I found a set of I beam 5140 connecting rods for $140, that seems REALLY cheap to me. I just read that I should only go with 4340 forged parts. Is there a huge difference? The previously mentioned rods were advertised for 500 HP (no name brand).

I was also looking into these pistons: Speed-Pro Powerforged Pistons. Supercharger or turbocharger piston with 21cc D-shaped cup and floating pin. Compression ratios:
8.35:1 w/std. stroke & rods, 64cc head.

Now, the pistons call for floating pins but the rods state that they are pressed. Which is the best way to go and what is cheaper? I have read that pressed rods are more reliable.. is that true?

The final step is a crank... forged would be nice but the $800 tag is a little much.

 

The first two numbers 43 or 51 specify the steel alloy. The last two numbers are tenths of carbon percent for instance 40 is .40% carbon. I don't remeber off hand what alloy 51 specifies. There is at least one metalurgist on this board. I'm sure he knows.

As far as the rods go, free floating pistons use "jesus" clips to hold the pin in the piston and the rod "floats" on the pin. DO NOT use pressed rods and the clips at the same time or you will fail a piston rod assembly. Just make sure the pins don't move out past the piston and you'll be fine. About the reliability, I'm not sure about that. I think they're about the same.

 

Thanks!

I figured you couldn't mix and match the rod types. Any perticular reason they are called "jesus" clips?

 

Floating pins are intended for those who change pistons regularly (like between rounds). You don't really need them.

The clips got their name from the words you use while fiddling with them...

 

According to my handy-dandy Machinery's Handbook I found the following:

Nomalaized: Tensile: Elong %: Hardness (Bhm):
5140: 1600F 115,000 27.7 229
4340: 1600F 185,000 12.2 363


Basicly 4340 is better and I bet more expensive. What HP are 4340 rods good for?

Can anyone recomend a set of $350-400 low compression pressed pistons?

 

If you find a set of pistons that are good for floating rods, you can still use them for pressed pins, provided the pin doesn't go out past the outer diameter of the piston. Most pistons that are forged that are for both, the only difference being there is a goove machined in the pin hole to put the 'jesus' clips in. but like 57kid said, do not put pressed rods on with the clips. The 5140 rods are stronger than most stock rods, the 4340 will be stronger, but more expensive. Depends on the usage. High amounts of nitrous, or supercharger with alot of boost, better to go with 4340. I dunno what you're used to running, but 500hp is pretty substantial for the street, if you're only gonna hit the motor with shot once in awhile(not a track only motor), the 5140's will work well. Likewise for the crankshafts. I've seen way too many guys get hung up on beefy bottom ends, without spending money on the important stuff....heads and valvetrain. Even the factory stuff will take more abuse than you can imagine. I've seen cast crank 400's easily hit 11:20's all day long in a 2900lb car. With a nitrous shot on top of that!HTH

 

whoops, my bad, ATOmonkey talked about the rods failing.

 

jwscab - where in NJ are you? Check the regional board for a mini gathering by "piany". If you have the time you should join us... plus I can pick your brain!



Well, I am quite used to my LB9 that "decimates all" so 500 odd HP is nothing to me

I am building a roller 355, 2 bolt block for a turbo. I figure 450 HP should be enough to soil my pants. I have just recently dipped my toes in the VAST pool of engine part specifics. I know some info on parts but just recently I found out there are QUITE a few variables within each part.

The top end will be as follows: Sportsman 2's, HOT cam, 1.6 rr, with an LT1 intake. I am thinking around 10 PSI of boost. All in a daily driver.. with the occasional waltz down the track.

 

How does one "make sure" that the pin doesn't go outside the piston? Does the section in the piston where the rod fits vary (and rod width) to the point you need shims? Or do you buy shorter pins?

 

Sorry, been awy from the PC for a few days....Located in central NJ, outside of Trenton. I'll check out the gathering, see if I can make it, but schedule is tough....

to answer your last question, the wrist pins won't insterfere with anything provided the machin shop installs them correctly, eg, centers the rod on the pin. I have seen them off a bit, but nothing ever to the point of interference. HTH

 

I finished striping my block the other day. I now understand what you are saying about floating or pressed pins.

Where should my money go, crank or rods?

 

Rods. Cranks can take more abuse than people think since they're thicker and heavier than rods.

Since we're on the topic of rods...anybody know how strong PM (powdered metal) rods are compared to regular stock rods and 5140/4340 rods? I'm wondering how they compare to other rods.

 

I just read that they are good up to 500 HP. I can't remember the site but I think it said they are $200 a rod!!!