STEEL vs ALUMINUM vs TITANIUM Connecting Rods

what is up engine heads today we're going to look at the differences between steel aluminum or aluminium if you will and titanium connecting rods and we're going to see which one is the right choice for your engine now let's start with good old steel steel is really great because it's strong it's affordable it's plentiful and it has been the material of choice for connecting rods for many many decades and you will find steel connecting rods in pretty much 99 of stock oem engines now steel conrad's can be either cast forged or billet cast rods used to be pretty common in the past back in the 60s and 70s and they're okay 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's the rods are stronger because they have a better grain structure during the forging process very large pressures are exerted onto the rod giving it a more uniform a more coherent grain structure and making it ultimately stronger compared to a cast rod and today forged steel rods are pretty common even in oem stock engines and they are a great choice for a very wide variety of applications billet rods start out by having the rough shape cut out from a plate of forged steel and then they're finished machined on a cnc machine and this is good because it gives the billet rod the same grain structure as the plate from which it came from and this means that build rods have a very nice uniform longitudinal grain structure which makes them very strong but there is a minor downside to this and that's that build rods lack the circular rainfall that you can find in the big end of forged rods which means that the big end of billet rods is a bit weaker than the big end of forged rods but experts agree that this is a minor difference usually 10 to 15 percent decrease in strength compared to the big end of a forged rod but billet rods do have an advantage and that's that they lack the surface degradations present in forged rods that occur during the forging process and this means that a build rod has the same material of the same carbon content and the same quality both in its core and on its surface which means that billet rods are better at resisting the formation of cracks compared to forged rods so those are the three main manufacturing processes of steel rods and as you have seen they influence the strength of the rod to a great extent but what about the material what kind of steel is actually used in steel rods well oem rods typically employ steels from the 51 series stuff like 5130 or 5140 for example now the last two digits are important because they indicate the carbon content in the alloy so 5140 for example has 0.4 percent of carbon in it and carbon is good you want carbon because it makes the material harder and the rods stronger now aftermarket forged rods typically employ stuff like 4340 which is a really good alloy and in addition to having a high carbon content it also has other elements in it which make it a superior and stronger alloy compared to pretty much anything in the 51 series so still rods are our benchmark this is what we're going to compare everything else to because they are excellent all-rounders and they pretty much do everything right and they fit an extremely wide variety of applications steel rods are great at handling both compressive and tensile loads and this is something a connecting rod gets to experience many 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 on top of this steel has excellent fatigue life the material doesn't get tired and this is very important for an engine if you want to do a lot of miles with it to understand fatigue life think of a paperclip a steel paperclip is just like a steel rod in the sense that it's never going to fail unless you push the material past its yielding point so if you use a paperclip normally it's going to last forever but if you bend it back and forth past its healing point it's going to fail and steel rods are just like that if something doesn't go wrong within an engine they're typically going to last many many hundreds of thousands of miles now let's take a look at aluminum or aluminium connecting rods now we all know that aluminum is a weaker material when compared to steel high carbon steels usually have a tensile strength of around 200 000 psi while aluminum alloys used for connecting rods typically manage 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 do that because aluminum is a lot lighter than steel and when it comes to performance engines 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 on spinning your wheels rather than spinning your engine internals a lighter rotating assembly also means that your engine can rev higher and that it can reach the high rpms faster which means you can keep it in the sweet spot longer now let's take a look at a chunk of aluminum and a chunk of steel of the same size now the chunk of aluminum is typically going to weigh just one third of what the chunk of steel weighs and as we have seen the chunk of aluminum is going to be approximately twice as weak as the chunk of steel so what does this all mean well it means that because aluminum is three times lighter but only two times weaker you can make an aluminum rod have the same strength as a steel rod for two thirds of the weight of the steel rod yeah you're gonna get it the result of this is in reality that aluminum rods look like steel rods that go to the gym too often they are very very beefy and have massive cross sections and these are needed to make up for the lack of strength of aluminum and in practice an aluminum rod because it has more material is only going to be 20 to 30 percent lighter than a steel rod now 20 to 30 percent doesn't sound like much but it adds up 20 to 30 percent on every rod makes a big difference for the weight of your rotating assembly the kind of difference that sets apart first place from second but there's more good news because aluminum rods can be the shock absorber of your engine compared to steel rods aluminum rods sort of give in and absorb the shocks and stresses and loads generated by engine operation in contrast to steel rods they transfer less shock and stress onto your bearings and onto your crankshaft and this is great because it means longer bearing life and at the end of the day it's cheaper to replace rods that cost maybe fifteen hundred dollars compared to a crankshaft that usually costs four to five thousand dollars in a racing engine so aluminum rods are pretty amazing they're light they're strong and they're the shock absorber of your engine let's all install aluminum rods into all of our engines well no there's a price to be paid for all the benefits aluminum actually has a much shorter fatigue life compared to steel with each heat and the load cycle aluminum gets a bit weaker and an aluminum rod is going to typically last just one or two tenths of what a steel rod is going to last in a racing environment this means that you need to replace aluminum rods a lot more often than steel rods and while there are some engine builders out there who claim to have aluminum rod equipped street motors with 100 000 miles on them installing aluminum rods into a street engine really isn't a good idea because you'll be getting all the downsides and almost none of the benefits and this is the case because an engine with aluminum rods in it needs to be opened up regularly and you need to measure rod stretch at scheduled intervals to prevent catastrophic engine failure and let's face it who wants to open up their street motor every once in a while to measure rod stretch on top of this an engine with aluminum rods needs to be warmed up pretty slowly and it needs to be fully fully warmed up before you can floor it because if you floor it and the engine isn't fully warmed up this can create clearance issues between the aluminum rod and your crankbait because aluminum expands twice as fast under heat and because of this you can have a spun rod bearing or even the engine fully destroyed if you floor it and the engine isn't fully warmed up and once it's fully warmed up and once you've beat on the engine you're gonna have to let it cool down before you beat on it again so even if a streak motor with aluminum rods can do a hundred thousand miles it's still gonna mean that you have to baby the engine all the time and open it up every once in a while and let's face it that's just a pain with a straight motor when it comes to the benefits of aluminum rods they're actually only realized under full engine load and as we all know street motors actually spent only a fraction of their time under full engine load and this is why we see aluminum rods mostly in drag racing drag racing is the ideal environment for aluminum rods during a drag race the engine gets loaded up fully for a pretty short period of time which means you're harnessing all the benefits of the rods but you're still giving them minimal abuse and stress because the race doesn't last very long on top of this most serious drag racers open up their engine and inspect it pretty often anyway and all this means that drag racing is the optimal application for aluminum rods so unless you want to push your quarter mile times 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 into any engine but be sure you're harnessing the benefits and are able to handle the downsides something else you have to be aware of when it comes to aluminum rods is that because of their chunky size sometimes they can have clearance issues with different parts in your crank case very often they don't clear the base of the cylinder so in some cases things like your engine block or maybe your girdle or something like that might need to be adapted or machined to suit the rod now on top of this because aluminum rods expand more when they heat up you're gonna have to leave greater clearance between the top of your piston and the top bottom of your cylinder head to account for the increased growth of the aluminum connecting rod and now the exotic dude in the bunch titanium 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 that it's even stronger than steel this is actually a bit misleading titanium is impressively strong when compared to its density and for example a typical titanium connecting rod always going to have a density of 4.8 grams per cubic centimeter a typical steel connecting rod always going to 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 that it's almost twice as heavy so if we would make a identical connecting rod out of steel and aluminum the aluminum rod will be 44 percent lighter this is really impressive half the weight but in practice titanium actually behaves a bit differently to steel and connecting raw design must take this into account so in reality on average titanium connecting rods are usually 20 to 25 percent lighter than a comparable steel rod and although there are some impressively strong titanium rods out there on average titanium rods do sacrifice a bit of tensile strength compared to forged steel rods and on average are maybe five to fifteen percent weaker than a comparable forged steel rod so titanium is less dense than steel which means it's lighter but it has very similar strength and that's great because it means that titanium rods don't need to be super chunky like aluminum rods to achieve the needed strength and in fact titanium rods usually look pretty similar to steel rods also they have a fatigue life that's better than aluminum rods in fact many titanium rods have a fatigue life pretty similar to steel rods which means you can chuck them into your daily driver and not have to worry about measuring rod stretch every once in a while and what's more is that as they heat up titanium rods don't expand as much and as fast as aluminum rods so you don't have to baby the engine as much and while aluminum rods are typically machined out of billets of high quality alloys like the 70-75 hours for example and are almost never forged if you want a strong titanium rod you better forge it as we said titanium isn't dense on top of that titanium grains are smaller than steel grains for example so the forging process really helps titanium rods it compacts the grain structure and it greatly increases the strength of a titanium rod so titanium is perfect right it combines the strength of steel with the lightness of aluminum what more could you ask for it's the ultimate rod there's got to be a price to be paid for of this of course there is and when it comes to titanium rods the price to be paid is the price 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 just because the material is expensive this is the case because titanium ranks really high on every machinist's list of materials that are an absolute nightmare to machine in fact in its raw unalloyed state titanium is next to impossible to machine and to make it machinable it needs to be alloyed with other different materials a very typical titanium alloy used for connecting rods is di6al4v basically it means that it has six percent of aluminum and four percent of vanadium added to titanium to make it machinable but even in this alloyed state titanium is still pretty hard to machine and it needs much slower feed rates and special tooling to prevent the material from gumming up when it's machined and basically from ruining your day so other than the sole and difficult machining driving up the price titanium rods have another disadvantage you cannot use titanium at all in any application where there is sliding between two metal surfaces involved why because titanium is very susceptible to galling what is going going is also called friction welding or cold welding by some people and it happens when you have two metal surfaces sliding against each other and they eventually start damaging each other by with some material being pulled off from one surface and cold welded or friction welded onto the other surface it looks nasty and you do not want this happening in your engine at all of course now steel isn't susceptible to gloving at all but titanium is pretty sensitive to it and for example when installing rod bolts into titanium conrad's when torquing them down galling sometimes occurs between the threads threads of the bolt and the rod itself of course again really bad scenario another possible bad scenario is when you're inserting a small and bushing into a titanium rod glowing can occur if you aren't doing things properly sometimes people even experience glowing or fretting between the big end and the rod bearing in a titanium rod again a negative scenario that can quickly end the life of your engine so how do you solve this well glowing issues have been sold to a great extent when it comes to many titanium rods by coating the rods with either chromium nitride or titanium nitride or molybdenum and this 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 take care of the little details and the possible negative scenarios a titanium rod is gonna work great but these things do require expertise and special attention and this is why many people and even many machine machinists and engine builders do you stay away from titanium rods by the way the first ever application in a production vehicle of titanium rods was honda's amazing rc30 motorcycle there's another little downside to titanium rods and that's the titanium is extremely notch sensitive aluminum is not sensitive but titanium is even worse what is not sensitivity basically it means that when you're handling a titanium rod and let's say you accidentally scratch it or make a tiny little notch on it if you install that rod into the engine without polishing out the notch completely that little notch and scratch is going to become a failure point of your rod and the rod is going to prematurely fail at that very point so when handling titanium rods definitely be very careful with them so yeah that's pretty much it when it comes to the differences between steel aluminum and titanium as connecting raw materials here we have a little table as you can see the table is pretty silly but it is still useful and it does give you a general overview of the advantages and disadvantages and the best sort of applications for each of the three different types of rods as a general rule of thumb eight out of ten scenarios a steel rod is gonna be just fine the other two scenarios might benefit from an aluminum or a titanium rod so yeah there you have it that's pretty much it when it comes to this little video i hope you found it useful and informative and even maybe a bit entertaining as always thanks a lot for watching and i'll be seeing you soon with more fun and useful stuff on the d4a channel

Channel: driving 4 answers

Views: 875,456

Keywords: conrods, conrod, connecting rod, connecting rods, steel connecting rods, steel conrods, aluminum conrods, aluminum connecting rods, aluminium connecting rods, steel vs aluminum connecting rods, forged rods, forged connecting rods, 4340, steel, aluminum, titanium, RC30, Honda NSX, Corvette Z06, LS7, titanium rods, titanium connecting rods, billet rods, billet rods vs forged, titanium connecting rods vs billet, aluminum connecting rods for street use, aluminum connecting rods vs steel

Id: PzblJe7cwCY

Length: 19min 16sec (1156 seconds)

Published: Sun Jul 12 2020