right now_ without balance shafts. Especially a big I4. It's an I6 that's perfectly palanced without the need for balance shafts.

ZV

EDIT: Also, the 3.0 litre I4 from Porsche was in the 968, not the 944. The 944 had a 2.5 litre I4 initially, and it was bumpped to a 2.7 litre I4 near the end of 944 production.

i was under the impression that I4 did not need a balance shaft. also that v8 doesn't.

I don't see why an I4 would need balance shafts.. when the two outer cylinders are going up, the two middle ones are going down... that's perfect balance. I have no idea how an I6 could be perfectly balanced though.. Three going up when the other three are going down? That means there is an imbalance along the length of the engine, causing rotational vibrations...

 

[Bulk Beef]

Originally posted by: ElFenix

Originally posted by: sward666
Back to your original question, the bottom line is more rpm=more power. A 3L V6 will spin higher than a 3L I4, b/c the 6 will have a shorter stroke. A 6 will also have more total valve area than a 4. Your statement

you should be able to get more power out of a 3 liter I4 than a 3 liter V6

is false. All else being equal, more cylinders will produce more power, to put it as simply as it can get.

eh, i really mean torque. and the torque would be quite a bit higher in the I4. they should burn gas at pretty similar rates if both engines are square though, and its hard to get a different amount of energy out of the same process.

OK- if you're talking torque, that changes everything for exactly the same reasons. Reduced to a simple machine, the crankshaft is a lever. Big 4 will have a longer lever than a big 6, ergo more torque, so you are right.

If Harley-Davidsons had a decent combustion chamber design, they would rip your arms out of their sockets.

 

[Bulk Beef]

Actually, all things being truly equal, (i.e. equal valve area, equal total displacement, equal redline, equal setup, etc), an engine with more cylinders will produce very slightly less power because of increased frictional losses

Well duh. Read my post again.

 

[Zenmervolt]

Originally posted by: Jellomancer
I don't see why an I4 would need balance shafts.. when the two outer cylinders are going up, the two middle ones are going down... that's perfect balance. I have no idea how an I6 could be perfectly balanced though.. Three going up when the other three are going down? That means there is an imbalance along the length of the engine, causing rotational vibrations...

Your ability to understand something does not have any affect on its being the truth. Look here for a more detailed explanation.

ZV

EDIT:

Well duh. Read my post again.

Yeah, I was agreeing with you, but clarifying what you had said.

 

[HokieESM]

The second order forces, as pointed out, are not balanced in an inline four. +5 points to he who noted it.

One common misconception is that V6s aren't as balanced as I4s. One reason for this is that a LOT of V6s (particularly American ones) are 90 degree designs--which are inherently unbalanced (and thus, need balance shafts). The 60 degree designs are much better balanced (although not perfect).

One big problem with making pistons that large is "piston slap"--a phenomenon that is frequently seen in large cylinder engines on cold starts/cold days. You can nearly discern the noise. But the bigger implication is vibration. The inline four is MUCH less balanced than a 90 degree V8 (hence why a 7 liter V8 might not vibrate too badly, but a 3.5L inline four would be rough). And vibrations also equal lost power... so you would like to avoid them whenever necessary. Inline-6s and V12s can be balanced to be buttery smooth--and think of the cars they tend to show up in.

Another issue is that, from a design point of view, MORE cylinders are frequently better for efficiency (material wise). Think of trying to drill four big holes in a rectangle versus six small ones (displacing the same amount of material). You also have a lot of reciprocating mass--which leads to more vibrations, and limits RPM potential--look at the difficulty F1 goes to in order to make their pistons lighter.

Not to mention, its hard to get the fuel/air mixture to distribute well (when you look at the fluid dynamics situation) in a large cylinder... which is very important in a gasoline (NOT diesel... most of this doesn't apply to knock-control ignition vehicles that run at very low RPMs) engines--it improves combustion efficiency. And most four-cylinder engines are designed for economy or high-revving performance--either of which demands very good mixture distribution.

Anyhow.... engineers would actually love to make more I6s and V12s--but they have a lot of moving parts and are hellishly expensive. Business types don't like them. Small inline fours have their place too--Honda is brilliant with them (from the very frugal mass-produced Civic engines to the high-revving four of the S2000). But big inline fours are really for diesels... they don't have to worry as much about reciprocating mass (low RPMs) and since their ignition is knock controlled, the fuel distribution isn't as critical (and something like direct injection can help a LOT).

I hope this helps!

 

[desertdweller]

Originally posted by: ElFenix
couple of things i'm assuming here
1) I4 doesn't waste power with balance shafts, etc
2) crankshafts for I4s don't need to be any stronger than a V8 of twice the size, and probably don't need to be any stronger
3) the V6 is only superior in that its shorter in 1 direction

so if you take all that you should be able to get more power out of a 3 liter I4 than a 3 liter V6... so why doesn't it happen?

You guys are looking way to far into this.

4 cylinder motors can be made to have the same horsepower as a v6, however, horsepower is only half the
equation. A v6 of the same size will have more torque to pull the vehicle through the low and mid range RPMs.

This is because there are more cylinders. If you have more cylinders, you have more compression strokes, if
you have more compression strokes per revolution. The more compression stroke you have per rev. the more
constantly the power is applied to the crank.

4 bangers have less torque because there is a longer time between when force is applied to the crank.

4 banger, fire at every 90 degrees of crank
6 cyl fire at every 60 degrees of crank
8 cyl fire at every 45 degrees of crank

DD

 

[Brutuskend]

I have a 2.8 liter four banger with a hemi head.

It moves right on down the road!

 

[ElFenix]

Originally posted by: sward666

Originally posted by: ElFenix

Originally posted by: sward666
Back to your original question, the bottom line is more rpm=more power. A 3L V6 will spin higher than a 3L I4, b/c the 6 will have a shorter stroke. A 6 will also have more total valve area than a 4. Your statement

you should be able to get more power out of a 3 liter I4 than a 3 liter V6

is false. All else being equal, more cylinders will produce more power, to put it as simply as it can get.

eh, i really mean torque. and the torque would be quite a bit higher in the I4. they should burn gas at pretty similar rates if both engines are square though, and its hard to get a different amount of energy out of the same process.

OK- if you're talking torque, that changes everything for exactly the same reasons. Reduced to a simple machine, the crankshaft is a lever. Big 4 will have a longer lever than a big 6, ergo more torque, so you are right.

If Harley-Davidsons had a decent combustion chamber design, they would rip your arms out of their sockets.

well since the torque arm is shorter in the 6 then wouldn't that do quite a bit to cancel out the rpm advantage, ceteris paribus?

 

[ElFenix]

Originally posted by: desertdweller

Originally posted by: ElFenix
couple of things i'm assuming here
1) I4 doesn't waste power with balance shafts, etc
2) crankshafts for I4s don't need to be any stronger than a V8 of twice the size, and probably don't need to be any stronger
3) the V6 is only superior in that its shorter in 1 direction

so if you take all that you should be able to get more power out of a 3 liter I4 than a 3 liter V6... so why doesn't it happen?

You guys are looking way to far into this.

4 cylinder motors can be made to have the same horsepower as a v6, however, horsepower is only half the
equation. A v6 of the same size will have more torque to pull the vehicle through the low and mid range RPMs.

This is because there are more cylinders. If you have more cylinders, you have more compression strokes, if
you have more compression strokes per revolution. The more compression stroke you have per rev. the more
constantly the power is applied to the crank.

4 bangers have less torque because there is a longer time between when force is applied to the crank.

4 banger, fire at every 90 degrees of crank
6 cyl fire at every 60 degrees of crank
8 cyl fire at every 45 degrees of crank

DD

ummm... no, torque is a direct result of the torque arm, which is longer in the 4 cylinder, ceteris paribus

 

[HokieESM]

One quick note: if you'd really like to understand this better, pick up a kinematics book.... Norton's Design of Machinery is a good example. This really isn't a simple phenomena--even neglecting things like fuel-air mixture, etc. Norton goes over the kinematics and talks about how certain engines are well balanced, and others aren't (and how to help!).

An interesting fact for you all--frequently V8s aren't balanced as well as they could be (and some V6s). Ideally, a V8 should have the crank attachments every 45 degrees for optimal balance. But pull out the crank on your Ford or Chevy--the crankpins are at the 90s (and two cylinders hook up on each). Some V6s have them on the 120s (when every 60 would help). But inline sixes MUST have six lobes--so they might as well put them every 60 and balance them out.

 

[HokieESM]

Originally posted by: ElFenix<brummm... no, torque is a direct result of the torque arm, which is longer in the 4 cylinder, ceteris paribus

Actually, this isn't true. It also depends on how many power strokes you're getting.... in addition to the overlap between the strokes. Note that a four-stroke Otto cycle demands that a four-cylinder engine only have one cylinder firing at any given time. A six can have more than this--albeit the cylinders are smaller. And there is NO reason that the strokes can't be identical..... the bore on the six could just be really small.

 

[desertdweller]

Originally posted by: ElFenix

Originally posted by: desertdweller

Originally posted by: ElFenix
couple of things i'm assuming here
1) I4 doesn't waste power with balance shafts, etc
2) crankshafts for I4s don't need to be any stronger than a V8 of twice the size, and probably don't need to be any stronger
3) the V6 is only superior in that its shorter in 1 direction

so if you take all that you should be able to get more power out of a 3 liter I4 than a 3 liter V6... so why doesn't it happen?

You guys are looking way to far into this.

4 cylinder motors can be made to have the same horsepower as a v6, however, horsepower is only half the
equation. A v6 of the same size will have more torque to pull the vehicle through the low and mid range RPMs.

This is because there are more cylinders. If you have more cylinders, you have more compression strokes, if
you have more compression strokes per revolution. The more compression stroke you have per rev. the more
constantly the power is applied to the crank.

4 bangers have less torque because there is a longer time between when force is applied to the crank.

4 banger, fire at every 90 degrees of crank
6 cyl fire at every 60 degrees of crank
8 cyl fire at every 45 degrees of crank

DD

ummm... no, torque is a direct result of the torque arm, which is longer in the 4 cylinder, ceteris paribus

That is part of it, the longer stroke means more torque.

Now I'll ask you the question, why does a 4 cylinder have less torque than a v6 of equal
CID if a 4 cylinder has a longer stroke.

DD

 

[Bulk Beef]

Fenix, I think I've over-simplified here. I didn't mean to suggest that the stroke was the only factor in figuring torque.