Thread: Connecting rods

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Originally Posted by DennyW

Nope, You would grit your teeth if you knew what clearances I run in that.

wee try a 4.600 bore with .007 on the wall with a ch of 1.125 they flop i know this ok

Originally Posted by 500caddy

we talk long rods short rods but were is the magic number.. i'm all ears.. it's funny you say the we can't compare a 6sec drag with a dirt tracker. well i build mostly boat engines know and still don't see it with a r&r of 1.48 are you guys going lower then that to see a piston scuff problem?? what oil are you running that there's this bad of scuffing?? i have seen more of a problem running a short skirt then running a short rr i.e broken ring lands, bad sealing, piston rocking, even skirts braking because of to much rocking. i will take the piston scuffing even if it was there..

In the 20 + years I have never had a problem with broken rings lands or broken piston rings,bad ring sealing,piston rocking or skirts breaking when we run a 6.0 or longer rod in any circle track application.
When we ran 5.565 rods in our 400 SBC we had all kinds of problems with piston scuffing,bores being out of round,ring seal problems.
We installed 6 inch rods or longer and everthing lasts longer.
No there is no magic number.
I could not even sell a short rod engine if I wanted to in a SBC.
In the BBC I have had a few problems in a 6.535 rod with a 300 shot of N20 just like you talked about above.

i would use a 5.7 or a 5.85 rod and have a good ring pack before i would ever go to a 1.125 comp height.. i'am using power adders and a 1.125 will not cut it. the top ring is way to close to the top of the piston. i need atleast .280-.300 from the top to the first ring. if i come across piston scuffing problems i find it's not the rod ratio doing it. i have run small blocks for 4hrs on the pump with a rod ratio of 1.425 with oil temp 200, water temp 200, rpms between 3500 7000 rpms and never get any scuffing.. what oil are you running?? i see alot of scuffing with alot of different brands of oil out there..

Hhmmmm......good question. Geometry saves your butt. Have yet to see an oil that covers it all alone without proper geometry. Caddy, please share. These guys who wish for success (along with myself) need to learn and know.

Originally Posted by 500caddy

i would use a 5.7 or a 5.85 rod and have a good ring pack before i would ever go to a 1.125 comp height.. i'am using power adders and a 1.125 will not cut it. the top ring is way to close to the top of the piston. i need atleast .280-.300 from the top to the first ring. if i come across piston scuffing problems i find it's not the rod ratio doing it. i have run small blocks for 4hrs on the pump with a rod ratio of 1.425 with oil temp 200, water temp 200, rpms between 3500 7000 rpms and never get any scuffing.. what oil are you running?? i see alot of scuffing with alot of different brands of oil out there..

Valvaline 50W with along with 1 qt.Lucas stabilzer.
The scuffing happened with a 400 many years ago with a 5.565 rod.
Since we went to 6 in rods and got out of the 400 block no problems what so ever.
The BBC was a customer of mine running Penzoil.

i'm sure you guy already know this but there's two points at which the piston has the most side load. it's 95deg and 265deg as for the piston location in the bore at these two degs. the 5.7 rod is 2.161 down in the bore and the 6" rod is 2.147. that's only .o15 differents between the 5.7 and 6" rod at its worse side loading. you think that .015 is enough to stop scuffing???? i don't have the magic number but i can tell you after yrs of building and testing rod ratio is a big myth. maybe if you went to 1.2-1.3 i don't know but anywere from 1.4-2 were 99% of engine are made there's just know differents.

well how about a 7.700 rod with a 5.500 crank well it is going to happen anyway

You're such an imp Pat. Stop teasing us

Originally Posted by nitrowarrior

You're such an imp Pat. Stop teasing us

what is a imp ?? well anyway the crank is here boy its big

IMP; devish creature that stirs grief and teases more than most can stand New crank has arrived?

Originally Posted by nitrowarrior

IMP; devish creature that stirs grief and teases more than most can stand New crank has arrived?

why yes thats me yes it here

Ooooo.......nice!!

Originally Posted by 500caddy

i'm sure you guy already know this but there's two points at which the piston has the most side load. it's 95deg and 265deg as for the piston location in the bore at these two degs. the 5.7 rod is 2.161 down in the bore and the 6" rod is 2.147. that's only .o15 differents between the 5.7 and 6" rod at its worse side loading. you think that .015 is enough to stop scuffing???? i don't have the magic number but i can tell you after yrs of building and testing rod ratio is a big myth. maybe if you went to 1.2-1.3 i don't know but anywere from 1.4-2 were 99% of engine are made there's just know differents.

I was talking about going from a 5.565 rod to a 6.0 rod.
Oh,try to sell a 5.7 engine to a I.M.C.A,USRA or a USMTS racer.
Every single one of them say's the 6.0 or a 6.125 is better off the corner's.
It may be a myth to you but it is very real to all my dirt burning customers.
Another area we can talk about is piston dwell.
I.M.O.,I am going to try a lite everything off the best I can by letting them piston dwell longer at T.D.C.
I always try and install the longest rod possible un-less it is a blown or a nitrous application where I have to have a thicker crown on the piston.
I have never spent day after day in the dyno room trying different rod length's but after going from a 5.565 rod to a 6.0 years ago it worked very well.

well i am doing a blown 383 and using a 5.7 rods the 6.000 rods sounds good till i look at the CH and runing on the street i think the pistons will work the rings harder and the pin way up in the oil ring land for a street engine is not to hot of a deal i think . i did machine up a355 sbc for the dirt track with the 6.000 rods the guy said that was the way he wanted to go and it was a runner BUT hard to say if the rod had any thing to do with it

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.