Search Posts
Current Specials

 

 

 

 

Wednesday
Jan052011

Selecting the best connnecting rods for your engine 

One of the most important and most stressed components in any high performance engine would have to be the connecting rods. These are the link between the crankshaft and the piston and if this particular component fails, the results are often catastrophic! (And expensive!)

Today I will explain what the differences are in the designs and different materials and what causes connecting rod failures. Firstly I will talk about the different designs and I will also add that there is absolutely no “right or wrong” in this game and certain engine builders will always favour a particular design and not always agree with what myself or anyone else writes about design for that matter, so I will go so far as to say what I am writing is merely based upon my own experiences.

H beam or I beam

The two most common designs are "H beam" and "I beam". This refers to the section profile of the rod beam. The two things that come into play here are weight and strength. The general rule here is that the H beam connecting rod will normally be the lighter of the two as there is simply more material on the I beam and therefore the I beam will normally be the stronger of the two. Now the next thing that you need to understand is that the lighter your rotating assembly is, the less parasitic loss you can expect through inertia and therefore the more horsepower you can expect to make, everything else being equal. The other thing here is that depending on the brand of any particular rod you use, its own proprietary design features may increase the strength of a given rod. An example of this is an  H beam Eagle rod, which is a fantastic rod for the price, but certainly would not hold a candle to a H beam Cosworth or Tomei rod in terms of quality or strength (or price) but again it is horses for courses here because if you are rebuilding your daily driver  you will probably eat into a large slice of your budget if you were to choose either of the latter brands and this may leave you short for other parts needed to finish the build and certainly in that application the Eagle would be more than up to the task. The other thing that needs to be taken into consideration is the length of the stroke of the engine and the rod length. For instance an RB26 uses a nice short stroke and a very short connecting rod meaning the actual rod itself is under a lot less stress than say something like an RB30 that is a long stroke engine and when the RB30 is revved hard you can rest assured that good quality connecting rods will be one of the most important investments you will ever make.  So as you can probably start to understand there is no “magic bullet”. It really does depend on your application.

Above; An I Beam Rod

As I said a H beam will be lighter and all other things being equal will possibly make more power BUT I believe the I beam is certainly the stronger of the two by design and therefore probably the “safer” option on a racing engine particularly if you plan on going nuts with a huge turbo, high boost and RPM limits. Having said that, there are many people around the world reliably running big power on H beam rods. Take a look at the Sierra Sierra Evo that is making 800 plus horsepower and running off the shelf Cosworth H beams, but then again, I am lead to believe the guy that is tuning that one has a fair idea what he is doing and as you are about to read that plays a big part in the life of the connecting rod! In fact the top three cars at World Time Attack all use H BEAM rods! Which, when you think about it does stand to reason, as a circuit race car needs the response of the lightest rotating assembly possible. Then again if you walk across the road to the drag strip you will more than likely find that many of the top cars are running I beam rods. Like I say, it really is horses for courses!

Above; A set of H Beam Rods

What can cause a connecting rod to fail?

I can confidently tell you that the three biggest causes of conrod failure are tuning, oil starvation and assembly incompetence. In fact these days it is reasonably rare to see a rod that has failed through actual rod breakage although it can happen. Normally it is caused by something else and the most common thing that we see is detonation that may cause the rod to break on the top where the shaft meets the top cap usually after damaging the bearing. More often than not the conrod will exit the block and leave a black and blue smashed up mess with the owner normally going straight for the jugular of the engine builder or connecting rod manufacturer because “it would never be their mate that tuned its fault!” “He has done plenty of these and knows what he is doing, and what has tuning got to do with the rod breaking anyway?”

Well the truth of the matter is that tuning is everything and the further you go up the horsepower ladder the more critical it is that it is right. Often detonation may not even show on the top of the piston but you can see it in the bearing shells and I certainly believe has caused way more rod failures than anything else by a long way.

Above; The aftermath of a connecting rod failure.

More often than not when a conrod terminally fails the damage is so great it is hard to tell what has happened but I can tell you first hand this is by far the biggest killer. Another really big one is oil starvation that will cause the bearing to fail first and then the connecting rod. This is particularly the case with the RB26 engine that has serious oiling woes as I discuss in a previous post and many with the many RB26 engines that have lost a rod, you can rest assured it was not the integrity of the rod that caused the failure. The bottom line is if the bearing doesn’t receive a continuous uninterrupted flow of clean oil then eventually the bearing will fail and quite often take the connecting rod with it.

 Another thing is assembly issues. There are several things that could go wrong here through incompetence but one of the big ones concerns the rod bolts. What you need to understand here is that most material that is of a high tensile strength such as a rod bolt is susceptible to Hydrogen embrittlement. This could be caused by something as simple as assembling the engine with sweaty hands. You see the moisture from your hands can deposit minute amounts of salt and acid on the surface of the material, which starts the corrosion process. The corrosion remains on the fastener until stress is applied (from tightening). Hydrogen then attacks this corroded area and promotes more corrosion, which attracts more hydrogen. The process feeds on itself and will ultimately cause the bolt to fail prematurely. NEVER use rod bolts with even the slightest sign of surface rust but if you have dummy assembled the engine over a couple of days it may not be even be noticeable until it is too late!

The final cause and one that you have no control over is an over rev, normally through a missed gear. Unfortunately the rev limiter will not catch the engine when it free revs and normally when you miss a gear you are up near redline so it will continue up to the stratosphere. This one is pure and simple “shit happens” but the better quality connecting rod you have in place here the more chance you have of surviving it!

What about Titanium?

Now you are entering the twilight zone and my advice is probably not to go there! Titanium is certainly the ultimate in materials with the highest strength to weight ratio of any metal known to mankind and a similar item in Titanium is on average around 45% the weight of a steel item which is a serious reduction. That is the good news. The bad news is that all this weight reduction comes at a serious cost. Like try around $1100 per rod!! Making a six cylinder set about five and a half times the cost of a similar steel set. Now that is only part of the problem. The next problem is that most of the US or UK based manufacturers make these to order with the usual lead time about 10-12 weeks and that is provided they can source the raw material which can be hard to get at times and can add further delays often stretching into many months. What this means is that you need to carry your own spares! Or you could be parked for 2-3 months minimum if you ever have a connecting rod or bearing problem unless you carry spares yourself, which is a lot of money to have laying around. So unless you have unlimited funds I feel the money could probably better be spent elsewhere. It is interesting to note that several production supercars are now running titanium rods as standard. Two that come to mind are the GT3 Porsche and the ZO6 Corvette. We can only hope that in the coming years the raw material may become more readily available, drop in price and Titanium rods may become more commonplace in the tuner marketplace but for the time being I’m not sure I can see the value in it. If however you feel you are in the 1% of people that could truly benefit from Titanium rods we can source them for you here.

So what brand do I buy?

Well I guess this is the sixty thousand dollar question! My suggestion is to buy the rod that best suits your budget and more importantly your particular application. If you are rebuilding your street motor then obviously you don’t need the same product as a 1500 horsepower drag engine but if you are building the latter then you better get it right or you are going to have one hell of an expensive mess. At Hi Octane Racing we stock a huge range of rods for all applications and I will talk you through the brands we sell in alphabetical order and if you need any advice whatsoever on which rod best suits your application feel free to call our friendly sales staff on +61-2 -9638 4643 or email us here.

Argo Connecting Rods

Argo are proudly Australian made by a family company that has been quietly producing performance products for many years and make an extremely high quality product at a veryreasonable price. Argo has manufactured specialty rods for everything from big OEM companies like Ford (from memory one of the FPV models is using their rods!) to V8 Supercars to many of the Superclass ski race boats which is where the company has its roots. Argo stock both H beam and I beam rods and will manufacture to any spec if required and have been used in many record holding engines around the world in all forms of motorsport. Argo use ARP 2000 rod bolts.

To see our range of Argo rods click here or to visit the Argo website click here.

Cosworth

Now here is a company that should need no introduction. When your background is Formula One and Indycar engine design and manufacturing it would be fair to assume that you would have the engineering capability to produce a superior design product and the Cosworth connecting rods are certainly all of that and more. As I said previously that whilst an I beam rod is traditionally stronger some companies have “proprietary” designs that can rewrite that theory and the Cosworth rod falls straight into this category. These feature a solid beam design with a “radial truss” to increase little end strength and are manufactured to the absolute highest of tolerances and are therefore priced at the higher end of the market. These rods feature 260,000psi H11 Cosworth rod bolts as standard

To enquire about Cosworth rods click here or to visit the Cosworth website click here.

Eagle

Eagle rods have been around forever and were originally manufactured in the USA but in recent years in order to produce a more cost effective product have moved their manufacturing operation to China. The good news here is that the place is still staffed by the Americans who import the correct material and rod bolts and oversee the quality control. If you are after a budget conscious rod then these are a good option and in many cases they may work out not that much more than resizing the original rods and replacing the standard rod bolts and we have customers with high powered engines that have had years of reliable service from this extremely well priced product. If you are going to use a budget Chinese made rod I would recommend using an Eagle as some of the “other” Chinese factories are now “copying” the ARP bolts but I know for a fact that these are of inferior quality. Enough said! Eagle use genuine 220,000 psi ARP 2000 rod bolts

To see our range of Eagle rods click here or to visit the Eagle website click here.

Nitto Performance

Nitto is the new kid on the block but has quickly been grabbing a large slice of the market with its philosophy of providing an absolutely no compromise top end quality component at an affordable and competitive price. Nitto manufacture a large range of H beam conrods for high performance road and track and I beam connecting rods for serious high horsepower applications and this conrod in particular is quickly finding its way into many top import drag race engines around the world a testament to its extremely high quality and superior strength. Nitto also manufacture connecting rods for engines that many others do not such as the TB48 Nissan and the Honda NSX engine and its range continues to grow. Nitto rods come fitted with 220,000psi ARP2000 bolts with the option to up spec them with 625 Custom age bolts for severe duty applications

To see our range of Nitto rods click here or to visit the Nitto website click here.

Pauter

Now this particular conrod  is different by design and has been encompassed by everyone from Winston Cup Nascar teams to top drag race teams worldwide. Pauter machine manufacture what we refer to as an “X beam” rod and this particular design has many favourable features. For starters, the simple beam design completely eliminates thin and non-uniform cross sections over the total length of the beam. This feature greatly improves resistance to crack-induced metal fatigue. In addition, the non-tapered profile of the beam helps to spread potentially harmful stress over a larger area, dispersing instead of concentrating these destructive loads. The design also efficiently places needed material in critical transitional areas, giving maximum support exactly where it is needed (such as directly under the wrist pin). The streamlined contour also provides subtle benefits in the form of windage reduction. My belief is this particular design is probably the one of the strongest of all and that is the reason we use this rod in the Hi Octane R34 GTR,but then again when your background is building 900 horse power plus air cooled Volkswagen engines like Pauter machine have done then I guess they must know a thing or two about “unorthodox” designs. Pauter rods are made in the USA are come fitted with 220,000psi ARP2000 bolts with the option to up spec them with 625 Custom age bolts for severe duty applications

To enquire about Pauter rods click here or to visit the Pauter website click here.

Tomei

Now here is another company with a motorsport history dating right back to the seventies in Japan and again we see another example of a lightweight H beam rod with proprietary features that move it into a league above and certainly strength comparable to many competitors I beam rods. For starters there is the material with which these rods are made. An exotic blend of Chrome alloy steel known as SNCM439. Then you have up-spec 260,000 psi L19 ARP rod bolts as standard fitment, twin oil orifices in the small end and numerous other unique features that you would expect from a company that has the moniker “The engine specialist” as its motto. With many race teams around the world using these rods in everything from 8 second drag cars to record setting Time Attack cars such as the Cyber Evo and the Tomei/Cusco WRX you can guarantee you will be getting something that has been pushed to the absolute limit!

To see our range of Tomei rods click here or to visit the Tomei website click here.

Now this is by no means the only quality connecting rods available today with Carillo and Oliver also producing extremely high quality rods in the USA with part numbers for most Japanese engines although a majority of their focus is obviously on V8 engines as you would expect in America. Again both of these companies have proprietary features that they believe make them better than their competitors and both carry a reputation big enough to back up their claims. Also companies like Manley, Howards, Cunningham and Crower have been making connecting rods in America since the early 1950s and are still turning out very high quality products today but like the other two are also primarily V8 focused. More recently in the USA, Bruce Crowers son Brian has released a range of quality components for import engines under the name BC which is short for Brian Crower. This has no link to the original company other than the fact they are father and son with most of the original Crower components still manufactured in the USA with a lot of the BC components made offshore to reduce costs. Regardless they are still high quality components with a very good reputation.

In Japan the giants like HKS and Jun still make really high quality components and companies like Arrows in the UK have been making connecting rods for everything from Formula one engines to go karts and also have part numbers for most Japanese engines. Hi Octane Racing can source most of the above mentioned brands at very competitive pricing so should you have a particular request click here or if you have any technical questions regarding anything in this post feel free to contact me personally here.

« Mazda RX8SP ready for Targa assault! | Main | Tsukuba Time Attack. Up close and personal! »

Reader Comments

There are no comments for this journal entry. To create a new comment, use the form below.

PostPost a New Comment

Enter your information below to add a new comment.
Author Email (optional):
Author URL (optional):
Post:
 
All HTML will be escaped. Hyperlinks will be created for URLs automatically.