Fitting uprated con rods - change rings?
Discussion
Hi, I've got a bigger turbo set up for my 40k mile 1.8t Golf and want to fit uprated rods. Question is - can I get away without fitting new piston rings? If I mark each piston i.e. 1,2,3,4 and the rings as they come out in case they get 'clocked' in assembly. Or would I be piddling in the wind? If I can avoid honing and having to run it in etc, it would be a bonus!
Thanks in advance!
Thanks in advance!
Got a bigger turbo, ~350 bhp, rods known to bend around 300, more about the torque delivery, but I just want it to be reliable for track work, doing the exhaust valves too as they like to separate themselves too - stems from heads! Could run it at 300 and not do the internals, but it could still let go...
stevieturbo said:
I cant imagine any manufacturer of a modern turbo engine, or even any modern sporty engine having such crap rods.
MK3 MX5s that had the cosworth supercharger bolted to them would bend the rods well below 300. Better rods were fitted when they gave the car a facelift.nobrakelights said:
Got a bigger turbo, ~350 bhp, rods known to bend around 300
Really? the original rods on a 1.8t are one piece and then split which gives amazing strength. Its massive overkill in fact for a road car.To put into context how good the standard ones are I worked on an LMP1 Le Mans car with a 500 bhp 1.8t engine (bored out to 2.0l) which used standard rods.
bhp doesn't bend rods! BMEP does!
So, saying 300bhp will bend a rod means nothing. Power is the result of torque (BMEP) x speed (rpm). For a typical std production engine with the boost wound up, peak power will be made a relatively low rpm (because the engines high rpm breathing will be limited by the design), hence you will require a large torque value to make that 300bhp. Also, look at a typical "tuned" turbo charged cars torque curve, and because the turbo is relatively large at medium rpm (in terms of excess airflow capability) they often show huge relatively uncontrolled mid range torque peaks, which then fall extremely rapidly to make only an "average" bhp number.
When you condider that the most powerful std 1.8t made only 220bhp, then 300bhp is a large percentage increase, certainly sufficient to easily exceed any of the normal "limits" set by the manufacturer for there std car/calibration etc!
It is however fairly unlikely that the rods are failing in pure compression. Much, much more likely is a combination of bend loads caused either by the load applied from the little ends (due to over temperature of the piston material resulting is piston loads being transfered to the rod) or by localised lubrication failure in the big ends resulting in bending loads being imposed on the rod etc.
In the "aftermarket" world, the number of failures that are properly researched and documented is imo precisely none....... ;-)
So, saying 300bhp will bend a rod means nothing. Power is the result of torque (BMEP) x speed (rpm). For a typical std production engine with the boost wound up, peak power will be made a relatively low rpm (because the engines high rpm breathing will be limited by the design), hence you will require a large torque value to make that 300bhp. Also, look at a typical "tuned" turbo charged cars torque curve, and because the turbo is relatively large at medium rpm (in terms of excess airflow capability) they often show huge relatively uncontrolled mid range torque peaks, which then fall extremely rapidly to make only an "average" bhp number.
When you condider that the most powerful std 1.8t made only 220bhp, then 300bhp is a large percentage increase, certainly sufficient to easily exceed any of the normal "limits" set by the manufacturer for there std car/calibration etc!
It is however fairly unlikely that the rods are failing in pure compression. Much, much more likely is a combination of bend loads caused either by the load applied from the little ends (due to over temperature of the piston material resulting is piston loads being transfered to the rod) or by localised lubrication failure in the big ends resulting in bending loads being imposed on the rod etc.
In the "aftermarket" world, the number of failures that are properly researched and documented is imo precisely none....... ;-)
Edited by anonymous-user on Thursday 8th September 22:20
Max_Torque said:
In the "aftermarket" world, the number of failures that are properly researched and documented is imo precisely none....... ;-)
Kind of hard to fathom that statement (my ignorance - I apologise). Are you incinerating that 'uprated rods are just good salesmanship and not essential in my position?By way of a sort of case study (from the 'internet'). It would appear that when upgrading from the 'smaller K03/s turbo (220bhp / 260 lb/ft) to a K04 with 270bhp and say 280 lb/ft, this is the point where the rod issues can start to show their face (allegedly). The problem being the quick spool up of the small turbo at low revs and the amount of torque that follows thus bending the rods - apparently!
There are known good engines - by code AGU and BAM as these both have the larger 20mm little ends rather than the 19mm that mine sports. Maybe it's the smaller little ends that have the issues what with having 'less meat' at that end?
A larger turbo producing say 4/500bhp delivering it's torque higher up the rev range with the 20mm pins might not see this issue? I'm sure there's an equation in there too!
Max Torque, are you saying that perhaps with 'proper mapping' that the piston temps might be kept to a safer level to stop issues with the rods and also perhaps with the exhaust valves falling apart too?
Guys, you know much more about this than I do and I do appreciate any clarification on this!
Basically i just meant that generally, when say a rod fails, people would just say "need better rods" whereas the issue might actually be something else that caused the rod to fail. Any "beam" that takes a compressive and tensile loads, likes to have those loads as pure compression and tension. Any additional "bending" loads cause high stress concentrations, which can result in a rod failing, even though it is well within it's elastic limit (in terms of the loading).
Bending loads must come from either (or both) of 2 places, the crank pin, or the piston pin. As the rod must change it's angle (relative to the bore cl) during the stroke, any "binding" or extra "friction" at either end puts a bending load into the rod.
Of course, often, the fix of stronger rods works, because the rod is now capable of dealing with the higher loading, but it may be a short term fix if serious issues are actually occuring in the rest of the system.
Broadly speaking, cylinder pressure scales with torque (i'll ignore the relative spark efficiency issue for now) so say your OEM calibration makes 300Nm, quite often you see aftermarket tunes making >450Nm, equivalent to something like a 50% increase in cylinder pressure and rod loading!
Bending loads must come from either (or both) of 2 places, the crank pin, or the piston pin. As the rod must change it's angle (relative to the bore cl) during the stroke, any "binding" or extra "friction" at either end puts a bending load into the rod.
Of course, often, the fix of stronger rods works, because the rod is now capable of dealing with the higher loading, but it may be a short term fix if serious issues are actually occuring in the rest of the system.
Broadly speaking, cylinder pressure scales with torque (i'll ignore the relative spark efficiency issue for now) so say your OEM calibration makes 300Nm, quite often you see aftermarket tunes making >450Nm, equivalent to something like a 50% increase in cylinder pressure and rod loading!
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