V4 Vs. V6/v8

[Calesta]

Originally posted by ledzep09@Oct 21 2005, 03:07 PM
i dont know if there are such things as V4s...the cylinders are in line in a 4 cylinder and are therefore called I4 or just 4 banger should do.
<div align="right">[snapback]94150[/snapback]

[/quote]

Yup, there are definitely such things as V4s. These days, they're all on motorcycles. Very few V4s made it into production automobiles... but if you look back in history, Honda started out making cars with V4s in the very very beginning, and Saab had an interesting production car called the Sonnet in the early 70s that had a V4 too. The base model only had an inline 3.

But yes, you're right- all current production cars in the US that have 4 cylinder engines are either set up with a flat 4 or inline 4 configuration.

Originally posted by gianthobbit@Oct 27 2005, 08:47 AM
I am looking for a little bit more here.

Why do v6 and v8 hit max hp at lower revs then I-4s?

Is this a good or bad thing?

if two cars wieghed the same and had the same hp but one was a I4 and one a v6 which one would get from point a to b the fastest?
<div align="right">[snapback]94437[/snapback]

[/quote]

Most V6 and V8 engines are larger in displacement than I4 engines, so they make more torque at lower revs- so most auto manufacturers choose to build them for more torque and not worry about revving up high. RPM = ruins people's motors. Remember that. If you don't have to go to high revs to make torque, then don't. Your engine will last longer. In applications where more top end power is wanted, large V engines can still rev quite high. Just look at the new LS7 engine and the Ferraris / Lamborghinis. All those engines have no problems running past 8000rpm.

Not revving up high isn't either a good or a bad thing. You have to see the overall package. A 3.0L V6 with more torque but a lower redline than a 2.0L I4 can be just as useful if you gear it correctly.

As for two cars weighing the same with the same power but different engine layouts- that's a question that you can't really answer. If both engines have the same power curves and same drivetrains, then they'll run the same times from A to B. Now assuming these are typical USDM cars, the V6 will be larger and have more torque down low than the I4, and it will also be geared taller because of a lower redline (if it had more torque and the same redline, it would make more power so you're safe to assume it doesn't rev as high)- then it's still a tossup. If both cars are the same, you can be pretty safe in assuming that the V6 model will be faster, but only because the auto manufacturer doesn't want you to pay for the cheaper car and be faster than the more expensive one. Again, too many factors... but the larger displacement car will usually win because it has more torque.

Originally posted by CivicSi04'@Oct 27 2005, 10:13 AM
but to honest if u have a v6 and ur only gettin the power of a stock I4, your car sucks major asshole.
<div align="right">[snapback]94442[/snapback]

[/quote]

Not necessarily... more torque is a good thing.

Originally posted by Lacuna@Oct 27 2005, 01:58 PM
All things being equal a v6 or I4 makes no difference in speed. It's all about torque and where it's at. As an example the 2003 6s has 220hp at 6300 rpm's and 197 lb-ft torque at 5000 rpms, and the 2006 has 215 hp at 6000 and 199 lbs @ 5000 rpms. By moving the peak hp to 6000 they increased the low end torque. Same motor different tuning.
<div align="right">[snapback]94462[/snapback]

[/quote]

Agree and disagree.

Yes, it's all about the torque curve. I agree 100% there. As for your example- you got it backwards. By shifting the torque curve down, Mazda created an engine that's slightly less powerful at the peak, but more responsive in the mid range "meat" of the power curve. You tune for torque. Power is the application of that torque at speed.

Engine geometry matters a LOT when it comes to engine speed. Sure, in a consumer car it doesn't matter all that much, but when it comes down to it, more cylinders = higher revs. Why do F1 cars and Ferraris run V10s and V12s? The higher cylinder count means that you can have shorter strokes but still maintain a high displacement design at high speeds. If you had a 3.0L I4, your bore would have to be impossibly large and the stroke really short to live at 8000rpm. Combustion chamber sizes and shapes wouldn't behave very well at those speeds, and piston stability, friction, and other factors would become an issue too. With the higher cylinder count, you can have smaller lighter components (less mass = less inertia = less loss), smaller combustion chambers that are easier to manage at high speeds, and you can have the shorter stroke without going too large on the bore.

Our 2 liter and under 4 cylinder engines can rev fairly high, but they're small. Go to a 3 liter or something even bigger, and engine geometry starts to catch up to you. It's not just rod/stroke ratio... you have to think about combustion chamber size/shape, flame front propagation, just how much air you can get in/out of a space in a fraction of a second etc.

[ledzep09]

prof calesta at work. i did know about them being in motorcycles but i didnt think they did that EVER with cars..interesting to find out. i would imagine thatd put alot of empty space into the engine bay. why isnt this done more? (the V4 config.)

[steronz]

V engines are more expensive because there's more of everything... 2 cylinder heads (this is the big one), 2 exhaust manifolds, a more complicated intake manifold, the spark plugs are harder to get to, you need 2 fuel rails, longer wires, etc. so a V4 would cost more than an I4 and only save a small amount of space. but with the width of todays cars (hell, pontiac and cadillac put V8s in FWD cars), horizontal space saving isn't really an issue.

[ledzep09]

2 more cylinders? i thought a 4 cylinder has 4 cylinders no matter inline or V

[steronz]

cylinder heads, not cylinders

[Calesta]

Thanks.

Steronz hit the nail on the head. Inline engines are cheaper to make than V engines of the same cylinder count. They can also be built to be smoother too... although it's questionable if a V or I is smoother with a 4 cylinder. An I6 is definitely much smoother than a V6 because of its geometry and firing setup.