does anybody know how much stretch in the rod is involved at 8000-8500 rpm. i have heard that it is close to .024 is that correct or way off.. please help

 

thats a pretty good question, but i dont think you are going to get an answer.

 

i wish i could get an answer cause i know that smoe ppl know.. but hey i guess ill just have to do more research

 

no 1 has any answers?

 

what kind of material are we talking about here exactly??

 

I typically allow .030 for rod stretch.That doesn't mean they stretch that much.There is no chart of rod stretch that I know of.It's just experience.

 

you could try and make some assumptions to come up with you answer, but its not going to be easy.

what it stretching(deflecting) most significantly? the rod? or the rod bolts? i would think the rod would stretch before the bolts do, but i dont know.

now you need to estimate the maximum axial force that could be placed on the rod. and that is where it becomes impossible for pretty much everyone including myself.

if you can find that out, put it into the equation for deflection at the point of smallest cross section. i think you would get an approximate answer from that.

 

well its said that aluminum rods stretch about .010-.015" during operating temps...but im not too sure about those numbers really...i highly doubt though 4340 rods would stretch enough to make anyone worried...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Lubo_25 &raquo;</TD></TR><TR><TD CLASS="quote">well its said that aluminum rods stretch about .010-.015" during operating temps...but im not too sure about those numbers really...i highly doubt though 4340 rods would stretch enough to make anyone worried...</TD></TR></TABLE>

Your right and 4340 rods do not see enough duty in all motor cars to worry that much. If you were into the 800 hp range and stuff of that nature you might need to check things out ever so often.

 

what would you say the stretch is on a heavy turbo set up?? approx numbers...(4340)

 

Stretch has little to do with hp.It's reciprocating weight,piston speed (rpm,stroke),and rod design (material).My statement of allowing .030" comes from experience of a common honda engine.If you get much closer with the piston to head clearance you start to see signs of contact.There are other factors but rod stretch is most of it.Aluminum rods grow from heat (thermal expansion).Its common to allow an extra .010-.015"clearance for aluminum rods.

 

I would have to agree with njin buildr on this one, here is another good question,
at 9000 rpm how much should a 100 grams weigh in a ls motor.
Next question when the rod is at operating temps, if you hung how ever much weight that is calculated on the rod, could you measure stretch??
I am by no means a math wiz but this makes perfect sense to me...

 

More HP ='s more piston speed ='s more heat and friction. Higher HP cars tend to stretch and bend parts at a greater rate than low HP cars. You guys can throw a thousand fractions and variables out there to make it sound like your smart but the basic works. Rod stretch and wear will still fall back on power your making regardles how your looking at it. If you think its a joke call Crower or Eagle and they will tell you what's up. Thats why rods are HP specific and come in different shapes and sizes to handle HP.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by NJIN BUILDR &raquo;</TD></TR><TR><TD CLASS="quote">Stretch has little to do with hp.It's reciprocating weight,piston speed (rpm,stroke),and rod design (material).My statement of allowing .030" comes from experience of a common honda engine.If you get much closer with the piston to head clearance you start to see signs of contact.There are other factors but rod stretch is most of it.Aluminum rods grow from heat (thermal expansion).Its common to allow an extra .010-.015"clearance for aluminum rods.</TD></TR></TABLE>

stretch has little to do with hp?

deflection = ((axial force)(length)) / ((crosssectional area)(youngs modulus))

the youngs modulus accounts for the material and the axial force is directly related to the piston acceleration. the greater the axial force, the more the deflection of the material.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by freakyty2.3 &raquo;</TD></TR><TR><TD CLASS="quote"> You guys can throw a thousand fractions and variables out there to make it sound like your smart but the basic works. </TD></TR></TABLE>

agreed

 

stretch only deals with rpm and weight of the piston traveling up and down.. the heavier the mass the more it will stretch simple as that. and if you rod bolts stretch then boom goes your motor. so basically thanks to njin buildr i c that .030 is gonna be as close as i want to go.. i know that .030 is good for piston to head but what about piston to valve?? can i run less piston to valve on the exhaust because it will be moving with the piston.. which is up?

 

so its OK to run the same piston to head clearance on a 500hp motor compared to a 200whp motor. well as long as the pistons weigh the same. thats what you guys are saying here.

 

one thing you have to realize....more power means more heat there for more clearence allowed