Splain-Nation- By Bro.D

PJ McCoy

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OK, I have pen and paper and my copy paste is working. So I can research links etc. Etc.

So let's get to Splain'in!
Boosted application doesn't effect piston speed?????

Go!!!!
 

5one9

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The speed of the piston in a given engine is the same at 5000 rpm no matter what the induction system. The rate at which it gets to 5000rpm may vary, but the speed is the speed. Stroke and rod length are the variables that increase or decrease piston speed.
 

Red98422

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As Bro D was trying to explain during a boosted application the overall speed will remain the same, however due to greater cylinder pressures the acceleration of the piston increases, not the overall speed.

think of it like a drag strip. You have two cars, and both go down the strip and both trap out at 110mph but one of those cars ran a 10.0 and the other ran an 11.5

the seed is constant it’s the acceleration that is different between the two applications.
 

Darius

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Bros Red and 5one9,

Ya'll said it much better than I did. Thanks for chiming in.

Greater stress is placed on an engine turning higher RPM to get power, than the stress place on the same engine with more boost giving that same power but at a lower RPM. "Speed Kills."

Bro. PJ,

I sincerely HOPE that my tone was not taken as being dismissive of you or condescending in any way. My concern was in how well - or poorly - I was 'splaining the thing. Our brothers on the forum have done it much better than I.

Anyway, here is a bit of ALMOST RELATED material.

Best,

bro. d

https://www.jepistons.com/blog/unde...oosted-and-naturally-aspirated-piston-designs

While optimizing skirt taper is still an effective method of reducing friction, JE has taken things to the next level with its forged asymmetrical pistons. Unlike conventional full-round pistons, JE’s asymmetrical skirts are very large and robust on the thrust side, and much smaller and lighter on the other side.

Granted that today’s crop of highly efficient naturally aspirated engines can easily exceed two horsepower per cubic inch, power adder combos can triple that figure. Consequently, they utilize thicker crowns, skirts, ring lands, struts, and wrist pins. To account for increased thermal expansion, skirt and ring land clearances are increased as well. “Even a great piston material has a finite level of strength, and we must tailor the design to work within these strength limits. We do this by increasing thickness in key areas, adjusting clearances, and modifying the design to accommodate the specific application,” Clayton Stothers of JE pistons explains.

Nevertheless, horsepower output isn’t always the best way to gauge piston load. “The amount of power an engine makes is only a piece of the puzzle. We must also take into account the application and duty cycle that a piston will see,” Stothers continues. “A 5,000hp drag racing engine may see less abuse than a 1,000hp offshore boat motor, simply because of the vastly different duty cycles. Naturally aspirated pistons can be made thinner and lighter while still maintain an appropriate level of stiffness and strength because the amount of stress they see is much lower.”

High RPM and Friction

Without the luxury of boost or nitrous to increase cylinder pressure, naturally aspirated race engines rely on rpm instead. Even so, the rigors of high-rpm operation still place substantial loads on the pistons. “A high-rpm naturally aspirated engine is similar to a power adder engine in the sense that the loads on the piston are increased. However, the difference is how that load is exerted on the piston,
” Clayton Stothers explains. “In a high-rpm application, the goal is making sure that the pin bore area is strong and durable to prevent the pin from being pulled out of the bottom of the piston.”

Since frictional power loss increases dramatically at high rpm, pistons designed specifically for max-effort naturally aspirated engines utilize unique skirt shapes and profiles that reduce friction without compromising stability. According to JE, a stable piston than improves ring seal while reducing friction can be worth 10-20 horsepower over a standard piston. Traditionally, piston manufacturers have optimized the profile and taper of the skirts and ring lands to minimize the surface area of the piston that comes into contact with the cylinder walls. The idea is to have just enough skirt-to-cylinder contact to stabilize the piston, which reduces surface area and friction.

https://nasaspeed.news/tech/engine/connecting-rod-physics/ ****

“There’s a lot of force in tensile, compression and a little bit of bending, so those are the main things we look at,” said Clayton Stothers, engineering lead for Wiseco. “The inertial case is pretty hard on connecting rods as well, because 10,000 rpm is a lot of load, so we look at the tensile loading a lot.

When a piston rises to top dead center and the crankshaft begins the second half its rotation, pulling the big end of the rod, the two ends of the rod are essentially being pulled apart from each other. That’s tensile load, and it also occurs when you lift off the gas and decelerate. That puts stress on the rod cap and rod bolts, which also transfer their load to the big end of the rod.

Compression load occurs when the piston transfers load from the combustion to the wrist pin and to the rod and crankshaft. Compression load also occurs on the compression stroke, albeit to a lesser extent. A connecting rod also undergoes bending stresses, which rise commensurately with rpm and power output."


http://www.theoldone.com/archive/rpm_n_piston_speed.htm

RPM's are nice...they are our friend


Posted by 82'Rolla on July 03, 1998 at 06:21:24:

I love the sound of a high revver as well. Unfortunately to make your engine do this, it must be very well guarded against the added stress.


"*Maximum piston acceleration is approximately 8,000g which puts a load of over 3 tons on each connecting rod."
This is where a lot of the damage comes from, and it increases non-linearly, not sure if it's exponential, plus the fact that the piston actually travels further. The stresses that your engine endures by raising the rpm's by 1000rpms is much worse than increasing boost by 10psi.”

http://blog.wiseco.com/stoker-crank-science-piston-speed-rod-angle-explained-0

https://danielmiessler.com/study/horsepower/

https://itstillruns.com/pick-correct-turbocharger-size-4436563.html

https://stratifiedauto.com/blog/load-based-versus-boost-based-tuning/
 

PSYKO_Inc

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My take on it (I am not an engineer, I don't even play one on TV) is to look at the basic physics going on in the engine. Boost is basically cramming more air and fuel into each cylinder than it could draw in on its own. For each given unit of fuel (combined with the proper ratio of oxygen to allow combustion,) there is a certain amount of stored energy, which gets released upon ignition. This energy is expressed by expansion, which acts on all areas of the combustion chamber (cylinder head, valves, cylinder walls, piston.) The only one which can move is the piston, which channels the energy downward into the piston, rod, and crankshaft. The crankshaft is basically a lever, which creates torque (force * lever length, aka pound foot.) Horsepower is a function of torque and rpm, so in general, more air+fuel = more cylinder pressure = more force = more torque = more horsepower. There was talk about acceleration earlier, acceleration is a simple function of force and mass. At the same engine load, yes the boosted piston will accelerate faster, because the car is accelerating faster! Not really a factor unless you miss a shift or something and over rev the engine, and with a Cadillac you'd probably float the valves first. The biggest factor in my opinion is cylinder pressure/force. Can the pistons, rods, and crank handle the additional load? What about detonation? With detonation your cylinder pressure spikes way higher, due to the combustion applying its force downwards, while the piston is still trying to go upwards, propelled by the other cylinders as well as inertia. Think of it like cruising down the highway and shifting into reverse. Anyway, this turned into a long post, hopefully I didn't get too derailed there.
 

MIHELA

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Piston speed is important because the piston comes nearly to a stop at the top and bottom of travel which cause a large velocity. Velocity is a rate of change in speed. Force=Mass*Velocity. Our pistons are quite large and massive so keeping the speed lower is far better. Also given the large bore it becomes counterproductive to increase the speed beyond a certain point because the flame cannot travel completley across the face of the piston in time to fully combust all of the fuel. Turbos increase the combustion pressure exerted on the top of the piston, which attempts to bend the rod and force the piston down and somewhat against the side of the bore. That is a much more manageable force in the design of the rod and piston. Those are the forces we are looking at.
 

PJ McCoy

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5one9,Red,Mihela, Bro,D-Splainen

Thank you all. I am humbled and honored that so many jumped in to help.

BroD, I didn't take your correction as anything but helpful. I believe I have a good grasp of your intention. I see you and others here as mentors.
I have a lot to read and focus on and will be asking more questions for clarification.

Thanks again everyone.
More to come
PJ
 

5one9

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PJ, my engine spins 6000rpm balanced, H-beam rods, forged pistons, studs, etc. When I boost it this winter it will get shifted at 5000rpm for this very reason, combination of boost and rpm together equals mucho stress in every direction.
 

PJ McCoy

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Alrighty Folks, if I understand the links that Darius has supplied along with the information everyone else supplied. It "Might" go like this??

The time it takes to get to a fixed rpm (5000)can change but the distance the piston travels doesnt. The piston travel is fixed because the stroke doesn't change.

The added power applied (turbo) doesn't effect piston speed either. The extra power from a turbo is applied to the crank but the piston speed is the same. So the added power is what gets you down the track.
think of it like a drag strip. You have two cars, and both go down the strip and both trap out at 110mph but one of those cars ran a 10.0 and the other ran an 11.5
So, I see how a turbo can help the pistons because compressed air can act like a spring and "cushion" the piston @TDC.

Does the extra volume of air also help on the exhaust stroke too?

In my mind, I think it could, expanded exhaust gas filling up and pressurizing the exhaust side of the stroke. Helping to equalize the load on top of the piston.

Am I on the right track here?? If not what am I missing? This is fun stuff.

Doesn't their have to be a trade off? If more power then more wear due to bigger loads on bearings etc???

Which really brings me back to the first point I was trying to make. I used piston speed but still, How much applied power before stock parts start to fail??
I guess that's the magic question for everyone.

LOL, I need to learn a lot more before I do any boosting.

PJ, my engine spins 6000rpm balanced, H-beam rods, forged pistons, studs, etc. When I boost it this winter it will get shifted at 5000rpm for this very reason, combination of boost and rpm together equals mucho stress in every direction.
This is my concern as well. But my understanding is changing, 5one9 might run 14-21 lbs boost and be safe, due to his build, I might be safe in the same or slightly lesser 4800 rpm shift point with 8-10 lbs of boost.

I gotta get my mind around the loads and stress the turbo puts on the different components of the engine. Then I can make an educated decision on boost numbers.

I guess that's enough questions for now. Please help in every area my thinking. I really enjoy this topic.
FYI, I've been reading about 2hrs a day on this topic. Well, reading a little and thinking a lot.
PJ
 

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If this isn't enough to worry about: There is also thermal stress- excessive heating or cooling in a short period. The rapid expansion or contraction can put a lot of stress on parts like exhaust manifolds, turbos, and pistons. Cast components don't like these extremes in cooling or heating. Add this stress on top of the other stresses discussed above.
 

PJ McCoy

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If this isn't enough to worry about: There is also thermal stress- excessive heating or cooling in a short period. The rapid expansion or contraction can put a lot of stress on parts like exhaust manifolds, turbos, and pistons. Cast components don't like these extremes in cooling or heating. Add this stress on top of the other stresses discussed above.
Oh boy!!! Lol these are the issues I need to be thinking about.
 

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After reading all of this post ,I am worn out with trying to think on this subject.While I would luv to be able to make 600 to 1000 HP its just not gonna work for me. i am waiting to hear good news from everybody that does boost their engines ,and wish them the best. Heck I have just spent a month trying to fit a radiator in the front of my corvair.I think I would have to put some blowers like roadkill did in a trailer behind my car to get boost!! Hey it did make boost :rofl:

Remember you gotta post pics or video:oops::laugh:
Richard richie49
 
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PJ McCoy

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Rich, we all you like videos. I'm just not sure others would lime the video? Something about rules and guild lines.
 

Red98422

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First off I would like to say, well damn look at that screen shot. Couldn’t have timed it better myself :laugh:.

Alrighty Folks, if I understand the links that Darius has supplied along with the information everyone else supplied. It "Might" go like this??

The time it takes to get to a fixed rpm (5000)can change but the distance the piston travels doesnt. The piston travel is fixed because the stroke doesn't change.

The added power applied (turbo) doesn't effect piston speed either. The extra power from a turbo is applied to the crank but the piston speed is the same. So the added power is what gets you down the track.


So, I see how a turbo can help the pistons because compressed air can act like a spring and "cushion" the piston @TDC.

Does the extra volume of air also help on the exhaust stroke too?

In my mind, I think it could, expanded exhaust gas filling up and pressurizing the exhaust side of the stroke. Helping to equalize the load on top of the piston.

Am I on the right track here?? If not what am I missing? This is fun stuff.

Doesn't their have to be a trade off? If more power then more wear due to bigger loads on bearings etc???

Which really brings me back to the first point I was trying to make. I used piston speed but still, How much applied power before stock parts start to fail??
I guess that's the magic question for everyone.

LOL, I need to learn a lot more before I do any boosting.


This is my concern as well. But my understanding is changing, 5one9 might run 14-21 lbs boost and be safe, due to his build, I might be safe in the same or slightly lesser 4800 rpm shift point with 8-10 lbs of boost.

I gotta get my mind around the loads and stress the turbo puts on the different components of the engine. Then I can make an educated decision on boost numbers.

I guess that's enough questions for now. Please help in every area my thinking. I really enjoy this topic.
FYI, I've been reading about 2hrs a day on this topic. Well, reading a little and thinking a lot.
PJ

a lot of what you are talking about is in the realm of “advanced understanding” and nothing wrong at all with those questions!

boost should by all means be taken seriously, however if you aren’t pushing the envelope to the bleeding edge you can take the worry down a notch.

as I understand it the boost does “cushion” to a small extent but what is worrisome is that it is also attempting to compress a greater amount of volume in the same speed, which can be stressful to the bearings as the see a greater load/time.

now for the super tricky stuff, boost actually will work better with less exhaust overlap (gotta keep cylinder fill) so there are cams specifically made for boost by turbo vs boost by supercharger. I wish I could be more detailed than that but I am still learning myself.

something I believe gets overlooked and or misunderstood is judging boost based on PSI. What we should really be talking about if CFM.

I get that the industry standard is psi, it’s just bothered me as depending on the housings you could be running the same psi but two totally different flow numbers and backpressure.

also @PJ McCoy and @5one9. You should both begin studying back pressure and it effects. Also a lesson in turbo sizing would be a great help as well. The math can be difficult, but it’s worth it to know so you can plot your own numbers without relying on a computer app.
 

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PJ McCoy

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First off I would like to say, well damn look at that screen shot. Couldn’t have timed it better myself :laugh:.




a lot of what you are talking about is in the realm of “advanced understanding” and nothing wrong at all with those questions!

boost should by all means be taken seriously, however if you aren’t pushing the envelope to the bleeding edge you can take the worry down a notch.

as I understand it the boost does “cushion” to a small extent but what is worrisome is that it is also attempting to compress a greater amount of volume in the same speed, which can be stressful to the bearings as the see a greater load/time.

now for the super tricky stuff, boost actually will work better with less exhaust overlap (gotta keep cylinder fill) so there are cams specifically made for boost by turbo vs boost by supercharger. I wish I could be more detailed than that but I am still learning myself.

something I believe gets overlooked and or misunderstood is judging boost based on PSI. What we should really be talking about if CFM.

I get that the industry standard is psi, it’s just bothered me as depending on the housings you could be running the same psi but two totally different flow numbers and backpressure.

also @PJ McCoy and @5one9. You should both begin studying back pressure and it effects. Also a lesson in turbo sizing would be a great help as well. The math can be difficult, but it’s worth it to know so you can plot your own numbers without relying on a computer app.
Thanks Red, I have studied back pressure and boost also done the math for my stock flowing heads. Ive "mapped" what turbo would be efficient from my math numbers with an efficiency rating above 64%. The turbo I mapped out using the chart with a bunch of island rings gave an efficiency of 76%. I have been studying turbos from Garrette's online learning program. This States for my son, who is a 4banger, and is also studying to become a mechanical engineer. So I had to "up my game" as his mind is fas and his vocabulary can be confusing. In this process I found myself enjoying the learning curve and excelling in the FREE ON LINE PROGRAM. I highly recommend it. So my sons math for his car/ my math for the Trans Am, My son will have around 800hp for that little scion to coupe. But he has to get a trans and fuel system tires etc ect . so anyway hopefully we will have a father son shoot out. Sometime in the future. But thats how my journey started. Screenshot_20200810-231438_Drive.jpg
 
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