Long Rod vs Short Rod
#1
Newbie
Thread Starter
Long Rod vs Short Rod
I've been searching though the forum trying to find info on the subject and have only found a bit here and there. There's a bit about it on the web but I'd like to hear it from people that own 4g63/64s.
So with that being said, what are the Pros and Cons of both.
It would be good to hear from you guys that own the Long Rod setups and why you built that particular setup over the Short Rod do you feel any notable difference or was your decision base on efficiency, longevity better Rod Ratio etc.
Thanks in Advance.
So with that being said, what are the Pros and Cons of both.
It would be good to hear from you guys that own the Long Rod setups and why you built that particular setup over the Short Rod do you feel any notable difference or was your decision base on efficiency, longevity better Rod Ratio etc.
Thanks in Advance.
#4
Evolved Member
iTrader: (18)
How many engine failures have you seen in the 2.4 due to sideload?
Also how does a longrod rev higher, how is this different then a long stroke motor, i was under the impression a shorter stroke engine allows for higher RPM operation?
Or am i confused and does the shorter stroke involve a smaller crank and longer rods?
Also how does a longrod rev higher, how is this different then a long stroke motor, i was under the impression a shorter stroke engine allows for higher RPM operation?
Or am i confused and does the shorter stroke involve a smaller crank and longer rods?
#5
Evolved Member
iTrader: (30)
How many engine failures have you seen in the 2.4 due to sideload?
Also how does a longrod rev higher, how is this different then a long stroke motor, i was under the impression a shorter stroke engine allows for higher RPM operation?
Or am i confused and does the shorter stroke involve a smaller crank and longer rods?
Also how does a longrod rev higher, how is this different then a long stroke motor, i was under the impression a shorter stroke engine allows for higher RPM operation?
Or am i confused and does the shorter stroke involve a smaller crank and longer rods?
Look at IHRA mountain motors for more direct application. They have added INCHES to the deck height of a big block Chevy, Ford, or Mopar in order to make their 815cid motors last as long as possible.
That I can think of, I have seen 4 SR2.4s fail after extended (and I mean LONG) time at high rpm. There are other factors that can cause the failure and when its catastrophic its not possible to point to one exact reason. However I look at F1 cars with a R/s of 4:1 running 18,000 for 2 hours at a time. Or even crazier, Volvo motors running almost a 2:1 ratio and running for 350k miles. They both do it for difference reasons but longevity is a key one.
2.3 or 2.4 with a R/s of 1.5:1 ratio- max angularity of 19.47*
2.4 with a R/s of 1.56:1 - max angularity of 18.75*
2.2 with a R/s of 1.659:1- max angularity of 17.58*
2.0 with a R/s of 1.7:1- max angularity of 17.06*
Last edited by JohnBradley; May 1, 2012 at 02:29 PM.
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#8
Evolved Member
iTrader: (8)
The rod ratio has very little impact on RPM capability with regards to piston/rod forces, "all things being equal." We are talking 50-100 RPM difference at the 10,000 RPM level between the 150mm rod and 156mm rod, it's nothing.
Things aren't equal though and the long rod setup can have a lighter piston which reduces wrist pin forces. While the long rod ends up heavier compared to the short rod, the net effect CAN BE a lighter rotating assembly.
My opinion, but if it is an engine that's going to see actual competition, the best bet is simply using shelf-stock parts so that when you blow them up, you can replace them with little down time. If you start buying rods and pistons in non-standard sizes, you have the potential to waste an entire season waiting for new parts. If that's not a concern, then you might as well optimize if you are willing to spend the extra.
It does seem the longer dwell time at TDC can cause problems on low-octane fuels though...
Things aren't equal though and the long rod setup can have a lighter piston which reduces wrist pin forces. While the long rod ends up heavier compared to the short rod, the net effect CAN BE a lighter rotating assembly.
My opinion, but if it is an engine that's going to see actual competition, the best bet is simply using shelf-stock parts so that when you blow them up, you can replace them with little down time. If you start buying rods and pistons in non-standard sizes, you have the potential to waste an entire season waiting for new parts. If that's not a concern, then you might as well optimize if you are willing to spend the extra.
It does seem the longer dwell time at TDC can cause problems on low-octane fuels though...
#9
Newbie
Thread Starter
My VIII will probably never see True competition as it is my DD, I only put 98 pump fuel in it, but will more the likely see racing fuel when it's finally built.
Thanks for the input guys, never such a thing as to much information so feel free to add. It'd be good to hear more opinions.
Thanks for the input guys, never such a thing as to much information so feel free to add. It'd be good to hear more opinions.