Ford Muscle Cars Tech Forum banner

Long rod 302

18K views 51 replies 22 participants last post by  Helmantel 
#1 ·
I'm looking for info on a long rod 302. I'm shooting for a 1.76 r/s ratio. I was thinking of using 351 rods to keep the price down. But from my limited searching so far it's looking like no matter which way I go it'll cost a few dollars. BTW it'd be a budget motor. Maybe gt40 heads, and flat-tops.
 
#52 ·
Here's a comparison the influence of rod lengths on a 302 with a compression ratio of 10. As you can see, the shorter rod moves away faster from TDC. The pink line shows the larger volume (cylinder + combustion chamber) of the short rod engine during the expansion stroke, while the red and blue lines show piston travel of the short and long rod respectively. The peak of the pink curve is closer to TDC than the max difference in piston travel, because the relative influence of the difference is larger when the volume is smaller.

The theory that long rods work better with smaller ports can be explained from this graph. The short rod increases the volume faster and small ports could possibly be a restriction for a rapid volume change. However, it's all very minimal, even with a rod length that would never even fit a 302.

The whole "dwell" story that always comes up is just confusing, IMO. Many people make it sound like long rods let the piston "rest" at TDC for a while, but in reality the difference between long and short rods is very small around TDC, but becomes largest around 90 degrees after or before TDC. That is not to say that the smaller differences around TDC have no influence. I guess it also depends on your definition of "around TDC".



<font size=-1>[ This Message was edited by: Helmantel on 4/21/05 4:08pm ]</font>
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top