Piston yes rods?

[yaristurbo]

Right half way through forge rebuild as bottom end started knocking are rod needed if not what horse power boot/nitrous can they take, because scat rods I've seen I've heard really bad reviews on them cheers dan

[*greg*]

Standard road spec rods are manufactured to withstand generally 20m/s piston speed. ( Think the piston has to go up ,stop dead and then come back down, stop dead and then go up again etc). This causes a lot of stress.

When you start turning the boost up and putting more pressure on the piston crown your increasing the speed of the pistons Meter/second up and down the cylinder bore and also the general combustion chamber temperature ( Ex gas temp close to 1100 deg c) if your upping the rev limit or moving the power curve further up the rev range then deffinetly use forged rods and fastners. Race application rods ( scat etc ) generally withstand 25 M/S MAX! The 1st failure point usually is not the rods themselves but the standard fastners in the big end, hense why people use forged rods along with ARP 2000 fastners( or similar brands )if you put too much stress on standard rods they will stretch and fail. So if your uping the boost and incresing the stresses on the engine and piston/rod setup then yes you deffinetly need forged rods and uprated fastners. Forged pistons are used due to the harder outer coating the forging process creates this is purely due to the higher temperatures created by more pressure/power.

Hope this helps , and i am using scat rods and they seem fine matey

[scot-ish]

doesnt the "pistons speed" as youve named it, only increases with rpm, not to do with boost, although yes, higher boost is generally acheived via higher rpm, but wether your at 0.5 bar, or 2 bar, 5000rpm, is the same piston speed on either boost level.

the forging process doesnt just give a harder outer coating, its strengtens the whole rod, due to the forging process, where as casting has alot of weak points.

answer to your questions, is yes, forged rods are pretty much a must imho, there are more out there than scat aswell.

[*greg*]

doesnt the "pistons speed" as youve named it, only increases with rpm, not to do with boost, although yes, higher boost is generally acheived via higher rpm, but wether your at 0.5 bar, or 2 bar, 5000rpm, is the same piston speed on either boost level.

the forging process doesnt just give a harder outer coating, its strengtens the whole rod, due to the forging process, where as casting has alot of weak points.

answer to your questions, is yes, forged rods are pretty much a must imho, there are more out there than scat aswell.

There is no direct link with boost and piston speed no. mean piston speed = (2)stroke length x engine speed.

but the general stress path heavily affects the conrod thats all i am saying and if your going for big power then do it once and do it properly it will save money in the long run!

[scot-ish]

There is no direct link with boost and piston speed no. mean piston speed = (2)stroke length x engine speed.

but the general stress path heavily affects the conrod thats all i am saying and if your going for big power then do it once and do it properly it will save money in the long run!

your formula doesnt make sense, well, stroke length has to be in metres, and engine speed is rps aye?

i use this. prob same, but longer way round lol.

Cm= 0.167 x L x N.

Cm mean piston speed

L being length of stroke, and N revs. oh and thats in ft/min, but its easily enough converted.

so for the 4efte

0.167 x 3.047inch stroke (77.4mm) x 7000(say a 7000rpm, around about the limiter)

3561.9 ft/min

in your m/s thats 18.09. and thats the max Mean piston speed within the 4efte, on standard rev limit.

so piston speed doesnt come into anything within the 4efte, and rods, with your theory, as it would take about 8000 rpm, to exceed 20m/s.

the weakening of the rods, and the cause of them bending, is due to opposing forces, say for example, you get to 5000 rpm(13ish m/sCm), the rod is on its way back up, your now filling the chamber wth 1.5bar boost pressure, at the same time the rod is rising, and in most cases of a rod failing, in comes the pre ignition(knocking or however its know) and bang, combustion before the rod passes TDC thus tryin to force it back down, and bending the rod like a banana.

the difference in having forged rods fitted, is that this pre-ignition wont bend a forged rod so easily, so its an extra safeguard.

this has been proved aswell in practise by the jamaican fella, and elsewhere around the world, with standard rods taking 300whp. due to the map being spot on.

[yaristurbo]

Thanks for the info guys, I'm wanting to do it properly and try and max out a 4efte Now to just see how much They can take as Theres a debate at work I wanna settle

The mapping will be spot on thanks to Dave Rowe at eps, anyone recommend a set of rods compatable with JE pistons as that's the route I'm going down I heard about some custom one built by corrilo???

[scot-ish]

what is the power that your chasing if you dont mine me asking? you got low comp pistons?

there are plenty of scat rods pushing more than 300 bhp with now problem.