300M vs 6AL4V connecting rods - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

Bleakley · 06-10-2023, 06:28 PM

Was wondering if someone a little 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?

jr_ss · 06-11-2023, 12:16 AM

Yes, people switch to aluminum rods because it acts more like a spring and absorbs more of the shock loads from combustion, increasing rod bearing life at high HP levels. The trade off is shorter life cycles and less fatigue resistance such as the other materials mentioned. It’s a balance.

Anything over 250-300hp/cyl should really be utilizing aluminum rods.

Bleakley · 06-11-2023, 02:17 AM

A balance for sure. I’m very curious about possibly bridging the gap between 300M and aluminum with 6AL4V though.

Might just say f*** it and be the Guinea pig. I’ve got a 1400-1500hp strip/street build coming down the pipe. Just need a couple more things to fall into place and then I’m all in.

06-10-2023, 06:28 PM	#1
Bleakley Zilvia Addict Join Date: Apr 2011 Location: Near Pittsburgh, PA Posts: 637 Trader Rating: (1) Feedback Score: 1 reviews	Aluminum vs Ti 6AL4V connecting rods Was wondering if someone a little 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? Last edited by Bleakley; 06-11-2023 at 11:53 AM.. Reason: Clarity

06-11-2023, 12:16 AM	#2
jr_ss Post Whore! Join Date: Dec 2005 Location: Pa Posts: 6,412 Trader Rating: (35) Feedback Score: 35 reviews	Yes, people switch to aluminum rods because it acts more like a spring and absorbs more of the shock loads from combustion, increasing rod bearing life at high HP levels. The trade off is shorter life cycles and less fatigue resistance such as the other materials mentioned. It’s a balance. Anything over 250-300hp/cyl should really be utilizing aluminum rods. __________________ My SR20VET Does your VTC gear rattle in your S14/15 SR? PM me.

06-11-2023, 02:17 AM	#3
Bleakley Zilvia Addict Join Date: Apr 2011 Location: Near Pittsburgh, PA Posts: 637 Trader Rating: (1) Feedback Score: 1 reviews	A balance for sure. I’m very curious about possibly bridging the gap between 300M and aluminum with 6AL4V though. Might just say f*** it and be the Guinea pig. I’ve got a 1400-1500hp strip/street build coming down the pipe. Just need a couple more things to fall into place and then I’m all in.