Talk:Straight-6

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I removed the passage about bad low rpm torque of small sixes, because it is simply not connected to the straight six principle per se, but rather to things like cylinder bore to stroke ratio. For the same ratio, a six is better than a four. The old Triumph 2000cc straight six had very good low rpm torque, as an example. Egil 06:50 Apr 25, 2003 (UTC)

The Suzuki Verona FWD midsize sedan has a 2.5L i6 - think it's worth a mention?

As rare as inline sixes are these days, it probably is, especially in that kind of car. --Morven 06:47, 21 Sep 2003 (UTC)
Added the Verona bit - sounds like a decent car. It's apparently meant to compete with other manufacturers i4's (in price and power), while being smoother and providing better side-to-side weight balance. -- stewacide

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   The smallest production straight-6 was found in the 1927 Alfa Romeo 1500, displacing just 1.5 L.

This is not true. The Kawasaki z1300 is smaller. 83.248.140.239 17:35, 20 May 2006 (UTC)

Is the straight-6 in the Benelli 750 Sei not a production engine? It has a displacement of 747.7cc. Here is a link: [1] PerDaniel 09:29, 15 June 2006 (UTC)
I haven't found any production numbers, but I found some info on the web that shows that it is a production engine: The members of this british club owns forty Benelli 750 sei [2]. And this page have details about a recall on the 1976 model 750 sei that potentionally affects 102 units [3].PerDaniel 14:52, 3 July 2006 (UTC)

Contents

[edit] Ford info wrong

I noticed that the article mentioned that Ford switched straight from I4 to V8. I changed it around and added a little bit of information which could probably be improved on.

[edit] Jaguar info wrong

It's correct that the XK-engine was discontinued in the mid 80s, but it wasn't directly replaced with a V8. Jaguar used AJ6 and AJ16 until 1997. Jaguar_AJ6_engine 81.230.16.36 18:09, 19 October 2006 (UTC)

[edit] vibration question

I'm an engine novice, but have heard something about this configuration reducing certain types of engine vibrations or resonances (or something along those lines). If so, could an editor please add a note into the main article? Santaduck 11:17, 10 August 2006 (UTC)

[edit] BMW Diesel I6s

BMW has a fairly new line of diesel I6s on their passenger vehicles (but not in the USA at this time). Perhaps someone would like to make a short addition to the diesel I6 section to reflect this and provide a more international context to the article. Indeed, this is at least as relevent as I6 diesel Mercedes no longer produces. 71.65.124.21 15:11, 20 November 2006 (UTC)

[edit] BMW Straight 6s

I removed the following line "BMW is known to have mastered the straight-6 cylinder configuration in its automobiles." This is pure conjecture, and there is no basis to suggest a BMW 6 is better or worse than any other 6! Jimio 21:42, 29 January 2007 (UTC)

[edit] Triumph Straight 6s

Added some more info on the Triumph 6s Jimio 22:00, 29 January 2007 (UTC)

[edit] Perfect Primary Balance?

I'd like a citation for the claim that the straight six has perfect balance- the counter-balancers on the GM 6-71 are pretty hefty- and make up for the end-to-end rocking native to straight engines (as cited in the original Grey Marine manuals) Jdos2 13:17, 31 May 2007 (UTC)

The statement only applies to four-cycle engines. In a four-cycle engine every cylinder fires every second revolution. In a straight-6 the cranks are at 120 degree angles to each other and the two ends of the engine are mirror images of each other. Piston #1 moves up and down in unison with #6, #2 with #5, and #3 with #4 - one being on the compression stroke and the other on the exhaust stroke - which cancels the end-to-end rocking couple. The Detroit Diesel 6-71 is a two-cycle marine/bus/locomotive engine. Every cylinder fires every revolution and the cranks would be at 60 degrees to each other. I have no idea what the firing order is, but it probably involves a lot of rock and roll since you can't balance pistons against each other. It's a boat engine, so nobody cares. RockyMtnGuy 20:31, 5 August 2007 (UTC)

[edit] Diesel applications?

Almost 99% of heavy-duty diesel engines in the United States today are massive inline-6s, does this warrant a mention in the article? --TopGear 07:54, 7 July 2007 (UTC)

[edit] Main bearings and power potential

From the article:

The predominance of the V8s in the muscle car era was largely a matter of marketing, since the seven-main-bearing design of the big sixes allowed racers to modify them to produce as much horsepower as small V8s, and the overhead cam of the Pontiac six allowed it to run at much higher speeds. However, automakers found it profitable to sell straight-6s as "economy" engines and V8s as "performance" engines regardless of their horsepower potential, since big, unsophisticated, overhead valve V8s were relatively cheap to manufacture, and fuel economy was not a concern during this period.

How does having 7 main bearings make for a better engine? Isn't 5 big ones in a V8 the same thing, with the added benefit of having a shorter crankshaft which is less prone to twisting? Also, the comment that the sixes had the same HP potential seems to have little basis in fact, given that stock vs stock, the V8s had way more power. The above paragraph wreaks of bias and opinion. If the points can't be proven, I'm going to zap it. Craigblock 17:41, 9 September 2007 (UTC)

It's somewhat awkwardly put. I think the distinction is between a 7 main bearing six and a 4 main bearing six, in that the former gets crankshaft flex under control and gives you more potential for high-end horsepower, which you can exploit with an easily added overhead cam or two. However, the general gist is that the American manufacturers went off down a technological blind alley with the big pushrod V8s and got sucker-punched by the fuel crisis, while BMW, Mercedes, and the Japanese managed to crank out as much power from more fuel-efficient overhead cam straight sixes. There's probably a better way to put it. The point is probably moot now that V6s have taken over the market, but American manufacturers are still off down a blind

alley with the big OHV gas guzzlers. RockyMtnGuy 21:07, 10 September 2007 (UTC)

[edit] Primary balance and zero Secondary problems?

Does the writer of this article own a bmw m3 or what? Where does this supra loving insanity come from? Yet another bias non-factually written article by someone who is a fan of the product written.The straight 6 is NOT a balanced engine. The only hope for any balance in 6 cylinders is a 120 degree v block, and that is found in aviation, where true engineers put real balanced engines. A slow giant thumping diesel does not need to be as precise as the gasoline engines, hence they are indeed mainstream, and they are terrible.My family has been in trucking my whole life. To prove to yourself with your own straight six.. find the rpm that vibrates under torque. It is very simple to prove. Hence the straight sixxes left in the car world are going for insane turbo pressured high rpms to avoid the FLAW of lack of BALANCE with the same manic the inline four world does. ~soob792~ 20:20, 6 November 2007 (UTC)

The straight six does have proper balance. The pistons are balanced fore and aft, just like a four cylinder, and if you were to derive the piston position versus crank angle equation with respect to time, you'd see that the net velocity of all of the pistons adds to zero for all crank angles, which implies that the assembly is balanced. The article is correct. Also, a V6 is not balanced correctly, regardless of v-angle, unless a balance shaft is used. 99.240.243.25 21:54, 7 November 2007 (UTC)
Yes, the 120-degree V6 suffers from primary dynamic imbalance, as do all V6's, and benefits from a balancing shaft to smooth it out. It's also too wide for most practical purposes and any manufacturer who can fit it into their engine compartment will probably prefer to use a horizontally-opposed flat-6 engine like Porsche, Subaru and the light aircraft engine makers. Both the flat-6 and straight-6 are in perfect primary and secondary dynamic balance, which explains their snob appeal amongst the connoisseurs of Teutonic sports/luxury cars (not to mention Japanese companies who used to build WWII aircraft). However, it's a little known fact that BMW had a series of V8s ready to go into production in the early 1970s, but when the first oil crises hit they canceled their V8 program, refined their straight-6s, and avoided the cost of setting up a V8 assembly line for nearly 20 years whilst scoring points with the snobbier car buyers and appearing to be marketing geniuses. It's like buying wine, if it's not a straight-6 it's not really a proper BMW, if it's not a flat-6 it's not really a Porsche, and if it doesn't come from France it's not really champagne. RockyMtnGuy 22:34, 8 November 2007 (UTC)
Of course it's balanced, or at least it's the best you can manage without a dozen pistons or a balance shaft. Coming from Australia, I find the notion that a straight-6 could have "snob appeal" very very amusing :) 202.7.183.132 (talk) 23:52, 5 April 2008 (UTC)
Granted, Australian straight sixes may be a bit humorous, but the German luxury car makers have managed to extract rather impressive amounts of power out of their sixes (not to mention rather large amounts of money out of their customers). RockyMtnGuy (talk) 00:56, 9 April 2008 (UTC)
The most powerful production straight-6 that I know of is the soon-to-be-released Ford Falcon FPV F6 - 310kW/565Nm for about the same money as a BMW 323i. Ha! 202.7.183.131 (talk) 13:55, 23 April 2008 (UTC)