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in-line 6 Cylinder Engines, 'straight-six'

Discussion in 'Engines' started by brian eiland, Jun 26, 2012.

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  1. Fishtigua

    Fishtigua Senior Member

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    This is news to me too. As Mack is owned by Volvo/Renault Trucks, I'm wondering if the motor/block is the same as the Penta D12? Those are a 12ltr as well.
  2. Pascal

    Pascal Senior Member

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    It s the first time I hear of a failure on the Merc box used in the Rs. I had both an 99XJR and a 00 XKR. I did go thru 3 differentials in 6 years on the XKR though, for some reason Jaguar though they could use the same diff as the normally aspirated models.

    Had the water pump and tensioner problems on both.. And a year after i sold the XKR I heard the buyer had to replace the engine Due to nikasil failure... BMW got bitten by nikasil too in the 90s...

    Back to straight 6, the engine used from the late 80s was the AJ6 engine, different from the XK engine. Both where great and valves adjustment wasn't a real issue.

    I still have my 72 E-type (V12, another great engine...), almost bought a V12 XJS last month...
  3. ddw1668

    ddw1668 Senior Member

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    No problems with the air suspension (CATS) on the Super V8. Crossed fingers as I understand it is $7grand repair. The car has 12,000 miles and is a garage queen so far. :cool:
  4. ddw1668

    ddw1668 Senior Member

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    I am in the plating business and I have done electroless nickel with silicon carbide plating (ie: Nikasil) years ago. It is absolutely bullet proof is you get perfect adhesion to the substrate. Since the Jaguar blocks are aluminum, that is the weak spot. Aluminum forms an oxide film almost immediately upon being exposed to atmosphere and plating Al is a crap shoot at best. I believe the plating was done at a plant in Wales and was very proprietary as they only plated the cylinders. Have not looked into it lately and I have had no problems with my Nikasil engines.
  5. ddw1668

    ddw1668 Senior Member

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    The PO had a turbo rebuilt under warranty and no further work has been done. The engines were marinized by American Diesel in New England. It is my understanding that Macks are popular among commercial fishing captains. The PO had an interest in a trucking company and was a fan of Mack engines.
  6. Capt J

    Capt J Senior Member

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    After all of the problems everyone has stated with Jaguar's, I sure as heck wouldn't want to own one. Differential failures 3x, valve adjustments, transmission failure, $7,000 air suspension, nikasil liner issues.......thanks but no thanks.......LOLOLOL
  7. SHAZAM

    SHAZAM Senior Member

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    There have been marinized macks running around for as long as I can remember. The first ones that I remember were built by Merlin and then later on I think it was some outfit named American Marine Diesel. I seem to remember Lauderdale Propeller Service being a dealer for one of the companies that was marinizing them for mack.
  8. brian eiland

    brian eiland Senior Member

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    Ultimately I am hoping that this subject thread leads to more discussions about MARINE 6 cylinder diesel engines, and the virtues and negatives of these various brands. But I do realize that there are lots- of experiences out there with auto engines, so all discussions are welcomed, and interesting. The point being that in many of the MARINE applications we are not concerned about a little extra 'weight per power ratios', but rather long term durability at continuous high outputs.

    There has been lots of development in lighter weight diesel engines over the past 15 years, but generally this higher power to weight ratio is gained with higher revving engines of square or over-square design. That means much higher piston speeds for the same work done, and that means more frequent overhauls. Some of these engines have overhaul periods of half, or even ¼ that of a good industrial six cylinder diesel. I believe that most of the trucking fleets utilize six cylinder diesels...for long haul and long durability??



    How about this Jaguar reference,
  9. brian eiland

    brian eiland Senior Member

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    REPOWER ?? GM Suburban, Denali, Escalade, ...Ford Explorer, Expedition, Excursion

    Since we have a lot of automobile talk here (in addition to that marine related ), I'm going to bring up a subject I was trying to get the automobile companies to consider. Back when the automobile companies in the USA where experiencing dire problems, and our fuel prices were shooting up big time as we approached $100 per barrel crude oil, this thought came to me, 'Why have these big car company executives not seen this coming? Why have they persisted in bringing out ever bigger V-8 engines, and/or not at least exploring other possibilities concurrently with this new world environment? Can they be so short-sighted?'

    Americans (and particularly the 'soccer moms') have come to love these big SUV's. But do we really need to power them with ever bigger displacement, fuel hungry V-8 engines ? Why doesn't someone in both GM and Ford take a little look back in their company history's and realize that both of these companies use to build a rock solid in-line 6 cylinder engine. Why not tweak these old designs a little bit by giving them an up-to-date electronic ignition system, and a modern fuel injection system?

    What might we end up with? By eliminating 2 cylinders out of the equation then each RPM requires that much less fuel consumption. I dare say with the updates, and the elimination of 2 cylinders a 12-15% gain in fuel economy could be had.

    Now these old sixes were noted for great torque output due to their longer piston strokes. So you modify the lower transmission ratio to give you great acceleration at the low end (likely as good as if not superior to that V-8), and you add an extra gear ratio to the top end to give you great hi-way mileage. You might even gain another 10-15% better fuel economy.

    So what do you end up with? The same size vehicle that everyone likes ...with much better fuel economy (25-30%), very little lost of power, and you didn't have to 'reinvent the wheel' or retool much of anything?? Why couldn't top management figure that one out?,...and they have yet to do it !!
  10. Capt J

    Capt J Senior Member

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    They did and it didn't work in their pickup truck line. Ford in their F 150's (the best selling US truck for decades) had a 300 cubic inch inline 6cylinder gas engine. It had less power and much less fuel economy than the 302cu inch v8. While the 6cylinder diesels work well, it appears the gas engines at least in the larger displacements aren't fuel efficient. I think that has to do with bore vs stroke ratio and the port designs exhaust and intake on a 6 cylinder. You're forgetting that a heavy truck, needs x amount of horsepower and x amount of torque to accelerate, get to, and stay at speed and they're not the most aerodynamic vehicles. So you're just pushing a 6 cylinder that much harder to do the same. The torque in a vehicle is used to accelerate it from a dead stop to speed, at that point horsepower is utilized and the v8's have more power in the same cubic inch package.

    They should offer more diesels, and I think Ford/GM would've pursued that route much more if the EPA didn't really clamp down on emmissions on the diesels. Right now both companies diesels have to have so many different emmissions systems on them to meet the EPA mandates, that it REALLY adds to the cost of the engines/vehicle and also makes them less reliable.
  11. Grecko

    Grecko New Member

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    My point was related to ANY application, both marine, automotive or even aircraft. The simple point being that a V8 (or an opposed) configuration, while slightly more expensive to produce than a inline six, provides smoother operation and better power to weight ratios. That applies to diesel or gas engines. The reason for this is that a straight six has a lot more cylinder block mass for a given displacement, and a heavier crank since the rods don't share crank throws. As a result, you can have a larger displacement engine with more power, or you have the option of slowing down the larger engine and having longer life. While many marine engineers "don't care" about the weight, if you strive for an efficient system, adding mass for no real reason isn't generally a good way to achieve it.

    If the designer shortens the stroke he can increase the rotational speed and maintain a similar piston speed. That's the beauty of a shorter stroke design. The downside is that the valves don't get as much time on their seats and it is a lot harder to keep them cool and valve life generally suffers.

    There is a strong relationship between specific output and life. Bottom line is that higher specific output engines have a shorter life. That is pretty much a fact of life and if you want really long life, you will slow any engine down and reduce the piston speed and the load on the components. What trades the designer makes in the design space and the manner in which the details are carried out also have a very strong influence on life so it's not not just a piston speed or temperature issue either.

    Well, actually the XK series of engines are relatively long stroke engines were never really high speed engines. Back in 1948 they were great engines, but they became obsolete in racing, in large part due to their inline configuration. They had (for the time) advanced cylinder heads and good breathing, and did well more from that aspect than their inherent configuration. While they won Le Mans in the 50's, by early 60's they were really pretty much relegated to back marker status. Same can be said for the Aston Martin six cylinder engines. Ferrari pretty much dominated sports car racing with their V12's through the mid 60's, and they were replaced by Ford V8's and Porsche V12's. Bottom line is that since the BMW CSL of the mid 70's, there hasn't been a competitive inline engine in endurance racing. That's over 35 years ago. The fact that the XK series remained in production for a long time is more indicative of how well it was designed originally than any inherent goodness of the in line configuration.
  12. Grecko

    Grecko New Member

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    Well actually Brian, there has been a trend to 6 cylinder engines, but these virtually all have been V6 engines and they are a lot lighter than inline engines and these also package much better in a front drive installation. When you consider the cost of tooling and how many applications you can put the package into, an inline engine doesn't make much sense. Most of those engines were leftovers from the early 50's, and, while torquey, they weren't powerful or all that efficient. It's relatively easy to quantify how much each pound costs you in terms of EPA rated mileage, and that's as good a measure as any to compare apples to apples. When you do that the much lighter V6 beats the inline six every time.

    Also remember that for a given road speed fuel mileage is a strong function of displacement per mile. That is, look at the gear ratio in top gear (actually multiplied by the tire size) times the engine displacement and that will tell you how much potential there is for fuel economy (assuming similar aerodynamics). Very tall gearing in V8's can give you the same displacement per mile as a smaller engine, and very similar fuel economy. My Corvette has a very tall sixth gear, at 75mph it is only turning 1700 rpm and it gets 32 mpg on the highway at that speed. Pretty impressive for a car that gets to 60 mph in four seconds flat.
  13. Capt J

    Capt J Senior Member

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    Yes, and the other trend I've been seeing a lot of in the last few years in gas vehicles is a smaller displacement 4 cylinder or v6 and utlitizing a supercharger or turbocharger for the power yet gaining more efficiency at cruising or highway speeds with the smaller displacement.

    As to the corvette, I've owned many back in the day and the fuel economy they get on the highway is a sheer miracle given the amount of horsepower and torque they have. I know one thing, you can chew through a TON of fuel in the city hotrodding around though......if you're constantly bottoming out the go pedal......hehehehe
  14. Fishtigua

    Fishtigua Senior Member

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    I had an old Chevy Diplomata, built in Brazil with the 4.1ltr straight six from the mid 70's. It put out 125hp and 200ft-lb on an autobox. The EPA fuel figures said it should give 18mpg but running in Antigua, often on dirt roads, at 30 to 40mph on low octane fuel, I got much better economy than stated.

    Those long stroke motors just purred along, burning very little at low revs. It was only when you floored the throttle did the fuel needle move toward the E mark.

    Attached Files:

  15. Grecko

    Grecko New Member

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    The basic Chevy "Stove Bolt" six traces it's lineage back to the late 20's. The 4.1 was designed in 1962. Good engine, but only 125 hp from 4.1 liters is pretty low specific output. A BMW 4 cyl of the same vintage could make the same power, but wouldn't be nearly as nice since it wouldn't have the torque of the bigger 6. This engine had 7 main bearings. Good for reliability, but that makes for a lot more bearing drag than a v6 with only 4 main bearings. This is another reason for the switch to V6's, when the EPA mileage is on the window sticker, the better number you can post often swings the sale. Also with CAFE standards, it helps the manufacturer to reduce the fuel consumption of any and all of his cars. While I'm sure a V6 is more expensive to produce than a straight six, they want the lighter, smaller, and more efficient engine in a car.
  16. brian eiland

    brian eiland Senior Member

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    Stroke-to-Bore Ratio: A Key to Engine Efficiency

    I was looking for some figures that might show what I believe to be the small affect the bearing loses are compared to piston ring loses in an internal combustion engine. Didn't find that yet, but I did find this interesting piece:

    Stroke-to-Bore Ratio: A Key to Engine Efficiency

    ....a few excerpts
    While there are many factors that contribute to an engine’s efficiency, the primary factor that needs to be considered is the engine geometry itself. Not only does the overall size of the engine matter, but the aspect ratio of the engine cylinders—defined by the stroke-to-bore ratio—also matters. To explain why, one must consider three factors: in-cylinder heat transfer, cylinder scavenging and friction.

    Simple geometric relationships show that an engine cylinder with longer stroke-to-bore ratio will have a smaller surface area exposed to the combustion chamber gasses compared to a cylinder with shorter stroke-to-bore ratio. The smaller area leads directly to reduced in-cylinder heat transfer, increased energy transfer to the crankshaft and, therefore, higher efficiency.

    For context, below is a plot of power density versus stroke-to-bore ratio of some current four-stroke engines designed for a wide range of applications. Note that all of the engines in the chart have cylinder heads, so the stroke describes the actual piston stroke. The data in the plot show a trend in which engines that require high power density—like those in race cars—have a small stroke-to-bore ratio, and engines that require high fuel efficiency—like those in heavy-duty trucks and marine cargo ships—have a large stroke-to-bore ratio.

    The limiting factor in this relationship is the inertial forces origination from the piston motion. To achieve high power density, the engine must operate at a high engine speed (up to 18,000 rpm for the Formula 1 engine), which leads to high inertial forces that must be limited by using a small stroke-to-bore ratio. For applications that demand high efficiency, a long stroke-to-bore ratio is necessary and, again because of the inertial forces of the piston, requires a slower engine speed and lower power density. For the marine application that has a 2.5 m stroke, the engine speed is limited to 102 rpm.
  17. brian eiland

    brian eiland Senior Member

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    Bearing Losses compared to Piston Ring Losses

    I did find this:
    http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA460134

    Engine bearings 20-30%
    Piston Ring Assembly 45-50%


    ABSTRACT
    This paper examines sources and contributions of friction in heavy-duty diesel engines. Current and past work done on the characterization of diesel engine
    friction will be reviewed. It is also a goal to analyze each component system from a basic mechanics viewpoint highlighting some of the key friction producing
    phenomena. Different regimes of lubricated friction will be illustrated using a generic Stribeck diagram, with a focus on loading and relative velocities.



    ....sorry, got off on an abstract thought process, but i wasn't buying into the BIG loses of a couple of extra main bearings on the HD inline 6 engine...
  18. Capt J

    Capt J Senior Member

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    I know that in the older Ford F150's where they offered an inline 6 (300Cu in) and a v8 (302 cu in). The fuel economy on the inline 6's in real life was poor and less than the v8, but here are the EPA figures

    6cylinder automatic city 12 mpg, combined 14mpg and highway 17mpg
    v8 302 automatic city 12 mpg combined 14 mpg and highway 17mpg

    Both 2wd.

    I don't know about the whole bore versus stroke. I know a shorter stroke can be revved higher and has the potential to make more hp. I know this, the 302 cu in Ford v8 and the 351 ford v8 shared the same cylinder heads and such. You could always make a lot more power with a 302 over a 351 with the same mods and the 302 always got much better fuel economy due to it's smaller displacement.
  19. brian eiland

    brian eiland Senior Member

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    Some interesting observations about those good old Ford inline 6's

    The Ford Inline 300 straight six is a Bullit proof motor. As other people have said, it's great for torque & pulling, but not that great at highway speeds over 75mph. You could abuse that motor and it would never die as long as it had oil in it, and was the most reliable motor Ford made. That explains why Ford discontinued the motor in 96 because they wouldn't break down, so they couldn't sell repair parts.

    ...and this one :D
    It is stronger torque wise which translates to more pulling power.
    Great engine.
    I had one in an old bread van. One time I was pulling my 23 ft. trailer over the mountains out of Bakersfield, Ca. when a Chev. pickup pulling about the same trailer passed me on the flats. He was very proud of his new truck as it was one of the first diesel Chev. pickups made & he had painted on the front fender "V8 Diesel, 4 speed, Fuel Injection". He would pass going downhill & on the flats as I only had top speed of maybe 70 mph but I would pass on the next hill! It got to be quite a game for me laughing at him as my old junker passed him on every hill while he would run off & leave me as he had a higher top speed (I don't think you should be pulling a trailer 70-90 MPH). Of course it didn't help that I was laughing at him every time I passed!

    I know the feeling, I had a friend of mine that had a ford with the 460, I told him I could pull a trailer full of steel up a hill faster than he ever could from a standing start for $100. He went first I did second run, his time was 8.5 seconds, Mine was 6 seconds flat. He was pissed,lost $100


    Is the Ford F150 inline-6 stronger than the V-8
  20. brian eiland

    brian eiland Senior Member

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    These in-line 6 car engines have gotten a bad rap related to fuel usage,...and yes some of them were fuel hogs. BUT look at the age they were developed. There weren't even Interstate Hwys at that point,..but rather mostly two lane roads with top speeds of 55MPH. Even automatic transmissions were new things so these trucks used 3-speed std shifts.

    Modernize these engines, and add some extra gearing to help then compete in this modern world, and you may have a 'powerhouse' errected from an older age.


    1979 F250 WITH INLINE 6 CYLINDER - Page 2 - Ford Truck Enthusiasts Forums

    ...couple of excerpts....

    The nice thing about the 300 is that you can about double the hp and retain nearly the same mpg. If you want to see some nice gains, you have to start with the head. It is the bottle neck of the engine. It needs to breathe easier, to flow more. That is done with a simple $350 porting job, cleaning up the bowls and runners, polishing the c.chambers. With that add a 30* back cut on the intake valves to a 3 angle v.job, and you are taking a major step to waking up your engine.

    Add to that a nice Offenhauser intake, and a good 4v carb, and the efi exhaust with dual 2" or 2.25" pipe, or single with 2.5" pipe, and you will have quite an engine.

    I have a series of articles about how to wake up the 300 in true blue trucks magazine, and write a column for them called backyard mechanic.

    ........and


    You need to get your answers over at the I6 forum. I have an F350 that I swapped from a 390 to a 300. My goal was to retain the hp, but yet achieve 50% better mpg.

    I now get 17 mpg on the freeway with 3.31 gears and a C6. Before I got 10, rain, shine, empty, loaded. I am now packing the nuts away so I can swap it over to a ZF five speed manual. Not only will you get better mileage with a manual, but you'll regain about 30 hp.

    Changing over to the 300 worked out great for me.