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Author Topic:   Rod length ??
5tbone
Dirt Full Roller

Total posts: 62
posted November 21, 2005 02:57 PM  
how does rod length effect compression. reason I'm asking is if I put 350 heads on a 305 block can i make up the compression loss w/ rod length (change 5.7 to 6.0) or is this way off the mark.

racer17j
Dirt Forum Champ
Total posts: 5414
posted November 21, 2005 03:44 PM  
Rod length increases the dwell at TDC and BDC like Racer17j said.

It has no effect on compression.

A 305 block has the same deck height as a 350, 9.025 from the crank CL to the top of the piston wall, the deck surface (where the head mates against).

This distance can be achieved in numerous different ways (stroker motors, 377's 410's etc). 3.5" stroke crank, 6" rod and compression height of the piston (distance between the top of the piston and the CL of the pin boss), or 4" stroke, 6" rod and the appropriate piston etc.

In any instance the complete length must be under the deck height or the piston will stick out above the deck, and thats not good. It will break something when this happens.

In your case you can deck the block off and raise the compression if you need to, but you have to makes sure the piston is at least even with the block at minimum (its what people referr to as a 0 decked block).

Hope that helps, Krom.

[This message has been edited by Kromulous (edited November 21, 2005).]

[This message has been edited by Kromulous (edited November 21, 2005).]

Flying Jack Ace
Dirt Roller

Total posts: 6
posted November 22, 2005 07:38 PM  
It won't affect static compression however it will affect dynamic compression for the reasons mention above.

Ego Racing
Dirt Forum Champ
Total posts: 750
posted November 22, 2005 07:47 PM  
You cannot put 6 inch rods in a motor that came with 5,7 inch rods without replacing the pistons.

5tbone
Dirt Full Roller

Total posts: 62
posted November 23, 2005 05:39 AM  
Thanks for all the good info. Guys


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