Ideal Drag Race Bore and Stroke

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ValiantRacing

ValiantRacing

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I typed this in and this is what AI says, i would swear @Newbomb Turk is writing for AI :D


For drag racing, an engine with a larger bore and shorter stroke is generally preferred because it allows for higher RPMs and more power output. This is often referred to as an "oversquare" engine. [1, 2, 3, 4]
Here's why: [2, 3]
  • Higher Revs: A shorter stroke means the piston travels less distance with each revolution, reducing piston acceleration and allowing the engine to rev higher.
  • More Power: Higher RPMs contribute directly to increased power output, especially at the top end of the rev range where drag racing engines are typically pushed.
  • Larger Bore: A larger bore allows for bigger intake and exhaust valves, improving airflow and further enhancing power.
In summary, a drag racing engine benefits from a smaller stroke and larger bore, enabling it to rev higher and produce more power at the top end. [1, 2, 3]
Rod Ratio: While bore/stroke ratio is important, rod ratio (the ratio of the connecting rod length to the stroke length) also plays a significant role, especially in high-revving engines. For very high RPM operation, rod to stroke ratios greater than 2:1 are typical. Rod ratios of 1.70 to 1.65 are also mentioned for Pro Stock drag racing. [1, 5]
 
That's something I don't like about AI.
It will always give you the currently accepted answer. It disregards thinking outside the normal (and programmed in) train of thought, which precludes any advancement or innovation. The same question will always generate the same answer, there is no "What if".
An AI will never say "Here, hold my beer while I try this"...
 
Depends on the car weight and class rules also. There is not one answer.

Like it mentions pro stock. What pro stock class? NHRA is 500 ci limit. Other have 800 inches.

Super comp guys like height MPH, they got 180++ now with lotsa cubic inches.

Top dragster and top sportsman only take the 32 quickest ETs so you need power, and power adders are commonplace. 7.00 is the bump area for 1/4 mile.
 
Last edited:
Professor Fate said:
That's something I don't like about AI.
It will always give you the currently accepted answer. It disregards thinking outside the normal (and programmed in) train of thought, which precludes any advancement or innovation. The same question will always generate the same answer, there is no "What if".
An AI will never say "Here, hold my beer while I try this"...
Click to expand...

The answer above hasn’t been the current answer for decades.

The answer is:

P
L
A
N

That is the only answer and thats what the answer is.
 
Professor Fate said:
That's something I don't like about AI.
It will always give you the currently accepted answer. It disregards thinking outside the normal (and programmed in) train of thought, which precludes any advancement or innovation. The same question will always generate the same answer, there is no "What if".
An AI will never say "Here, hold my beer while I try this"...
Click to expand...

Exactly, and "I" in AI is a misnomer. There is no actual intelligence, rather pattern recognition and regurgitation.
 
413 said:
Depends on the car weight and class rules also. There is not one answer.

Like it mentions pro stock. What pro stock class? NHRA is 500 ci limit. Other have 800 inches.

Super comp guys like height MPH, they got 180++ now with lotsa cubic inches.

Top dragster and top sportsman only take the 32 quickest ETs so you need power, and power adders are commonplace. 7.00 is the bump area for 1/4 mile.
Click to expand...
Top fuel cars I think are 500 cubes too
 
Another possibility that rpm has an advantage that occurred to me. I don't know how to put in words so I'll give an example. Take two engines making same peak power and same lbs-ft per cid but one engine is half the size of the other and the smaller one makes peak power at twice the rpm. And say both make peak torque 1,500 rpm's less than peak hp.

So lets say engines A & B make
A. 600 hp at 6,000 rpm and 584 tq at 4,500 rpm
B. 600 hp at 12,000 rpm and 292 tq at 10,500 rpm

Even though both engines make same hp but one at half the rpm and even though torque is half the other but it's peak torque is way more than twice the rpm of the other (4,500 vs 10,500) so the power at peak torque for engine B. is gonna be greater and probably most of it's under curve area. eg.. A 584 tq = 500 hp at 4,500 rpm and B's 292 tq at 10,500 rpm = 584 hp.

So engine B. is only down 16 hp at peak torque where A. is down 100 hp at peak torque and if you took it to shift points I imagine engine B. be making at least similar power there too, so B. has way more average power from peak torque to peak hp and probably to shift points.

Even though this is extreme example and requires both to be similarly efficient it would still play out with a 6000 rpm vs 7000 rpm or whatever rpms just to a lesser degree as long efficiency are similar. Which in a highly competitive race class where this would matter they should be.


Plus I remember in one of my old Mopar mags, one of the Max Wedge Super Stock racers said mopar engineers found that a stroke of 92% of the bore gives the best power, don't how true that is but always stuck with me.
 
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273 said:
Another possibility that rpm has an advantage that occurred to me. I don't know how to put in words so I'll give an example. Take two engines making same peak power and same lbs-ft per cid but one engine is half the size of the other and the smaller one makes peak power at twice the rpm. And say both make peak torque 1,500 rpm's less than peak hp.

So lets say engines A & B make
A. 600 hp at 6,000 rpm and 584 tq at 4,500 rpm
B. 600 hp at 12,000 rpm and 292 tq at 10,500 rpm

Even though both engines make same hp but one at half the rpm and even though torque is half the other but it's peak torque is way more than twice the rpm of the other (4,500 vs 10,500) so the power at peak torque for engine B. is gonna be greater and probably most of it's under curve area. eg.. A 584 tq = 500 hp at 4,500 rpm and B's 292 tq at 10,500 rpm = 584 hp.

So engine B. is only down 16 hp at peak torque where A. is down 100 hp at peak torque and if you took it to shift points I imagine engine B. be making at least similar power there too, so B. has way more average power from peak torque to peak hp and probably to shift points.

Even though this is extreme example and requires both to be similarly efficient it would still play out with a 6000 rpm vs 7000 rpm or whatever rpms just to a lesser degree as long efficiency are similar. Which in a highly competitive race class where this would matter they should be.


Plus I remember in one of my old Mopar mags, one of the Max Wedge Super Stock racers said mopar engineers found that a stroke of 92% of the bore gives the best power, don't how true that is but always stuck with me.
Click to expand...
My engine combo the stroke is 88%
 
273 said:
Another possibility that rpm has an advantage that occurred to me. I don't know how to put in words so I'll give an example. Take two engines making same peak power and same lbs-ft per cid but one engine is half the size of the other and the smaller one makes peak power at twice the rpm. And say both make peak torque 1,500 rpm's less than peak hp.

So lets say engines A & B make
A. 600 hp at 6,000 rpm and 584 tq at 4,500 rpm
B. 600 hp at 12,000 rpm and 292 tq at 10,500 rpm

Even though both engines make same hp but one at half the rpm and even though torque is half the other but it's peak torque is way more than twice the rpm of the other (4,500 vs 10,500) so the power at peak torque for engine B. is gonna be greater and probably most of it's under curve area. eg.. A 584 tq = 500 hp at 4,500 rpm and B's 292 tq at 10,500 rpm = 584 hp.

So engine B. is only down 16 hp at peak torque where A. is down 100 hp at peak torque and if you took it to shift points I imagine engine B. be making at least similar power there too, so B. has way more average power from peak torque to peak hp and probably to shift points.

Even though this is extreme example and requires both to be similarly efficient it would still play out with a 6000 rpm vs 7000 rpm or whatever rpms just to a lesser degree as long efficiency are similar. Which in a highly competitive race class where this would matter they should be.


Plus I remember in one of my old Mopar mags, one of the Max Wedge Super Stock racers said mopar engineers found that a stroke of 92% of the bore gives the best power, don't how true that is but always stuck with me.
Click to expand...


More rpm is more firing cycles per time unit.

More firing cycles means more power.

Plus the rpm lets you use lower ratio (higher numeric) gearing.

That makes it easier to get the load moving.
 
Cuda416 said:
Exactly, and "I" in AI is a misnomer. There is no actual intelligence, rather pattern recognition and regurgitation.
Click to expand...
Just regurgitating of what it sees posted .
AI the deck height of a 5.9 block . But don’t order your pistons based on what it tells you !
 
Newbomb Turk said:
More rpm is more firing cycles per time unit.

More firing cycles means more power.

Plus the rpm lets you use lower ratio (higher numeric) gearing.

That makes it easier to get the load moving.
Click to expand...
What I was trying to show was two engines of the similar hp and lbs-ft per cid (efficiency) but at different rpms (displacement) the higher revving one I THINK has more chance of making more hp at peak torque and therefore should be a better under the power curve than the lower revving one.
 
273 said:
Another possibility that rpm has an advantage that occurred to me. I don't know how to put in words so I'll give an example. Take two engines making same peak power and same lbs-ft per cid but one engine is half the size of the other and the smaller one makes peak power at twice the rpm. And say both make peak torque 1,500 rpm's less than peak hp.

So lets say engines A & B make
A. 600 hp at 6,000 rpm and 584 tq at 4,500 rpm
B. 600 hp at 12,000 rpm and 292 tq at 10,500 rpm

Even though both engines make same hp but one at half the rpm and even though torque is half the other but it's peak torque is way more than twice the rpm of the other (4,500 vs 10,500) so the power at peak torque for engine B. is gonna be greater and probably most of it's under curve area. eg.. A 584 tq = 500 hp at 4,500 rpm and B's 292 tq at 10,500 rpm = 584 hp.

So engine B. is only down 16 hp at peak torque where A. is down 100 hp at peak torque and if you took it to shift points I imagine engine B. be making at least similar power there too, so B. has way more average power from peak torque to peak hp and probably to shift points.

Even though this is extreme example and requires both to be similarly efficient it would still play out with a 6000 rpm vs 7000 rpm or whatever rpms just to a lesser degree as long efficiency are similar. Which in a highly competitive race class where this would matter they should be.


Plus I remember in one of my old Mopar mags, one of the Max Wedge Super Stock racers said mopar engineers found that a stroke of 92% of the bore gives the best power, don't how true that is but always stuck with me.
Click to expand...
Here's where the practical side of me has to step in, where an AI wouldn't.
While I agree with the above in theory, you have to take longevity into account at higher RPMs. You don't win races if the engine lets go at half track, nor do most of us have a Top Fuel budget to rebuild the engine between each round... You have to find your happy medium that you're comfortable with and your wallet can handle.
 
R/S ratio is an important factor to consider.
 
Professor Fate said:
Here's where the practical side of me has to step in, where an AI wouldn't.
While I agree with the above in theory, you have to take longevity into account at higher RPMs. You don't win races if the engine lets go at half track, nor do most of us have a Top Fuel budget to rebuild the engine between each round... You have to find your happy medium that you're comfortable with and your wallet can handle.
Click to expand...


True, but it’s not 1980 any more TBO has gone dramatically way up IF a you don’t build the engine like it’s 1980.

Of course, the shoe polish racers always talk about TBO like it’s the end of the world, but the longest TBO would be the slant 6.

TBO only matters when your budget isn’t enough to build the engine for rpm. That’s why the /6 should be the bracket racers dream.
 
Newbomb Turk said:
True, but it’s not 1980 any more TBO has gone dramatically way up IF a you don’t build the engine like it’s 1980.

Of course, the shoe polish racers always talk about TBO like it’s the end of the world, but the longest TBO would be the slant 6.

TBO only matters when your budget isn’t enough to build the engine for rpm. That’s why the /6 should be the bracket racers dream.
Click to expand...
TBO?
 
I find interesting that a NHRA Pro Stock engine stroke is only 3.600, it seems like most people are about the 4 inch crank for a small block and a 4.15 or 4.25 for big block.
 
RustyRatRod said:
Ideal is whatever you have. Use it.
Click to expand...


This is why I’m now suggesting to ALL bracket racers to swap to the slant 6.

Time Between Overhauls is exceptional, between race maintenance is drastically reduced and therefore the fun factor is through the roof.

It’s not about the ET or MPH, it’s about fender racing, playing the game, hiding a tenth in your dial in and turning on win lights all while never opening the hood between two season oil change intervals.

All that savings means you can now buy an enclosed trailer, a new motor home to pull it with, and all the extra special fixings for those trailer side BBQ’s.

Oh yeah, and the best part is you can buy MORE beer of the expensive brands so the bench racing after a long day of shoe polish racing is done is all cooled off and washed down with style.

The slant 6 bracket engine program is a win, win, win, win win on every level.

Hell, you don’t even need a throttle stop. You caint beat that.
 
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