Box Stock

Standard rod vs +10

Disclaimer: (On too-many occassions, you guy's make my day!) My advocation of the Long-Rod is a 'factual' rule-of-thumb that is followed by highly knowledgeable engine builders everywhere! However, In these 'little-monsters', I am Not advocating scraping what you have, as I am simply saying use the best (longest) of your choice in which you have!! On the other-hand...."I" have (at times) Not-liked of which I had! Maybe I should blame my fore-fathers for that! :)
 
Clone King, I looked at his graphs and charts which if your building a V8 long rod would be beneficial but on these little buggers you have to use what will apply to your motor. not all deck heights are the same, crank strokes are different and rod lengths as well as pin locations so your correct in saying use what works in your application. Like I've said before if I have .010 more stroke than I have .010 chamber area even though it's minimal i'll take it and rod length i'll take all the dwell time as well. You had a well written post and thanks for your reasoning.
 
clone king said:
This is a slap.. your saying kart43 is incorrect, is Exactly what you said... both agree the longer rod will let the piston dwell longer at tdc, but less at bdc ....meaning the piston speed changes from accel to dell, ect in time.. Yet you are Confused in calling kart43 and yourself using the same mathmatical formula to both be wrong...... You sir are Incorrect, on being Incorrect... Here's your Sign COBB .
the others are wrong on stroke, in saying it moves the piston up .010, or More stroke will dwell at tdc & bdc. lol we wish,,... then the Second slap Sir was telling me to go look up graphs and charts, degrees arc, rod lenghts charts, because you found some new cool interweb site with all the charts, here's the SLAP,, When i posted longer rod, max stroke for this application every time. Pretty well says what your graphs and charts will recommend..... OK> back the to .010 more stroke moves the piston up .010 Wrong...> the piston or stroke would move up the wall .005, and .005 down..
Now to the other. sucks all the old Bob stuff is gone... Dynodon No one ever gave a critic an award... That's Funny.... WHY ? early morning roflmbo....:)
Clones have Dynodon Protection, and Barry's Affection !!! lol along with many others to Help here, iv'e shared all, and again, most info or stories, and data lost.. i feel like Sneak's.
but Death brings new life, and hope.. it has to, or there would be no continuation.
Back to Slapper,, i may be a nut in fantasy land, but i have that choice, here in America, at least where i'm at.. it's my choice to as you say , "slap" lol don't they do that in France ?
oh. back to original post, no machining needed other than the cylinder honed if wore. to diy build back is not hard, but if building back to rules, or specs. like akra bsp, then you will need the tools, .. degree wheel, dial iindicator, fixtures, burrette, no go gauges, and ect.. to make the measurements to know if it's truly legal wthin the specs, or rules..
question the dyno numbers, and tests you want, it will tell you a lot, in this situation, or application of engine, yes... you want the maximum amount of stroke allowed, and the longer +.010 rod for this application... . some blocks you only may use a .010 over max. crank to move the piston where you want +.005 up the bore.
KEY...these math arguments are really irreleavent to your question, some posts very rite, some vary wrong...
just have no more time to for these debates, certainly not an arc degrees, and piston speeds, and rod lenghts chart, ect.. which brings another point, every small change, can effect the tune of the engine package, installing the max. stroke crank, and +.010 over rod does effect the tune, is it better than before without a dyno proving it ? it should.. i
KEY 2... changing or increasing the dwell time, (as already stated above correctly by kart43 posted) is KEY 3.. piston timing to cam, & ignition timing in degrees, and getting the vlvs opened, and closed at the rite time is Most Important Key Here... These Events Tune Properly will put you up front, not that a dyno..
piston speeds, mean, average, acceleration/ deceleration rates, are all happening, they will do what they do, as a first time diy builder you need Guidance here from another builder, not math gurus, or charts, or dyno... become familiar with your motor, if already a mechanic, Great, if not Great. these guy's can guide you through as said...
Click to expand...


Way to come in here and call everyone wrong... That helps this thread.

And for the record I never once claimed which rod was better short vs long.
Nor did I mention anything about stroke.

All i was trying to explain is piston acceleration at tdc and bdc are not the same.
 
Ssrperformance said:
Way to come in here and call everyone wrong... That helps this thread.
And for the record I never once claimed which rod was better short vs long.
Nor did I mention anything about stroke.
All i was trying to explain is piston acceleration at tdc and bdc are not the same.[/QUOTE
Ssrperformance
Ssrperformance is online now
Junior Member
Join Date:Nov 2013Posts:17

Quote Originally Posted by Kart43 View Post

Rod length directly affects engine performance, you are correct displacement stays the same.
-- Long rod will improve top end and also reduce piston and cylinder wear.
--Short rod can improve bottom end performance but causes an increase in piston and cylinder wear

--The long rod will cause the piston to dwell at TDC longer and move away from TDC more slowly, same at BDC.

The relationship between connecting rod length and crankshaft stroke is crucial in engine development.

The stroke controls the piston velocity -- if the crankshaft travels from TDC to BDC in one sec and the stroke is 1 inch the piston must travel 1" per sec. now if the crank travels from TDC to BDC in one sec. and the stroke is 2" the piston must travel at 2" per sec. The time does not change the piston velocity changes.


That's not correct. The longer rod will dwell more at TDC, but less at BDC. Opposite is true for short rod. A short rod will also have a faster peak piston speed than a longer rod (not to be confused with mean piston speed). Shorter rod will have more demand at peak piston.
So who's calling everybody wrong?
__________________
Click to expand...
 
Last edited:
--The long rod will cause the piston to dwell at TDC longer and move away from TDC more slowly, same at BDC

this is the post that is incorrect. i am calling this post wrong.

quit trying to muddy up the water in here. if you dont have anything usefull to add to the conversation why post?
clone king said everything that everyone posted was wroong haha ....so what is his third answer that is correct?
this was Posted by clone king

This is a slap.. your saying kart43 is incorrect, is Exactly what you said... both agree the longer rod will let the piston dwell longer at tdc, but less at bdc ....meaning the piston speed changes from accel to dell, ect in time.. Yet you are Confused in calling kart43 and yourself using the same mathmatical formula to both be wrong.

...no we didnt agree on what i put in bold thats why i commented with USEFUL INFO, then sais im confused and me and kart 43 are both wrong? so correct us clone king ...
 
jgm motorsports said:
The longer the stroke of the crank. It takes longer to pull the piston down top to bottom and longer to push it back up. It does change the the displacement of the motor. Its like taking a short breath or a long deep breath.
Click to expand...
This is not true at all. At, let’s say 6000 RPM, the long stroke and the short stroke, the long rod and the short rod, all pistons take exactly the same time to complete one cycle. What does change is the acceleration, deceleration, rate of the piston. With one or the other, shorter or longer, the distance traveled is different, in the case of the longer, or shorter, stroke, but the time is exactly the same. So what you’re talking about with different rod lengths, and different strokes, is the acceleration rates of the pistons, not the time of one stroke. At 6000 RPM, the time it takes for one RPM is not going to change, only the acceleration rate of the piston changes. There are other things happening true, but the time of one cycle doesn’t.
And with .010” change in rod length, the dwell time change is insignificant. I showed that in post #12.
As far as dwell time is concerned, if you go out enough decimal places, you find that the “dwell time” shrinks to almost nothing. With 6 decimal places, you find the piston has moved .000004” at .1 degree of crankshaft rotation.
All this information comes from my “Nine Sheets” Excel spreadsheet. You can request your :Free: copy at anunley@austin.rr.com
Comments, Compliments, Criticisms and Questions always welcome.
 
ssperformance if I read you right you do not agree with my statement that the piston connected to a longer rod will dwell at BDC longer than the piston connected to a short rod.
 
I have 1 question. how will the dwell time change from tdc or bdc. The rod is sweeping the same arc whether its at the top or bottom long rod or short. I know the rate of piston movement increases as it falls away from 0 degrees and 180 but speed of the crankshaft stays the same as kart 43 and clone king suggested
 
not what I'm saying, I'm saying the longer rod doesn't dwell the same amount of time at tdc as it does at bdc. it does dwell the same amount of degrees at tdc as bdc but the amount of dwell time is not the same.
 
Ssrperformance said:
not what I'm saying, I'm saying the longer rod doesn't dwell the same amount of time at tdc as it does at bdc. it does dwell the same amount of degrees at tdc as bdc but the amount of dwell time is not the same.
Click to expand...
I am having hard time with thids as well . it must be an asymmetrical thing.
Jere sthal was right up there with smokey so the findings are obviously good.
Saved the link for further pondering.
 
--The long rod will cause the piston to dwell at TDC longer and move away from TDC more slowly, same at BDC.
Click to expand...

The above is directly from my original post I wiil make a slight amendment:
--The long rod will cause the pistons dwell angle at TDC will be longer and move away from TDC more slowly, the dwell angle will be the same at BDC.

My postings in fairly condensed form, quite accurately tried to clarify statements made from jgm motorsports, now perhaps you can make some accurate statements to assist this poster in terms that they can digest. In my attempt to simplify and clarify I inadvertently failed to include degreess of dwell compared to dwell in a time frame, I apologise for the confusion.

jgm motorsports
jgm motorsports is offline Junior Member

Join Date
Oct 2013
Location
Gainesville Ga
Posts
17

A longer rod changes the angle Of how it pushes the piston up the side wall in the cylinder. Longer rod in theory makes it easier to push the piston up. On dyno it dont show up that Ive seen.

Crank stroke on the other hand is huge. More stroke will dwell at the top and bottom of the stroke longer. Lets say you have a crank that cks at .123 and one at .133. 10 thousands different. On the dyno that a good hp between the two.

With that being said. Id check the stroke. If it cks over .128 Id run it in a Saturday night motor. Rod same thing dont worry bout it for Saturday night racing. Your more likely to get out run on tires than motor.
Click to expand...

The rod effects nothing other than How low in the cylinder the piston starts back up and the point it stops at the top. It does not change how long it stays the. If you have a rod that is .010 longer the pistons lowest point is .010 higher. At the top of the stroke it is .010 higher in the cylinder. It does not change the engines disparagement.

The longer the stroke of the crank. It takes longer to pull the piston down top to bottom and longer to push it back up. It does change the the displacement of the motor. Its like taking a short breath or a long deep breath.

If you have a 200cc engine with a 2 inch rod or a 10 inch its still a 200cc and will make x hp. But the 10 inch rod will turn up faster because it has less drag on the side on the cylinder,
Click to expand...
 
If you looked carefully at my information I did not mention peak or mean piston speed, I simply clarified the incorrect statement t6hat a longer stroke takes longer to move the piston through a stroke. That is incorrect At any given RPM the piston has to follow the crankshaft, if the stroke increases and the RPM is the same the piston must increase in velocity. Of course velocity is a little more in depth than the term speed and again velocity nor speed would be the perfect term to use here but velocity is the better.

This is a statement that you can argue:
If you have a 200cc engine with a 2 inch rod or a 10 inch its still a 200cc and will make x hp. But the 10 inch rod will turn up faster because it has less drag on the side on the cylinder,
Click to expand...
Does the longer rod not change the compression ratio? yes piston displacement remains the same, but chamber size changes at TDC: therefore stock rod may be x hp, but the long rod should be x hp plus benefit of improved compression ratio.
 
Kart43 said:
ssperformance if I read you right you do not agree with my statement that the piston connected to a longer rod will dwell at BDC longer than the piston connected to a short rod.
Click to expand...
this shows the dwell time difference, @ BDC with a .0100" difference in rod length.
Rod Length Stroke Rod Length Stroke

3.7795 1.811 3.7695 1.811
piston crank piston crank
1.810 177.8 1.810 177.8
1.811 177.9 1.811 177.9
1.811 178.0 1.811 178
1.811 178.1 1.811 178.1
1.811 178.2 1.811 178.2
1.811 178.3 1.811 178.3
1.811 178.4 1.811 178.4
1.811 178.5 1.811 178.5
1.811 178.6 1.811 178.6
1.811 178.7 1.811 178.7
1.811 178.8 1.811 178.8
1.811 178.9 1.811 178.9
1.811 179.0 1.811 179
1.811 179.1 1.811 179.1
1.811 179.2 1.811 179.2
1.811 179.3 1.811 179.3
1.811 179.4 1.811 179.4
1.811 179.5 1.811 179.5
1.811 179.6 1.811 179.6
1.811 179.7 1.811 179.7
1.811 179.8 1.811 179.8
1.811 179.9 1.811 179.9
1.811 180.0 1.811 180
1.811 180.1 1.811 180.1
1.811 180.2 1.811 180.2
1.811 180.3 1.811 180.3
1.811 180.4 1.811 180.4
1.811 180.5 1.811 180.5
1.811 180.6 1.811 180.6
1.811 180.7 1.811 180.7
1.811 180.8 1.811 180.8
1.811 180.9 1.811 180.9
1.811 181.0 1.811 181
1.811 181.1 1.811 181.1
1.811 181.2 1.811 181.2
1.811 181.3 1.811 181.3
1.811 181.4 1.811 181.4
1.811 181.5 1.811 181.5
1.811 181.6 1.811 181.6
1.811 181.7 1.811 181.7
1.811 181.8 1.811 181.8
1.811 181.9 1.811 181.9
1.811 182.0 1.811 182
1.811 182.1 1.811 182.1
1.810 182.2 1.810 182.2
Even at 3.7295 rod length, there is no change in dwell at the bottom of the stroke. Maybe someday I will try an even shorter, or longer, rod. It takes some time. If someone has a rod length they would like to see just email me here.
Dwell at 3 decimal points and degrees of stroke at 1 decimal point.
 
Al Just a simple question is that dwell time in Inches Or Seconds? Or is it Degrees of dwell.
As I believe the ssprerfomance person is speaking in second or parts there of.
appears that its small increments.
 
flattop1 said:
Al Just a simple question is that dwell time in Inches Or Seconds? Or is it Degrees of dwell.
As I believe the ssprerfomance person is speaking in second or parts there of.
appears that its small increments.
Click to expand...
Piston travel ver degrees of crank rotation.
What would you like to see?
 
This is surprisingly a very touchy subject. I will pass along some of my experience and TIFIW. The standard deck height for a small block chevy is 9.020. About 20 years ago Chevy introduced several new blocks with deck heights of .0500 to one inch shorter. Chevy offered these because of request from racers for a number of years. We were cutting our decks up to .200 to arrive at a shorter deck height. Allot of money was spent to retool to produce a new line of blocks.They soon became the rage in drag racing.

In the late 1970's many were running the long rod. The ideal rod length ratio was believed to be somewhere from 1.75 to 1.9. As time passed into the late 1980's this became a thing of the past as the better blocks, known as the bow tie blocks with the thicker Siamese designed cylinder walls and high nickel material this started changing. We spent allot of money in the early 1990's going to the short deck blocks (about $3000 for a block before we added the roller cam bearings and we also went to larger base circle camshafts because we had the room with the relocated camshaft that was part of the upgrade with the new blocks. The larger base circle camshafts help make power because it reduced torsional twist as we were running lifts close to one inch and seat pressures of 400 lbs.The fact is everyone started going to shorter rod lengths. Why? Because the assembly was lighter and the rod length was of no consequence as far as horse power loss or gain.

In my early days of drag racing (late 70's) we spent time sonic checking blocks for cylinder wall thickness and higher nickel material found in marine blocks. We could not keep the cylinder walls round and would lose power the more we ran the motors so we honed and reringed often to keep the motors sealed up. We also new that a longer rod was much easier on cylinder walls and piston skirts. David Reher of Rher Morrison was a famous Pro Stock engine builder put out a technical paper about 20 years ago and claimed that the rod length has no bearing on performance after extensive testing.

IMO the thin sleeves run in these aluminum blocks may like a longer rod because of poor sealing. If we damaged a block and had to sleeve a block we would repair the block and sell it. A sleeve was a 10 hp loss. In drag racing you could not give up any hp loss even if it was such a small percentage. If one sleeve was a 10 hp loss think of what it would be if we sleeved all 8 cylinders?

IMO horse power gains from a long rod may be due to these terribly thin sleeves. I didn't write this to step on toes but hopefully to enlighten!
 
alvin l nunley said:
this shows the dwell time difference, @ BDC with a .0100" difference in rod length.
Rod Length Stroke Rod Length Stroke

3.7795 1.811 3.7695 1.811
piston crank piston crank
1.810 177.8 1.810 177.8
1.811 177.9 1.811 177.9
1.811 178.0 1.811 178
1.811 178.1 1.811 178.1
1.811 178.2 1.811 178.2
1.811 178.3 1.811 178.3
1.811 178.4 1.811 178.4
1.811 178.5 1.811 178.5
1.811 178.6 1.811 178.6
1.811 178.7 1.811 178.7
1.811 178.8 1.811 178.8
1.811 178.9 1.811 178.9
1.811 179.0 1.811 179
1.811 179.1 1.811 179.1
1.811 179.2 1.811 179.2
1.811 179.3 1.811 179.3
1.811 179.4 1.811 179.4
1.811 179.5 1.811 179.5
1.811 179.6 1.811 179.6
1.811 179.7 1.811 179.7
1.811 179.8 1.811 179.8
1.811 179.9 1.811 179.9
1.811 180.0 1.811 180
1.811 180.1 1.811 180.1
1.811 180.2 1.811 180.2
1.811 180.3 1.811 180.3
1.811 180.4 1.811 180.4
1.811 180.5 1.811 180.5
1.811 180.6 1.811 180.6
1.811 180.7 1.811 180.7
1.811 180.8 1.811 180.8
1.811 180.9 1.811 180.9
1.811 181.0 1.811 181
1.811 181.1 1.811 181.1
1.811 181.2 1.811 181.2
1.811 181.3 1.811 181.3
1.811 181.4 1.811 181.4
1.811 181.5 1.811 181.5
1.811 181.6 1.811 181.6
1.811 181.7 1.811 181.7
1.811 181.8 1.811 181.8
1.811 181.9 1.811 181.9
1.811 182.0 1.811 182
1.811 182.1 1.811 182.1
1.810 182.2 1.810 182.2
Even at 3.7295 rod length, there is no change in dwell at the bottom of the stroke. Maybe someday I will try an even shorter, or longer, rod. It takes some time. If someone has a rod length they would like to see just email me here.
Dwell at 3 decimal points and degrees of stroke at 1 decimal point.
Click to expand...


This shows nothing in degrees vs time.
 
You must log in or register to reply here.
Back
Top