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Doc Holliday

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With the lack of new information circulating, I decided to do some calculations based on the little information we have. Mean piston speed (MPS) can be an interesting way to compare engines. It tells us a little bit more about the stresses put on the internals at high rpm. We were told at the initial reveal that the 5.2L's increase in displacement over the 5.0 is "all bore," so we can deduce that they share the same 92.7mm stroke. Several shots of the cars show that the redline on the tach to be at 8,200 rpm. I compiled the bore/stroke for several modern, high revving, naturally aspirated performance engines of various configurations and calculated the piston speeds. I have them listed in order from highest MPS to lowest. Bore is not used to calculate piston speed, but I included it on the list anyway, just for comparison sake.

Engine / Bore x Stroke / Mean piston speed in feet per second @ redline


Audi 5.2L V10 / 84.5x92.8mm / 88.294 fps @ 8,700 rpm
Honda S2000 2.0L I-4 / 87x84mm / 84.514 fps @ 9,200 rpm
Audi 4.2L V8 / 84x92.8mm / 83.727 fps @ 8,250 rpm
Ford 5.2L Voodoo V8 / 94.5(est)x92.7mm / 83.13 fps @ 8,200 rpm [engine photos]
Honda S2000 2.2L I-4 / 87x90.7mm / 81.336 fps @ 8,200 rpm
Ford 5.8L Trinity V8 / 93.5x105.8mm / 80.993 fps @ 7,000 rpm
Ferrari 4.5L V8 / 94x81mm / 79.724 fps @ 9,000 rpm
GM 7.0L LS7 V8 / 104.775x101.6mm / 77.778 fps @ 7,000 rpm
Porsche 911 GT3 3.8L flat 6 / 102x77.5mm / 76.28 fps @ 9,000 rpm
Ferrari 6.3L V12 / 94x75.2mm / 71.549 fps @ 8,700 rpm
Lamborghini Aventador 6.5L V12 / 95x76.5mm / 71.112 fps @ 8,500 rpm
Ford 5.0L Coyote V8 / 92.2x92.7mm / 70.965 fps @ 7,000 rpm
BMW E90 M3 4.0L V8 / 92x75.2mm / 69.081 fps @ 8,400 rpm
GM 6.2L LT1 V8 / 103.25x92mm / 66.404 fps @ 6,600 rpm


There are a few things I would like to point out. The 5.8 Trinity is obviously not N/A, but with it's very long stroke (the longest on the list) and the over-rev function that will allow short runs up to 7,000 rpm in certain conditions, I knew it would have a high mean piston speed. Despite all of that, the Voodoo piston speeds are even higher.

Notice how much lower the piston speeds are on the standard Coyote, the GM LT1, and even the highly regarded BMW 4.0L V8. The very short stroke on the BMW gives it a much lower average piston speed, despite the slightly higher redline when compared to the Voodoo.

Also, notice that most of the engines are oversquare in design. The Audi engines are an interesting exception. I guess the engineers at Audi forgot that an engine has to be oversquare to turn high rpm. ;)

To me, this is one illustration of the level of engineering that likely went into the 5.2 for it to reliably achieve those piston speeds. Ford openly admits that they had to overcome several hurdles during development and that this was one of their most ambitious powertrain programs. There are some pretty exotic engines on that list.

I think we're in for a real treat.
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908ssp

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RPM is the single largest motor killer. Usually not within the factory recommendation granted but over revs from missed shift can be instant death to a motor. Whether it is the rods going or the valve train revs was the initial cause. Second would be knock. Preignition is like hiting the piston dome with a ball peen hammer. Boost pressure and the resulting torque rarely actually breaks motors.
 

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Another thing to take into account is rod/stroke ratio. Your projected mean piston speed may be a bit conservative as a result.

Many modern engines are now focusing on longer stroke builds for efficiency reasons but in order to keep up performance they're moving into higher rod/stroke ratio designs of their engines that allow the engines to safely operate in higher rpm ranges than they normally would. I'd not be surprised to see the Voodoo running a high ratio in order to keep piston speeds down.
 

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In regards to the longer rod idea.
My question would be does using a longer rod smooth out the moment of accel/decel of the piston as it changes direction at the top and bottom of the stroke? In effect reducing the maximum stresses experienced by the piston/rod combo.
 
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Doc Holliday

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Yes, rod ratio is another factor, but average (mean) piston speed should be the same for an engine with a given stroke at a given rpm, regardless of rod length.

Rod ratio is a very complex topic, to which hours of study can be devoted. Differing rod ratios do effect piston acceleration and peak piston speeds. Conventional wisdom has been that a greater rod ratio is better in a high rpm engine. Basically, a longer rod (greater rod ratio) gives the piston more dwell time at TDC. The simplest way to look at this, is that it gives the piston more time to change direction. This results in lower peak accelerations of the piston, and peak piston speed is also slightly lower with a longer rod. This is easier on parts in the rotating assembly. There are some decent graphs to illustrate this on these 2 sites: http://ftlracing.com/rsratio.htm
http://www.epi-eng.com/piston_engine_technology/piston_motion_basics.htm

However, a greater rod ratio is not always better or possible. There are constraints to how long a rod can be used in an engine's architecture, such as deck height. Modern materials are also improved such that they are able to stand up to much greater stresses, allowing smaller rod ratios to be used. Also, an engine with a shorter rod is said to be more responsive and accelerate quicker. The coyote has a rod ratio of 1.62:1, so I think we will see something similar in the voodoo.
 

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Yes, rod ratio is another factor, but average (mean) piston speed should be the same for an engine with a given stroke at a given rpm, regardless of rod length.

Rod ratio is a very complex topic, to which hours of study can be devoted. Differing rod ratios do effect piston acceleration and peak piston speeds. Conventional wisdom has been that a greater rod ratio is better in a high rpm engine. Basically, a longer rod (greater rod ratio) gives the piston more dwell time at TDC. The simplest way to look at this, is that it gives the piston more time to change direction. This results in lower peak accelerations of the piston, and peak piston speed is also slightly lower with a longer rod. This is easier on parts in the rotating assembly. There are some decent graphs to illustrate this on these 2 sites: http://ftlracing.com/rsratio.htm
http://www.epi-eng.com/piston_engine_technology/piston_motion_basics.htm

However, a greater rod ratio is not always better or possible. There are constraints to how long a rod can be used in an engine's architecture, such as deck height. Modern materials are also improved such that they are able to stand up to much greater stresses, allowing smaller rod ratios to be used. Also, an engine with a shorter rod is said to be more responsive and accelerate quicker. The coyote has a rod ratio of 1.62:1, so I think we will see something similar in the voodoo.
Agreed, and I mispoke as it was very early in the morning for me. :headbonk: Dunno what I was thinking. Larger rod/stroke ratio motors tend to last longer, make more power, etc than the alternative. My point was while the mean piston speed on this motor is high, I'm thinking its no cause for alarm as I think Ford will be maximizing the rod/stroke ratio usable in the Coyote block as to maximize dwell time and soften piston jerk (rates of acceleration change).

Thanks again :clap2:
 

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Thanks for the explanation and the link. Some good reading there.
 

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Here's the article I remembered written by an expert about rod/stroke ratios.

http://rehermorrison.com/tech-talk-10-by-the-book/

An excerpt:
We also wanted to point out some of the common myths and misconceptions about high-performance motors. For example, I’ve seen dozens of magazine articles on supposedly “magic” connecting rod ratios. If you believe these stories, you would think that the ratio of the connecting rod length to the crankshaft stroke is vitally important to performance. Well, in my view, the most important thing about a connecting rod is whether or not the bolts are torqued!
If I had to make a list of the ten most important specifications in a racing engine, connecting rod length would rank about fiftieth.
 

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Here's the article I remembered written by an expert about rod/stroke ratios.

http://rehermorrison.com/tech-talk-10-by-the-book/

An excerpt:
We also wanted to point out some of the common myths and misconceptions about high-performance motors. For example, I’ve seen dozens of magazine articles on supposedly “magic” connecting rod ratios. If you believe these stories, you would think that the ratio of the connecting rod length to the crankshaft stroke is vitally important to performance. Well, in my view, the most important thing about a connecting rod is whether or not the bolts are torqued!
If I had to make a list of the ten most important specifications in a racing engine, connecting rod length would rank about fiftieth.
I think that quote kind of points out a clash of understanding between an engineer and a technician. An engineer worries about rod/stoke ratio because it is part of the design of the engine. He/she does not worry about the connecting rod bolts being properly torqued because he/she assumes the technican can do his/her job.

The rod/stroke ratio comments in this case, are talking about the design of the engine itself; like the bore increase's effect on the heads, the switch to a FPC itself, the selection of valvetrain components to handle the increased rpm, the design of the exhaust manifold, etc. Not header bolts being tightened or coolant being in the radiator. :thumbsup:

EDIT:
I read more of what that guy had to say. I think an F1 engine designer would seriously disagree with what he said regarding rod/stroke ratio. So do a lot of EVO engine builders.
 
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Doc Holliday

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I think you both make good points. Reher Morrison specializes in drag racing engines, the demands of which are very different than an endurance racing engine, like say NASCAR or F1, which will see long sustained periods of high RPM. The drag racing engine may actually see higher mean piston speeds, but for much shorter bursts. The drag racing engine is also able to take advantage of the some of the benefits of a shorter rod ratio for its intended purpose.

I do think that the rod ratio is not quite as critical as it once was with the quality of modern materials and machining tolerances. Engine components are able to more reliably withstand stresses today than they once were. This allows engines designs to 'get by' with lower rod ratios. However, I'm sure it's something that is still considered in the design.
 

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I think you both make good points. Reher Morrison specializes in drag racing engines, the demands of which are very different than an endurance racing engine, like say NASCAR or F1, which will see long sustained periods of high RPM. The drag racing engine may actually see higher mean piston speeds, but for much shorter bursts. The drag racing engine is also able to take advantage of the some of the benefits of a shorter rod ratio for its intended purpose.

I do think that the rod ratio is not quite as critical as it once was with the quality of modern materials and machining tolerances. Engine components are able to more reliably withstand stresses today than they once were. This allows engines designs to 'get by' with lower rod ratios. However, I'm sure it's something that is still considered in the design.
You make good points, but I think for production motors and motors with a longer intended service life (like street engines) for the higher performance areas will still see a lot of benefit. I know it is still extensively used in F1. It's harder to 'get by' when you're pushing the envelope in high-performance, production-level, emissions-legal, gas-sipping petrol engines :) Any advantage is an advantage. Just my opinions though :)
 

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RPM is the single largest motor killer. Usually not within the factory recommendation granted but over revs from missed shift can be instant death to a motor. Whether it is the rods going or the valve train revs was the initial cause. Second would be knock. Preignition is like hiting the piston dome with a ball peen hammer. Boost pressure and the resulting torque rarely actually breaks motors.
Is there any way to quantify how much damage a missed shift would do? Like say 5th to 2nd instead of 5th to 4th? Would it matter if it's for a split second? This is my nightmare.
 

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Is there any way to quantify how much damage a missed shift would do? Like say 5th to 2nd instead of 5th to 4th? Would it matter if it's for a split second? This is my nightmare.
Quantify? Yeah whatever the price of a new Voodoo is ;) Seriously though, money-shifting can sling a rod through a block pretty easily. And you're right to worry about money-shifting. There's been a few M3 owners that did the same thing. It's not as prevalent as you might be thinking though.

There's always the possibility of Ford's TCU programming locking out gears when you're not at the right mph to handle them.
 
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Doc Holliday

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You make good points, but I think for production motors and motors with a longer intended service life (like street engines) for the higher performance areas will still see a lot of benefit. I know it is still extensively used in F1. It's harder to 'get by' when you're pushing the envelope in high-performance, production-level, emissions-legal, gas-sipping petrol engines :) Any advantage is an advantage. Just my opinions though :)
No disagreement here. My opinion is that in an engine that could see sustained high rpm can potentially benefit from an increased rod ratio. NASCAR engine builders use rod ratios around 1.9:1 and F1 around 2.5:1 for a reason. :thumbsup:

I just think modern engine builders can get away with more than they used to. For instance, the LS7 uses a rod ratio of 1.52:1, something that would have once been considered heresy in an engine with piston speeds that high. While the LS7 has had some valvetrain issues, you don't hear much about issues with the rotating assembly at stock power levels.
 
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Quantify? Yeah whatever the price of a new Voodoo is ;) Seriously though, money-shifting can sling a rod through a block pretty easily. And you're right to worry about money-shifting. There's been a few M3 owners that did the same thing. It's not as prevalent as you might be thinking though.

There's always the possibility of Ford's TCU programming locking out gears when you're not at the right mph to handle them.
So let's just say hypothetically, you do a half-second money shift coming from 60-75 and slot it in second; revs spike, rear locks up for a sec, and the clutch gets pushed back in. Would that do any kind of measurable damage?











Hypothetically speaking... yeah...

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