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Old 11-02-2010, 11:27 AM
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square bore/stroke and high rod/stroke ratios

I am a mechanic so I obviously work on a lot of different vehicles cars and trucks all day. So naturally we get to drive such vehicles and see what is wrong with them (or what is so great about them). No offense intended to you modular guys but the reason for my research into this was because doggy your trucks are compared to other trucks.

It is about a lot of different factors but it really comes down to bore/stroke ratios and Rod/stroke ratios. If you look at bmw, honda, nissan, chevrolet, mitsubishi,etc and look at what motors are revving higher making more power and lasting longer the best of all the worlds combined they have some things in common. They a square bore/stroke ratio and a fairly high rod/stroke ratio. as in 1/1 ratio for bore and stroke and Rod/stroke ratio: 1.745 for a b16a honda motor for example. (btw the ls7 is very close to square bore/stroke this is not "an import thing")

So my question is this why not have all the motors closer to this? aside from the motors that need to pull a house (ie a truck motor) which btw the ls series motors have a shorter stroke compared to teh ford 4.6 or 5.4 which who has a stroke way higher than their bore. so.... yeah ford finally is catching this with their 5.0 cammer and coyote motors.

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Old 11-02-2010, 11:39 AM
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bore/stroke and rod/stroke have FAR less to do with it than you think.

I don't know why but for some reason people like to latch on those two values and describe how the universe was built around them...
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Old 11-02-2010, 12:01 PM
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Easy statement to make - please enlighten me more on your perspective.
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Old 11-02-2010, 12:32 PM
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Quote:
Originally Posted by blight
I am a mechanic so I obviously work on a lot of different vehicles cars and trucks all day. So naturally we get to drive such vehicles and see what is wrong with them (or what is so great about them). No offense intended to you modular guys but the reason for my research into this was because doggy your trucks are compared to other trucks.

It is about a lot of different factors but it really comes down to bore/stroke ratios and Rod/stroke ratios. If you look at bmw, honda, nissan, chevrolet, mitsubishi,etc and look at what motors are revving higher making more power and lasting longer the best of all the worlds combined they have some things in common. They a square bore/stroke ratio and a fairly high rod/stroke ratio. as in 1/1 ratio for bore and stroke and Rod/stroke ratio: 1.745 for a b16a honda motor for example. (btw the ls7 is very close to square bore/stroke this is not "an import thing")

So my question is this why not have all the motors closer to this? aside from the motors that need to pull a house (ie a truck motor) which btw the ls series motors have a shorter stroke compared to teh ford 4.6 or 5.4 which who has a stroke way higher than their bore. so.... yeah ford finally is catching this with their 5.0 cammer and coyote motors.
There are reasons for going either way all of them defensible. The effect on power output is mostly 6 of one and half dozen of another.

The idea behind an over-square engine is to both slow the piston speed within the bore and to increase the bore diameter to accommodate valves large enough to provide adequate breathing. This has always been a traditional limit on large displacement long stroke engine designs inhibiting high RPMs. But there can be found an exception to every rule.

Under-square engines have been used to emphasize torque at lower RPMs. The Chevy 305 using the same stroke as the 350 a case in point. For an equally prepared short stroke 302 and long stroke 305, the 305 will demonstrate its torque peak at a lower RPM. This allows the vehicle designer to select higher overall gearing for better fuel economy without sacrificing bottom end acceleration with those gears. To a large extent these days this is a selection made to meet DOT dynamometer fuel economy tests which have little to do with the real world.

Rod length selection is rather inconsequential across a pretty broad range of ratios. On the long end extremes one can find the Chrysler B and RB where the intake port design being rather squished on the port floor turn into the pocket can benefit from the longer dwell time at TDC given by a long rod. At the other extreme is the 400 Chevy with a pretty short rod. The Chevy breaths pretty well so that wasn't a concern, their need was to stuff a long stroke into a low block height using production rate time limitations in the factory. The resulting short rod tends to push a lot of thrust into the cylinder bore. This was partially offset by the tying of the cylinders together which had a result of offering greater stiffness in the cylinder block to withstand these forces. That, with the expectation that the engine needed to last but 100,000 miles was an adequate design point for its day.

The much maligned Ford 400 which is a square bore to stroke design is more a victim of the reduced spark timing, low compression and mild cam timing dictated by the chosen solutions to emission requirements of the time not of bore to stroke ratio. A fully dressed 400 with performance orientated ignition and cam timing, and compression is a formidable opponent to meet on the street or track.

Being an American, I really don't know much about foreign cars, I do think our government should limit them to 36 gross horsepower, then lets see how popular they remain.

Bogie
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Old 11-02-2010, 01:09 PM
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i am not talking just imports look at what gm is doing with the ls series
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Old 11-02-2010, 01:18 PM
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Sweet topic. Here is my take:

High rod ratios are easier on parts due to piston acceleration/deceleration near tdc, have longer dwell at tdc requiring less total advance for the same effect, the different geometry requires a different cam stetedgy using a tighter lsa, and the only bad thing about them I can think of is maybe is the less displacement due to the shorter stroke required.

Most people on here love the short rod motors with the longest possible stroke to get the most cubic inches to get the lowest rpm grunt and most amount of air/fuel through there at speeds that I consider just above idle they can get to pull the tall gears and overdrive that they also love.

Some people also hate it when you disagree with them on anything too. There is going to be more than one way to accomplish something. No surrender, no retreat I say.

Not everybody wants the same kind of motor though, and as Martha Stewart would say, "That's a good thing!" Variety is the spice of life.
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Old 11-02-2010, 01:32 PM
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Quote:
Originally Posted by blight
i am not talking just imports look at what gm is doing with the ls series
GM's LS series is a study in modern lessons learned. The Ford Modular is an older idea that suffered much at the hands of indecision as to which avenue to pursue. The modular clearly shows the result of a long running internal battle between differing groups of thought within the company. I'd have to say they are about equal in strength given the constant turmoil over the modular's detail design i.e. 2 valve heads, 4 valve heads, 3 valve heads being one example. This clearly is a long standing problem for Ford, I would think Allen would have gotten a grip on this by now and applied some thought alignment to these people.

Frankly I think GM's decision to go with a cam in block design to be the better solution. The result is a lighter, more compact design than is achievable with overhead cams. For the vast majority of modern engine use, the overhead cam brings nothing useful to the table except excess weight, complication, space usage and cost.

If I was running Ford engineering we'd leap to a camless engine at this point going with electro-mechanical or pneumatic valve actuation run off the computer. This offers totally variable "cam" timing that can be tied from a mild set for idle and cruise to top end wild at WOT and red line RPMs, something that just isn't practical with camshafts, though lots of money is being spent here to achieve this technology, I just don't think variable cam shaft lobe timing and lift is mechanically practical.

Bogie
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Old 11-02-2010, 01:38 PM
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All of the arguments presented so far, ESPECIALLY the original post are VERY subjective. None of them are hard and fast truths.

If it was really that easy then we would already have the perfect enigne designed and built, but designs are continuously changing because it is not as simple as we like to assume.

In your original post you are comparing an LS7 to a 4.6L sohc... The only thing they share is the same number of cylinders, which means you really can't make any claim based on that comparison. To make a valid comparison you would have to compare an almost equal engine with only one parameter changed. Then you would have to run a controlled test changing every other parameter in every imaginable fashion to demonstrate an inclusive theory otherwise your finding would still only hold true when using all of the same parts as that particular test.

One instance of this is comparing a 302 to a 305, sure the displacement may be the same, but is EVERYTHING else? I have never seen a test that fulfilled that requirement performed.

The OP's post has nothing to offer but a few thoughts that are in almost no way linked, and certainly not by any means conclusive. Furthermore there is no quantitative evidence nor even any reasonable qualitative data.

BUT the fact that bore/stroke ratios are continuously changing as well as rod/stroke ratios signifies that no definitive value has been found with the 100+ years and trillions of dollars spent on engine research and design.

Then again the billions of man hours spent on engine design and research through the years were all by people that were obviously far less intelligent than the average Hotrodders.com forum member.



If things begin the appear simple then change your point of view so you can see more of the picture.
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Old 11-02-2010, 01:49 PM
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Quote:
Originally Posted by oldbogie
If I was running Ford engineering we'd leap to a camless engine at this point going with electro-mechanical or pneumatic valve actuation run off the computer. This offers totally variable "cam" timing that can be tied from a mild set for idle and cruise to top end wild at WOT and red line RPMs, something that just isn't practical with camshafts, though lots of money is being spent here to achieve this technology, I just don't think variable cam shaft lobe timing and lift is mechanically practical.

Bogie
THAT is an interesting argument, the limitations of camless VS cam driven valve actuation systems... One that in the end will rely on material selection.

If I was in charge we'd be running an SOHC inline 6 with DI and a inter-cooled turbocharged intake system. Displacements ranging from about 1.0L (inline 4 instead of 6) to 4.0L. You'd only need two different head and block castings, and could greatly reduce manufacturing costs while still producing a line up that is capable of 50+mpg and power levels up to about 500-600 hp.

The foreign market really excels in this type of engine design, and in a lot of ways its simpler than a cam in block V8, and IMO is generally a better approach.
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Old 11-02-2010, 03:27 PM
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the only cam-less engine i have heard of are two stroke motors, do you have any pictures or something that can help explain that?

also I am starting a list of motors that use the technique that I am referring to with the square design or close to it.

Mazda
FE 86.0 X 86.0
ZL 78.0 x78.4
L8-DE, L8-VE 83.0 X 83.1

Nissan
CA18 83.0 x 83.6
SR20 86.0 x 86.0
RB30 86.0 x 86.0

Honda
B17a1 81.0 x 81.4
K20A 86.0 x 86.0

Toyota
2R 78x78
3A 77.5 x 77.0
3S 86.0 x 86.0
1RZ 86.0 x 86.0
3RZ 95.0 x 95.0
1AZ 86.0 x 86.0
M 75.0 X 75
1G 75.0 X 75.0
2JZ 86.0 x 86.0
1GR 94.0 X 95.0
1GZ 81 X 80.8

Mitsubishi
4B11

VW
6.2 V12 48v 430-471kW (Lamborghini) 87.0 X 86.8
8.0 WR16 64v4T 736-816kW (Bugatti) 86.0 X 86.0

GM
20NE, 20SE, 20SEH, C20NE, C20GET (ECOTEC FAMILYII) 86.0 X 86.0
20XE, 20XEJ, C20XE, C20LET (ECOTEC FAMILYII) 86.0 X 86.0
LK9, LNF, LSJ, L34 (ECOTEC FAMILYII) 86.0 X 86.0
gmc 302 (l6 measured in inches vs mm) 4" x 4"
L81 3.0 86.0 x 86.0
LA3 3.2 87.5 x 88.0
Vortec 2200 (RPO codes L43 and LN2) 89.0 x 88.0

Ford
Duratec18 83.0 x 83.0
5.0 L Coyote 92.2 x 92.7

Jaguar
AJ26 86.0 x 86.0
AJ30/AJ35 86.0 x 85.0
AJ133 92.5 x 93.0

There will be more posted when I have time
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Old 11-02-2010, 03:34 PM
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Just as a note- from personal experience in working with jap engines note the ones that are square or close, funny thing is these engines are more power among enthusiasts? Why is that would you think- I don't think your average honda guy says hey i want the k20 for such and such reason, more it revs high and is easy to make power from. same for the sr20 guy and so on. also lastly to note notice the commonality of the 86.0 x 86.0 - I wonder if there is any significance in it, (gm has started using it obviously as well so there must be a reason)
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Old 11-02-2010, 03:47 PM
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perhaps the bore/stroke has nothing to do with their preference, perhaps its the valve arrangement, the bearing arrangement, or one of the MANY other factors that describe an engine.

BTW, the camless valve actuation is not in any production automotive engine that I know of, basically you use an electronic/hydraulic system to control the valves giving full control and near instantaneous response. Its not in production primarily due to production costs (material and manufacturing technology).
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Old 11-02-2010, 04:20 PM
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Quote:
Originally Posted by blight
the only cam-less engine i have heard of are two stroke motors, do you have any pictures or something that can help explain that?

also I am starting a list of motors that use the technique that I am referring to with the square design or close to it.

Mazda
FE 86.0 X 86.0
ZL 78.0 x78.4
L8-DE, L8-VE 83.0 X 83.1

Nissan
CA18 83.0 x 83.6
SR20 86.0 x 86.0
RB30 86.0 x 86.0

Honda
B17a1 81.0 x 81.4
K20A 86.0 x 86.0

Toyota
2R 78x78
3A 77.5 x 77.0
3S 86.0 x 86.0
1RZ 86.0 x 86.0
3RZ 95.0 x 95.0
1AZ 86.0 x 86.0
M 75.0 X 75
1G 75.0 X 75.0
2JZ 86.0 x 86.0
1GR 94.0 X 95.0
1GZ 81 X 80.8

Mitsubishi
4B11

VW
6.2 V12 48v 430-471kW (Lamborghini) 87.0 X 86.8
8.0 WR16 64v4T 736-816kW (Bugatti) 86.0 X 86.0

GM
20NE, 20SE, 20SEH, C20NE, C20GET (ECOTEC FAMILYII) 86.0 X 86.0
20XE, 20XEJ, C20XE, C20LET (ECOTEC FAMILYII) 86.0 X 86.0
LK9, LNF, LSJ, L34 (ECOTEC FAMILYII) 86.0 X 86.0
gmc 302 (l6 measured in inches vs mm) 4" x 4"
L81 3.0 86.0 x 86.0
LA3 3.2 87.5 x 88.0
Vortec 2200 (RPO codes L43 and LN2) 89.0 x 88.0

Ford
Duratec18 83.0 x 83.0
5.0 L Coyote 92.2 x 92.7

Jaguar
AJ26 86.0 x 86.0
AJ30/AJ35 86.0 x 85.0
AJ133 92.5 x 93.0

There will be more posted when I have time
Formula one technology. The valves are actuated by individual solenoids for each valve either electrical or pneumatic. These are controlled by a computer reading sensor demands by the driver upon the engine. Similar to how electronic fuel injection works, the computer signals the solenoid for a period of duration with an amount of lift as determined by driver demand. BMW, Mercedes and Renault are well along with production development of these systems.

Bogie
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Old 11-02-2010, 05:59 PM
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Well between all of them renult or bmw will be the ones to do it. benz has slacked for the past few years -
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Old 11-02-2010, 06:32 PM
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BMW
M52B28 84.0 x 84.0

Is the last one chrysler and benz have nothing
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