WheelsUp84z

iTrader: (2)

Just wondering what the advantages and disadvantages of a 383 with either a 5.7" or 6" rod were. i have 5.7" right now but am considering the 6"ers. Thanks

5678TA

this is what i do know:

5.7" is better for lowend.. faster piston speeds increase friction and wear on cylinders.. better for cam clearance.. lighter rod but heavier piston

6.0" is more for upper rpm.. slower piston speed for less friction and ability to hit upper rpms easier.. but the wrist pin is in the ring lands and that could result in weaker pistons.. more clearancing for cam and heavier overall..



i could be wrong so please correct me..

unknown_host

iTrader: (1)

Isn't the difference almost non existant for most street motors?

IHI

iTrader: (1)

I've talked to local machine shops, read some articles from reher morris and on a dyno there is no advantage to either rod in the hp/tq...just is'nt happening. The biggest reason they push long rod is it does'nt side load the piston as bad using a 6" vs a 5.7" rod and you can also use a lighter piston since your moving the pin heigth up in the piston itself. Either way, if somebody tells you they made more power using a 6" rod over the 5.7, for sake of making yourself laugh as if they also stepped up to 1.6 rockers over 1.5 LOL!!

If your buying new rods anyways, go ahead and get the 6" for what little bit of advantage it will have with piston loading, but if you already have 5.7 stuff you can use, put the money for the 6" rods towards better use.

WheelsUp84z

iTrader: (2)

well i have 5.7" i-beams and i want to upgrade to H-beams thats why i asked, will i have to go with different pistons as well? I've already upgraded from a cast steel crank to a 4340 callies compstar crank, and i had forged pistons, so i figured i'd trade in my scat i-beams for some h-beams to make the bottom end bulletproof. thanks guys

AlkyIROC

When I had a 383, I was using the short 400 rods. The engine pushed my car into the high 11's.

Using a longer rod moves the wrist pin higher into the piston (special pistons). With the short deck height of a SBC, the wrist pin can only go so far. Moving it into the oil control rings isn't too big of a problem as they'll use a support rail. Move it up too far and it gets into the compression rings.

Using 400 rods for a 383 means using factory stock style 350 pistons. Using 5.7" 350 rods means needing a stroker piston. In the early days of building 383's these were not available or very expensive. Now with the huge aftermarket supply, 6" rod pistons are available. Not sure on the cost for either stroker piston but as mentioned above, the engine won't make any more power from a longer rod. It's unlikely you'll see a performance difference unless it's an all out drag car operating above 6000+ rpm.

V8Rumble

iTrader: (2)

Everything I've heard says that in practical terms (HP, etc.), there's little-to-no difference between the 5.7" & the 6" rod. As IHI & Stephen have written, it'll affect your piston setup, but if you know that going in, there shouldn't be any problem.

Myself, I'm going to get the 6" rods for my 383 for two reasons: One, it might be a slightly more long-lasting combo with the slightly-lower side loading, and Two, I'm told that the 6" rods are a little quieter (mechanically) so the knock sensor won't have as much "ambient noise" to deal with. Is that a big issue? Probably not, but as long as I'm buying new rods anyway...

ross

I like the 6'' rod combo also but if you are running a power adder a 5.85 rod length will work better to keep the strength in the piston. Worked on a procharged 383 with the 6'' combo that loved to break ring lands.

V8Rumble

iTrader: (2)

Thanks Ross, that's good to know!

1989GTATransAm

iTrader: (3)

Ditto on not making a difference.

izcain

V8Rumble: So youve found the 5.7 rod motors to have a slightly more audible knock then the 6" motors or is that just something that has been said in the past? Just curious.

WheelsUp84z

iTrader: (2)

knock isnt a problem as i am carbed, i guess i will just go with 5.7" h-beams as i am not really wanting to buy new pistons. Thanks guys

MaNiAk86

iTrader: (2)

my machinist said that a 6" rod motor will produce more torque than a 5.7, but for the street a 5.7 is better due to not interfering with the oil control ring.