Carbon Fiber Inside the Engine - How CF rods and pistons change engines and why you can't have them
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Published 2022-06-05
To ensure that connecting rods can survive the violent loads inside the engine we usually make them from steel. But sometimes we also make them from aluminum. Now steel is strong. A high grade alloy like 4340 steel can survive a load or stress that is equivalent to nearly 75.000 newtons exerted on every square centimeter of the part before breaking apart. Aluminum isn’t as strong and even high grade alloys like 6061 or 7075 can only manage a maximum of 55.000 newtons per square centimeter. Now carbon fiber is completely is in a league of it’s own….it can survive 250.000 newtons per square centimeter before breaking.
Now here’s the interesting thing we actually put rods from the weakest material here, aluminum, into the most extreme engines out there which generate the highest loads and have the highest chances of destroying their internals. Why? Well that’s because aluminum is lighter than steel.
But aluminum plays a price for it’s low weight and the price is longevity. So with metals we have to compromise, we can either have low weight OR long life, we can’t have both. Now let’s look at carbon fiber again. Just like it blows steel out of the water in terms of strength it blows aluminum out of the water in terms of weight.
So carbon fiber is the absolute champ? It’s super strong, it’s super light and it has no real fatigue life issues. So if it’s the best material out there why are there zero mass produced engines with carbon fiber internals and zero aftermarket carbon fiber rods you can purchase today? I mean we make wheels, car chassis, spoilers and so many other things from it. Why not engine internals if they offer so many benefits?
Here’s the first issue. Carbon fiber does not exhibit isotropic properties. When a material is isotropic it exhibits pretty much the same mechanical and thermal properties in all its parts.
For example this block made from steel is equally strong everywhere. Applying the load here or here will have the same results in terms of the amount of force required to deform or break the block. But carbon isn’t like this. Carbon fiber isn’t isotropic, it’s orthotropic in other words it’s a bit like a wood. Parts made from carbon fiber can’t be one solid chunk as is the case with metals.
Another major problem is the manufacturing process. If you wish to make strong carbon fiber parts you really have only two options. Using dry carbon fiber layers and then bonding them manually together by brushing or rolling resin onto them or by using prepreg. Advanced manufacturing process than involve an autoclave which exposes the part to both high pressure and high temperatures during the curing process to ensure the best possible part uniformity and surface finish.
And as you can see this process of manual stacking of layers, long curing times and the high cost of the raw material itself explains why carbon fiber parts are so expensive. Another issue is that this type of manufacturing process can be very difficult to apply on parts with complex and intricate shapes.
But in 2010 at the Paris Motor Show Lamborghini unveiled something called the Sesto Elemento, a striking limited production run race car. It’s name means “the sixth element”, which is the atomic number of carbon and indeed the car’s chassis, body, drive shaft and suspension components are all made from carbon fiber, but it wasn’t the first to have so many parts made from carbon fiber, instead it was the first to feature something called Forged composites. A brand new unique "forged "carbon fiber manufacturing process which was employed in the tub and suspension arms of the car.
A special thank you to my patrons:
Daniel
Daniel Morgan
Pepe
Brian Alvarez
Jack H
Dave Westwood
Joe C
Zwoa Meda Beda
Toma Marini
#d4a #carbonfiber
00:00 Carbon fiber vs steel vs aluminum
10:29 "Forged" carbon fiber
16:46 I contacted Lamborghini and other pioneers
All Comments (21)
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CF cloth: amzn.to/3xjc5ai DIY: www.easycomposites.co.uk/starter-kits AWA: www.awacomposites.com/ Patreon: www.patreon.com/d4a Titanium rods: https://youtu.be/PzblJe7cwCY Motivation: www.youtube.com/channel/UCt3YSIPcvJsYbwGCDLNiIKA
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Technically, Aluminium connecting rods will also last the life of the engine --- considering the consequences of a rod snap
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I'm an engineer with carbon fibre experience and I absolutely agree with everything you said except for one thing. You can stack up layers of carbon fibre with different fibre orientation. This way it can sustain loads coming from different angles and making the part more isotropic. This doesn't change the final verdict though, CF parts are only economically feasible for very exotic cars.
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One thing you didnt mention about aluminum rods are they are "Shock Absorbers". That is a big reason why they are used in racing engines. They lesson the "hit" on the bearings, ect. Top fuel rods actually shrink after a run. That is how much force is being put on engine connectiong rods.
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Composite Technician here: Very well explained. Absolutely well done.
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An incredible video, thanks! Never asked for it, but definitely loved it and helped me to understand the theory behind it
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A pro stock team experimented with carbon fiber connecting rods and found out that every time the car experienced tire shake it destroyed the rods. They decided the CF rods weren't worth the expense and were too fragile when subjected to the stress encountered in an imperfect world.
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On that Lamborghini connecting rod sample, the bolts thread into that hunk of metal that makes up the logo. Also, you can just use nuts on the other side of connecting rod bolts, it’s not necessary to have the thread in the rod itself. Titanium rods usually are set up this way. 👌
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You are a breath of fresh air, I build my own engines for Drag Racing and Road Racing. Every time I was Drag Racing at Fremont Drag Strip, when I came home I took the engine apart, at that time I was running a D/Gas 1955 chevy four door sedan, I ran a Chrysler 4 speed transmission and 1957 Pontiac Rear Axle, leaving the staring line at 10.000 RPM, I was able to lay a big gate job on my competition, 6-14 rear axle ratio, the 288 cubic inch chevy engine was screaming at the finish line. When I got home I found the Con Rod Bearings were moving a round, so I added a windage tray to the back of the pan, but when checked the Rods I had Boxed in I found the pistons were hitting the heads because the rods were Stretching even though I had right at 001. of and inch clearance. The next time I ran the Bearings looked great the windage tray worked, but the Pistons were hitting the heads too much. So I bought a new set of Carrilow, Steel Con Rods. Those Connecting Rods were So "Good", I was able to use those same Rods in other Engines I ran. Never "Broke" and Engine because of making sure I had "Good-Equipment" and that I checked the engine after hard Racing. I would like to get more information on the New "Carbon-Fiber" Rods being sold through Carrilow.
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"Nothing like a thick black strong rod..." - Rob Dahm.
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When we see carbon fiber/carbon carbon connecting rods in Formula 1 engines, then we'll know that they have overcome the obstacles inherent with CF/CC. Until then, it is pretty cool to think about the performance advantages of such a lightweight and rigid material inside of a reciprocating engine.
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Aluminum rods are used in topfuel racing because aluminum does not transmit the forces to the bearing, it acts like a shock absorber. A steel rod would destroy the the bottom end in a topfuel engine.
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This channel has developed beautifully over several years, and keeps providing technically accurate observations and facts. Very well done, please keep up the great work that have been doing.
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I'm not really a car buff, or especially interested in this subject, but I found your presentation absolutely fascinating, informative and easy to understand. Additional knowledge about anything, is never a waste of time. It is a brilliant video. Thanks.
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Would have been interesting to see titanium rods compared as well, such as those found in the LS7
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Congratulations! You are awesome! Nobody has ever so perfectly illuminated me the differences of CF vs CC. It was driving me nuts. Now for my purposes I will use the correct resin along with CF. Thank you.
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This was fantastic, your explanations were so clear and well-delivered. I'm looking forward to more stuff like this, glad to be a new subscriber
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Aluminum rods are also used in big boost applications because of their ability to take the shock away from the crankshaft.
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Four things from a former aerospace composites M&P Engineer: 1 - “Forged Composites” is nothing more than compression molding, which has been done for decades in Aerospace for lower strength parts. We used ribs made from compression molded graphite in some ribs that didn’t see much load. 2 - The anisotropy of composites is not a detriment for connecting rods. The load is only in one direction: compression/tension with a little torsion and bending. Connecting rods could be made with properly aligned fibers (some along the length, some at 45 degree angles) to take any load in the engine. 3 - Epoxy would be not great for connecting rods, but BMI resin can handle the heat and oil very easily. 4 - Adding threaded inserts to composites for bearing loads has been done, and I don’t see an issue with this application. If I were tasked with designing composite connecting rods, I would use BMI resin with Resin Transfer Molding. This would allow for making the connecting rod hollow or foam filled, with precision placed inserts or metal sleeve inserts that can post machined later.
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Impressive video. Awesome details while staying relatively short and concise. Deep dive on something few people would even consider a topic, but one which is quietly really interesting. That's a sub from me, looking forward to watching more👍
