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Discussion Starter · #1 ·
I was reading around a bit on the growing fad of titanium rods, especially after learning that GM has used a few. One item that came up was a blurb about the rods producing "30 to 40 more HP". This is obviously just a vague statement, but it does seem to hold to logic. The reciprocating mass of the rods is a mass that must be accelerated and decelerated during each rotation of the crank. The larger this mass, not only the more force exerted on the crank but also the more work required to complete each rotation. For a rod that is, say 450g total versus 800g total (with proportional reciprocating masses I would assume) it seems the difference could be large enough to show up on a dyno as RPM increases.

This is all theoretical and not quantified; does anyone have real experience with titanium connecting rods to share? :secret:
 

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Discussion Starter · #3 ·
An interesting post; another factor stated in that link is that the rod stretches less reducing the necessary piston to head clearance. Although, I am not sure that this really means additional power. It probably means that power will be lost if the clearance is not decreased.

Otherwise, it sounds like similar hype to what I have seen so far that only makes the claims without providing information that supports the claims.

Keep it coming, good info!
 

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Discussion Starter · #4 ·
I just found a long series of posts on LS1Tech.com that roughly calculated the HP gain at 6000 RPM to be about eight HP. The calculations and thoughts seemed correct and some people were claiming to be experts in the art. This blows the previous claims out of the water and sounds more realistic. There is some power to be gained, and the higher the RPM the more power to be gained, but it is not enough to justify the cost provided that the engine is not producing the maximum power possible under the rules of a particular racing class.

Still, anybody out there with dyno time with titantium rods?
 

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With Aluminum rods you can gain 10-30hp depending on application, Titanium rods is said to have the light weight of aluminum but the long life nature of steel rods.

If the mass is larger but it is lighter how does that make it harder to accelerate the larger mass? The heavier the rod, regardless of mass, the harder it is to accelerate or de-accelerate.

A Super Stock 327 GT engine will make 550-575hp, How do they do it? First they use Bill Miller 340gram pistons, .875" pins verses stock .927" that weigh 85-88grams, then they use the legal steel rod which is about 550-580grams, an aluminum would be about 100grams lighter, The big reason the pistons are so light is they have to run a heavy steel rod so they run lighter pistons to put less load on the rods and all - Any reduction in rotating assy is good as long as you do it without compromising strength - Aluminum rods need to be changed every 150-250 passes depending on HP level. Titanium rods Should {i have not used titanium rods} last longer than aluminum rods, aluminum rods act like a shock absorber between the piston and crank/bearing.
 

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If the mass is larger but it is lighter how does that make it harder to accelerate the larger mass? The heavier the rod, regardless of mass, the harder it is to accelerate or de-accelerate.
How would the rod have more mass but be lighter when used in the same gravitational field? F = ma, when you weigh the rod you are measuring the force caused by the acceleration of gravity on the mass of the rod. Less mass means lighter rods.
 

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How would the rod have more mass but be lighter when used in the same gravitational field? F = ma, when you weigh the rod you are measuring the force caused by the acceleration of gravity on the mass of the rod. Less mass means lighter rods.
Read the way i used to compare the two, Aluminum rod weighs less than steel rod but the aluminum rod has more mass. Titanium i cant say but i do think titanium in the same given size as steel would be lighter, i know aluminum is, You cant take a Eagle h beam 4340 rod that weighs 630-645grams and replace it with a GRP Aluminum rod and it weighs 480grams but has alot more mass and is much larger but lighter
 

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I was reading around a bit on the growing fad of titanium rods, especially after learning that GM has used a few. One item that came up was a blurb about the rods producing "30 to 40 more HP". This is obviously just a vague statement, but it does seem to hold to logic. The reciprocating mass of the rods is a mass that must be accelerated and decelerated during each rotation of the crank. The larger this mass, not only the more force exerted on the crank but also the more work required to complete each rotation. For a rod that is, say 450g total versus 800g total (with proportional reciprocating masses I would assume) it seems the difference could be large enough to show up on a dyno as RPM increases.

This is all theoretical and not quantified; does anyone have real experience with titanium connecting rods to share? :secret:
Keep in mind that the deceleration is giving energy back to the crank...possibly offsetting the acceleration of another rod/piston??

The way I see it, the lighter rotating assembly wouldn't change an engine's power output at steady state (constant rpm), but would certainly increase the rate of acceleration of the engine. The lighter rotating assembly absorbs less of the engine's power during acceleration than the heavier rotating assembly.


I looked up some densities, titanium is about 60% the density of steel, and aluminum is about 36% the density of steel. These are for pure metals.
 

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The relationship between mass and volume is called density.
 

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In my opinion, a particular type of rod is not going to "make more power" than another type of rod will. What a lighter connecting rod will do however, is allow the engine to reach maximum RPM quicker and a lighter rod "might" allow the engine to reach a higher maximum RPM level. I say might because just changing to lighter rods will not necessarily make the engine rev higher. High RPM is the result of a well engineered combination of intake track, combustion chamber, exhaust system and of course the cam/valve train must be compatable.
High RPM = more power due to the fact that you are firing the cylinders more frequently and each cylinder firing produces power. This is why you will see Pro Stock and Comp Eliminator cars turning very high RPM, which results in a very narrow power band and necessitates the use of five speed transmission.
 

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In my opinion, a particular type of rod is not going to "make more power" than another type of rod will. What a lighter connecting rod will do however, is allow the engine to reach maximum RPM quicker and a lighter rod "might" allow the engine to reach a higher maximum RPM level. I say might because just changing to lighter rods will not necessarily make the engine rev higher. High RPM is the result of a well engineered combination of intake track, combustion chamber, exhaust system and of course the cam/valve train must be compatable.
High RPM = more power due to the fact that you are firing the cylinders more frequently and each cylinder firing produces power. This is why you will see Pro Stock and Comp Eliminator cars turning very high RPM, which results in a very narrow power band and necessitates the use of five speed transmission.
Narrow powerband? You call launching at 7,400rpm and pulling gears at 9,300rpm-9,500rpm in a Pro Stock 500cid NHRA engine a narrow powerband? What would you consider a wide powerband?

Fact is Pro Stock launches at 7,000rpm-7,600rpm, some viewers think they launch at 8,000rpm because thats what you see on the tach when they use the onboard cam, what you are seeing is the engine revving so quick thats the RPM as soon as they come off the chip, they are not using a chip, they are using MSD digital 7's with built in rev limiter. The data logger will show you true rpm, the engine accelerates so fast it does indeed look like they launch at 8,000rpm but they do not

A lighter rod/piston will make more HP, this is a fact, take a 575hp Super Stock 331 and remove the 340gram piston and install a TRW NHRA legal piston and it will loose power due to the piston weighing well over 100grams heavier than the 340gram Bill Miller

Another fact, lighter pistons and rods are easier on wrist pins and cranks and rod bolts. When a motor is turning up in rpm, over 6,000rpm, the crank and piston is launching off the crank and this launching effect strains the rod bolts and big ends of the rods, the lighter parts do also but not as much

Fact is a lighter rotating unit will indeed run quicker in a drag race engine, Fact is a lighter car runs quicker because it accelerates quicker, lighter engine parts accelerate quicker too

If lighter parts dont make more hp or make the engine more reliable, why do all Pro Stock, Super Stock and Comp Eliminator engines use the lightest parts possible when it comes to pistons and rods? If you want it to be durable over 7,500rpm, you must have lighter pistons and rods. Same goes with valvetrain {valves}, you must use lighter valves such as titanium intake valves and if your class says you must run stainless valves your gonna need more spring pressure to control the valves which is gonna put more wear on the rockers, pushrods and lifters
 

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A lighter rod/piston will make more HP, this is a fact, take a 575hp Super Stock 331 and remove the 340gram piston and install a TRW NHRA legal piston and it will loose power due to the piston weighing well over 100grams heavier than the 340gram Bill Miller

Are you talking about power or accelerating capability?

If a change of 800 grams in piston/rod weight (roughly 2#) produces a change of 'x' power, would a change of 10# in flywheel weight produce a change of 5'x' power or better?
 

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Narrow powerband? You call launching at 7,400rpm and pulling gears at 9,300rpm-9,500rpm in a Pro Stock 500cid NHRA engine a narrow powerband? What would you consider a wide powerband?
The powerband is relative to the overall rpm. A 2000 rpm powerband is still only 21% of the 9500 rpm peak that you state. Considering that the difference in gears on these cars runs in the mid-teens to low 20s (percentage wise). And, when you look at the data logger graphs, the actual rpm change is less than that. So, yes, that is a relatively narrow power band.
Fact is Pro Stock launches at 7,000rpm-7,600rpm,…
I have limited experience with Pro-Stock cars, but the RacePak data that I have seen shows them launching at significantly higher than 7000 – 7600 rpm.
A lighter rod/piston will make more HP,…
Make “steady state” dyno pulls and I believe you will see that there is no difference in the power made with heavy versus light rotating assemblies.
Another fact, lighter pistons and rods are easier on wrist pins and cranks and rod bolts…
I agree.
Fact is a lighter rotating unit will indeed run quicker in a drag race engine,…
I agree that the lighter rotating assembly will probably make it down the track quicker due to quicker engine acceleration. (Note – This is not a universally accepted fact. Many claim to have proven that there is no difference.)
 

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Don't most dynos use the acceleration of a known mass to calculate power output? Generally, that acceleration is kept to some sort of standardized rate, correct?

You can really make the horsepower of an engine whatever you want by monkeying with the acceleraion rate or the mass being accelerated.
 

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most dynos are a water pump with a variable outlet. I haven't seen one that accelerates a mass.
 

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Narrow powerband? You call launching at 7,400rpm and pulling gears at 9,300rpm-9,500rpm in a Pro Stock 500cid NHRA engine a narrow powerband? What would you consider a wide powerband?

Yes, narrow powerband. With the intake design, header configuration, valvetrain, etc., Pro Stock cars have a very narrow powerband. Many are now turning over 10,000 RPM but they are only producing maximum horsepower through a range of 1000 to 2000 RPM. That is a narrow powerband. Ditto for many Comp Eliminator cars as well.

What do I consider a wide powerband?? A well engineered combination of parts that will allow a vehicle to idle at an acceptable RPM, can be driven on the street with mufflers but will turn high 10's or low 11's at the dragstrip. A car with an automatic transmission, especially a Powerglide, will need a fairly wide powerband in order to be driven on the street successfully.
 

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Not Ti but Jager aluminum. Jagers aluminum rods were about 100gm lighter then a set of Ti rods in an IHRA prostock engine. By reducing the rod mass by this amount the engine picked up an average of 35HP on the dyno and a peak of 51HP. At the track the rod change yielded a quicker ET.
 

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Discussion Starter · #20 ·
Not Ti but Jager aluminum. Jagers aluminum rods were about 100gm lighter then a set of Ti rods in an IHRA prostock engine. By reducing the rod mass by this amount the engine picked up an average of 35HP on the dyno and a peak of 51HP. At the track the rod change yielded a quicker ET.

Very interesting, so in a high-RPM engine 100gm of reduced total rod mass produced an average increase of 35HP. Do you know anything about what RPM range that average was taken across? It seems that this could be a somewhat special case where the engine was ran from 7500RPM to 9500RPM and produced some interesting results.
 
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