connecting rods and bolt strength

[grumpyvette]

I build mostly BBC engines but this also applies to SBC connecting rod sellection, I was asked if stock rods were ok or should they swap to better ARP bolts or BUY the BETTER RODS WITH THE UPGRADED BOLTS

 

look most stock chevy connecting rods are rated at no more than 6000rpm and 450-500hp

 

now I may be in the small minority here, but I have always given away 3/8" bolt sbc or bbc rods rather than use them and purchased the 7/16" versions or aftermarket 7/16" cap screw rods, WITH the L19 bolt upgrade,the 7/16" rods ARE significantly stronger. rod bolts are critical, high stress items and one of the areas most likely to cause problems at high rpms and loads.

cross sectional area of a 3/8" bolt is approx .11 sq inches, a 7/16" bolt is aprox .15 sq inchs

use those good L19 bolts and assuming you sellected the good L19 bolts that test at 220,000 psi, for each the differance is 24.2 thousand lbs vs 33 thousand lbs or a 36% increase in strength, but the stock rod bolts are 160,000 psi so your really swapping from about 17.6 thousand to 33 thousand in strength or an 88% stronger rod bolt

 

http://www.arp-bolts.com/Tech/TechWhy.html

 

http://www.arp-bolts.com/Tech/Tech.html

 

http://www.arp-bolts.com/Tech/TechMetals.html

 

 

reasonable quality connecting rods are CHEAP

 

http://www.cnc-motorsports.com/product.asp?ProdID=3150

 

http://www.cnc-motorsports.com/product.asp?ProdID=8817

 

keep in mind if a rod comes loose at high rpms youll be LUCKY to save the intake, heads, blocks and cam are frequently damaged, spending an extra $90 for the better rod bolts is a total no brainer, in my opinion, if spending an extra $400-500 on rods and $90 on better bolts prevents rod failures, thats a minor consideration, when you may be spending $5500-$12,000 plus on an engine build.

you might also want to be aware that over reving and floating the valves, and useing a poorly designed oil system is a major potential source of engine failures

[jakeshoe]

I agree with grumpy here,

the rod bolts are one of the most stressed items on an engine.

Besides the items grumpy mentioned you also get fatique over time due to the stresses encountered.

Additionally,

a quality fastener like an ARP will fit tighter in the rod and rod cap and provide a more exact fit of the cap to the rod when disassembled and then re-assembled. While this makes it harder to get the cap off the rod, it is an advantage when using a stock type rod.

Just one of the advantages.

 

My opinion differs from grumpy on the strength of the stock 3/8" bolt variety rods. There are lots of combos out there with even the heavy stock BBC 3/8" rods that see relatively high rpm (over 7K rpm) and load. Some builders argue that the 3/8" rods have more rod material around the bolt than the 7/16" variety and are therefore stronger. I've seen both work well.

 

However,

even though the stock rods with ARP bolts and reconditioning are adequate in very stout combos, when you analyze the cost of the rod bolts ($40-up), reconditioning ($80-up), and the cost of the rod cores if you have to purchase them, it is hard to argue with some of the aftermarket offerings available.

As an example,

if you have an existing set of SBC rods and were to recon them with good bolts, you would be into them probably $120.

You then have a set of rods that have already seen stresses and oftentimes don't know what their usage has actually been.

You could purchase these rods new for $179. This is a stock equivalent rod with good bolts.

http://www.cnc-motorsports.com/product.asp?ProdID=1118&CtgID=1003

 

That $59 difference is good peace of mind.

 

If you have a stout combo this rod is an excellent quality deal:

http://www.cnc-motorsports.com/product.asp?ProdID=6922&CtgID=1003

 

The SCAT I beam capscrew rods seem to offer the best clearance to the cam in stroker applications for a "budget-concious" build. Crower and others make some stroker profile rods that are super nice but the price is about double that of the Scats.

[grumpyvette]

I see rods and rod bolt failures blamed frequently when engines self destruct at high rpms, but its NOT always what it at first might appear to be....are there any detailed pictures of the rods or rod bolts that failed??? in many cases the source of the problem can be seen with a careful detailed exam, if you don,t know the SOURCE of the problem your doomed to repeat the sequence... and keep in mind a good deal of what might appear to be rod/rodbolt failures, are ACTUALLY the result of over reving the valve train,and loss of valve train control, OR detonation, theres no way to compress a bent valve or broken piston ring land without potentially damaging the rods

 

 

http://www.arp-bolts.com/Tech/T4_WhyPages/T4_01_Why0.html

 

http://www.arp-bolts.com/Tech/T4_WhyPages/T4_01_Why1.html

 

http://www.arp-bolts.com/Tech/T4_WhyPages/T4_01_Why2.html

 

http://www.arp-bolts.com/Tech/T4_WhyPages/T4_01_Why3.html

 

http://www.arp-bolts.com/Tech/T4_WhyPages/T4_01_Why4.html

 

http://www.arp-bolts.com/Tech/T4_WhyPages/T4_01_Why5.html

 

http://www.arp-bolts.com/Tech/T4_WhyPages/T4_01_Why6.html

[grumpyvette]

seven words

 

 

USE A STRETCH GAUGE and ARP BOLTS

 

http://store.summitracing.com/partdetail.asp?autofilter=1&part=ARP%2D100%2D9942&N=700+310053+115&autoview=sku

 

or at a MINIMUM, READ THE INSTRUCTIONS CAREFULLY,at least tighten then loosen and re-tighten to spec EACH BOLT ,THREE SEPERATE TIMES with a QUALITY torque wrench

 

 

great

http://www.nationaltoolwarehouse.com/xq/asp/prodid.51600/TID./qx/product.htm

 

ok

 

http://www.nationaltoolwarehouse.com/xq/asp/prodid.10452/TID./qx/product.htm

 

 

 

http://www.hotrodshack.com/torque_settings.htm

 

http://www.arp-bolts.com/Tech/TechTorque.html