Standard rod vs +10

drvred

New member
Is there a difference into torque/HP between standard stroke and rod vs the max stroke and +10 rod combo.
And if a motor is built for the standard is there machining that has to be done to convert it?
I know I am asking a lot of stupid questions, but my motor came home in a box Saturday night and I am gonna try to build it myself this time.
 

JRW31526

Member
i run a max stroke crank and a .020 rod and it seems like it had a little more bottom end, couldnt really tell about the top end i had a stock carb on, i would imagine the piston would be less in the hole with the max stroke and the .010 rod, in return would make for more compression which would make more power :)
 

Yakattack

Member
It would also depend how for you are in the hole now...
Might have to make that up with a thicker head gasket, for head to valve clearance.
 

metalmagic

New member
If rules alow u to deck the block as much as u want then u will always be better running a shorter rod and decking the block. (less weight for crank to move = better)
 

Freezeman

Site Supporter
If rules alow u to deck the block as much as u want then u will always be better running a shorter rod and decking the block. (less weight for crank to move = better)
I have to disagree with that. As a rod gets shorter it increases the rods angle at mid point of the stroke which increases friction on the sides of the cylinder. Mechanical efficiency is reduced.
Yet in this case where we are talking about .010-.020 inch length changes neither weight changes or rod angle are going to be even measurable.
 

alvin l nunley

Site Supporter
I have to disagree with that. As a rod gets shorter it increases the rods angle at mid point of the stroke which increases friction on the sides of the cylinder. Mechanical efficiency is reduced.
Yet in this case where we are talking about .010-.020 inch length changes neither weight changes or rod angle are going to be even measurable.
He’s right. Good post.
While there is a “theoretically” correct rod length to stroke ratio, (and that number has changed over the years) the 4cycles you’re running are not even close to that ratio.
If your CCs are right now, the longer rod and longer stroke could put you under on the CCs. Not good.
Longer stroke, more cubic inches, that’s good, but .010” isn’t much. Right at 9 tenths of a cubic inch. And tell me, do you have the measuring tools to verify the increase? In the stroke or in the rod length?


Comments, compliments, criticisms and questions always welcome.
 

flattop1

Dawg 89
.010 is only going to move piston up in cylinder .010 inch. depending on how much you were in the hole to begin with and your cc's would be what decide if any thing would need to be done. max stroke crank same deal. both would swap in with out any extra work. the tech side would be the real concern. As stated you will need to cc it to be in spec, likely adding head gasket thickness. if it came home in a box you must have passed, which is good, nothing wrong with that.
 

drvred

New member
My bottom end was built before the days of max stroke cranks.
Just wondering if it was worth messing with.
 
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.
 

metalmagic

New member
On a stronger u guys are right but on a stock clone I think the lighter rotating mass would help the most.... What is your bore and stock on the stickers?
 

alvin l nunley

Site Supporter
I have a spreadsheet, (I know I know) and I can set the crank and the rod to any length I want, and I can set the crank rotation degree step down to .1 degrees. I can set the precision of the piston travel to 6 decimal places.
Tell me the stroke you are using, and the length of the rod, center to center, and I can tell you exactly how much things change with a chang in stroke or a change in rod length.
In the differences we are talking about in stroke and length, I’m pretty sure there is so little difference you will be surprised.
For instance:
Stroke 2.6772 Rod 3.3030
Piston Travel Crank Shaft Rotation In Degrees ATDC
0.000000 0.0
0.000004 0.1
0.000008 0.2
0.000024 0.3
0.000046 0.4
0.000076 0.5
0.000094 0.6
0.000135 0.7
0.000184 0.8
0.000241 0.9
0.000272 1.0
0.000340 1.1
0.000415 1.2
0.000498 1.3
3.3130 2.6772
Piston Travel Crank Shaft Rotation In Degrees ATDC
0.000000 0.0
0.000004 0.1
0.000008 0.2
0.000023 0.3
0.000046 0.4
0.000076 0.5
0.000094 0.6
0.000135 0.7
0.000184 0.8
0.000241 0.9
0.000272 1.0
0.000339 1.1
0.000414 1.2
0.000497 1.3
With this you can see that with a .010” longer rod, in the range pictured, there is no change. At 1.0 degrees of crank rotation. The change at 1.3 degrees is insignificant. .000001 is nothing.
Comments, compliments, criticisms and questions always welcome.
 
I would be willing to bet you could go from the longest stock rod available to the shortest and with deck height the same, never see a on track difference.
 

C&L_MOTORSPORTS

New member
I would be willing to bet you could go from the longest stock rod available to the shortest and with deck height the same, never see a on track difference.
what about the preditor with stock crank,3.707 rod and weisco piston vs. stock crank,rod and piston and same deck height? any difference. That's like saying theres no difference in a 5.7 or 6. inch rod in a small block.
your better off with the max stroke crank, long rod, stock piston then deck your block .003-.005 in the hole.
 
what about the preditor with stock crank,3.707 rod and weisco piston vs. stock crank,rod and piston and same deck height? any difference. That's like saying theres no difference in a 5.7 or 6. inch rod in a small block.
your better off with the max stroke crank, long rod, stock piston then deck your block .003-.005 in the hole.

I was talking about stock rods, that vary in small amounts. And, the 5.7 vs 6" thing has been beat to death. I have built limited sportsman dirt engines to late model stock asphalt. The 5.7 won and set on the pole just as much as even the 6.250 rod engines did in the dirt engines. I have even did a 6.300 rod (had a smaller wrist pin to make it work as a 1" compression height piston was the shortest available in a .927 pin). I also did a 5.7 Late Model Stock engine and it won many poles, and races. I stand by what I said, your results may vary. If given the choice, I would run the max stroke crank and get the piston where I want it regardless of the rod length. JMO. And as far as the predator, I have a 3.595 rod/wiseco piston hemi headed engine with a 390 carb that makes 26hp, I also have a stock rod length/stock piston old style predator (thick ring pack piston cut to a flat top) that makes 25hp with a 390 carb. The difference in the two is in the upper rpm, and I believe that difference is the head.
 
The length of the stroke does not affect the dwell time but the length of the rod certainly does, sorry.

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,
 

alvin l nunley

Site Supporter
what about the preditor with stock crank,3.707 rod and weisco piston vs. stock crank,rod and piston and same deck height? any difference. That's like saying theres no difference in a 5.7 or 6. inch rod in a small block.
your better off with the max stroke crank, long rod, stock piston then deck your block .003-.005 in the hole.
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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