And you aren't paying the bills. Look for even fewer top fuel / funny car teams next year. As it is the bottom qualifing positions are often filled with locals & they usually go out in the first round
NHRA Pro Stock Bearings
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userfriendly said:
Lots of people like the circus...
I don't go to see TF and FC. I go to see PS, PM, amd S/SS. I'm usually wondering around the pits while the fuel cars are running.
What are you wondering about, while in the pits?
Here are some comparative graphs of a hypothetical pro stock engine with a 4.72" bore x 3.57" stroke. I have done calculations with rod lengths giving a length/stroke of 1.5 and 2.0, basically in the range where race engine builders normally work, and giving a wide range of value to show the major trends. My spreadsheet calculates piston velocity, acceleration, and side thrust. The calculations are all done at 10500 rpm.
Here is piston velocity with the 1.5 rod ratio. Peak velocity is 172 ft/s, and is at 73 degrees ATC.
Here is piston velocity with 2.0 rod ratio. Peak piston velocity is 168 ft/s, occurring at 77 degrees ATC. Considering the large difference in rod length, there is not much effect on piston velocity, only about 2.5%. Consequently there would not be much effect on inlet port Mach number and engine breathing.
Graph of piston acceleration with 1.5 rod ratio. Peak acceleration is -7447 G's (downward) at TDC.
Piston acceleration at 2.0 rod ratio. Peak acceleration is -6982 G's. This is about a 6.2% decrease in rod tension and peak rod bearing load at TDC overlap. But since the longer rod has more mass, it can't be assumed that there will be less bearing load (and friction). Keep in mind that this is a rod that is 1.785" longer.
Graph of rod side thrust with 1.5 rod ratio. Peak side thrust is 1135 G's, with an absolute average of 676 G's.
Rod thrust with 2.0 rod ratio. Maximum rod thrust of 774 G's, with an absolute average of 479G's. I think this is where the true difference to engine power would be; the average piston side thrust on the cylinder wall decreases by 29% with the longer rod. Whether or not the increase of power due to decreased piston friction balances out the increased engine weight on vehicle performance is another matter. That would mostly depend on if the car could still get down to class minimum weight.
Questions? Comments? Or have I stepped on the cake again?
@A_Harman That's correct in theory, but doesn't really translate into the real world. There's mountain motor pro stockers with rod ratios as low as 1.41 with great ring seal. The piston is what's important. A long rod with a piston that's too short, with too narrow of ringlands, oil ring in the pin, etc.. will not seal as well as a taller piston that's built properly for the engine. Just recently, I spoke with a guy who shoved a 6.125" rod length in a 383ci SBC with a set of 1" c/h pistons, from his old build with 6" rods and 1.125" c/h pistons, and he lost ~20 hp on the dyno. One look at the smoke coming from the breathers above 5k rpm showed the issue. The piston was so short that it wasn't stable at high rpm causing it to warp and rock around, losing ring seal, and increasing blow-by into the crankcase. It now has the old shorter rods and taller pistons back in it.
Get the piston right with the stroke you need and throw in whatever length of rod connects the two. If the piston isn't right, it doesn't matter what length of rod is in it, because the advantage won't be there.
Get the piston right with the stroke you need and throw in whatever length of rod connects the two. If the piston isn't right, it doesn't matter what length of rod is in it, because the advantage won't be there.
Did your involvement include writing the checks for a top fuel team? They are being screwed by the NHRA even in good times. 50k to win? when a run costs about 10k x 6 if you win. You have to figure in everything - shop, shop employees, road crew + actual expenses of operating the car.
Ring seal is a separate issue. That's more related to piston rock than average thrust load.
What is your rule of thumb for piston length to diameter ratio? I think 65-70% is OK for high performance. I get really uninterested in a piston if it requires oil ring rail supports.
Over the tight range of rod length in the 383 you mention, the rod ratio has only changed by about 2%. That's not enough to get any significant amount of friction out of the cylinder kit. The calculations I have shown are over a range of 33%, mostly to be able to show a big difference from a big change. I have done similar calculations on other engines, covering the range from 1.4 to 3.0 in length/stroke. I was searching for an "optimum", but the curve of peak rod thrust vs length/stroke is a gentle downward curve, almost linear. The "optimum" I got was at 2.5, and that was only because the slope of the curve started decreasing at a decreasing rate.
But over the range of 1.5 to 2.0 in the hypothetical pro stock engine, the average rod thrust decreased 29% for a 33% increase in rod ratio. A little bit less than 1 for 1.
What is your rule of thumb for piston length to diameter ratio? I think 65-70% is OK for high performance. I get really uninterested in a piston if it requires oil ring rail supports.
Over the tight range of rod length in the 383 you mention, the rod ratio has only changed by about 2%. That's not enough to get any significant amount of friction out of the cylinder kit. The calculations I have shown are over a range of 33%, mostly to be able to show a big difference from a big change. I have done similar calculations on other engines, covering the range from 1.4 to 3.0 in length/stroke. I was searching for an "optimum", but the curve of peak rod thrust vs length/stroke is a gentle downward curve, almost linear. The "optimum" I got was at 2.5, and that was only because the slope of the curve started decreasing at a decreasing rate.
But over the range of 1.5 to 2.0 in the hypothetical pro stock engine, the average rod thrust decreased 29% for a 33% increase in rod ratio. A little bit less than 1 for 1.
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i know a little but this thread taught me a LOT, thanks to all contributors. in the real world of street cars oil temperature effects on viscosity is rarely mentioned + especially with hot running motorcycle engines!! on the EV comment i seen Slamin-Sammy Miller run his ROCKET car prolly in late 60's at York US30!! pop-pop sheee shut off at 300 mph, strip too short!!! NO burning tyres etc NO drama, like watching grass grow!!! search will show much faster speeds overseas after he was banned in USA, his eyes were BLEEDING!!!!!
The rod ratio in a PS engine is around 1.60-1.65:1 these days. It keeps getting lower. As you can see in the OP, there's very little piston on the thrust side. In teardown of these engines, no exceptional wear pattern is observed from side loading, or at least none that a simple hone job can't clean up. The friction increase is hardly noticeable due in part to there being hardly no piston skirt to speak of and because the oil they use has 1500+ ppm Mo.
For those engines, ring seal is a very big deal. They're already so closely matched that if you can find an extra 0.25 inHg vacuum at idle from improved ring seal, that's huge!
For those engines, ring seal is a very big deal. They're already so closely matched that if you can find an extra 0.25 inHg vacuum at idle from improved ring seal, that's huge!
I would agree with both of your points. Drag racing at the professional level is, for the most part, just a bunch of rich people and their friends playing with their toys. There aren't any qualifications needed to ascend to the professional ranks as a driver other than the ability to bring money. A circus act. But it's OK to enjoy the circus.
The nitro classes are good as a sensory experience. I'll usually take in one session of any event I'm attending or competing in.
Pro stock is so competitive, every little bit helps.
To achieve "ram effect", necessary for VEs over 100%, the intake port velocity must be very high. To get monsterous ps ports moving with only
500 cubic inches to play with, must take a few tricks nobody will talk about.
We just went over con-rod length. A short rod will move the piston away from tdc quicker per crank degree than a longer rod in the same engine.
The graphs posted shows by very little, but it is still there. We can theorize that a short rod engine will be more sensitive to valve overlap at tdc and
in turn, exhaust tuning. (Keeping the heat in the exhaust system by wrapping the headers should increase the exhaust velocity and in turn increase the
intake velocity if the valve timing and exhaust tuning are just right.)
An increase in compression raito will improve intake port velocity. To prove that, you'll need a lawn mower, spark plug socket and fish scale.
Delaying the intake valve opening point and/with high ratio rocker arms will increase the intake port velocity.
An increase in the bore/stroke ratio, intake valve diameter and rpm should increase intake port velocity, and of course, more cubic inches.
Get it right and the mess goes super sonic.
500 cubic inches to play with, must take a few tricks nobody will talk about.
We just went over con-rod length. A short rod will move the piston away from tdc quicker per crank degree than a longer rod in the same engine.
The graphs posted shows by very little, but it is still there. We can theorize that a short rod engine will be more sensitive to valve overlap at tdc and
in turn, exhaust tuning. (Keeping the heat in the exhaust system by wrapping the headers should increase the exhaust velocity and in turn increase the
intake velocity if the valve timing and exhaust tuning are just right.)
An increase in compression raito will improve intake port velocity. To prove that, you'll need a lawn mower, spark plug socket and fish scale.
Delaying the intake valve opening point and/with high ratio rocker arms will increase the intake port velocity.
An increase in the bore/stroke ratio, intake valve diameter and rpm should increase intake port velocity, and of course, more cubic inches.
Get it right and the mess goes super sonic.
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Nice to see activity in this thread. Erica was able to back up last year’s performance.
www.nhra.com
Erica Enders wraps up fourth NHRA Pro Stock world championship
Erica Enders won her second-straight Camping World NHRA Pro Stock championship and fourth overall on Sunday at the Dodge NHRA Finals in Las Vegas. Enders came into the event as the championship leader but struggled during qualifying and landed No. 12 on the grid. On Sunday, she did her part by...
I've heard that periodically over the years. Always said (at least so far) by someone who has never sat in a TF/D or F/C, let alone driven one. They do in fact require more ability than just stomping on the pedal and hanging on. Most who have been successful, started out in much slower machinery, and worked their way up. Some never do get the hang of it.
Most people I know on the tour, often refer to it as The Circus.
What about the camshafts in ps engines? One would assume as the rpm increases, the intake valve closing point is delayed somewhat.
There would be no point in closing the intake valve before the cylinder pressure and intake manifold pressure equalize.
Time for a rule change to allow solinoid or compressed air actuated valves and variable valve timing.
There would be no point in closing the intake valve before the cylinder pressure and intake manifold pressure equalize.
Time for a rule change to allow solinoid or compressed air actuated valves and variable valve timing.
You are correct, and there is a little more nuance to my opinion than what I typed.
It's a unique motorsport in that there really aren't any 'feeder' series a racer can use to climb the ladder to the top. Sure, there is Top Alcohol and that is/can be used as a stepping stone to get the feel for the speed, but there is no real correlation between success in Top Alcohol and getting a fuel seat. Now, the crew chief is probably more successful to the success of any car than the driver, and that's true in Top Alcohol or Fuel.
This isn't to say that no skill is required to drive in either series. There are some exceptions such as Shawn Langdon and Jack Beckman who were world champions in the sportsman ranks who ascended to Fuel, but you could also argue that each of them had the right connections to get there. They didn't necessarily ascend due to the prowess they showed in the lower ranks.
The disconnect between sportsman (amateur) and professional drag racing is so wide, and unlike any other form of motorsport. Myself and my best friends are drag racers, and none of us care one bit about the highest level of the sport. We were all in Vegas for the Finals, since one of us was racing there. Watched just a few pair of nitro cars over the weekend.
I don't have any great ideas on how that dynamic could be improved, but it seems like a bad thing for the sport.
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