I am thinking of building a 491 RHS tall deck block motor. I am going to be using a Lunati 4.6" stroke crank with Diamond 4.125" nitrous 10cc dome pistons. I will be using a little bit of nitrous with this motor, maybe up to a 400 shot. I see that Lunati makes there Pro Series rods in 6.125" and 6.3" lengths. What rod would work better? What are the uses of a 6.3" rod? I don't plan on spinning the motor to high, around 8000 to 8500 at the most. Thank you.

 

Without doing any math, I'm going to say with that long of a stroke, you will want the longer rod to clear the bottom of the cylinders.

 

Ok, that make sense. What would change in the motor with the longer connecting rod? I would have to let Diamond know that I am using a longer rod right? That would change the piston height?

 

Yup. You got it. Call diamond and let them know your stroke and rod length. They will make the pistons with custom compression depth to suit the longer rod. The wrist pin will surely protrude into the ringland area which you will need a better set of rings than stock(ish) to work but will make one awesome screamer.

 

If you can get the deck height of the block, i can tell you what compression depth of a piston you will want based on your desired compression ratio.

 

The block is a tall deck block. Comes with a 9.750" height. Here is the link to the block:
http://http://www.texas-speed.com/p-606-rhs-tall-deck-ls-race-block-9750-deck-height.aspx

 

For zero deck, you will need a 1.15 compression height piston, or for .005 out of the hole, 1.20

 

What would I need as far as heads to get a 12.5-1 to 13.0-1 compression ratio?