lm7 piston question.
03-06-2015, 08:06 AM
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lm7 piston question. i have a 99 lm7 5.3 in my s13 240sx drift car and picked up another 5.3 from a guy that had 40 miles on a rebuild and broke the timing chain due to starving the cam bearings. His problem, not mine. anyways it dropped all the valves and knicked every piston, not terrible, but a few worse than others and im not going to just buff them out, i want to replace them with atleast good, non gashed pistons while im here lol. My question is.. what pistons/rods can i use that are stronger than the factory other than aftermarket forged? didnt they use a stronger rod and flat top piston in like 05? but something about one has floating wrist pins and one doesnt? I plan to boost this motor but nothing crazy, just want to make it stronger if i can using oem parts. i know there is a lot of write ups, but couldnt find my answer. thanks in advance.
03-06-2015, 02:38 PM
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i have a 99 lm7 5.3 in my s13 240sx drift car and picked up another 5.3 from a guy that had 40 miles on a rebuild and broke the timing chain due to starving the cam bearings. His problem, not mine. anyways it dropped all the valves and knicked every piston, not terrible, but a few worse than others and im not going to just buff them out, i want to replace them with atleast good, non gashed pistons while im here lol. My question is.. what pistons/rods can i use that are stronger than the factory other than aftermarket forged? didnt they use a stronger rod and flat top piston in like 05? but something about one has floating wrist pins and one doesnt? I plan to boost this motor but nothing crazy, just want to make it stronger if i can using oem parts. i know there is a lot of write ups, but couldnt find my answer. thanks in advance.
03-12-2015, 05:21 PM
#3
05+ LM7 had the LS2 style rods....stronger design.
L33 and 4.8s used the flat top piston as noted....increases compression over dished.
Make sure to have the assembly balanced after changes as the crank was balanced to a specific configuration.
I say buy aftermarket rods with upgraded bolts and keep high comp pistons if you can't swing aftermarket pistons.
L33 and 4.8s used the flat top piston as noted....increases compression over dished.
Make sure to have the assembly balanced after changes as the crank was balanced to a specific configuration.
I say buy aftermarket rods with upgraded bolts and keep high comp pistons if you can't swing aftermarket pistons.
03-13-2015, 07:51 AM
#4
As much as this is a budget project, I'd strongly suggest in at least upgrading some of the parts to forged, especially with boost and the type of driving you do. If this was going to be a regular daily driver/fun street car I'd agree with you and not think it's necessary to go crazy.
But seeing how you will be beating the **** out of it and keeping the engine in high RPMs most of its life, I would say it's beneficial to forge stuff. It's going to be cheaper in the long run to do so rather than havine to rebuild or replace the engine everytime it breaks.
There are plenty of budget stuff, like the junkyard pistons from Wiseco specifically made for the 5.3 with 2618 alloy and very good price. Scat makes some forged steel rods with ARP bolts for under 300 which are worlds better than even the stout Gen IV rods.
Other than that, there aren't really any good upgrade options OEM. Hypereutectic pistons are as strong as they get regardless of year. You won't see 09+ pistons being that much stronger than pre 04 ones for example. Rods yes, but even those are decently expensive and by the time you put in ARP bolts you spend the same kind of money that you would've paid for forged steel rods.
But seeing how you will be beating the **** out of it and keeping the engine in high RPMs most of its life, I would say it's beneficial to forge stuff. It's going to be cheaper in the long run to do so rather than havine to rebuild or replace the engine everytime it breaks.
There are plenty of budget stuff, like the junkyard pistons from Wiseco specifically made for the 5.3 with 2618 alloy and very good price. Scat makes some forged steel rods with ARP bolts for under 300 which are worlds better than even the stout Gen IV rods.
Other than that, there aren't really any good upgrade options OEM. Hypereutectic pistons are as strong as they get regardless of year. You won't see 09+ pistons being that much stronger than pre 04 ones for example. Rods yes, but even those are decently expensive and by the time you put in ARP bolts you spend the same kind of money that you would've paid for forged steel rods.