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mazdaspeed 3 stock piston rods

13871 Views 5 Replies 6 Participants Last post by  aero_student
I'm currently having my motor rebuilt with forged pistons, gt3076r turbo, hp fuel pump and the block is getting bored out, So, I was wondering can the stock rods handle 400whp, so about 450 flywheel horsepower. B/c the rods i'm looking at are 800 dollars. So can the stock rods handle that power safely? Thanks.
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If you're opening the motor up to build it, do it the right way the first time, get a good set of rods.
There have been more than a few engines (MS3 & MS6) that have broken connecting rods in the last couple of years. I have yet to see anyone give a good reason ("my engine blew up, #@%*& stock rods") backed up by any real failure analysis (Failure analysis is the process of collecting and analyzing data to determine the cause of a failure and how to prevent it from recurring.) I have seen a picture of one person's connecting rod that was BENT, he figured it was from a 30 psi boost spike (once again a guess on his part, altho it might be correct) If you are planning on increasing the power output of your engine by 70% I sure would not consider using factory stock connecting rods on ANY engine, and definitely not on a TURBO CHARGED engine where the Torque it going to go up nearly as much.

Normaly aspirated engines make more HP by continuing to make reasonable amounts of torque at higher engine speeds. 1.5 lb/ft of torque per Cubic Inch of displacement is considered GREAT even for good N/A race engines (think 750 HP 454 CI big block Chev engines that make 620 lb/ft of torque peak, that's 1.36 lb/ft per Cubic inch.)

Our engines already make 2.03 lb/ft of torque / cubic inch of displacement Stock. To get 450 crankshaft HP at 6500 rpm you will need to be making 365 lb/ft of torque at the crank (that's 2.6 lb/ft per cubic inch) if you want 450 hp at 6000 rpm you will need to be making 396 lb/ft and that won't even be the peak torque for the engine. I'm guessing peak will be somewhere around 3500-3800 rpm and be somewere around 425-450 lb/ft , that would be 3.2 lb/ft per Cubic Inch!!! I sure would not trust STOCK RODS under that kind of load!!!

Believe me if you can't afford $800 for a set of rods you sure can't afford the cost of a new block, Crank, rods and pistons and maybe even a head when it comes apart.

Don't be in a hurry save up some more money and do it right.
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no they cannot,buy forged rods.And you cant even use the stock rods with forged pistons anyways.
the fact that you are even asking this question is a good indication that you should stop now.

do it right or don't do it at all.
It's also scary that he thinks he can have it "bored out"; there isn't enough liner thickness to increase displacement any appreciable degree and the only way to do it is to remove the sleeves, bore the block and insert sleeves from a company like Darton. IIRC they make a nice set of interlocking liners.
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