GM 3.8 litre v6 specifications

[powerabout]

Originally Posted by DCockey

Even fire vs odd fire is only affected by the crankshaft geometry, not the block. The original Buick V6 was essentially 3/4 of a V8, and the V6 used a crankshaft with shared rod bearing journals, the same as a V8. The rods for opposite cylinders shared a common journal on the crankshaft which resulted in uneven firing intervals. Around 1977 GM changed the crankshaft to one with offset journals so that the firing intervals were even.

The bore offset in the earlier engines was relatively small, 5 mm or so, and may not have been very noticeable.

The bore offset would be the thickness of the conrod and for US engines left bank forward
The only engine I know that has right bank forward is/was the Holden 253/308 as purpose built for right hand drive cars

( not imposible to build and engine without an offset but why would you you would have the rods not centered in the pistons and need offset rockers to get to the pushrods or do OHC and share big ends like a Rolls Merlin)

[DCockey]

Originally Posted by powerabout

The bore offset would be the thickness of the conrod and for US engines left bank forward
The only engine I know that has right bank forward is/was the Holden 253/308 as purpose built for right hand drive cars

( not imposible to build and engine without an offset but why would you you would have the rods not centered in the pistons and need offset rockers to get to the pushrods or do OHC and share big ends like a Rolls Merlin)

Different bore offset.

The bore offset of the early Buick V6's which has been mentioned was an offset of the cylinder centerlines relative to the crankshaft centerline such that the cylinder centerlines did not intersect the crankshaft centerline.

[powerabout]

Originally Posted by DCockey

Different bore offset.

The bore offset of the early Buick V6's which has been mentioned was an offset of the cylinder centerlines relative to the crankshaft centerline such that the cylinder centerlines did not intersect the crankshaft centerline.

thanks for the info
next question, why did they do that?
trying to fix the vibration or something?

[DCockey]

I know of two reasons given for offset bores. One is packaging internally within the engine. The other is so that the expansion strokes take longer than the compression strokes. The benefits of the latter are small, and on a V engine would require cylinders to be offset asymmetrically. Offsets of the magnitude generally used would have only a small to negligable effect on engine vibration.

The Buick V6 geometry goes back to the Buick aluminum 215 cubic inch V8 which was introduced in the 1961 model year and designed around 1958. My guess, and only a guess, is the cylinder banks were offset outwards to provide more space in the engine "valley".

[srimes]

Y'all are confusing engines here. The Buick 3.8 v6 is COMPLETELY different from the GM 3800 (series 2). Yes they're bot v6 engines that displace 3.8 liters, and they came in Buicks, but that's it. The 3.8 is a 90 degree motor, and the 3800 is 60 degrees.

The 3800 is great. Compact, powerful, light. Great motor.

[DCockey]

Originally Posted by srimes

Y'all are confusing engines here. The Buick 3.8 v6 is COMPLETELY different from the GM 3800 (series 2). Yes they're bot v6 engines that displace 3.8 liters, and they came in Buicks, but that's it. The 3.8 is a 90 degree motor, and the 3800 is 60 degrees.

The 3800 is great. Compact, powerful, light. Great motor.

The 3800 is a 90 degree, pushrod V6. It was directly developed from the early 3.8 Buick V6.

You may be confusing it with one of the other 60 degree V6 engines GM has built.

[srimes]

Ok my bad. It is a 90 degree block, but it uses the 60 degree bellhousing. That's where I got confused. Pretty much everything is different from the older ones (parts don't swap).