Box Stock

Standard rod vs +10

alvin l nunley said:
Now you’re talking, (.300”) a significant difference. I remember a guy doing the small block thing back in the early 60’s. I heard he was putting 409 rods in a 327.
But .010” is insignificant. Even at 90 degrees you’re only talking a .00094” difference in piston travel.
Comments, compliments, criticisms and questions always welcome.
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the point I was trying to make was if you have say a blue max with piston .032 in the hole but choose not to deck the block that much use a max stroke crank and a longer rod which in 2014 +.015 is legal so by doing this you have moved the piston up the cylinder .025 and your piston now is only .007 in the hole. By using the .01 longer stroke crank you have also picked up 1 cc in the cylinder. .0096" or bore = 1 CC.
now blast me for that!
 
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jgm motorsports said:
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,
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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.
 
The longer dwell period is most beneficial at TDC just after a properly timed ignition event, the piston is at TDC longer allowing greater pressure to build while the chamber is at it's smallest size.

Before the crash a poster claimed he used a screwdriver in the spark plug hole to find TDC, you will find you can roll these engines about 3-4 degrees either side of TDC on your degree wheel without the dial indicator indicating piston movement.
 
Kart43 said:
The longer dwell period is most beneficial at TDC just after a properly timed ignition event, the piston is at TDC longer allowing greater pressure to build while the chamber is at it's smallest size.

Before the crash a poster claimed he used a screwdriver in the spark plug hole to find TDC, you will find you can roll these engines about 3-4 degrees either side of TDC on your degree wheel without the dial indicator indicating piston movement.
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this is why you should use a piston stop to find TDC.
 
AML_RACING_DAD_98 said:
the point I was trying to make was if you have say a blue max with piston .032 in the hole but choose not to deck the block that much use a max stroke crank and a longer rod which in 2014 +.015 is legal so by doing this you have moved the piston up the cylinder .025 and your piston now is only .007 in the hole. By using the .01 longer stroke crank you have also picked up 1 cc in the cylinder. .0096" or bore = 1 CC.
now blast me for that!
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I hope I didn't come across as "blasting" you, not what I was wanting to do at all. I have done a lot of testing, and just do what I do, I could be wrong, just stating what I do. One of my best engines in my car was a 434 sbc. That's a 4" stroke and a 6" rod (not a good rod to stroke ratio) but it lived a long time, and I actually sold it to some other guys who raced it a long time too. And again, I hope I didn't make you mad.
 
youngengines said:
I hope I didn't come across as "blasting" you, not what I was wanting to do at all. I have done a lot of testing, and just do what I do, I could be wrong, just stating what I do. One of my best engines in my car was a 434 sbc. That's a 4" stroke and a 6" rod (not a good rod to stroke ratio) but it lived a long time, and I actually sold it to some other guys who raced it a long time too. And again, I hope I didn't make you mad.
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no need for apology here, sometimes I come across here snappy and not meaning anything by it. just the way I type or should I say try to type.
I have gotten alot of good info from bobs and your recommendations are right at the top.
 
Post #23 has a valid point. Set the degree wheel up with a piston stop. then use a dial indicator in the spark plug hole. ( you probably need the set up I have ) Using a short rod, roll the engine to TDC. Roll the engine backwards until the dial indicator moves and read the dial indicator. Then roll the engine the other direction past TDC until the dial indicator starts to move again and read the degree wheel. Then do the same with a long rod. You will see how much dwell the difference is between a long rod and a short rod.
 
Kart43 said:
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.
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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.
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Ssrperformance said:




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.
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please explain how the dwell time at BDC would be different that TDC. The crankshaft is swinging the same arc top and bottom and the pivot point at the piston pin is unchanged so how would it be any different and the distance traveled would be unchanged..
 
AML_RACING_DAD_98 said:
please explain how the dwell time at BDC would be different that TDC. The crankshaft is swinging the same arc top and bottom and the pivot point at the piston pin is unchanged so how would it be any different and the distance traveled would be unchanged..
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Well it's a little more involved than that, but for the sake of a long explination, you might start here with some research:

http://www.stahlheaders.com/Lit_Rod Length.htm
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plenty there to read kinda hard to take in though a short scan taught me a little already plus got the olwheels turnin
 
drvred said:
My bottom end was built before the days of max stroke cranks.
Just wondering if it was worth messing with.
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don't worry about long/short rod as mentioned its a mute point as far as length vs performance.

now that said you can use your rod length to adjust your cc if they need adjusting.
check your cc of motor and if good don't change rod.

if your at 28 29 cc stick a longer rod in use cc calculator to determined how much longer of a rod you can use.
make sure no pop up
 
long or short, thick or thin....one thing that you need to look at regardless of the length of the rod, crank or anything is what the wrist pin can handle. i've seen what a good billet rod and wiseco piston and wrist pin looked like after being run up to max rpm....also saw what a good billet rod with a stock piston and wrist pin looked like....the guy was very luck he didn't ventilate the block...the wrist pin holes in the piston had started cracking and the wrist pin was really wobbly.

just sayin....if your going to look at making changes, make sure that the parts you are going to put into the motor can withstand what your asking it to do..
 
drvred said:
My motor was worn out and was trying to decide on standard or max stroke/+10 kit
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In that situation go max stroke +.010 on the rod adjust your cc's with the head gasket.
Otherwise you are always going to be second guessing your choice of not having the max stroke crank.
 
Aml dad.. because he has the new max. duel stroke crank ! It has .010 more stroke @ tdc. and .010 less stroke @ bdc.... Really. ????!!
Max stroke & long rod for me everytime for this application .
:)
 
clone king said:
Aml dad.. because he has the new max. duel stroke crank ! It has .010 more stroke @ tdc. and .010 less stroke @ bdc.... Really. ????!!
Max stroke & long rod for me everytime for this application .
:)
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It has nothing to do with stroke ...he said --The long rod will cause the piston to dwell at TDC longer and move away from TDC more slowly, same at BDC.

This just simply isn't the case. the rates at which it slows down (and accalerates) are different at TDC than at BDC. Look at piston speed per crank degree of rotation at TDC vs BDC and then compare rod lengths/ratios.
I'm not expecting you to just take my word for it, but if you're not willing to do your own research and look at some graphs or some illustrations, then I can't help you more than this.
 
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