Maybe i'm looking in the wrong place (searching the wrong words), but i can't find anything on this topic. How you do you know what connecting rod bolt diameter I need? What is better?

Let me know if you guys need to know any other information.

Any info would be greatly appreciated.

Thanks,

 

3/8" on a stock rod. I thought ARP was the only company that made bolts.

 

Stock is as listed above, (3/8). Bigger is usually better. Most of your higher end rods come with 7/16 bolts, then you get into better grade bolts, 8740, Wave-Loc, and L-19. Better grade bolts = higher cost, but relatively reasonable considering what they do. You can greatly increase the strength of a stock rod or any by upgrading the bolts, provided that the machining is done properly.

 

93ZM6Tally hit it on the nose.

Rod Bolts come in all shapes and sizes. The standard performance grade from ARP (which by far is the #1 choice) is 8740. 8740 is a grade of steel that's extremly good for fasteners because of it's high nickel content. It's basically the main material in all rod, main and head bolts and studs that you use. The base material itself has a 20-40% higher tensile strength depending on heat treatment. As in any bolt the larger bolt the stronger the bolt if they are of equal design and material. Usually size comes up when you talk about Scat I Beam rods, they come in bolt 3/8 and 7/16 rod bolt sizes. So the rod with the bigger bolts is stronger, plus they also polish the beams on those rods to take the stress risers out of the beams to make them stronger. That's why they cost more, but they are still cheap and a awesome deal.

Then there are the bolts we now commonly talk about on here like ARP2000 and L19. This has to do with the grade of material in the bolts.

ARP2000 was developed by ARP and is basically a upgrade from 8740 and is about 15% stronger in tensile strength, takes high heat loads better (it was originally developed for steam locomotives) and has high notch toughness. (meaning that it doesn't scar as easily from misstreatment and break due to nicks in the bolt) This strength upgrade allows you to make the bolt smaller or to keep it the same size and handle more RPM, HP or part mass in the motor. IMHO it's the best grade for the average guy to have in his motor when he needs an upgrade.

L19 is similar to ARP2000. It's almost a stainless steel due to the high levels of chromium and carbon in it. The problem with it is that it develops a situation called hydrogen embrittlement due to it's heat treatment process and them grade of materal. Most high strength steel alloys (L19, H-11 (tool steel), 300M) will get this characteristic when they are as ARP puts it "quench and tempered" in heat treating. This coniditon develops when minor amounts of water (sweat being the main killer) get on the surface of the bolt. This develops rust cracks and then bolt failure. The good thing about it is that it's 20% higher tensile strength. This bolt is usually used in high RPM situations where the high inertia of the parts exceeds the clamping capability of ARP2000 bolts. This is mostly where IMHO Mindgame gets the use from, he's been drag racing motors for a long time and high RPM is the name of the game there so that bolt is comon for him. Normally is better to use a ARP2000 bolt in street motors. A high RPM (7,000+) 396 or 4.000" stroke LS1 could definately use it.

There are other fastener companies out there but ARP has the highest pedigree in terms of metalurgists and engineers and they've been doing it the longest.

Bret

 

Wow! That was a lot of great info. Based on that I would want 7/16 for a forged bottom end correct?

The real question that I have (no sense starting a new thread) is whether or not this engine rebuild kit (with forged pistons) will work with the crank and connecting rods I found. It prob seems like a weird way to go but I want to keep stock displacement and without buying everything seperate this was the only way i can think of where i would still get all the misc. stuff of the rebuild kit.

So will all these parts work together?
Rebuild kit (forged pistons)

Forged Crank

These connecting rods

PS: If anyone has a better way that I have missed please let me know. I do not want to do anything larger (355/383/396) as of right now.

 

Anyone?

TTT - This section moves fast tonight

 

I don't know how to answer that and here's why.....

Getting a rebuild kit with TRW pistons and then putting Manley H Beams and Forged Eagle crank seems like a completely backwards way to do it. $1500 for a rebuild because someone thinks you need forged parts to make the bottom end strong is silly.

I guess the whole rod bolt answer was way off base here since you should probably look to match the rest of the parts up correctly for the motor and put some parts in there that are in line with what you should be spending on these things.....

IMHO the pistons are the most critical part of the bottom end mainly because their mass, strength and accuracy have the biggest effect on HP and longevity. If the pistons don't seal the rings then they are pointless, and if they are too weak for what you are doing then it's also pointless. The mass is critical because the lighter they are the less the stress the crankshaft and rods and ROD BOLTS!

Going into this setup deeper......

Manley H Beams are great rods, but unless you want to spin this motor 8,000rpm for a whole season of circle track racing and make 600hp they are way more than you need.

The Eagle Forged crank is a strong piece for the money. The problem here is that what it sounds like you want to do here doesn't need it. The stock crank all though it's cast is a stout piece. Guy have done 400+rwhp NA pacakges with 150-200hp N2O shots on top of it and the thing works awesome. Somewhere lately there is a post about stock cranks on here.... do a search with my name and maybe that will help.

The rebuild kit is not a bad idea..... If it was me I would get Eagle SiR or Scat I beam rods and junk the stock rods (not that they are bad, but it's cheaper to get new ones than to resize and fix old ones), polish the stock crank AND make sure you get a "deglaze" (hone the bores) to put a fresh cross hatch in the bores. That setup would be good to 7,000rpm and some N2O.

If you still want to spend $1500 on all of this..... I would do the following:

Mahle Pro Pack Pistons or SRP Piston and Ring kit..
Scat 4340 Forged I Beams or Eagle SiR 5140 I beams (Scats are stronger)
Polish the stock crank
Cleviete H Bearings (Rod, Cam, Main)
Felpro Head Gaskets
Use the stock oil pump
ARP Main Studs for a windage tray
Bore and hone to .030 over
Zero Deck the Block
Clean and install cam bearings
Put the stock windage tray back on
Bolt it all together.

That setup is very strong, will have better ring seal, make more power and probably be cheaper in the end.

Shoot me a e-mail or PM about this if you have some questions on it....

Bret

 

Probably a stupid question, but is it possible to go to lowes or ace hardware and pick up some Grade 10 7/16 bolts and nuts that will fit the stock rods? If so, what size and thread size would you need?

 

LOL....... in a word NO! The stock bolts are better than grade 8. It's not a stupid question if it keeps you from doing it to see if it's a stupid idea.

Study this page there are many reasons why you don't use parts from the hardware store on engine components. This is one of those things that's not really "why do you do that" kind of thing, some people know and understand everyone else just does it because it works.

What are you doing exactly? Why the rebuild.... I'm starting to think the motor didn't have oil in it or something.

Bret