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PostPosted: Wed Jul 20, 2022 11:01 am 
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3 Deuce Weber
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Joined: Thu Oct 21, 2021 8:14 pm
Posts: 65
Location: Tennessee
Car Model: Mazda RX8 slant six swap
I am planning a long rod, 2.2 turbo piston build in the future. I would like to get more rpm than stock from a 1.70 and 1.44 valve, ported head with a Gill Welding EFI intake.

I have looked in vain for connecting rod weights. I've read hundreds of threads while researching.

From what I can find, the stock piston weighs 16.4 oz, and the wrist pin weighs
4.137 oz.
The 2.2 cast piston w/pin weighs 17.0 oz.
Molner 7.005 cast crank rods (.940 big end width) weighs 21.27 oz.

So, can anyone tell me what a stock 225 cast crank rod weighs?

I would like some idea how much weight I will save with the change. Thanks.


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PostPosted: Wed Jul 20, 2022 12:18 pm 
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Supercharged

Joined: Wed Sep 17, 2008 6:48 pm
Posts: 3805
Location: Indianapolis
Car Model:
use a late 85-86-87 light weigh cast crank and you will cut more weight from the engine than you ever will by substituting in 2.2L pistons and K1 rods.
along with the late cast crank being much lighter, the cast crank rods are lighter than the forged crank rods because the big end of the cast crank rods are narrower.
The narrower bearing should also reduce operating friction.
And I doubt if lighter weight rotating - reciprocating components will get you more RPM, lighter weight will spin up faster, but the RPM band is really determined by the cam shaft profile, the intake tract and exhaust manifolds also play a part to a lesser degree.

Another place to lose reciprocating weight is by using beehive springs and light weight lifters. A reground cam and an aluminum oil pump and a small Nippondenso alternator and mini starter also are general engine weight reduction items.

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PostPosted: Wed Jul 20, 2022 2:01 pm 
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Turbo EFI
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Joined: Mon Jan 12, 2015 5:55 am
Posts: 1387
Location: Brightwood, VA
Car Model: 1965 Plymouth Belvedere I
The piston assembly from my 65 slant (forged crank) weighs 3.0 lbs - piston, rings, rod, pin, and rod bolts.
The piston assembly from my 79 slant (cast crank) weighs 2.6 lbs - piston, rings, rod, pin, and rod bolts.
I weighed a forged crank rod, by itself, and got 26.88 oz. I believe that the early and late pistons/pins are the same, so that would make the cast crank rods about 6.4 oz less than the forged crank rods, but I have not weighed them by themselves, so that is just a guess.
Just my personal observations.

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