STEEL vs ALUMINUM vs TITANIUM Connecting Rods

What's wrong with engine heads today? We're going to look at the differences between

steel

,

aluminum

or

aluminum

, so to speak, and

titanium

connecting

rods

, and see which is the right choice for your engine. Now let's start with the good old

steel

. Steel is really great because it's strong, it's affordable, it's plentiful and it's been the material of choice for

connecting

rods

for many decades and you'll find steel connecting rods in almost 99 of the original OEM engines. Steel Conrads can now be forged or cast. Billet cast rods used to be fairly common back in the day, back in the '60s and '70s, and are fine for stock applications, but if you're interested in increasing the power and torque output of your engine, cast rods are usually a pretty bad idea.

On the other hand, Ford rods are stronger because they have a better grain structure during the forging process. Very large pressures are placed on the rod, giving it a more uniform and coherent grain structure and ultimately making it stronger compared to a cast and today forged rod. Steel rods are quite common even in OEM engines and are an excellent choice for a wide variety of applications. Billet rods start with the rough shape cut from a forged steel plate and are then machined on a CNC. machine and this is good because it gives the billet rod the same grain structure as the plate it comes from and this means that the building rods have a very nice uniform longitudinal grain structure which makes them very strong, but there are a slight downside to this. and that is that the building rods lack the circular rain that can be found at the large end of the forged rods, which means that the large end of the billet rods is a little weaker than the large end of the forged rods , but experts agree that this is generally a minor difference. 10 to 15 percent decrease in strength compared to the large end of a forged rod, but billet rods have one advantage and that is that they lack the surface degradations present in forged rods that occur during the forging process and This means that a building rod has the same material, the same carbon content and the same quality in both its core and its surface, which means that billet rods resist cracking better compared to rods forged, so those are the three main manufacturing processes for steel rods and how you.

I have seen that they influence the resistance of the rod to a great extent, but what about the material? What type of steel is actually used in steel rods? Well, OEM rods generally use 51 series steels like 5130 or 5140, for example, now the last two digits. They are important because they indicate the carbon content in the alloy, so 5140 for example is 0.4 percent carbon and carbon is good, you want carbon because it makes the material harder and the rods stronger . Now, aftermarket forged rods generally employ material like 4340 which is a really good alloy and in addition to having a high carbon content, it also has other elements that make it a superior and stronger alloy compared to almost any thing in the 51 series, so the rods are our reference point, this is what we're going for. to compare everything else because they are excellent all-rounders and pretty much do everything well and suit an extremely wide variety of applications.

Steel rods are excellent at handling both compressive and tensile loads and this is something that a connecting rod experiences many times. many thousands of times per minute steel has a tensile strength of 200,000 psi, which means you have to do something pretty crazy or stupid to break it. In addition, this steel has an excellent fatigue life, the material does not tire and this is very important. for a motor, if you want to put a lot of miles on it to understand fatigue life, think about a clip, a steel clip is like a steel rod in that it will never fail unless you push the material further of its yield point, so if you use a clip it will normally last forever, but if you bend it back and forth past its healing point, it will fail and steel rods are like that, if something doesn't go wrong inside of an engine, they usually will.

They lasted many hundreds of thousands of miles now let's look at aluminum or aluminum connecting rods. Now we all know that aluminum is a weaker material compared to steel. High carbon steels generally have a tensile strength of around 200,000 psi, while aluminum alloys are used. cranks typically handle around 95,000 psi, so why in heaven's name would you put something that's twice as weak inside your engine and then expose it to all the extreme loads of engine operation? Well, you would because aluminum is much lighter than steel. and when it comes to high performance motors the light is right, the lighter your rotating assembly the better because a lighter rotating assembly is easier to spin which means more energy is spent turning the wheels in instead of rotating the internal parts of the engine.

A lighter rotating assembly also means your engine can rev higher and can reach high revs faster, meaning you can keep it in the sweet spot longer. Now let's look at a piece of aluminum and a piece of steel of the same size. Now the chunk of aluminum is typically going to weigh only one-third as much as the chunk of steel and, as we've seen, the chunk of aluminum is going to be about twice as weak as the chunk of steel. So what does it all mean? It means that because aluminum is three times weaker than the piece of steel. lighter but only twice as weak, you can make an aluminum rod have the same strength as a steel rod for two-thirds the weight of the steel rod.

Yes, you will get it. The result of this is actually that the aluminum rods look like steel. The rods that go to the gym too often are very, very robust and have huge cross sections and are necessary to compensate for the lack of strength of aluminum and in practice an aluminum rod because it has more material will only be 20 to 30 percent lighter than a steel rod, now 20 to 30 percent doesn't seem like much, but it adds up to 20 to 30 percent on each rod and makes a big difference in the weight of your rotating assembly. The kind of difference that distinguishes first place from Second place, but there is more good news because aluminum rods can be the shock absorber of your engine compared to steel rods.

The aluminum rods yield and absorb the impacts, tensions and loads generated by the operation of the engine. In contrast to steel rods, they transfer less impacts and stresses. in the bearings and in the crankshaft and this is great because it means longer bearing life and at the end of the day it is cheaper to replace connecting rods that cost maybe fifteen hundred dollars compared to a crankshaft that normally costs four to five thousand dollars on a race car. engine, so aluminum rods are pretty amazing, they're light, they're strong, and they're the shock absorber for your engine.

Let's install aluminum rods in all our engines. Well, no, there is a price to pay for all the benefits that aluminum really has. a much shorter fatigue life compared to steel with each heating and loading cycle, aluminum weakens a bit and an aluminum rod will typically last only one or two tenths as long as a steel rod will last in a racing environment, this means that aluminum rods need to be replaced much more frequently than steel rods, and while there are some engine manufacturers that claim to have street engines equipped with aluminum rods with 100,000 miles, installing rods Aluminum on a street engine really isn't a good idea. idea because you will get all the disadvantages and almost none of the benefits and this is the case because an engine with aluminum rods needs to be opened regularly and the stretch of the rods needs to be measured at scheduled intervals to avoid catastrophic engine failure.

And let's face it, who wants to open up their street engine every once in a while to measure rod stretch? Additionally, a motor with aluminum rods must warm up quite slowly and must be fully warmed up before you can hit the ground. This is because if you step on it and the motor is not fully warmed up, this can create clearance problems between the aluminum rod and the crankbait because aluminum expands twice as fast under heat and because of this you can have a bearing of rod rotated or even the motor. completely destroyed if you step on it and the engine is not fully warmed up and once it is fully warmed up and once you have hit the engine you will have to let it cool before hitting it again so even if a streak engine with Aluminum rods can go hundreds of thousands of miles, that means you'll have to take care of the engine all the time and open it up from time to time, and let's face it, it's a pain with a straight engine when it comes to The Benefits of Aluminum Rods.

Aluminum rods really only come at full engine load and as we all know street engines actually spend only a fraction of their time at full engine load and that's why we see aluminum rods mostly in racing. of resistance. Ideal environment for aluminum rods during an endurance race, the engine is fully loaded for a fairly short period of time meaning you are reaping all the benefits of the rods but still giving them a minimum of abuse and stress because the race does not In addition to this, they last a long time. Most serious drag racers open up their engine and inspect it fairly frequently anyway, and all of this means that drag racing is the optimal application for aluminum rods, so unless you want to beat your drag times. quarter mile and want to take your drag racing engine to the next level, you really don't need a moment of engine rods, you may want them and you can go ahead and install them on any engine, but be sure to reap the benefits and of be able to handle the disadvantages.

Another thing you should keep in mind when it comes to aluminum rods is that due to their thick size they can sometimes have space problems with different parts of the crankcase, very often they do not clear the base of the cylinder, so in some cases things like the engine block or maybe the fascia or something may need to be adapted or machined to fit the rod, now on top of this because aluminum rods expand more when heated you will need to leave more free space between the top. of your piston and the top bottom of the cylinder head to account for the further growth of the aluminum connecting rod and now the exotic type in the

titanium

group, how does it compare to steel and aluminum as a connecting rod material?

I'm sure you've heard of people describing titanium as an incredibly impressive material, some even saying it's even stronger than steel. This is actually a bit misleading. Titanium is impressively strong compared to its density and, for example, a typical titanium connecting rod will always have a density of 4.8 grams per cubic centimeter, a typical steel connecting rod will always have a density of 7.8 grams per cubic centimeter. , so as you can see, steel is almost twice as dense as titanium and that of course means it's almost twice as heavy, so if we were to make an identical steel and aluminum connecting rod.

The aluminum connecting rod will be 44 percent lighter. This is really impressive, it weighs half as much, but in practice titanium behaves a little differently to steel and the connection design needs to take this into account, so in reality, on average. Titanium connecting rods are typically 20 to 25 percent lighter than a comparable steel rod, and while there are some impressively strong titanium rods out there, on average titanium rods sacrifice a bit of tensile strength compared to rods are forged steel and, on average, weigh between five and fifteen. percent weaker than a comparable forged steel rod, so titanium is less dense than steel, which means it's lighter but has very similar strength and that's great because it means titanium rods don't need be super thick like aluminum rods to achieve the necessary strength. and in fact, titanium rods generally look quite similar to steel rods and also have a better fatigue life than aluminum rods.

In fact, many titanium shafts have a fairly similar fatigue life to steel shafts, meaning you can put them in your daily driver and not have to worry about measuring theStretch the rods from time to time and what's more, as they heat up, the titanium rods do not expand as much and as quickly as the aluminum rods, so you do not have to take as much care of the motor and while the aluminum rods. They are typically machined from billets of high-quality alloys, such as 70-75 hours, for example, and are almost never forged. If you want a strong titanium rod, you'd better forge it, as we said, titanium is not dense and the titanium grains are smaller. than steel grains, for example, so the forging process really helps titanium rods, compacts the grain structure and greatly increases the strength of a titanium rod, so titanium is perfect, It combines the resistance of steel with the lightness of aluminum, what more could you ask for?

It is the ultimate rod, there has to be a price to pay for this, of course there is, and when it comes to titanium rods, the price is the price to pay. Titanium rods are very expensive, usually two to three times more expensive than a set. of comparable aluminum or steel rods and this is the case not only because the material is expensive, but because titanium ranks very high on any machinist's list of materials that are an absolute nightmare to machine, in fact, in their raw unalloyed state, titanium is the following It is impossible to machine it and, to make it machinable, it is necessary to alloy it with other different materials.

A very typical titanium alloy used for connecting rods is di6al4v. It basically means that it has six percent aluminum and four percent vanadium added to the titanium to make it. machinable, but even in this alloy state, titanium is still quite difficult to machine and requires much slower feed rates and special tools to prevent the material from binding when machined and basically ruining your day, apart from the machining. Unique and difficult makes the price go up. Titanium rods have another disadvantage: you cannot use titanium at all in any application where there is sliding between two metal surfaces.

Because titanium is very susceptible to irritation, what is happening is also called friction or cold welding. Some people do welding and it happens when you have two metal surfaces that slide against each other and eventually start to damage each other by removing some material from one surface and cold or friction welding it on the other surface, it looks nasty and you do it. You don't want this to happen on your engine of course, now steel is not susceptible to gloving at all, but titanium is quite sensitive to it and for example when installing rod bolts on titanium Conrad, when tightening them, Sometimes irritation occurs between the threads of the threads. the bolt and rod itself of course, again, a really bad scenario.

Another possible bad scenario is when a small ferrule is inserted into a titanium rod. Shining can happen if things are not done correctly. Sometimes people even experience shine or jitter between the connecting rod and the connecting rod bearing on a titanium rod again is a negative scenario that can quickly end the life of your engine, so how do you resolve this? Shiny issues have been big sellers when it comes to many titanium rods coating the rods. with chromium nitride or titanium nitride or molybdenum and that is why you can find titanium rods in mass produced vehicles like the Honda NSX or the Corvette Z06 equipped with the LS7 engine when you do things right with a titanium rod and when You are careful of the small details and possible negative scenarios, a titanium rod will work very well, but these things require experience and special attention and that is why many people and even many machinists and engine manufacturers stay away from titanium rods. titanium by the way.

The first application of titanium rods in a production vehicle was Honda's incredible RC30 motorcycle. There is another small disadvantage to titanium rods and that is that titanium is extremely sensitive to nicks. Aluminum is not sensitive, but titanium is even worse. What is not sensitivity basically means that when you are handling a titanium rod and let's say you accidentally scratch it or make a small nick in it, if you install that rod in the engine without polishing the nick completely, that small nick and scratch will become at one point of failure of your rod and the rod will fail prematurely at that same point, so when handling titanium rods definitely be very careful with them, so yeah, that's it when it comes to the differences between steel, aluminum and titanium as connection raw materials, here we have a little table like You can see that the table is quite silly, but it is still useful and gives you an overview of the advantages and disadvantages and the best type of applications for each Of the three different types of rods, as a rule of thumb, eight out of ten scenarios a steel rod will be fine, the other two scenarios could benefit from an aluminum or titanium rod, so yeah, there you go, that's it all when it comes to this little video.

I hope you found it useful and informative and maybe even a little entertaining as always thanks so much for watching and I'll see you soon with more fun and useful stuff on the d4a channel.