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
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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.
 
But us in the peanut gallery are impatient. Us loafing freeloaders paid good money to find out lol. No worries brother. Was just curious
 

middleagecrisis said:
Have you had any time to work on the 318? This is exactly why I'll never do a build thread, too much life happens between updates!
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I have the shortblock complete and the cam degreed in, but am currently sidelined doing customer work. The project will continue, as soon as I get caught up
 
A minor update, I believe I might use a set of the new AFR heads on this build rather than the speedmasters. Got a couple sets here, and would be run strictly out of the box.
 
NC Engine Builder said:
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.
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This solid worked exceptionally well in a flat top small block. Good luck with your build.

image.jpg
 
Illahe said:
What do you believe that the 318 caps are good too, Hp/Torque. Considering set of aftermarket caps and a line hone may kill a budget build.

Additionally, some builds list GM 6.2" con rods, but I thought they were wider than Chrysler 6.125" con rods at the journal.
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That's a good question, but the caps wont be any problem on this build, as it is pretty mild.
 
Progress has been slow, due to a bunch of customer work, but "rodney" is finally assembled, and primed. Hope to test run and break in the cam this week.

20250722_112352.jpg
 
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