318 build with dyno session

Stock stroke or 4" stroker?

  • Stock stroke 318

    Votes: 48 88.9%

  • 4" stroker 318/390

    Votes: 9 16.7%
  • Total voters
    54
  • Poll closed .
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NC Engine Builder said:
And this is another sorta "psa" post, it's been discussed many times, that the 318 and 340 main caps are the same. They are NOT! they will interchange, but 340 caps are taller, and have more material around the bolt holes. Hes a few pictures to show the difference. Rodney's 318 caps on the right, '71 340 caps on the left

View attachment 1716399345
Click to expand...
That shows the difference pretty clearly. Doesn't look like much, but apparently the engineers thought it was important enough to justify additional molds and machining setups. That costs money and speaks volumes to the importance of the difference in parts, because they didn't do anything to add cost without a pretty good reason. Personally, I don't think you would get into trouble until you are over 500hp with 318 caps, but I have no proof.

Do you happen to have a set of 360 caps handy to see how they compare to those two? I know the bearing bore is larger, but I'm curious how much more or less meat there is in the web because of that. There are some pretty stout 360/408 motors out there an nobody ever mentions worrying about the main caps, outside of the supposed 600hp limit for stock blocks.
 
gzig5 said:
That shows the difference pretty clearly. Doesn't look like much, but apparently the engineers thought it was important enough to justify additional molds and machining setups. That costs money and speaks volumes to the importance of the difference in parts, because they didn't do anything to add cost without a pretty good reason. Personally, I don't think you would get into trouble until you are over 500hp with 318 caps, but I have no proof.

Do you happen to have a set of 360 caps handy to see how they compare to those two? I know the bearing bore is larger, but I'm curious how much more or less meat there is in the web because of that. There are some pretty stout 360/408 motors out there an nobody ever mentions worrying about the main caps, outside of the supposed 600hp limit for stock blocks.
Click to expand...
360 caps are significantly bigger, with a wider bolt spread
 
Always liked the 340 everything is beefier. When yammering back and forth with 318 guys I used to say "you have to take both apart and lay things side by side and compare then you'll appreciate the 340...?
 
It's a 236/242-.502/.511 on a 110, solid flat tappet. I'll be using 1.6 rockers however, which would provide a theoretical lift of .536-.545 minus the lash, and the lift loss from the poor pushrod angle.
 
Nice, a little more duration and a bit less lift than mine ( Howards SFT 230°@0.050" .574" theoretical lift with 1.6 rocker, 110LSA).
Your dyno results will help me settle on the stall speed for the convertor.
 
Dartswinger70 said:
Always liked the 340 everything is beefier. When yammering back and forth with 318 guys I used to say "you have to take both apart and lay things side by side and compare then you'll appreciate the 340...?
Click to expand...
Just don’t get in that same discussion with 360 guys!
 
But us in the peanut gallery are impatient. Us loafing freeloaders paid good money to find out lol. No worries brother. Was just curious
 
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