[SUPRAMIR]

i am curious as to what the major differences are between the 2 engine configurations? what does the V6 offer that the I6 doesnt and vice versa?

 

[sloopercat]

V6 offers a more space efficient package. The I-6 is a much better balanced smoother running design.

 

[Supraa_luva]

Yeah, if you drive a V6 and then a I6 you can tell the difference in smoothness. This also gives a smooth exhaust tone which I find sounds much better than a V6 does.

I havn't ever worked on a V6 but from my experience with the supra it seems like it's much easier to work on a I6, there is alot of room on both sides of the engine, not much in front or back of course but both sides seem to have alot of room. The V6's seem to not have much room on the sides but a bit more in the front. Maybe it's just cause I've only seen newer V6's though that look like you can't fit your hand anywhere inside the engine bay and have to spend 5 hours removing things to change the spark plugs.

As for benefits from design I've heard that I6's are a bit more reliable as since the pistons are straight up and down there is equal wear and stress on both sides of the cylinder walls. V6's engine components wear quicker as they are slanted causing wear on the sides of the cylinder walls.
Also as the I6's are smoother causing less vibration, V6's have more vibration and that can put strain on studs and bolts, also loosening them, panels, wireing, and other components over the years.
This is just what I've heard from a few car guys. I don't really know for sure so dont' quote me, lol.

 

[Dave A.]

There was a big discussion about this topic on the Yahoo list some time back, but I don't recall anyone mentioning the effects of gravity on a V6 and a inline 6. Right on Supraa-Luva! V-block engines do suffer a bit from the effects of gravity on the weight of the pistons and rods being placed off center of the crankshaft. This is one reason why inline engines have the inherent ability to produce good torque with minimal vibration and with less wear on the piston skirts and cylinder bores.

 

[Norbie]

The effect of gravity on the pistons is neglibible compared to the forces they're subjected to in normal operation. A free-falling piston accelerates at 9.8 m/s/s at sea level, but how much do you suppose a piston is accelerated at 5000 rpm? Remember that (in the case of my engine) that piston has to move 86mm, come to a complete halt, reverse its direction, move 86mm, and come to a complete halt again - and repeat that process 83 times in a second!

 

[Flyin' Hawaiian]

That's what I was thinking too! The amount of force exerted on the head of each piston would greatly overcome any gravitational pull to one side of a cylinder, besides, the rings are compressed in such a way that it exerts its own gravity equally throughout the circumference of each cylinder.
As for I-6 vs. V-6, there's also a higher torque rating with an inline 6 vs. the V-6, although I'm too tired right now to explain why that takes place.
In any case, its a good question, and one that many people have pondered but haven't found an answer-keep the discussion going!!!

 

[Sparky]

To toss a bone into this conversation (since I understand the v6-i6 relationship) how does the flat 6 (aka Porsche engines) compare with these?

 

[SupraFiend]

I think Dave and Supraa_luva got it right. We're not talking about the effects of gravity in one piston stroke here, we're talking about the effects over a decade of use. Of course gravity is going to have an effect on the wear characteristics, it wouldn't be much but over time it will add up. These engines can go forever!

 

[Dave A.]

Yes, that's precisely what I was trying to say. Thanks for clarifying! On another note, this may sound way far out, but inline engines have the inherent ability to use gravitational force to an advantage by allowing gravity to assist in the downward motion of the pistons, which can be of benefit during the power stroke. Opposed (flat) engines just wear that much more unevenly than V-block engines over time. Inline (straight) engines are also far more easy to balance since the forces exerted on the crankshaft all take place on a common axis. The inline engine basically tries to blow the crankshaft straight through the oil pan. V-block engines exert force on the crank in a slight side to side fashion, which is why V-block engines have a slight side to side rocking motion, especially at idle with a radical cam. Horizontally opposed cylinder engines exert even greater side to side force on the crank. This is why some hopped up air cooled VW engines have a tendecy to literally pound the markings on the crank bearing inserts into the aluminum crank bearing saddles of the split case and also try like heck to split the case apart at the center. :wink:
I know this all sounds way far out , so please let me know if I've left something out here or if I'm way off base.

 

[SilverMk2]

Gravity causing more piston wear is BS. Its not like the piston never touchs the cylinder wall in a inline engine. In all engines the pistons rock around in the cylinder bores. Its a function of rods angles, accelerations, blah blah blah. Any engine when you take it apart has piston scuffing on the skirts. The piston rocking is what that familar noise is when you have forged pistons in the motor (which require a greater clearance and make a louder slaping sound).

The big deal with inline 6s vs V6s is the packaging. The inline 6 is a long narrow tall motor. Try and install one in a transverse engine FWD car is a pain. Imagine having a Camry that has to be 2 feet wider to fit the engine. The other problem is the length and height. Most cars today want a low hood line so a tall motor doesn't help. Many RWD cars today also try and push the engine as far back as possible for weight distribution. The big downside on a V6 is cost, you end up with many extra parts. But with most cars FWD today V6s are the choice, and because of that they get used in RWD cars as well for cost reasons. There was a time when almost all 6s were inline, but the cars were all RWD back then. I6s also have a long crank which doesn't help crank torsional rigidity.

The difference in engine vibrations from a 60 degree V6 and a inline 6 are relatively minimal. All engine vibrations are classed in terms of "order". There are 1st order, 2nd, 3rd, 4th ...... one millionth etc. Each progressive one is weaker than the next. Something like a one cylinder mower engine isn't balanced in 1st order shaking in the piston bore direction and shakes like crazy. The typical inline 4 has shaking of the 2nd order in the bore direction. 60 degree V6 have a twisting moment about the crankshaft in the 2nd order range. I6s are balanced up till the 4th or 6th order or something like that. You usually don't care beyond the 2nd or 3rd order because the shaking forces are minimal. Basically the order thing is like a funcition of crankshaft speed. 2nd order forces are cyclical at 2X crankshaft speed. This is why balance shafts in most engines run at 2X engine speed. The counterweights on the crank are designed to minimize shaking at engine speed, since the crank can only spin at engine speeds.

Engine vibration comes from the piston moving up and down in its bore (F=ma, a piston has mass and the accelleration is huge so big F) an the weight of the crank pin/big rod end moving round and round (think of spinning around with a dumbell outstretched at 6000 RPM, you'd be lucky to stand up ). Usually you can counteract these forces with equals and opposites. This is why most engines are symmetrical along the length (i.e the I4 the two center piston are at TDC the outside 2 are at BDC, this counteracts the pistons up and down force at 1x engine speed). Oh well enough rambling..... can you tell I studied this stuff way too much in college.

 

[Supra Bob]

Gravity causing more piston wear is BS.

Tear apart a V configuation motor after 100K miles and measure the bore... then do the same on an Inline motor. I can promise ya, the side that had gravity pulling the piston against it will have in the neighborhood of twice the wear that the "higher" side has. Coulpe that with the natural balancing that is inherent with an Inline motor as opposed to a V motor, and you have the reason why so many inline motors regularly last between 250 and 300K miles reliably, while you rarely see a V motor go for much more than 140k...

 

[SupraFiend]

of course the piston never touchs the cylinder wall, the rings would be in between. But why wouldn't the weight of the piston push the ring into the cylinder wall? Once again, the extra wear would only start to show after many many years of use, there are tons of other things that would affect the wear of the engine more. Think about it, if the cylinder wall was instantly removed, what would the piston do? On a v6 the piston would instantly fall with the rod, swinging around the crank, while with the i6, assuming it was balanced perfectly, it would just sit there.

 

[Supra Bob]

Your forgetting about one thing... the time when most engine wear takes place is at startup and shutdown... those times when the engine is not operating at normal conditions. And yes, we are talking about years of wear here. Something that will only be measureable over the space of 8 to 10 years to even be measureable.

 

[Dave A.]

Lets take things to an even more extreme with this example: If it were physically possible to flip an inline or V-block engine upside down by rotating the engine in the chassis 180 degrees, would the engine run more efficiently facing right side up or upside down? The oil would of course flow down into the cylinders if the block were flipped, but lets forget about that for now and concentrate on the effects of gravity on the rest of the engine.
I hope I'm not starting some sort of a flamethrowing contest with all of my rambling, as that is most certainly not my intention here!! I'm merely just trying to help expand on some of the basic laws of physics and nature and how they apply to the internal combustion engine in different block configurations. Please let me know if anyone is feeling offended or angered by my thoughts and views and I will try to put my views into a lighter perspective! Sometimes I get too technical to the point where I end up driving myself bonkers!

 

[Dave A.]

In all engines the pistons rock around in the cylinder bores. Its a function of rods angles, accelerations, blah blah blah. Any engine when you take it apart has piston scuffing on the skirts.



AKA, piston slap due to the effects of sideloading on the pistons. The more piston skirt to bore clearance you have with a given rod ratio , the more piston slap and sideloading that takes place, thus more wear on the skirts. Different block configurations use pistons with a different offset on the wrist pin to help minimize the detrimental effects of sideloading, etc..

 

[CarFreek]

Volvo has stuffed an Inline 6 into a transverse FWD app in one of there new models-And lets not forget the hated VW and their VR-6 Inline/Offset FWD Applications-Both done in the name of that first three order balance inherent in an inline 6-Also, only certified nut case car makers like alfa and saab have made V-4 Engines-Also, any odd cyl engine is usually inline-3 popper Metro/Daihatsu- 5 Popper Audi/Acura/Volvo-This to take advantage of at least 2 orders of balance versus V configuration-So why no Modern Inline 8? Crank whip is at its best Compromise w Inline 6-Thats why you dont see any 9000 RPM Inline 6-(Alive!)

 

[SupraFiend]

Another advantage of an DOHC inline 6, much simpler construction. 2 cams and cam gears instead of 4, and a way simpler belt/chain routing. You ever do 100,000km maintenace on a v6? Ouch! A friend did on his Mazda Milenia with supercharged v6. 5 idler pulleys vs 1 for an inline 6! New idler pulleys, water pump, timing belt, labour and a few other little things set him back 2500 bucks! Mazda parts are pricy.

 

[suprathepeg]

I am probably only adding to the discussion more contorversy but..... I was told 2 things about the inline configuration:
1. The I6 is a naturally balanced motor so there are no weights on the crank shaft thereby reducing the ammount of energy to move the crank and generating more power per pound.
2. Inline engines' cylinders typically have a longer throw creating more torque. I think the formula is torque x RPMs = HP? Anyhow, they typically have more torque.

 

[Dave A.]

No weights on the crankshaft? Where did you hear that? Any weight placed on the crankshaft that is placed away from the crankshaft centerline always requires a counterweight placed on the opposite side of center in order to keep the rotating assembly in balance. The engine would tear itself apart if their were no counterweights on the crank.

 

[suprathepeg]

and the controvercy continues. lol, I freely admit I could be wrong.