Inline 6, why not 8?

[Franco Cozzo]

I was just thinking the other day, we've got an I6 right? Why don't we have I8s? Obviously it isn't just going to be as easy as slap on an extra 2 cylinders but how come we don't have them?

I'm guessing it would be a tad bit too long, but would it offer any benefit over a V configuration?

[jasjul]

It would be very smooth, but too long for packaging requirements in modern cars.

[Iggypoppin']

There used to be..years ago bentley, Mercedes etc used them. I think they just where too big to use in the cars, or maybe economically they where less viable than
V engines.

[buickman]

Originally Posted by Iggypoppin'

There used to be..years ago bentley, Mercedes etc used them. I think they just where too big to use in the cars, or maybe economically they where less viable than
V engines.

Big and very heavy.
Bent a A bar removing a straight 8 out of a Buick that had no problems with a Buick 455cu and 360cu Chrysler V8.
The Holden grey engine looks like a baby brother to the Buick 8.

[lofty]

http://en.wikipedia.org/wiki/Straight_eight

[Windsor220]

The I6 is long enough as it is. I8 would be a nightmare to fit in the bay.

[calais]

Apart from being unbelievably smooth, the longitudinal 8 is inherently balanced, much like most I6 designs.

Buick and Oldsmobile made the most of the engine design, and are still renowned for it amongst veteran car enthusiasts. Many other manufacturers had a good crack, and had variants in a few special models, but none sold more than Buick.

Unfortunately it died in the 50's as the V8 became mainstream, in the search for higher performance, less weight and better packaging.

Today, with current suspension and bodywork designs, there is no sense to the I8 design as far as manufacturers are concerned, not when a V8 does the same job in half the space, and will handle better kilo for kilo because the centre of mass is further back.

All in all, a nice design, but sadly obsolete today.......

[Kamshaaft]

Originally Posted by Big Damo

I was just thinking the other day, we've got an I6 right? Why don't we have I8s? Obviously it isn't just going to be as easy as slap on an extra 2 cylinders but how come we don't have them?

I'm guessing it would be a tad bit too long, but would it offer any benefit over a V configuration?

Well to simplify things, it really would be as easy as throwing an extra two cylinders on and changing everything do with the valves and piston movement, but engine bays these days are very square and really not long enough.

Technically number of cylinders doesn't dictate engine size or mass - you can have a straight 12 or whatever you wish be no longer than the Barra - but in the real world such an engine would likely have a small bore (and you can only have so much stroke for so much bore in good practice, besides you'd have to peep over your rocker covers) most likely very thin cylinder walls or both. And as such it would likely have a tiny displacement, and could also be inheriantly unreliable.

Only brought that up because not enough folks realise nothing's set in stone with engines, although in reality most engines do stick within the guidelines laid out by their steretypes. But those stereotypes also change through time.

In reality it'd more than likely be just as everyone has said, that they'd make a very long narrow block, which worked well in yesteryear, but doesn't fit in with the shape of cars/engine bays which are short and very wide in the sedan of today.

P.S. V12s are about the smoothest cylinder engien configuration you will find, and the straight 6 is not far behind.

[Kamshaaft]

^Well calais, you said that very well. Far more eloquent than the part in the last half of my post, anyway!

[Raptor]

I've seen a staright 8 in an old Buick, it was massive.

The torsional forces on the crank at modern power/rev levels make it unpractical not to mention problematic re packaging.

Here's one I found on google

[Professor Farnsworth]

Originally Posted by Raptor

Here's one I found on google

is that a 180sx?

[XW500 4V]

Originally Posted by Raptor

I've seen a staright 8 in an old Buick, it was massive.

The torsional forces on the crank at modern power/rev levels make it unpractical not to mention problematic re packaging.

Here's one I found on google

^^Exactly what I was thinking!
Any crank that long wouldn't last for performance apps.

[Iggypoppin']

On the subject of balance, isn't an inline 6 the best balanced engine config available ? Just wondering

[melon466]

Originally Posted by Iggypoppin'

On the subject of balance, isn't an inline 6 the best balanced engine config available ? Just wondering

5 cylinder is the best balanced engine you can get

[lofty]

Originally Posted by melon466

5 cylinder is the best balanced engine you can get

Where'd you get that gem, Melon?

[lofty]

What I want to know is, is it theoretically possible to design a V8 crank to replicate the balance factors of a straight 8? In case that makes no sense, consider that you can make a parallel twin sound and feel like a 90 deg V twin by phasing the big end journals 90 deg apart. Yamaha did it with the TDM and TRX. So why wouldn't the reverse be possible, giving the character of a straight motor with the benefits of a V?

[XW500 4V]

Originally Posted by lofty

What I want to know is, is it theoretically possible to design a V8 crank to replicate the balance factors of a straight 8? In case that makes no sense, consider that you can make a parallel twin sound and feel like a 90 deg V twin by phasing the big end journals 90 deg apart. Yamaha did it with the TDM and TRX. So why wouldn't the reverse be possible, giving the character of a straight motor with the benefits of a V?

I'm pretty sure I follow what you mean. Am I on the mark below?

Most v8's we have come to adore have a 90degree crank. i.e the conrod journals are in two planes; like a + sign.

180degree cranks, being in a single plain ( | ) have an inherently better balance that is suited to high rpm usage (think F1).
With a V8, they tend to lose this "superior" balance when the engine capacity exceeds 4.2L. Ferrari use a 180degree crank, and the engine note is vastly different.

I found this in a text book somewhere. I'm sure you could google "180 degree crank" if you were keen to find any pros and cons.

Raptors link above goes through it (I'm reading now).
http://www.autozine.org/technical_sc...ne/smooth4.htm
Very nice read.

[aussie muscle]

Originally Posted by lofty

What I want to know is, is it theoretically possible to design a V8 crank to replicate the balance factors of a straight 8? In case that makes no sense, consider that you can make a parallel twin sound and feel like a 90 deg V twin by phasing the big end journals 90 deg apart. Yamaha did it with the TDM and TRX. So why wouldn't the reverse be possible, giving the character of a straight motor with the benefits of a V?

There's a bit of that stuff in the last Australian Muscle Cars magazine about the old F5000 engines. relating to how the angle of the big ends and crank were made in them.

as for straight 8's, it helps when you have a bonnet longer than half the car's length, like a Cord or Dusenburg. :

[Saraco]

Originally Posted by lofty

What I want to know is, is it theoretically possible to design a V8 crank to replicate the balance factors of a straight 8? In case that makes no sense, consider that you can make a parallel twin sound and feel like a 90 deg V twin by phasing the big end journals 90 deg apart. Yamaha did it with the TDM and TRX. So why wouldn't the reverse be possible, giving the character of a straight motor with the benefits of a V?

And YAMAHA have done it again! The new R1(2010 MODEL) is an inline 4cyl but has a 90 degree i.e. two plane crank (all other inline 4cylinders have a single plane 180 degree crank) this thing is the most V8 like sounding inline 4 I have ever heard! Sounds even more V8 like than a V4!

[Raptor]

Originally Posted by melon466

5 cylinder is the best balanced engine you can get

Well you fail :

Recommended reading for those interested in exploring this further;
http://www.autozine.org/technical_sc...ne/smooth1.htm

and my favourite quote;

Inline-6 is not the only configuration can deliver near perfect refinement, but it is the most compact one among them.

[lofty]

Here's a vid of that car in Raptor's pic: http://www.youtube.com/watch?v=917bo0fmpIo

[jpd80]

Originally Posted by melon466

5 cylinder is the best balanced engine you can get

Far from it, they have terrible NVH.
I-6, V12 and horizontally opposed engines are the best balanced engines.

[buggo]

Originally Posted by melon466

5 cylinder is the best balanced engine you can get

XR5 owner/fanboy?

[Boosh Brus]

This bad boy had an straight 12

[JC807]

stolen from wiki:

There are four different forces and moments of vibration that can occur in an engine design: free forces of the first order, free forces of the second order, free moments of the first order, and free moments of the second order. The straight-6, flat-6, and V12 designs have none of these forces or moments of vibration, and hence are the naturally smoothest engine designs. (See the Bosch Automotive Handbook, Sixth Edition, pages 459-463 for details.)

[cosmo20btt]

From what I remember straight eights had a common problem of breaking cranks, that is one of the reasons v8s replaced them.

[Road_Warrior]

Originally Posted by cosmo20btt

From what I remember straight eights had a common problem of breaking cranks, that is one of the reasons v8s replaced them.

This is my understanding of them as well. The looong crank couldn't deal with the stresses imposed on it very well.

Anyway, forget the I8 concept. I'd like to see 2 Barra I6 motors joined at the hip to make one big f-k off V12

[The Yeti]

Originally Posted by cosmo20btt

From what I remember straight eights had a common problem of breaking cranks, that is one of the reasons v8s replaced them.

thats not entierly true, braking cranks isnt a real issue this can be adressed with adding extra main bearings but the reason was simply real estate, to get cubic inches you need bore size X stroke so to get the size engine you eaither had a really long bonnet or went wit ha V configuration

theres still plenty of healthy straight 8's arround in the nostalgia seen

pitty classics.com are such tools about posting images on other forums perhaps if they did more people would see the image and follow it through to find more and they would get more traffic :

[Franco Cozzo]

That sounds pretty awesome, what was the last year they where made?

[MaTTe]

lofty, when i first read your post i thought of the Nailhead V8, but after reading XW500's post I can see how he thought more along the line of a boxer motor..

for nostalgia factor i advise having a look at a Nailhead V8 tho.