Arp or grade 8
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Fleet Mechanic
Joined: May 2004
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From: Montana
Arp or grade 8
Are these the same? is there a way to tell....? I know you can tell a grade 8 bolt by the markings on the head..so if my motor has a grade 8 bolt in the main can and rods am i good or should i get ARP's...? im going to call the machine shop and ask them if there good fasteners or not im just wondering though....I dont want to pull the block apart to put rod bolts in.....
Posting Guru
Joined: Mar 2005
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From: western montana
Personally I think grade 8 are fine though they are not as strong as arp- (((this is from what I have learned..so NOT gospel)))
I would replace bolts that have been retorqued often and I would strongly consider using arp for rod bearings- especially if it's a performance build- thats where the rotating pressure is in a motor.
hope that helps
rog
I would replace bolts that have been retorqued often and I would strongly consider using arp for rod bearings- especially if it's a performance build- thats where the rotating pressure is in a motor.
hope that helps
rog
Posting Guru
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From: Kiefer, Northeastern Okla
Ditto on the ARP's. They are way stronger than even a grade 8. In fact, ARP recommends NOT using grade 8's, which have a yield strength of 120,000 lbs, and a tensile strength of 150,000 lbs. ARP's lowest grade is their "Stainless 300", which are for accessory bolts and studs, and head studs, @ 140,000 and 170,000. They make 11 different grade fasteners up to their "AerMet 100" @ 258,000 psi yield strength and 300,000 psi tensile strength for connecting rod bolts. I won't use any other brand of fastener on my engines, period. 
Moderator
Joined: Jun 2003
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From: Calhoun GA
Grade 8 is plenty strong enough for many types of builds. My stock rotating assmebly routinely sees 13+psi of boost, on the street and at the track, and no issues thus far...make no mistake, i drive it like I stole it!
Also, a fellow farm truck racer I know has over 120k and he has thrown the kitchen sink at his stock assembly (351w with boost and nitrous), and he drives it everywhere.
ARP hardware is stronger than Grade 8. Me personally, the Windsor block could've used a couple more head bolts to keep the head gaskets in check, and that's where an ARP fastener might help.
Also, a fellow farm truck racer I know has over 120k and he has thrown the kitchen sink at his stock assembly (351w with boost and nitrous), and he drives it everywhere.
ARP hardware is stronger than Grade 8. Me personally, the Windsor block could've used a couple more head bolts to keep the head gaskets in check, and that's where an ARP fastener might help.
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Fleet Mechanic
Joined: May 2004
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From: Montana
So your sayin most likely the grade 8 fasteners are good for 400hp at 5,00to 5,500 k rpm...? I really dont want to strip it back apart..its not like im gonna race it..but i want to rape it when ever i feel the urge on the street.....
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Post Fiend
Joined: Jun 2002
Posts: 13,873
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From: Atlanta GA
When you buy a grade 8 bolt, it is only as good as the OEM that makes and "self" tests it and "self" verifies it conforms to standards. For internal parts, I would rather use a ARP bolt, that has been extensively tested, then something I took off a hardware store shelf.
Get ARPs.
Get ARPs.
Fleet Owner
Joined: Sep 2005
Posts: 28,609
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From: Lake Tahoe, Nevada
I have always used factory bolts for cranks and heads with unblemished results. Even in some fairly high output engines.
My reason for doing so is my own ignorance. By that, I mean that I DO know, that using a different strength bolt requires a differing torque spec, and I don't know how to determine what that would be. But I do know that a stronger bolt will require a higher torque, and I am not willing to distort a rod cap or cylinder head by going beyond the factory torque specs.
My reason for doing so is my own ignorance. By that, I mean that I DO know, that using a different strength bolt requires a differing torque spec, and I don't know how to determine what that would be. But I do know that a stronger bolt will require a higher torque, and I am not willing to distort a rod cap or cylinder head by going beyond the factory torque specs.
Moderator
Joined: Jun 2003
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From: Calhoun GA
ARP fasters are stonger than stock/grade 8 hardware, but how often to you see a thread about hardware related failure while driving.
Honestly, if it'll allow you to sleep better at night, then install the ARP stuff and be done with it.
Honestly, if it'll allow you to sleep better at night, then install the ARP stuff and be done with it.
Fleet Owner
Joined: Sep 2005
Posts: 28,609
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From: Lake Tahoe, Nevada
Over four decades automobile and truck service, I would estimate that 75% of the thousands of repairs I have done are directly attributable to things that owners have done to their vehicles, not having thought through what and why they were doing what they were doing, often, with the intention of "improving" their vehicles, without respect for what they don't know. Such as, why is a torque specification what it is.
A bolt that is given a torque spec is designed to stretch a given amount at that specification. When you change the bolt type, just be certain that you ascertain what the correct torque for that bolt is. If it is greater than stock, can you be sure that you are not going to over-strain that parts being fastened? There is no general rule on this. I'm not saying that you will cause a problem, what I am saying is, just consider the consequences.
A bolt that is given a torque spec is designed to stretch a given amount at that specification. When you change the bolt type, just be certain that you ascertain what the correct torque for that bolt is. If it is greater than stock, can you be sure that you are not going to over-strain that parts being fastened? There is no general rule on this. I'm not saying that you will cause a problem, what I am saying is, just consider the consequences.
Post Fiend
Joined: Nov 2001
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From: Topsfield, MA
Bolt "strength" comes in different ways.
It can be in the form of load strength, shear strength, strength in stretching...etc...
There are all different types of fasteners...even if they look the same.
For example, a grade 5 bolt is stronger than a grade 8 bolt in certain aspects...so it is used over a grade 8 bolt in certain circumstances. Even though in all general discussion, a grade 8 is "stronger"...
Use an automotive engine fastener where appropriate, most people use ARP bolts on such things as rod bolts, head bolts, etc.
Use what is correct for the application, not what is a possible cheap way out.
It can be in the form of load strength, shear strength, strength in stretching...etc...
There are all different types of fasteners...even if they look the same.
For example, a grade 5 bolt is stronger than a grade 8 bolt in certain aspects...so it is used over a grade 8 bolt in certain circumstances. Even though in all general discussion, a grade 8 is "stronger"...
Use an automotive engine fastener where appropriate, most people use ARP bolts on such things as rod bolts, head bolts, etc.
Use what is correct for the application, not what is a possible cheap way out.