Automotive

Two-piece con rods claimed to boost low-end engine torque by 30%

Two-piece con rods claimed to boost low-end engine torque by 30%
Transcend says its two-piece Thunder Rods replace standard connecting rods, and deliver a huge whack of additional low-end torque while eliminating piston rock
Transcend says its two-piece Thunder Rods replace standard connecting rods, and deliver a huge whack of additional low-end torque while eliminating piston rock
View 5 Images
Transcend says its two-piece Thunder Rods replace standard connecting rods, and deliver a huge whack of additional low-end torque while eliminating piston rock
1/5
Transcend says its two-piece Thunder Rods replace standard connecting rods, and deliver a huge whack of additional low-end torque while eliminating piston rock
Transcend says its Thunder Rods deliver a dramatic increase in engine torque, by adding an extra pivot to the connecting rods
2/5
Transcend says its Thunder Rods deliver a dramatic increase in engine torque, by adding an extra pivot to the connecting rods
Transcend brought the Thunder Rods to SEMA
3/5
Transcend brought the Thunder Rods to SEMA
These rods are currently only developed for GM LS V8 engines
4/5
These rods are currently only developed for GM LS V8 engines
Saddles in the sides of the upper section of the Thunder Rods actively engage the sides of the piston skirt when installed
5/5
Saddles in the sides of the upper section of the Thunder Rods actively engage the sides of the piston skirt when installed
View gallery - 5 images

Utah's Transcend Energy Group claims it has a relatively simple and cheap way to dramatically increase the torque output of combustion engines, simply by replacing the standard connecting rods with new two-piece designs with a secondary joint.

As the pistons in an engine move up and down, driven by expanding gases as the air and fuel burn, connecting rods, or con rods, transmit the linear force of the pistons into a rotating motion of the crankshaft. The small end links to a gudgeon pin in the back of the piston, with a bearing to allow it to change angle as the crank rotates, and the big end wraps around a crankpin so it can spin 360 degrees as the pistons push the crank around.

Transcend's "Thunder Rods" caused a bit of a stir at SEMA earlier this month. They add a secondary joint to the typical con rod design, sitting well below the gudgeon pin and outside the piston skirts. The company claims this arrangement makes the pistons drop farther and faster when the crank's at a 90-degree angle, delivering better leverage to the crankshaft and boosting "dynamic compression" by 25-30%.

Transcend says its Thunder Rods deliver a dramatic increase in engine torque, by adding an extra pivot to the connecting rods
Transcend says its Thunder Rods deliver a dramatic increase in engine torque, by adding an extra pivot to the connecting rods

Transcend tells Road and Track this effectively means the piston moves faster when it matters – when you're drawing air in through the valves, when you're compressing it, and when it leaves top dead center in response to gas expansion. And the company says the lower pin mount gives the piston more leverage on the crank. The additional speed and leverage create extra torque, particularly at low revs.

Transcend also claims that its two-piece con rods eliminate piston rock – this is a side to side tilting of the piston in response to lateral forces from the con rods; the piston and crank operate most efficiently upon one another when the crank's at 90 degrees, with the maximum possible offset between the crankpin and the big end, and the resulting lateral forces push the piston sideways into the cylinder walls. That's a problem, since it can wear the cylinders into an oval shape and unload the piston rings, causing a loss of compression.

In addition to the pin, the Thunder Rods actively engage the side walls of the piston using a pair of saddles with their own ability to rotate slightly. Transcend tells Road and Track these stop the piston from tilting and equalize pressure against the sides of the cylinder.

Saddles in the sides of the upper section of the Thunder Rods actively engage the sides of the piston skirt when installed
Saddles in the sides of the upper section of the Thunder Rods actively engage the sides of the piston skirt when installed

The company has only developed the rods as drop-in replacements for 5.3- and 6.2-liter LS V8 engines from General Motors thus far. In its own testing, Transcend says it was able to tune the 5.3 to match the torque output of the stock 6.2 – a leap of around 30% – between 1,500 and 3,500 rpm. Static compression in the 6.2-liter engine was raised from 155 psi to 198 psi, and the Thunder Rod-modified motor peaked at 32 degrees of timing, where the standard unit is best around 26 degrees.

Transcend says that while the LS is a popular drop-in engine for tuners, it's not optimized to take maximal advantage of the Thunder Rod design, and eventually the company hopes to see what it can do with purpose-designed cranks, cylinder heads and pistons.

While Transcend is confident, many are not convinced, particularly given the current lack of third-party testing and the paucity of results presented by the company. The two-piece con rods are heavier than standard items, creating additional inertial forces that will increase substantially as the engine revs faster, so there's a good chance that even if there are low-end gains, they might come at the expense of high-RPM horsepower.

These rods are currently only developed for GM LS V8 engines
These rods are currently only developed for GM LS V8 engines

And the design would also appear to create extra lateral force on the pistons, since the lower pivot point and shorter main arm make the angle between the con rod and the cylinder bore even greater. Not only that, but the distance between the main gudgeon pin and the new, lower pivot now effectively appears to become a torque arm that'll amplify the forces making the piston want to tilt.

So Transcend will certainly need to prove its con rods do what they say on the tin, and that they can do it without increasing engine wear. Either way, it's an interesting piece of engine tech that hasn't been used on gasoline engines before, even if it's similar in some ways to the crosshead con rods sometimes used in marine diesels and steam engines.

Check out a (short, silent, rendered) video below.

Transcend's "Thunder Rods" claim a 30% increase in engine torque

Source: Transcend Energy Group via Road and Track

View gallery - 5 images
20 comments
20 comments
Chase
Sooo... it's just an adapter that moves the wrist-pin down a couple inches and shorter connecting rods. It has the scent of snake oil to me, but I'd like to reserve final judgement until I see some third-party testing.
pmshah
I have a question. How much angular movement does the upper short part of the connecting trod have at the gudgeon pin with respect to the piston? From the very short video running for a few seconds what I ca gather is you have made the skirt of the piston much shorter and moved the gudgeon pin, the actual oscillating motion part, out of the piston. May be made the manufacture of the piston less complex.
MonacoJim
I dont see it. The swivel point has been moved to just below the piston, like an extended piston, with a shorter arm, how does this benefit? The engine in the lightweight butterfly car (1980?) had a geared joint to the crankshaft, so that the piston rod was at right angles to crankshaft on the explosive piston push, that made for a very efficient engine with high miles per gallon. It may be me, but I dont see this one working as claimed. hey ho good luck to them though.
WONKY KLERKY
Wot will they think of next - Yoking the stroke?
That said:
To the faint echo in me brain cell this, ye '2 piece con-rod' has been done before.
Can't renenber where / can't remember when.
Can't be bottomed to do the research but thought Fred Lanchester was involved.
+
Don't forget Mr Toyota's current treatment of his H2 engines nether end.
martinwinlow
Great, but given that even the best piston-based ICEs throw away 70% of the thermal energy available in their fuels I have to ask, who the heck cares?
Bob Stuart
It would be lighter to make new pistons, but the biggest problem is that they are referring to the torque at one part of the stroke, which then gets averaged out as usual.
Karmudjun
If this is so fantastic Loz, why haven't piston manufacturers started setting the wrist pin lower in the skirts of the piston to allow for shorter connecting rods? The piston would be a little heavier so greater piston inertia to change direction but the connecting rods would be a little lighter so slight decrease in connecting rod reciprocating inertia. If these wonky extra joints give a beneficial increase in low power torque, I guess the altered piston wrist pin location might not improve the low end torque - or would it?

Yep, it seems like the free lunch we have all been promised - along with life time oil changes by our local dealership! All it takes is extra effort on our part.....
CraigAllenCorson
So why is that UPPER pivot still needed, the part inside the piston? It doesn't appear to be pivoting very much at all in your video. Why not just redesign the piston with a lower pivot point?
ljaques
Color me unimpressed. Piston skirts prevent piston tilt. Has Car and Driver done a dyno test on anything with these rods? They add a lot of mass to the piston, and the shorter stroke of the shorter lower rod creates additional lateral forces, so I don't see any minimizing of cylinder wear in that case. Reeks heavily of snake oil, but good luck to them.
Catweazle
This just seems to reduce the rod length to stroke ratio - known as the "rod ratio".
The higher the rod ratio, the higher the RPM at which the engine will produce peak power and the lower the ratio, the lower the RPM at which the engine will produce peak torque - all other things being equal, of course.
This has been known to builders of competition engines for decades and is used to tune the RPM at which the engine produces peak power and torque.
The increased angularity will also increase the loading on the piston skirt and cylinder wall and the piston acceleration.
Load More