3.1 to 3.4 top conversion - Buick Forum - Buick Enthusiasts Forums


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Old 09-20-2012, 03:50 PM
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Default 3.1 to 3.4 top conversion

Ok my cousin has a '99 3.1 Century and it is leaking from the rear headgasket on the passangers side. Since i have to tear it down for him anyway a local guy from a local forum has a 3.4 from the heads up that i can have for $100 with all sensors and everything minus i think the valve covers. Anyway what else would i need to convert and is it really a bolt on mod and is it even worth it? if so i'll have him pick up the parts and we will do the swap. I assume i'd need a 3.4 gasket/bolt set or would i do a 3.4 gasket set and get 3.1 bolts? just looking for some direction as to what the swap would entail and tricks/tips. Appreciate any help i can get guys thanks
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Old 09-20-2012, 04:14 PM
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also the top came from a Buick crossover
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Old 08-11-2013, 10:45 PM
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im subscribing to this thread to see what the end project will be, sounds good and will be different if no major mods needed other than the aforementioned parts
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Old 12-10-2013, 12:39 AM
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$100 not including labor is not a bad deal so long as the heads don't need any work done. 3400 heads will fit that year L82 motor as the 2000 and up LG8 Century shares heads with the 3400 engine(reason you see the small HP jump). The 3500 heads won't work on the 3100 block but 3500 upper and lower intake manifold will work on the 3400 heads. The L82 3100 UIM/LIM besides the throttle body will be useless as it won't bolt up to the 3400 heads. You may want to recycle the throttle body for the linkage for LG8 and LA1 are difrent.


Best UIM/LIM and throttle body is the ones found in the LA1 Impala with 00 stamped on the lower intake manifolds in top left and bottom right corners. Worst would be the alero as they have a design flow that slightly leans out 2 cylinders. The ones in the SUV and van are also not that great. If you aren't too pressed on getting another UIM/LIM from a JY then you should still be fine. Valve covers should still fit. Just be careful of cheap head gasket kits and UIM/LIM kits so you aren't back in there again. Head bolts should also be the same.

Picture below has UIM of Alero on top and Impala on bottom

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Last edited by Merc6; 12-10-2013 at 12:42 AM.
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Old 04-02-2015, 09:45 AM
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I may be totally off base here but isn't that kinda similar, if not the same, to making it like a "rocket" type engine? Or the start of it anyways?
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