Anything special about I-6 engines? (Volvo,BMW...)

[440Magnum]

Originally Posted By: KenO
Agreed on almost everything above. The only downfall of the I6 is the long crankshaft. As long as they are, they need to be treated as a flexible rotor re: balancing & harmonics. The only BMW I6's that can safely rev much higher than ~7200 or so rpm are the Motorsports engines, like the S38 & the S54.


The length of the crank is a trade-space issue on almost all engines- you can reduce number of bearings and increase crank stiffness and per-bearing area for example, but that tends to increase rotating mass. Just gotta find the sweet spot for rhe intended application. Concrete example time: shorter crank length was a design choice that the Chrysler slant-6 engineers (led by Bill Weertman) made for that engine when it was on the drawing board back in the late 1950s. Its NOT a 7-main engine like a Jeep 4.0, it has FOUR mains (each the same size as the big-block v8 family mains) and its shorter as a result. the water pump is offset beside the block to further shorten the package. What was the price for 4 mains instead of 7? Nothing as far as I can tell- it didn't have massive crank failures even in its factory race "Hyper Pak" configurations, and in fact its widely regarded as one of the most reliable engines of the 20th century. So there are alternatives.

As for not revving as high... a) I think an I6 can be built to rev as high as any v6 of comparable displacement and output if that is a requirement, and b) who cares? High-revving is a band-aid for inadequate displacement. Everyone "oohs" and "ahhs" over an engine with a 13k RPM redline, but I just don't get it. If you can produce the power and speed at 6000 RPM and don't HAVE to wind out to >10k, so much the better. Yes, you can tell I'm biased to big engines by my .sig, I admit it But I also love F1 technology. F1 engines are mosquitoes because of the artificially imposed displacement limits in the rulebook. They're freqkin' AWESOME, but if that limit weren't there, I guarantee you there would be bigger displacements and lower redlines for higher overall performance. But I'm glad they're working off in one corner of the design envelope, because DANG is it ever cool!

 

[440Magnum]

Originally Posted By: blackman777
Thought the Toyota I6s were unreliable?


There were some VERY different Toyota I6s. The original Land Cruiser B-series was a torque monster like an American I6... because it was originally a Chevrolet design IIRC. The F-series that followed was a Toyota design, but still an OHV/pushrod torque monster, well suited to the application really.

Then there was the DOHC Supra engine from the 90s...

I've personally seen a stock lower-end Toyota Supra I6 with a giant turbo and a ton of top end modifications pull over 700 rear wheel horsepower (granted, the torque "curve" looked like a cone with a very sharp peak, but still... Its a beast.

The problems I've heard about are gasket leaks and annoyances, not anything to do with the core of the engine itself. My guess is those were because it was a low-volume engine that wasn't around all that long. It was pretty incredible, actually. And I generally hate on Toyota, as anyone who's read my posts knows...

 

[hattaresguy]

Originally Posted By: blackman777
Thought the Toyota I6s were unreliable?


If I remember off the top of my head I want to say the Toyota I6 in typical Japanese fashion at the time borrowed a lot from the M103 I6.

I know the Chinese at least until a few years ago were still producing new M104 I6's.

 

[KenO]

Originally Posted By: 440Magnum
Originally Posted By: KenO
Agreed on almost everything above. The only downfall of the I6 is the long crankshaft. As long as they are, they need to be treated as a flexible rotor re: balancing & harmonics. The only BMW I6's that can safely rev much higher than ~7200 or so rpm are the Motorsports engines, like the S38 & the S54.


The length of the crank is a trade-space issue on almost all engines- you can reduce number of bearings and increase crank stiffness and per-bearing area for example, but that tends to increase rotating mass. Just gotta find the sweet spot for rhe intended application. Concrete example time: shorter crank length was a design choice that the Chrysler slant-6 engineers (led by Bill Weertman) made for that engine when it was on the drawing board back in the late 1950s. Its NOT a 7-main engine like a Jeep 4.0, it has FOUR mains (each the same size as the big-block v8 family mains) and its shorter as a result. the water pump is offset beside the block to further shorten the package. What was the price for 4 mains instead of 7? Nothing as far as I can tell- it didn't have massive crank failures even in its factory race "Hyper Pak" configurations, and in fact its widely regarded as one of the most reliable engines of the 20th century. So there are alternatives.

As for not revving as high... a) I think an I6 can be built to rev as high as any v6 of comparable displacement and output if that is a requirement, and b) who cares? High-revving is a band-aid for inadequate displacement. Everyone "oohs" and "ahhs" over an engine with a 13k RPM redline, but I just don't get it. If you can produce the power and speed at 6000 RPM and don't HAVE to wind out to >10k, so much the better.



Yes and no. No you cannot take say, an M50 BMW engine, and make it rev to 10k reliably. If you can, you'll make a mint, because nobody's been able to do it yet. Mike Radowski is the only guy I know of who's revving one to 8k, but thats because he's turbo'd making nearly 1000 whp, and is zinging past that harmonic frequency so fast it doesn't have the time to shake itself to bits. VERY few places, if any, in the US can properly balance a BMW crank. I would be very suspect of anybody who claims they can, truthfully.


And as far as how high to rev the engine - it depends. Depends on the power goals, the overall power band, and where it's most efficient. Also depends heavily on gearing.

 

[440Magnum]

Originally Posted By: KenO

Yes and no. No you cannot take say, an M50 BMW engine, and make it rev to 10k reliably. If you can, you'll make a mint, because nobody's been able to do it yet.


I was talking clean-sheet designs, not something that exists. Crank harmonics may limit the I6, but higher-order imbalance will likewise become an issue with a v6 at some point. I was merely saying that the engine with the shorter crankshaft doesn't automatically win ;-)

 

[artificialist]

My dad had friends with Datsun Z-cars, and he was amazed with what they could do. They were fun to drive, and the engines lasted for ages.

Nissan made diesel version of the L, called the LD28. It was only sold during the early 80s Maxima, and few people bought them, but I don't know if they were troublesome or not. They probably weren't popular because around the same time, some of the worst diesel powered cars were built.

Around the time the Datsun name was eliminated, the L-series inline 6 was replaced by the VG-series V6. If Nissan used a timing chain instead of a belt, The VG would every bit as good as the L. Nissan wanted to make an FWD car with 6 cylinders, so the VG was created. It was the only good thing about the 1985-1988 Nissan Maxima.

He also thought of anther I6 that he liked, the Ford 300. It wasn't exciting at all to drive, but he saw how much his co-workers abused the company trucks, so he was stunned by how much a Ford 300 could take. He once dealt with a guy who over-reved the engine, and one connecting rod cap was thrown off and put a hole in the oil pan. The engine kept going until all the oil was gone.

The Nissan RB-series inline 6 is amazing. The only thing I don't like is that it uses a timing belt. Same could be said for the Toyota 2JZ engine.

I was thrilled back when the Chevy Trailblazer came out and used an all new aluminum inline 6, but it just wasn't as good as I had hoped.

 

[jrustles]

Originally Posted By: artificialist

The Nissan RB-series inline 6 is amazing. The only thing I don't like is that it uses a timing belt. Same could be said for the Toyota 2JZ engine.


Haha, who buys either of those engines for high-mile longevity?? I can't imagine having much fun pulling chain covers each time to adjust cam timing on a chain setup

V6 and I6 can essentially sound exactly the same, all you need is an exhaust pulse every 120 degrees of crank rotation. The sound all entirely depends on equal exhaust header primary and secondary lengths- as long as the exhaust pulse of each cylinder travels the same distance, then the engine will sound smooth and awesome! In reality though, much production V6 installations put equal exhaust lengths at low priority to packaging.

Otherwise I6 is perfectly balanced as previously mentioned, where a 60 degree V6 for example has a noticible imablance at around 2100rpm.

Also despite not really presenting a problem in I6 apps, crankshaft torsional vibration is anoteh consideration and is vitually eliminated with the shorter V6 crank.

 

[artificialist]

Originally Posted By: jrustles

Also despite not really presenting a problem in I6 apps, crankshaft torsional vibration is anoteh consideration and is vitually eliminated with the shorter V6 crank.

I think the reason Henry Ford wanted a V8 during the 1930s was because he didn't believe a straight 6 crankshaft was going to be durable enough for the job.

Other companies went with an OHV inline 6, and Ford had the flathead 8.

 

[jrustles]

Originally Posted By: artificialist

I think the reason Henry Ford wanted a V8 during the 1930s was because he didn't believe a straight 6 crankshaft was going to be durable enough for the job.

Other companies went with an OHV inline 6, and Ford had the flathead 8.


Interesting. Perhaps his cranks couldn't stand up, he was a notorious cheapskate and economizer

 

[supton]

Originally Posted By: jrustles
Originally Posted By: artificialist

I think the reason Henry Ford wanted a V8 during the 1930s was because he didn't believe a straight 6 crankshaft was going to be durable enough for the job.

Other companies went with an OHV inline 6, and Ford had the flathead 8.


Interesting. Perhaps his cranks couldn't stand up, he was a notorious cheapskate and economizer

The Ford Flathead used 3 bottom main bearings! Shorter crank, but not well supported, and doing some reading indicates it was not a light crank at that (68lb?).

Odd reading here, about altering the firing order on this old V8: http://midstateantiquestockcarclub.com/flat_heads5.html

 

[hattaresguy]

Originally Posted By: KenO
Originally Posted By: 440Magnum
Originally Posted By: KenO
Agreed on almost everything above. The only downfall of the I6 is the long crankshaft. As long as they are, they need to be treated as a flexible rotor re: balancing & harmonics. The only BMW I6's that can safely rev much higher than ~7200 or so rpm are the Motorsports engines, like the S38 & the S54.


The length of the crank is a trade-space issue on almost all engines- you can reduce number of bearings and increase crank stiffness and per-bearing area for example, but that tends to increase rotating mass. Just gotta find the sweet spot for rhe intended application. Concrete example time: shorter crank length was a design choice that the Chrysler slant-6 engineers (led by Bill Weertman) made for that engine when it was on the drawing board back in the late 1950s. Its NOT a 7-main engine like a Jeep 4.0, it has FOUR mains (each the same size as the big-block v8 family mains) and its shorter as a result. the water pump is offset beside the block to further shorten the package. What was the price for 4 mains instead of 7? Nothing as far as I can tell- it didn't have massive crank failures even in its factory race "Hyper Pak" configurations, and in fact its widely regarded as one of the most reliable engines of the 20th century. So there are alternatives.

As for not revving as high... a) I think an I6 can be built to rev as high as any v6 of comparable displacement and output if that is a requirement, and b) who cares? High-revving is a band-aid for inadequate displacement. Everyone "oohs" and "ahhs" over an engine with a 13k RPM redline, but I just don't get it. If you can produce the power and speed at 6000 RPM and don't HAVE to wind out to >10k, so much the better.



Yes and no. No you cannot take say, an M50 BMW engine, and make it rev to 10k reliably. If you can, you'll make a mint, because nobody's been able to do it yet. Mike Radowski is the only guy I know of who's revving one to 8k, but thats because he's turbo'd making nearly 1000 whp, and is zinging past that harmonic frequency so fast it doesn't have the time to shake itself to bits. VERY few places, if any, in the US can properly balance a BMW crank. I would be very suspect of anybody who claims they can, truthfully.


And as far as how high to rev the engine - it depends. Depends on the power goals, the overall power band, and where it's most efficient. Also depends heavily on gearing.


Maserati had their I6's screaming to 7k in the 60's.

 

[Spazdog]

Originally Posted By: hattaresguy


Maserati had their I6's screaming to 7k in the 60's.

The Honda CBX 6 cylinder had the same 9500 rpm redline as the 4 cylinder CB1100F.

 

[nleksan]

I absolutely love inline 6's! You can probably guess from my signature, lol.

The only better engine, IMO, is a Ferrari V12, and

 

[hattaresguy]

Their is very little that sounds better in this world than a V12 F car at full stride!

 

[fsskier]

Originally Posted By: jrustles
Originally Posted By: artificialist

I think the reason Henry Ford wanted a V8 during the 1930s was because he didn't believe a straight 6 crankshaft was going to be durable enough for the job.

Other companies went with an OHV inline 6, and Ford had the flathead 8.


Interesting. Perhaps his cranks couldn't stand up, he was a notorious cheapskate and economizer

Exactly!! The old flathead V8's....all of my friends inherited them and became our first cars. While the flathead Plymouth inline 6's still had decent oil pressure at 100,000 miles, the Ford's had NONE that would show on the pressure gauge after the engine got hot....especially in the summer. Idling they would go clear to a reading of 0....revved up maybe 10 lbs.

Still, they ran fine! Of course oil pressure on a flathead....no overhead valves and rockers to pump oil up to....is not really needed. The oil flow would have been wonderful, the bearing flow would have been huge, and throwing copious amounts of oil up onto the cylinder walls, etc. Mostly just a sign of worn out bearings.

I did not mention the Chevrolet dipper 6 cyl engines of course.....oil pressure used to pump oil to the overhead valves but no pressure in the crankshaft at all. Or a Briggs and Stratton today yet!

 

[artificialist]

Originally Posted By: Spazdog
Originally Posted By: hattaresguy


Maserati had their I6's screaming to 7k in the 60's.

The Honda CBX 6 cylinder had the same 9500 rpm redline as the 4 cylinder CB1100F.

Yes, rev limit is determined by the size of each cylinder than anything else. That is why I had to spend a lot of time explaining why the Ford 300 had an extremely low rev limit, and simply loads of low end torque, but a Datsun Z car needed to be pushed, and had a very high rev limit.

He then believed that V6 engines were made for higher rpm winding. He though that because Mom's '85 Maxima had a 3.0L engine. I then explained that if you had a Chevy 4.3 V6, it would be similar to comparing the Datsun Z versus the Ford 300.

I explained it to him using some of the vehicles he owned as an example. I said: You had a Honda 4-cylinder motorcycle in the 70s, and it revved to numbers that none of your 4 cylinder cars ever reached.

During the 1960s, Nissan created the first GT-R, and used a 2.0L DOHC engine that reached 8,000 RPM due to the small size, and the use of 3 carbs.

 

[blackman777]

Based on what I read here, the I-6 doesn't sound like an engine worth pursuing. I already get outstanding longevity on my V6 and I4 engines (360,000 miles on the I4).

 

[SteveSRT8]

Originally Posted By: artificialist
Originally Posted By: Spazdog
Originally Posted By: hattaresguy


Maserati had their I6's screaming to 7k in the 60's.

The Honda CBX 6 cylinder had the same 9500 rpm redline as the 4 cylinder CB1100F.

Yes, rev limit is determined by the size of each cylinder than anything else. That is why I had to spend a lot of time explaining why the Ford 300 had an extremely low rev limit, and simply loads of low end torque, but a Datsun Z car needed to be pushed, and had a very high rev limit.

He then believed that V6 engines were made for higher rpm winding. He though that because Mom's '85 Maxima had a 3.0L engine. I then explained that if you had a Chevy 4.3 V6, it would be similar to comparing the Datsun Z versus the Ford 300.

I explained it to him using some of the vehicles he owned as an example. I said: You had a Honda 4-cylinder motorcycle in the 70s, and it revved to numbers that none of your 4 cylinder cars ever reached.

During the 1960s, Nissan created the first GT-R, and used a 2.0L DOHC engine that reached 8,000 RPM due to the small size, and the use of 3 carbs.


Quite frankly in most modern engines the valve gear and cam design are the primary factor in determining rev limits. Of course the rotating assembly gets some credit here, too, but for most cars it is the valve gear that is the limiting factor...

 

[RobertISaar]

Originally Posted By: jrustles
where a 60 degree V6 for example has a noticible imablance at around 2100rpm.


this is the first time i've ever heard of this.... care to elaborate/link for more information? i've never heard of specific RPMs being problematic, especially since none of my 60V6s have ever had an issue at that speed.

 

[jrustles]

Originally Posted By: RobertISaar
Originally Posted By: jrustles
where a 60 degree V6 for example has a noticible imablance at around 2100rpm.


this is the first time i've ever heard of this.... care to elaborate/link for more information? i've never heard of specific RPMs being problematic, especially since none of my 60V6s have ever had an issue at that speed.


Both our personal 60degree'ers have this- and they couldn't be further apart in design. The thing they share in common is that they're both even-fire, 60degree V6's.

1) the Japanese 2.5L has a super-stiff two-piece aluminum block, short stroke, long rods, light recip. assy, is DOHC and sings to 8000rpm while simultaneously being able to pull from 500 RPM in gear smoothly, without bucking AT ALL.

2) the American 3.5L is an iron-block design featuring OVH pushrod valvetrain (GM LX9).

...they both rumble in that RPM range. The urethane motor mounts on engine 1) don't help either

Quote:

A 60-degree V-6 engine isn’t quite as successful. The rotational and reciprocating forces can’t be completely balanced because this type of V-6 is essentially two three-cylinder engines stuck together. Inline-three engines, because of their odd number of cylinders, are inherently imbalanced and will tend to rock from end to end.


With two of them mounted 120degrees out of phase with each other, the rocking combines into somewhat of a gyration that is usually snuffed by engine mounts