Thread: Connecting rods

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i can run a 5.5" Rod in a 350 Small Block Chevy and make more horsepower (we're talking top end here) than you would with a longer rod. Why? Because with a longer dwell time at BDC the short rod will actually allow you a slightly later intake closing point (about 1 or 2 degrees) in terms of crank angle, with the same piston rise in the cylinder. So in terms of the engines sensitivity to say reversion with the shorter rod lengths you can run about 2-4 degrees more duration (1-2 degrees on both the opening & closing sides) without suffering this adverse affect! So much for the belief that longer rod's always enhance top end power! i'm not questioning your cam,heads,intake chose or your ability but i have proving this over and over again on the dyno.

i think at time to put this one to bed ? the ones that think they need a long rod to run fast are going to do it . the only time i run a longer rod is to have some kind of counter weight on the crank . when going with a stroker crank . from what i see the piston CH and how it made and the cam have more bearing on how good it will run . but what the hell do i know ?

I agree with Pat, put it to bed. It's hard for me to understand piston dwell being controlled as to controlling piston rise(same thing) and giving my engine an opportunity to create "free" horsepower during this cycle. What was I thinking? In the words of the late George Burns, "Goodnight Gracie!"

denny i wouldn't tell the old lady the rod is only 5.488. lol lol just joking with you..

Originally Posted by pat mccarthy

i think at time to put this one to bed ? the ones that think they need a long rod to run fast are going to do it . the only time i run a longer rod is to have some kind of counter weight on the crank . when going with a stroker crank . from what i see the piston CH and how it made and the cam have more bearing on how good it will run . but what the hell do i know ?

I here you Pat. I've built a couple of long rod motors (different brands) over the years and I was never happy with them. Enough said.

Originally Posted by nitrowarrior

I would like to interject something for thought processes. Piston dwell, combustion travel, harmonic deflection on piston skirts and Ring stabilization (ring chatter and land wear to name a few small matters). I appreciate angles and degrees. I am very anal when it comes to geometry, Other factors for longevity and producing horsepower have effects that have been substantiated and this is a subjuct this forum needs to hae discussed. All that have an opinion to attest are more than welcome in my mind to bring forth their ideas and let this forum go forward with better ideas of what works and what doesn't.

Nitro,you have read my mind.
What you say in this post and what you say in your last post you made have been proven to me over and over again on the track and on the dyno.

have you built the same engine with a 5.7" rod and a 6" rod or for that matter built a couple hundred engines with everything in the engines being = but the rod lengh?? the differents is only .012 from 5.7 to 6 rod on a sbc with the piston down into the bore at its worse point and only .019 from the 5.565 to the 6". as for rod angle putting side load and causing piston scuffing. the 400 with a 5.565 rod has a rod angle of 19.33, 5.7=18.87, 6"=18.0. the rod angle is only 1.33deg's from the 5.565 to the 6"...so from the 5.565 to a 6" rod there only .019 differents in location from top to bottom in the bore and 1.33 degs of rod angle.. as for power from a long rod to a short rod. there needs to be atleast 12% differents in rod lenght to make a very small hp and ftq differents like the most i have ever seen was 5-7hp and 4-5ftq.

Originally Posted by 500caddy

have you built the same engine with a 5.7" rod and a 6" rod or for that matter built a couple hundred engines with everything in the engines being = but the rod lengh?? the differents is only .012 from 5.7 to 6 rod on a sbc with the piston down into the bore at its worse point and only .019 from the 5.565 to the 6". as for rod angle putting side load and causing piston scuffing. the 400 with a 5.565 rod has a rod angle of 19.33, 5.7=18.87, 6"=18.0. the rod angle is only 1.33deg's from the 5.565 to the 6"...so from the 5.565 to a 6" rod there only .019 differents in location from top to bottom in the bore and 1.33 degs of rod angle.. as for power from a long rod to a short rod. there needs to be atleast 12% differents in rod lenght to make a very small hp and ftq differents like the most i have ever seen was 5-7hp and 4-5ftq.

I think you are "preaching to the choir".

Although I thought we put this subject to bed, I find myself drawn to this matter. (Morbid aquisition I suppose). Many articles written by "Pro" engine builders have many differing opinions. One theory is, the rod moves the piston at different speeds and dwell time from top to bottom. Others still firmly believe that the arc of the crank pin does not change through out it's cycle. I lean more to the true physics of the true circle theory myself. The constant action and reaction of the the piston having to stop and restart on it travel up and down it's path has to be controlled for longevity and full usage of the expansion of the gases that exert itself upon the the piston. If I can anyway use it's full potentional even in the most miniscule micro-second of this process, I will take what advantage I can. Oh, by the way, all theories are based upon a computer assisted program. Real time happens within the cylinder and if I could stick my head in there during that process, I would have better ideas and solutions to this great mind boggling question that haunts us all.

all good and fine ?? so what point do you run the longer rod how long ? will you run a longer rod if you know you will have a short CH bad ring pack short piston ? i would not .so at what point is that 5hp worth. i build stuff that gets run hard and guys want it to last can you tell me how long rings will last with a short CH and short ring pack and what about NOs guys do use this stuff you are going to tell someone to use this on a short CR piston .tell them that they will not see any long time use out of them at all ? who will? so then all engine need a longer rod ? NO... to the point where the piston has no ring pack ? and no top to 1st ring land for any hard use ? i think having the piston work good as thats were the power is hitting and the ring s you hope are sealing some of it i think it is more crucial having the piston ch and a good ring pack with room for a power adder and coat the skrits

Good job Pat... I like it when you jump in. More info that wasn't really asked for get's answered. Every combo in my building get's addressed. Ring packs, Comp Heights, Dwell locations within the cylinder, Longevity, etc. This poor thread is gonna get a lot of exposure and press time. Good deal.

i envy any one that get paid to run a dyno or has the money to buy one or have the work to buy one . i go buy what i have done and seen with out the use of a dyno and what i feel would work the best .5hp is alot to someone that need very drop of power yes but i would not look there for it .if that means no top to .1st ring and a poor ring pack i would look at a coating on the top and skrits of the pistons

Where's Richard at?
I wonder what he has to say about all this.

Originally Posted by DennyW

Richard, Dick, Tech, pm'd me, and said good bye.

Denny are you trying to be a smart a--?

Seriously, I got one too. He felt like it was time to go do something else.