| quote | Originally posted by MadMark:
The lower in idle speed you go the worse it will get with the 3800 SC, since the firing is not equal due to the way the crank is made and the 90 degree of the cylinders.
So you can increase the idle some, but you will always have the lumpy idle with the 3800. |
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Sorry, but that's not true.. Some of the old 3.8 buick motors were odd-fire, but for the last 30 years they've been even fire.
Both the 3800 series II's and the 60 degree V6's fire every 120 degrees of rotation. In the 60 degree motors, the crank pins are separated by 60 degrees, and in the 90 degree motors, the crank pins are splayed 30 degrees.
From a smoothness point of view, the 90 degree motors actually have 2 advantages in that they have a balance shaft, and the 90 degree banks help cancel secondary harmonics.
My 3800 NA is on an 88 cradle (solid mounted), poly engine mounts, and with a poly dog bone. With the idle set to 940ish, it's got a bit of vibration at idle, but not bad, and once you're over 1300 RPM it's smooth as butter. Perhaps the vibration is somewhat due to the fact that you're running an auto and there is more load on the engine at idle.. Try upping the idle speed a bit.
Edited to add pics:
60 degree crank (notice the separation between 1-2, 3-4, 5-6 pairs)
3800 crank:
Notice that the crank is shorter and the 1-2 pairs have a 30 degree difference but no space b/t them. This in my opinion is why the 3800 bottom ends are so strong.

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Build thread for my 88 + 3800NA swap[This message has been edited by aaronkoch (edited 08-22-2013).]