Aluminum vs Ti 6AL4V connecting rods

[Bleakley]

Was wondering if someone more knowledgeable could shed some light.
Been researching connecting rods for an upcoming build. I’m pretty well versed in 4340 vs 6AL4V vs 4340M (300M).

I think either Aluminum or 6AL4V will do the job, but something I am curious about. I’m not sure the exact number, but I think over that 250-300hp per cylinder mark I see people switching to aluminum connecting rods. I4, I6, V8, etc.
I’m ASSUMING this is related to the shock absorption characteristics of the aluminum? Otherwise why not just go 300M and call it a day?

I was wondering if Ti6AL4V would be a valid middle ground? Rather than switching from 4340/300M to aluminum, go to titanium 6AL4V instead. I’m wondering if it would have similar characteristics to the aluminum in regards to how it’s able to absorb the shock forces from extreme hp ignition.

We know 6AL4V is ~20% weight savings (though larger dimensions) at same strength vs 4340 connecting rods. So why not beef up the 6AL4V a little more to match a 300M rod. The result will likely be a weight savings (not as much as Aluminum) at similar strength (larger dimensions) than 300M, but less of a footprint than that of aluminum… But would it also perform between 300M and aluminum in regards to that shock absorbing characteristic?

 

[donniekak]

I’ve only ever found the need to use 3 styles of rod. Stock, h-beam steel, and aluminum. I use aluminum in anything over 800hp.

I’ve pulled rod bearings out of 1300hp aluminum rod engines that looked better than the same bearing in a 750whp steel rod engine.

These are high boost, high back pressure turbo engines. Most exotic rods materials are to make the rod stronger in tension, a problem more for big displacement/high rpm naturally aspirated engines.

Us high cylinder pressure turbo guys just need strength in compression.


For example, rods usually come with “arp 2000” fasteners. You can upgrade to l19 or other tool steel bolts for more strength in tension to keep the cap on the rod. We used the standard arp bolts in an 11,000 rpms 7 second car with zero rod bolt issues. These engines just don’t pull on the rods much, especially at really high boost and back pressure.

The turbo back pressure acts like a cushion at tdc on the exhaust stroke. That pressure pushing down on the piston lowers the tension on the rod.

 

[1cleangsx]

Hey Donnie what’s your favorite H beam? I went with “turbo tuff” tri beams on my build for strength but I know their heavy. I’m about to hit 1,000 miles on the motor, or a year and a half of street use. I was skeptical of an H beam and not to call him out but @Vegas Smith snapped a Manley h beam in half at maybe 600ish, he’ll have to correct me if I’m wrong. I’m sure some manufacturers may be better than others, just curious who you like for a typical high power 2.0

 

[babyviper]

I would choose Ti-6Al-4V over 7075 aluminum rod only for fatigue strength. The fatigue strength of titanium is close to steel's fatigue strength, and a little over 3 times the fatigue strength of 7075 aluminum. But at $4500 for a set of rods, you can replace 4 sets of Aluminum rods and still have money left over. Financially, it makes no sense to run titanium rods, but if you got the cash, go buy a set and share some pictures .

 

[ist dwa]

STEEL FTW! My 2 cents

 

[1cleangsx]

You know one of my other thoughts on the matter of the “I beams are heavy and beat up bearings” argument is that when your making power what’s cheaper to replace? Those steal I beams will never fatigue and weaken like an aluminum rod and when you tear down your 6-700hp street car you can re use your rods and replace your bearings. I’d rather replace the latter. There’s an HP Acadamy pod cast I listened to with Devin Schultz and they only get a limited number of passes on the car before the rods stretch and have to be replaced, so again it’s just my opinion but I’m banking on re using my rods whenever this engine either lets go or I decide to change it up

 

[babyviper]

You know one of my other thoughts on the matter of the “I beams are heavy and beat up bearings” argument is that when your making power what’s cheaper to replace? Those steal I beams will never fatigue and weaken like an aluminum rod and when you tear down your 6-700hp street car you can re use your rods and replace your bearings. I’d rather replace the latter. There’s an HP Acadamy pod cast I listened to with Devin Schultz and they only get a limited number of passes on the car before the rods stretch and have to be replaced, so again it’s just my opinion but I’m banking on re using my rods whenever this engine either lets go or I decide to change it up

Another fact in favor of steel rods is, the factory 1G big rods are around 700 grams. They obviously last forever under 450whp and don't wear out bearings fast. Most h-beams are around 150 grams lighter and most I beams weigh the same weight as factory 1G big rods. So not even a big I beam like pauter or manley is heavier than a factory 1G big rod. You wanna save a few pounds of rotational mass in your rotating assembly, go for a Magnus gun drilled crank. That $1600 spent on a crank will last longer than any titanium or aluminum rod.

 

[donniekak]

These threads always make me chuckle. We went 7.80’s @ 180 with a stock block, crank, and $1200 in rods and pistons. The head was a bone stock casting with springs retainers abs cams.
It’s not that complicated folks.

 

[familyMAN]

2.0 aluminum rod,,, you know that's eventually where the mr2 will end up . I don't know why I kid myself

 

[biglady112]

These threads always make me chuckle. We went 7.80’s @ 180 with a stock block, crank, and $1200 in rods and pistons. The head was a bone stock casting with springs retainers abs cams.
It’s not that complicated folks.

We went 228mph at Bonneville with second hand, actual used rods and pistons (Manley H beam, Ross pistons with .190” wall pins) with a $150 Holset HX52. Crower 64413 cams.

Far from ideal.

I chuckle with you.