jfm

iTrader: (4)

What would be gained using 6.125 rods over the 6.100s,stock crank ?

Block machined for 3.905 pistons[348CI].

The stock rod,piston,crank combo leaves the piston up above the deck,will the 6.125 rod add to that?

<small>[ April 23, 2003, 06:44 AM: Message edited by: jfm ]</small>

jfm

iTrader: (4)

ttt

jfm

iTrader: (4)

Anyone?

jyeager

Typically longer rods are paired with pistons that move the rod bushing up higher inside the piston so that deck height is maintained, rather than increased.
The longer rod provides a better angle of force against the crank. I don't think it makes a difference that can be measured on the dyno, but according to a world-class engine builder that I talked to a while back, the longer rod has the effect of allowing the engine to 'rev up quicker'. (not wind higher, just accelerate faster).
It is an advantage, but might not be worth the cost because it will require custom pistons.

jfm

iTrader: (4)

Thanks for the info,I am about to redo my motor and will be ordering pistons and rods.

The cost is about the same for 6.100 and 6.125 rods.I will order the 6.125s.

Crazyquik

The longer rods will give you more dwell at TDC. This will allow more time for better cylinder filling.

I'm a big fan of long rods in naturally aspirated motors, but if you're going to use power adders I'd rather get my ring spacing correct and moved down on the piston instead of running a little extra rod length, as the power adder is where you're really going to make your power.

Probably a better selection of 6.125" rods available too?

J.

1999_SS_M6

go to yahoo, or some other search engine and do a search on "rod ratio". You should find several theories on what effects are had on the engine by changing these dynamics.

Hawk

I did this with Pro Mod Lunati's rods (full floating)and Diamond pistons 401 grams ea Well its got more power every where. call paul @ thunder racing rods pistons rings bearings was around $1200. During install ensure the Lunati side faces crank and USA goes together on all rod jounals.

ChrisB

I would agree with Crazyquick in this instance, but add a few qualifiers.

For most of the LS1 combinations around here a numerically greater r/s ratio will probably help - in that with the great heads but somewhat restrictive intake (at least at higher rpm's) the motors tend to work similarly to a restrictor plate motor (though not quite to the same extent).

But realistically the difference in r/s ratio with a 6"-6.125" rod is going to be negligible. As Crazyquick pointed out the #1 issue (especially with PA) should be getting a good ring package - and with PA you should be concerned about getting a thick first ring land also.

You should also check the price on pistons and make sure they are the same also (for either rod combination), and see if the piston manufacturer feels comfortable with the ring package for your intended application.

But assuming the ring package, piston, everything else is fine, then I would go for the longer rod (in this instance)