NHRA Pro Stock Bearings

[RDY4WAR]

The crew chief is definitely a big part of a successful driver. Austin Coil, George Bryce, Rick Jones, etc... Behind a great driver is a great crew chief. While John Force is an outstanding driver, it was Austin Coil who made it so he could put the power to the ground.

 

[02SE]

I always enjoy Vegas.

It's interesting what you say about not caring about the highest level of the sport. I and most of my friends in the Nitro ranks on the tour ARE solely focused on our respective classes too. I almost never watch the Sportsman classes, as I am focused on what I'm there to do.

2020 was a strange year. It started out with me not being sure I wanted to be a part of it anymore, just from the demands it places on my time, and ended with the China Virus restrictions. 2021 will start the same way.

 

[RDY4WAR]

It's not that I don't care about the top classes. I just don't feel a connection with them as a competition. To me, they're an exhibition. The "sport" of it was lost to me long ago.

I like seeing more variation in the competition. I like seeing a 588ci twin 98mm turbo car on alcohol go against a 704ci nitrous car on NO2 leaded. Such as that excites me.

 

[02SE]

My last reply was in response to 'Lenny5160'.

 

[Lenny5160]

As RDY4WAR stated, to me it's more a show than a competition with an interesting outcome. Being inside that part of drag racing, I'm sure you feel very differently about it as you should.

My biggest concern is that the nitro fields seem to only be shrinking, the TV audience is small. If die-hard racers like myself and a great number of other sportsman racers can't connect with nitro racing, why would the general public be interested in watching it? I know they are out there, but it seems to be an aging and shrinking group. That has a big impact on NHRA who coordinates the whole enterprise.

 

[02SE]

Before the China Virus, the stands would be full only when the Nitro classes were running. So the interest seems to still be there to some degree.

In TF/D and F/C, the biggest hurdle is the ever-changing regulations increasing the cost of competing. Then the case has to be made whether it's worth the cost to continue. I and many of my colleagues think that limiting the classes which were intended to be unlimited, has had a negative effect on who is willing to continue to participate.

But you're right, all forms of Motorsport are slowly dying. Less people interested in cars and motorcycles in general beyond just being viewed as appliance transportation.

Lots of kids today don't care about driving, or even bothering to get a Drivers License. So they certainly don't care about racing them.

 

[sunruh]

My biggest concern is that the nitro fields seem to only be shrinking, the TV audience is small. If die-hard racers like myself and a great number of other sportsman racers can't connect with nitro racing, why would the general public be interested in watching it? I know they are out there, but it seems to be an aging and shrinking group. That has a big impact on NHRA who coordinates the whole enterprise.

i care about the nitro field
i love the fuel cars and ps cars.
i love the 9.90 cars and sportsman
but im a racer
when i spend the entire day in ennis, i watch them all and as 02se says, the stands are only full for the tf/ps classes ... not for the others
and ive gone for the 90s,00s, 10s (so 30ish years). heck i took a friend for the 1st time...his son got a rear tire from a tf/d car as we waited for the rain to clear and the track to dry. it filled the bed of that ram3500. for a year it set in his garage and his son had a new nickname of "Big Tire". the 1st time someone is there in person to witness 20k+ hp on the line...they remember it for the rest of their life.
everything has shrunk back since the pandemic. 135 other countries have felt the same pain.
gieco just pulled their 20year sponsorship of an mx team where they advertise on tv about insuring motorcycles

 

[benjy]

its unfortunate only the pro classes are heads up racing!! because of course not enough racers as it was YEARS ago + i feel using just a few classes racing heads up would better the "electronics" involved in bracket classes! BUT it is what it is + i still like it!!

 

[userfriendly]

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.

View attachment 33277

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.
View attachment 33278

Graph of piston acceleration with 1.5 rod ratio. Peak acceleration is -7447 G's (downward) at TDC.
View attachment 33279

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.
View attachment 33280

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.
View attachment 33282

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.
View attachment 33283

Questions? Comments? Or have I stepped on the cake again?

Nope, perfect. I would like to learn more about "intake port mach numbers". I think I know how to get big ports on a small engine moving
in the right direction, but it's all theory without proof.

 

[A_Harman]

Nope, perfect. I would like to learn more about "intake port mach numbers". I think I know how to get big ports on a small engine moving
in the right direction, but it's all theory without proof.

I have another spreadsheet that I use to estimate engine performance parameters based on basic design dimensions and intake manifold conditions. In the process of creating the spreadsheet I ran across an equation called the Mean Inlet Mach Index in my old IC engine textbook. (The Internal Combustion Engine In Theory and Practice, CF Taylor, MIT Press, 1977, Volume 1.) On page 173, there is the equation:

Z = (b/D)^2 x (s / C x a) where
b is engine bore diameter
D is inlet valve diameter
s is the engine mean piston speed at an operating point in question
C is the mean inlet port flow coefficient based on the valve diameter
a is the speed of sound evaluated at intake manifold charge air temperature

The text shows that engine volumetric efficiency begins dropping off rapidly once Z exceeds 0.6. It is a tool for sizing intake valves and estimating what the peak power speed should be if efficient breathing is to be maintained. The basis of the calculation is the fact that the piston descending in the cylinder drives the flow of air in the inlet tract. Since the bore diameter is always larger than the intake valve diameter, the velocity of air in the inlet port will always be higher than the velocity of the piston. Contrary to what many hot rodders in the world think, high velocity in the intake tract is something to be avoided. High velocity drives high pressure drop, makes for inefficient breathing, and high pumping work to pull charge into the cylinder.

 

[userfriendly]

I have another spreadsheet that I use to estimate engine performance parameters based on basic design dimensions and intake manifold conditions. In the process of creating the spreadsheet I ran across an equation called the Mean Inlet Mach Index in my old IC engine textbook. (The Internal Combustion Engine In Theory and Practice, CF Taylor, MIT Press, 1977, Volume 1.) On page 173, there is the equation:

Z = (b/D)^2 x (s / C x a) where
b is engine bore diameter
D is inlet valve diameter
s is the engine mean piston speed at an operating point in question
C is the mean inlet port flow coefficient based on the valve diameter
a is the speed of sound evaluated at intake manifold charge air temperature

The text shows that engine volumetric efficiency begins dropping off rapidly once Z exceeds 0.6. It is a tool for sizing intake valves and estimating what the peak power speed should be if efficient breathing is to be maintained. The basis of the calculation is the fact that the piston descending in the cylinder drives the flow of air in the inlet tract. Since the bore diameter is always larger than the intake valve diameter, the velocity of air in the inlet port will always be higher than the velocity of the piston. Contrary to what many hot rodders in the world think, high velocity in the intake tract is something to be avoided. High velocity drives high pressure drop, makes for inefficient breathing, and high pumping work to pull charge into the cylinder.

I thought that high intake manifold and port velocity are needed for "ram tuning", necessary for VE's over 100%.

edit... What is the HP/liter of multi valve motorcycle engines? How do they compare to 2 valve PS engines?

 

[RDY4WAR]

I thought that high intake manifold and port velocity are needed for "ram tuning", necessary for VE's over 100%.

It is but in moderation (like anything else). You want it high enough to prevent stall but not so high that there's excessive pumping losses. There's a crossover where the power lost to pumping exceeds the power gained from short ramming.

You also have to consider that peak VE occurs at or just after peak torque. A PS engine may launch near peak torque but then never sees peak torque again. They sweep the peak HP curve through the shifts.

 

[A_Harman]

I thought that high intake manifold and port velocity are needed for "ram tuning", necessary for VE's over 100%.

edit... What is the HP/liter of multi valve motorcycle engines? How do they compare to 2 valve PS engines?

Since we're on the subject of 2-valve pro stock engines, here is output from my spreadsheet showing the Mach Index calculation.

The 2-valve pro stock engine at 10500 rpm has a Mach Index of .65 with a 2.5" intake valve. A larger valve would be necessary to get the Mach Index down to .60, as shown by the 2.6" valve in the manual sizing column. I wouldn't say if the Mach Index exceeds .6 for a given engine design, that it "won't work". I would try to fit a larger intake valve, or look elsewhere for performance gains. I have looked at flow bench data for many cylinder heads on the internet, and have seen that pro stock heads are generally in the range of 2.5" intake valves. But I wouldn't be surprised if they have been trending up, or engine builders are putting larger bores in the engines. 4.75" should be feasible within the 5.0" bore spacing limit that NHRA puts on the class.

To show the effect of a 4-valve cylinder head, here is output showing the effect of two intake valves on an engine of the same bore and stroke.

The 4-valve pro stock engine at 10500 rpm has a Mach Index of .54 using two 1.94" intake valves. This represents a 17% drop, and would allow a 17% increase in operating speed, and a large increase in power. But since pro stock has a 10500 rpm rev limit, a 4-valve engine could benefit from lower required valve lift, lighter valves, and higher effective compression due to earlier intake valve closing.

I don't know much about motorcycle engines, but here is output showing a Formula 1 4-valve engine from the 3.0L V10 era.

The maximum allowable bore size was 98mm, so the maximum stroke possible was 39.6mm to stay within the 3.0L displacement limit. Honda was said to have the most powerful engine at 950 hp at about 19000 rpm. With two 1.58" intake valves, the Mach Index was a conservative .43. For comparison, how well would a common automotive valve work in the 98mm F1 engine? The LS1 engine had a 99mm bore, and a 2.0" intake valve. The Mach Index with the single big intake valve is below .6, the engine should be able to breathe efficiently, but the larger valve would have higher mass, and require more spring load. Presumably, nobody would be crazy enough to attempt a pushrod valvetrain that could go to 19000 rpm. But a DOHC hemi would be feasible.

 

[RDY4WAR]

Before NHRA set the 10500 rpm limit starting with the 2016 season, many PS engines were hitting 12000 rpm and going higher as they kept finding more power. They're still running the same 2.5"/1.8" valves as before.

 

[wpod]

The only time I go to the drags is when Funny car or top fuel is running I adore the top fuel hydro drag boats. The violence is amazing. . Even better is being able to watch the crews rebuild the engines. They are so impressive.

 

[wpod]

I doubt $15,000.00 doesn't cover the cost of the sparkplugs for the season. I have a friend from high school that runs What a Tomato top alcohol drag boat,,,, world champion in fact. While visiting him at the drags I was able to talk to a top fuel drag boat owner. He mentioned under breath that with out sponsors the boat wouldn't be there . It has been years since meeting him but the cost factored out to about $5000.00 per run.

 

[RDY4WAR]

I doubt $15,000.00 doesn't cover the cost of the sparkplugs for the season. I have a friend from high school that runs What a Tomato top alcohol drag boat,,,, world champion in fact. While visiting him at the drags I was able to talk to a top fuel drag boat owner. He mentioned under breath that with out sponsors the boat wouldn't be there . It has been years since meeting him but the cost factored out to about $5000.00 per run.

Actually they use cheap NGK $3/ea nickel v-tipped plugs and change them every 20-30 passes though they may pull them more frequently to ensure proper gaps are still there. They usually end up around .015-.020" gap though some venture as high as .030". From what I've seen and heard, there's no performance advantage seen at the wider gaps so many keep it around .020" to ensure there's no misfires.

Top Fuelers of course blow out the plugs every pass.

 

[02SE]

Delete

 

[userfriendly]

I suppose that the 10,500 rpm limit rule was put in place, otherwise the team with the deepest pockets and best valve spring sponsors would win all the races. Much like salary caps on pro sport teams. It keeps the teams with ther most money from buying championships.

Rules level the playing field, but end devolopment and innovation. If 500 cid was the only rule, and anything went.... we would have a V24 F1
style engines by now running 2,500 HP. How awsome would a pair of those sound?