honda tuning rod stroke ratio experiment
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From: mt. pee, sc, usa
honda tuning rod stroke ratio experiment
i was just wondering if anyone saw the new honda tuning. in it they take two blocks,
identical in all aspects except rod length. test went as follows: take long rod complet engine to dyno, make pulls and tune to best performance, next morning remove head,install on "short rod" short block and tune to best performance. i don't recall the exact numbers, i believe the long rod made like 268 whp and the short like 10 more.
bottom line is the short outperformed which is suprising, at least to me, i've seen and been under the impression that a longer rod generally make more power with a compromise in torque. anybody care to shed light on this. preferably someone with a lot building experience. i.e. waffles , tbone, etc.
thanks
identical in all aspects except rod length. test went as follows: take long rod complet engine to dyno, make pulls and tune to best performance, next morning remove head,install on "short rod" short block and tune to best performance. i don't recall the exact numbers, i believe the long rod made like 268 whp and the short like 10 more.
bottom line is the short outperformed which is suprising, at least to me, i've seen and been under the impression that a longer rod generally make more power with a compromise in torque. anybody care to shed light on this. preferably someone with a lot building experience. i.e. waffles , tbone, etc.
thanks
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From: Somewhere South Of Earth
Re: honda tuning rod stroke ratio experiment (greenbee)
the longer the rod the more torque its gonna create the shorter the rod the faster its gonna rev and i think that means its gonna make more hp. correct me if i am wrong....
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Re: honda tuning rod stroke ratio experiment (greenbee)
taking a specific setup and chucking two rod sets at it is no way to destinguish that "rod A" is better than "rod B". I'm not an auto engine builder, tuner, or anything I feel above an average wrench-head, but I think this subject can't be solved with one simple test. There are certain reasons that you would want a short rod, and there are an equal number of reasons to have long rods.
This is my thoughts about the subject, but please feel free to 'shoot them full of wholes'... but be respectful and use reason or proof, not slander.
A short rod built engine has a couple advantages over a long rod setup. 1) being that the rod physically weighs less and the interia is easier for the engine to transfer from upward stroke to downward stroke. 2) being the rod has a shorter distance to travel within the cylinder, making from the time of combustion to the time of BDC shorter. These two reasons (which I know their are more, but I dont know them yet) would make a short rod engine able to produce power easier, also at a higher RPM potential. Yet it would make less power at a lower RPM range (I think) because it is physically harder for the engine to keep the interia within the rotating assembly without very frequent (upper RPM range) combustion. Although this is my new thought, so Im completely speculating.
A long rod engine, on the same engine, would effectly have an advantage over a short rod since (on the same engine) a longer rod would mean that it would have a higher compression ratio due to the fact that the rod travels father up the bore. Due to my previous thought of the reason a short rod would make less power at a low RPM due to interia (that is my new thought), a longer, "heavier" rod would make interia easier between combustions at a lower RPM (therefor having a lower RPM potential aswell).
A good thing to remember is that in a properly built engine, one will not outshine another in the same area... each setup has its benefits and pitfalls. It is up to the person who builds an engine to know how to achieve the outcome they wish.
As I said before, if you have reason to believe I am incorrect on any reason, or wish to add, lets make this freindly. Enlighten us both if someone can...
Rich
This is my thoughts about the subject, but please feel free to 'shoot them full of wholes'... but be respectful and use reason or proof, not slander.
A short rod built engine has a couple advantages over a long rod setup. 1) being that the rod physically weighs less and the interia is easier for the engine to transfer from upward stroke to downward stroke. 2) being the rod has a shorter distance to travel within the cylinder, making from the time of combustion to the time of BDC shorter. These two reasons (which I know their are more, but I dont know them yet) would make a short rod engine able to produce power easier, also at a higher RPM potential. Yet it would make less power at a lower RPM range (I think) because it is physically harder for the engine to keep the interia within the rotating assembly without very frequent (upper RPM range) combustion. Although this is my new thought, so Im completely speculating.
A long rod engine, on the same engine, would effectly have an advantage over a short rod since (on the same engine) a longer rod would mean that it would have a higher compression ratio due to the fact that the rod travels father up the bore. Due to my previous thought of the reason a short rod would make less power at a low RPM due to interia (that is my new thought), a longer, "heavier" rod would make interia easier between combustions at a lower RPM (therefor having a lower RPM potential aswell).
A good thing to remember is that in a properly built engine, one will not outshine another in the same area... each setup has its benefits and pitfalls. It is up to the person who builds an engine to know how to achieve the outcome they wish.
As I said before, if you have reason to believe I am incorrect on any reason, or wish to add, lets make this freindly. Enlighten us both if someone can...
Rich
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From: chino, ca, us
Re: honda tuning rod stroke ratio experiment (greenbee)
by having a long rod you can decrease piston speed thus taking advantage of the duration of the cams, depends on specs. Also there should be an increase in torque on the long rod (theoretically) because we've calculated the statics and dynamics on a crank/piston/rod system. 
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From: So Cal
All other things being equal, youd get more torque of out a short rod. The shorter rod engine accellerates faster from TDC so at any given degree of crank angle from 0 to 180, the shorter rods piston is further down in the bore.
SJ civic, some of your thoughts are right on the money. The shorter rod (typically) weighs less and makes power lower in the RPM range. This is usually becase as the revs increase, the shorter rod becomes less volumetrically efficient due to the piston running away from the flame a little too fast and maybe not getting a complete burn on the power stroke.
Longer rods can actually run LESS compression typically, due to the fact that the piston crown dwells around TDC longer than a short rod counterpart, enabling a place for hot spots to start, where the short rod has already begun its descent back down the bore. Yyes, if you used the same piston compression height on both engines, the longer rod would have higher compression, but it would also be more prone to knock/ping. To counter this, you could use some cams with more overlap to bleed off the compression, but then youre shifting your powerband up in the rev range, furthering the long rod=high rpm horsepower.
There are always exceptions to the rule however.
SJ civic, some of your thoughts are right on the money. The shorter rod (typically) weighs less and makes power lower in the RPM range. This is usually becase as the revs increase, the shorter rod becomes less volumetrically efficient due to the piston running away from the flame a little too fast and maybe not getting a complete burn on the power stroke.
Longer rods can actually run LESS compression typically, due to the fact that the piston crown dwells around TDC longer than a short rod counterpart, enabling a place for hot spots to start, where the short rod has already begun its descent back down the bore. Yyes, if you used the same piston compression height on both engines, the longer rod would have higher compression, but it would also be more prone to knock/ping. To counter this, you could use some cams with more overlap to bleed off the compression, but then youre shifting your powerband up in the rev range, furthering the long rod=high rpm horsepower.
There are always exceptions to the rule however.
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From: NW, FL
Re: honda tuning rod stroke ratio experiment (greenbee)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by greenbee »</TD></TR><TR><TD CLASS="quote">i was just wondering if anyone saw the new honda tuning. in it they take two blocks,
identical in all aspects except rod length. test went as follows: take long rod complet engine to dyno, make pulls and tune to best performance, next morning remove head,install on "short rod" short block and tune to best performance. i don't recall the exact numbers, i believe the long rod made like 268 whp and the short like 10 more.
bottom line is the short outperformed which is suprising, at least to me, i've seen and been under the impression that a longer rod generally make more power with a compromise in torque. anybody care to shed light on this. preferably someone with a lot building experience. i.e. waffles , tbone, etc.
thanks </TD></TR></TABLE>
Building it “undersquare” works well (to some extent).
In that tune, it looks like piston speed won slightly.
But, remember that this is with 2 things staying the same:
The deck height (piston modified at wrist pin to not overstroke past the deck)
The crank (stroke) remaining the same.
Long rod gave more piston dwell time at TDC.
Short rod increased piston speed per crank rotation, and had less dwell time at TDC.
You can say that more air was moved in & out of the head.
If more piston speed per crank rotation is good for NA (with some exceptions),
then the opposite can be true for dense mixtures such as Boost.
identical in all aspects except rod length. test went as follows: take long rod complet engine to dyno, make pulls and tune to best performance, next morning remove head,install on "short rod" short block and tune to best performance. i don't recall the exact numbers, i believe the long rod made like 268 whp and the short like 10 more.
bottom line is the short outperformed which is suprising, at least to me, i've seen and been under the impression that a longer rod generally make more power with a compromise in torque. anybody care to shed light on this. preferably someone with a lot building experience. i.e. waffles , tbone, etc.
thanks </TD></TR></TABLE>
Building it “undersquare” works well (to some extent).
In that tune, it looks like piston speed won slightly.
But, remember that this is with 2 things staying the same:
The deck height (piston modified at wrist pin to not overstroke past the deck)
The crank (stroke) remaining the same.
Long rod gave more piston dwell time at TDC.
Short rod increased piston speed per crank rotation, and had less dwell time at TDC.
You can say that more air was moved in & out of the head.
If more piston speed per crank rotation is good for NA (with some exceptions),
then the opposite can be true for dense mixtures such as Boost.
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From: Somewhere South Of Earth
Re: honda tuning rod stroke ratio experiment (Quick 200k Mile Motor)
yeah i always figured taht the long stroke was better for boost do to the rod bieng heaver and having a longer power stroke whyle the shorter stroke was better for n/a applications due to the rods bieng lighter adn shorter, wich equals higher revs and moving air in and out faster to make more hp....
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Re: honda tuning rod stroke ratio experiment (greenbee)
to see what works best, you have to have the combo prepared ideally for each condition. absolute piston speed is not determined by r/s ratio; it's determined by stroke alone.
if you have the same stroke, a higher r/s will mean that the piston accelerates more slowly from TDC to BDC and back, which effects breathing per crank degree, per rpm. slower accel means slower breathing, which is often better at higher rpm if you have smaller ports and valves relative to the engine's bore and displacement. the air flows in more smoothly and steadily, and the fuel is better suspended in the air, which maintains a constantly higher velocity (in the smaller ports).
an engine with the same stroke and bore with shorter r/s will breath harder with the same sized port as its longer r/s cousin, trying to gasp in more air/fuel per same crank degree per rpm. this will often make it pull harder at lower rpm, but 'run out of steam' up higher, where the longer r/s engine still pulls. all other things =, the shorter r/s engine will do better with a bigger, 'lazier' port, especially up high, so it can ingest air more quickly as it 'huffs and puffs' harder.
a longer rod may weigh more, but it's arguable that this is (sometimes) countered by its engine having less friction from reduced sideloading, and fewer pumping losses if it has more time to suck and spit the same amount of fluid (air/fuel and exhaust) through the same size holes.
if the article didn't emphasize that the 'better' engine had the dimensions better suited to work together as a package for the particular application, it's results can be misleading and it's conclusion deceptive, if not incorrect.
also, do you want a (bigger) torquier engine (to pull a heavier car) at a lower, more constant rpm, as in NASCAR, or does your application require smaller displacement over which you have to make power, basically demanding that you rev higher, as in F1? we all know that it's important to build an engine which suits your demands. one way isn't alwys best.
Modified by slofu at 11:09 AM 10/10/2005
Modified by slofu at 11:12 AM 10/10/2005
if you have the same stroke, a higher r/s will mean that the piston accelerates more slowly from TDC to BDC and back, which effects breathing per crank degree, per rpm. slower accel means slower breathing, which is often better at higher rpm if you have smaller ports and valves relative to the engine's bore and displacement. the air flows in more smoothly and steadily, and the fuel is better suspended in the air, which maintains a constantly higher velocity (in the smaller ports).
an engine with the same stroke and bore with shorter r/s will breath harder with the same sized port as its longer r/s cousin, trying to gasp in more air/fuel per same crank degree per rpm. this will often make it pull harder at lower rpm, but 'run out of steam' up higher, where the longer r/s engine still pulls. all other things =, the shorter r/s engine will do better with a bigger, 'lazier' port, especially up high, so it can ingest air more quickly as it 'huffs and puffs' harder.
a longer rod may weigh more, but it's arguable that this is (sometimes) countered by its engine having less friction from reduced sideloading, and fewer pumping losses if it has more time to suck and spit the same amount of fluid (air/fuel and exhaust) through the same size holes.
if the article didn't emphasize that the 'better' engine had the dimensions better suited to work together as a package for the particular application, it's results can be misleading and it's conclusion deceptive, if not incorrect.
also, do you want a (bigger) torquier engine (to pull a heavier car) at a lower, more constant rpm, as in NASCAR, or does your application require smaller displacement over which you have to make power, basically demanding that you rev higher, as in F1? we all know that it's important to build an engine which suits your demands. one way isn't alwys best.
Modified by slofu at 11:09 AM 10/10/2005
Modified by slofu at 11:12 AM 10/10/2005
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From: So Cal
Re: honda tuning rod stroke ratio experiment (slofu)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by slofu »</TD></TR><TR><TD CLASS="quote">to see what works best, you have to have the combo prepared ideally for each condition. piston speed is not determined by r/s ratio; it's determined by stroke alone. </TD></TR></TABLE>
Wrong. Stroke can only tell you average piston speed, r/s ratio can give you piston speed for any given crank angle. Two different engines with the same strokes and different rods will yeild very different piston speeds.
Wrong. Stroke can only tell you average piston speed, r/s ratio can give you piston speed for any given crank angle. Two different engines with the same strokes and different rods will yeild very different piston speeds.
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Re: honda tuning rod stroke ratio experiment (LsVtec92Hatch)
i meant absolute piston speed. i edited it. read the first line to my next paragraph and my meaning is clearer.
two engines with the same stroke and different r/s ratios will have the same absolute piston speed.
also, speed is only measurable over time, so at any [one] given crank angle, the piston speed is always zero. knowing the r/s ratio or stroke does nothing more to help you conclude this.
Modified by slofu at 5:17 PM 10/10/2005
two engines with the same stroke and different r/s ratios will have the same absolute piston speed.
also, speed is only measurable over time, so at any [one] given crank angle, the piston speed is always zero. knowing the r/s ratio or stroke does nothing more to help you conclude this.
Modified by slofu at 5:17 PM 10/10/2005
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From: Charlotte, NC
Re: honda tuning rod stroke ratio experiment (greenbee)
This wasn't in Honda Tuning this was in D-sport, the dyno took place at Carbo Engineering, same spot as the B series showdown.
figured id make the correction in case anyone wants to see the write up
figured id make the correction in case anyone wants to see the write up
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From: mt. pee, sc, usa
Re: honda tuning rod stroke ratio experiment (Casey@Burns)
thanks for the correction. i was with my wife at bn just passing time.
i must agree with some of you, i don't think the benefits of both styles of engines
could be fully realised with the test setup. perhaps it was flawed from the start?
i must agree with some of you, i don't think the benefits of both styles of engines
could be fully realised with the test setup. perhaps it was flawed from the start?
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Re: honda tuning rod stroke ratio experiment (greenbee)
i read the article... as i recall, it didn't address things like how they corrected the deck height and compression ratios for the different rod lengths... maybe there is more detailed test info online somewhere?
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From: Charlotte, NC
Re: honda tuning rod stroke ratio experiment (danimal)
I'm sure if you guys wrote a letter to the editor explaining thats you would like to have some more info on the article, that they would be happy to provide it if it is available
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From: mt. pee, sc, usa
Re: honda tuning rod stroke ratio experiment (Casey@Burns)
lord knows i might have to do that. i've always thought the longer the rod the better "in a sense". i don't know if i can stand being wrong. 
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From: not riding any bandwagons in, massachusetts, usa
i personally think the short rod combo can make better peak power with the right cam profile and timing.
the short rod pulls away from BDC faster for greater vacuumm at low lift. the valve can be slammed open sooner and increased vaccuum should create increased intake velocity. at BDC, the piston rises slower with a short rod, therefore the chamber volume shrinks slower and has less tendency to reject the intake charge. the previously mentioned increase in velocity will mean an increase in inertia as well. the two coupled together make for greater cylinder filling after BDC, which IMO, is critical to power production.
i am led to the conclusion that a short rod motor should idle better with long duration cams and come into the "powerband" sooner than a comparable long rod motor.
the short rod pulls away from BDC faster for greater vacuumm at low lift. the valve can be slammed open sooner and increased vaccuum should create increased intake velocity. at BDC, the piston rises slower with a short rod, therefore the chamber volume shrinks slower and has less tendency to reject the intake charge. the previously mentioned increase in velocity will mean an increase in inertia as well. the two coupled together make for greater cylinder filling after BDC, which IMO, is critical to power production.
i am led to the conclusion that a short rod motor should idle better with long duration cams and come into the "powerband" sooner than a comparable long rod motor.
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From: Hudson, NH, 03051
Re: (greenbee)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by greenbee »</TD></TR><TR><TD CLASS="quote">good info. this starting to become a thread worth watching. very impressed by
everyones civility. lets keep it that way
</TD></TR></TABLE>
You had to go and say that...Anyway after being involved in a few articles over the years you really have to be careful about what you believe in these articles.There are always compromises do to the free parts that are available.
With that being said the trend in local circle track cars was longer and longer rods.This was driven by the desire to make the rotating assembly as light as possible so the car would accelerate quicker.Then some one decided to go all the way back to stock length and found that the car pulled a lot harder off the turn than the long rod engine.Just some food for thought.
Just swapping rod lengths with out optimizing (cams ignition fuel) the whole package it isn't a true comparison.
Glenn
everyones civility. lets keep it that way
</TD></TR></TABLE>You had to go and say that...Anyway after being involved in a few articles over the years you really have to be careful about what you believe in these articles.There are always compromises do to the free parts that are available.
With that being said the trend in local circle track cars was longer and longer rods.This was driven by the desire to make the rotating assembly as light as possible so the car would accelerate quicker.Then some one decided to go all the way back to stock length and found that the car pulled a lot harder off the turn than the long rod engine.Just some food for thought.
Just swapping rod lengths with out optimizing (cams ignition fuel) the whole package it isn't a true comparison.
Glenn
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From: So Cal
Re: (NJIN BUILDR)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by NJIN BUILDR »</TD></TR><TR><TD CLASS="quote"> the trend in local circle track cars was longer and longer rods.This was driven by the desire to make the rotating assembly as light as possible</TD></TR></TABLE>
Good info in the above post, but how is adding material to rod to lengthen it going to reduce its weight? Unless they made the beam section of the rod thinner, but that weakens it.
Also, you say they did the above to make the vehicle accellerate faster. Theres a fine line between having lightweight components that rev up quickly, and a heavier components that have greater leverage behind them on the power stroke. Just something to think about.
Good info in the above post, but how is adding material to rod to lengthen it going to reduce its weight? Unless they made the beam section of the rod thinner, but that weakens it.
Also, you say they did the above to make the vehicle accellerate faster. Theres a fine line between having lightweight components that rev up quickly, and a heavier components that have greater leverage behind them on the power stroke. Just something to think about.
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From: frozen hell, Vermont
Re: (NJIN BUILDR)
which would be better for a street car. short rod im guessing because of better low rpm cylinder filling, correct? long rod would be better for drag racing right, because of better high rpm breathing? also...with the short rod engine you could run more cam (bigger lift, more duration) because it fills the cylinders so well. anyone know how long of a rod you would need for a 92mm stroke in a b18, and what the rod/stroke ratio would be?
Re: (greenbee)
Man, my head hurts! But this is why I joined h-t. I've learned so much. I hope We do get more info from that magazine, though. I'll have to read this one several times to completly obsorb it. I hope it get's me to understand my motor better.
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Re: (Televator)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by LsVtec92Hatch »</TD></TR><TR><TD CLASS="quote">Yes, if you used the same piston compression height on both engines, the longer rod would have higher compression, but it would also be more prone to knock/ping..</TD></TR></TABLE>
In my little analogy, I was referring to using the same piston... but I am intrguiged when you say that a longer rod will make the piston stay at TDC longer. Doesnt that have to do with where the connecting rod journals are located (rod ratio stuff)? Can anyone chime in here?
Rich
In my little analogy, I was referring to using the same piston... but I am intrguiged when you say that a longer rod will make the piston stay at TDC longer. Doesnt that have to do with where the connecting rod journals are located (rod ratio stuff)? Can anyone chime in here?
Rich
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From: So Cal
I like to see people eager to learn ill try and answer what i can right now, but im in the middle of homework.
Whats better for a street car? You have to have a balance between power and logevity, so "best" is a relative term. On engines that have to last a while and spin relatively high, yes a longer rod is ideal, but it carries a weight penalty. Youre also correct in being able to run more cam with the short rod engine. Alot of drag honda's that rebuild frequently run in the 1.5-1.6 range.
SJcivic, heres something cool for you to look at, if youre a visual learner. Try pluggin in shorter/longer values for the rod and watch how long the rod stays at TDC on the long rod motor using the sine wave graphing method. You may have to plug in some unrealistic length values to really 'see' a trend, but it will help you understand. And no r/s ratio doesn have anything to do with where the rod journals are located, since rod length is measured from the centerline of the crankpin.
http://www.wfu.edu/~rollins/pi...aph_1/
ill try and answer what i can right now, but im in the middle of homework. Whats better for a street car? You have to have a balance between power and logevity, so "best" is a relative term. On engines that have to last a while and spin relatively high, yes a longer rod is ideal, but it carries a weight penalty. Youre also correct in being able to run more cam with the short rod engine. Alot of drag honda's that rebuild frequently run in the 1.5-1.6 range.
SJcivic, heres something cool for you to look at, if youre a visual learner. Try pluggin in shorter/longer values for the rod and watch how long the rod stays at TDC on the long rod motor using the sine wave graphing method. You may have to plug in some unrealistic length values to really 'see' a trend, but it will help you understand. And no r/s ratio doesn have anything to do with where the rod journals are located, since rod length is measured from the centerline of the crankpin.
http://www.wfu.edu/~rollins/pi...aph_1/
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From: not riding any bandwagons in, massachusetts, usa
the first few sections of this article will really help you guys.
http://victorylibrary.com/mopar/rod-tech-c.htm
for a daily driven honda street motor i think a 1.52-1.54 is good. they feel like larger displacement engines at 1.5k-4k RPM which is where you spend 90% of your time driving like a law abiding citizen. and if you make enough power at 7500 to have fun, why shift at 9200 every time? the less time you spend beating the snot out of your street car the more times it will drive your *** to work.
short rod ratios also have better detonation resistance so if the next hurricane to hit lousiana affects your wallet at the pumps as much as it did mine... theres always 87 octane.
http://victorylibrary.com/mopar/rod-tech-c.htm
for a daily driven honda street motor i think a 1.52-1.54 is good. they feel like larger displacement engines at 1.5k-4k RPM which is where you spend 90% of your time driving like a law abiding citizen. and if you make enough power at 7500 to have fun, why shift at 9200 every time? the less time you spend beating the snot out of your street car the more times it will drive your *** to work.
short rod ratios also have better detonation resistance so if the next hurricane to hit lousiana affects your wallet at the pumps as much as it did mine... theres always 87 octane.