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.

[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.

[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.

[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.

[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]

^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

[Iggypoppin']

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

[Boosh Brus]

This bad boy had an straight 12

[Professor Farnsworth]

Originally Posted by Raptor

Here's one I found on google

is that a 180sx?

[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

[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.)

[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?

[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.

[cosmo20btt]

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

[lofty]

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

[Franco Cozzo]

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

[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.

[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.

[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.

[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

[rodderz]

They sound like a V8 at idle but have that inline note when revved

Check out this old Buick, a header manufacturer's dream!
http://www.youtube.com/watch?v=71QbhORKCb0&NR=1

[Bud Bud]

When you look at the vid, they actually sound crap by what we call a V8 note by comparison but they do sound like a healthy big cubed six though!

Also I seem to remember that De Soto was renown for their straight 8's as well for some reason. (Didn’t Mr C have a straight 8 that Fonzie (not GM motorsport) souped up for a drag race in “Happy Days”?)

It is worth noting too that if there is too much stress on the crank with this configuration, then imagine how hard it would be to keep today’s stretched alloy head sealed as well.

[Quicksand]

Originally Posted by rodderz

They sound like a V8 at idle but have that inline note when revved

Check out this old Buick, a header manufacturer's dream!
http://www.youtube.com/watch?v=71QbhORKCb0&NR=1

After listening to the I8's rev in these youtube video's, this is probably the best way to describe what i'm hearing. It's veryyyyy interesting to hear this sound. Almost like a.....deeper sounding Skyline or F6...like someone has taken the I6 sound track and added more bass...??

Definitely a distinctive note for the inline engine!!!

[Quicksand]

Originally Posted by Bud Bud

When you look at the vid, they actually sound crap by what we call a V8 note by comparison but they do sound like a healthy big cubed six though!

Yes i feel the same. The Ford I6 does a good job in sounding tough all by itself without trying to be a V8 (IMO the I6 goes much further than a V6 in reaching the 'toughness' of a V8). The I8's in the vid are like an I6 trying to sound like a V8 but not quite getting it right...again the note is very distinctive and not entirely unpleasant to the ears

[Raptor]

How about VW groups W12 ;)

Similar size to a V6 but with 12 cylinders :