ARP Rod Bolts - REALLY essential?
03-06-2018, 11:03 PM
#1
ARP Rod Bolts - REALLY essential? I had been planning on putting my motor together with ARP rod bolts. But after what I have been told, I am wondering if it is worth it. Basically, LOTS of people and even a few machine shops have told me that they are not worth the trouble. Almost everyone seems to think stock LS2 rod bolts are plenty strong, and that people are making pretty good power using them without problems. All of this makes me wonder whether the expense of resizing rods is REALLY worth it. Would it be a TERRIBLE idea to just put the motor back together with new OEM bolts rather than having to pay for ARP bolts PLUS the even greater cost of resizing?
03-07-2018, 12:19 AM
#2
TECH Senior Member
How much power are you planning on? You are right; it is widely known that LS stock lower end can handle over 700HP. And that is proven right time after time.
03-07-2018, 09:35 AM
#3
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Cracked Rod Resize Hi Matt, I should ADD you have "cracked" rods.
When ARP bolts are added, resize required, the housing bore is made larger.
FIND the rod bearing first if this is done.
Lance
When ARP bolts are added, resize required, the housing bore is made larger.
FIND the rod bearing first if this is done.
Lance
03-07-2018, 12:41 PM
#5
I agree, LS2 rod bolts are quite capable.
However, I see all too often where people rate rod bolt strength in terms of HP. In fact, actual power production doesn't put the greatest amount of LOAD on the bolt itself.
The highest load on a rod bolt occurs at TDC overlap (exhaust stroke). This load is correlated to the weight of the reciprocating components (rod small end, piston, pin, locks, rings) and the peak RPM, nothing to do with HP at all. When the rod is in a state of compression, the load goes through the beam. At the point where the rod changes direction it goes from a state of compression to tension. Think of that the piston wants to keep traveling up, but reaches the end of its leash and the rod pulls it back down.
It takes a much more complicated formula than F=m*a, so while I don't guarantee my figures are 100%, I'd be willing to bet they are pretty close.
Based on MY component weights (Wiseco 4.070" 4032 pistons, stock rods and stock crank) and a targeted maximum of 7200 RPM, I get a load of 85,104 psi PER BOLT.
I'm making a guess that Rod Bolts are grade 10.9 and have a minimum tensile rating of 150 ksi. Not quite a safety margin of 2x (85 ksi x 2 = 170 ksi safety margin).
IF Rod Bolts are actually grade 12.9, then they have a minimum tensile rating of 177 ksi which would meet the 2x margin of safety.
Cole
However, I see all too often where people rate rod bolt strength in terms of HP. In fact, actual power production doesn't put the greatest amount of LOAD on the bolt itself.
The highest load on a rod bolt occurs at TDC overlap (exhaust stroke). This load is correlated to the weight of the reciprocating components (rod small end, piston, pin, locks, rings) and the peak RPM, nothing to do with HP at all. When the rod is in a state of compression, the load goes through the beam. At the point where the rod changes direction it goes from a state of compression to tension. Think of that the piston wants to keep traveling up, but reaches the end of its leash and the rod pulls it back down.
It takes a much more complicated formula than F=m*a, so while I don't guarantee my figures are 100%, I'd be willing to bet they are pretty close.
Based on MY component weights (Wiseco 4.070" 4032 pistons, stock rods and stock crank) and a targeted maximum of 7200 RPM, I get a load of 85,104 psi PER BOLT.
I'm making a guess that Rod Bolts are grade 10.9 and have a minimum tensile rating of 150 ksi. Not quite a safety margin of 2x (85 ksi x 2 = 170 ksi safety margin).
IF Rod Bolts are actually grade 12.9, then they have a minimum tensile rating of 177 ksi which would meet the 2x margin of safety.
Cole
03-07-2018, 01:18 PM
#6
In addition, both of these are available with various crankshaft sizes, from standard through .030" undersize.
Clevite CB-1776A Aluminum Series (.002" oversize rod housing)
King CR865SI Silicon Aluminum Series (.002" oversize rod housing)
My thoughts on the lack of a "performance" bearing for an oversize STOCK cracked cap rod is that if you're wanting a performance bearing then you probably aren't using a stock rod or crankshaft.
Cole
12-20-2018, 12:31 AM
#7
Sorry to bring back this dad horse to life. I'm in the process of rebuild a Ls2 motor. It worth to spend the money to resize the Ls2 rods to use ARP bolts? The goal is to have like 450-480rwhp NA probably in the future i can trow some 150 shot but not for now. I expect to spin it max to 6800rpm. Or should I stay with the factory bolts?
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12-20-2018, 12:41 AM
#8
TECH Senior Member
I think honestly, at that power level, you could get by with stock rod bolts. Totally stock bottom ends have done well at those power levels and rev limits. The ARP bolts ARE a good insurance policy and will give peace of mind. It's ultimately your call.
12-20-2018, 07:57 AM
#10
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I would base it more on rpm than hp. Especially in that power range. If you plan to hit 7200 on a regular basis, do it. If not, stock is fine
12-20-2018, 09:38 AM
#12
ARP rod bolts are not only not essential, I wouldn't mess with an engine that had them fitted to stock rods. I've seen more issues with people that fiddled with the ARP bolts then I have with people leaving the bottom end alone.
Plenty of stock Gen 4 stuff has been zinged to 7000+ every day of its life and rod bolts are perfectly fine. Mine has seen 7500+ and the last thing I worry about is rod bolts.
If you're going to the effort to do rod bolts then buy new rods to actually make it worth it.
Depends on your goals, if you aren't doing forged rods and pistons then I wouldn't bother. I also wouldn't bother with forged rods and pistons under 1000hp, so basically under 1000 just leave it alone.
If you're going to the effort to do rod bolts then buy new rods to actually make it worth it.
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12-20-2018, 04:49 PM
#14
Rod bolts are for RPM
Power pushes down on the rod. Don't even need rod bolts for that. The rod pulling the piston back down pulls on the rod cap which pulls on the rod bolts. If you zing it up higher in RPM the piston is traveling faster and takes more force to pull it back down.
Around 7k is where I set my comfort with stock rod bolts. However in late gen3 and all gen 4 people say they go up to around 7500 no problem, makes me cringe personally but a lot say they have done it and haven't had issues.
Power pushes down on the rod. Don't even need rod bolts for that. The rod pulling the piston back down pulls on the rod cap which pulls on the rod bolts. If you zing it up higher in RPM the piston is traveling faster and takes more force to pull it back down.
Around 7k is where I set my comfort with stock rod bolts. However in late gen3 and all gen 4 people say they go up to around 7500 no problem, makes me cringe personally but a lot say they have done it and haven't had issues.
12-20-2018, 04:51 PM
#15
Necessary for either of them is subjective to what you're gonna do with the engine. Or subjective to your taste in build.
The stock mains hold tons of power in SBE "builds" (see what I did there).
So do the rod bolts
But rod bearings let go at real high rpm when the rod bolts stretch.
Personally I'd stick with a 7300 ish max build. Above that you need to start thinking about rod bolts (which leads to new rods or resizing) and some serious valve train parts, and things start snowballing like crazy at that point $$$$$$
12-20-2018, 04:57 PM
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@SlowSedan:
Good point. I was thinking gen 3 rod bolts when I typed that.
Good point. I was thinking gen 3 rod bolts when I typed that.
12-20-2018, 08:06 PM
#18
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