Can I replace my tired OMC 3.8L V-6 with a Chevy 350

[Johnqpubiam]

Will a mid 80's Chevy 350 bolt up to my '85 OMC Selectrim 3.8L V-6 outdrive? Is the bolt pattern the same? Thanks.

 

[Bondo]

Re: Can I replace my tired OMC 3.8L V-6 with a Chevy 350

Is the bolt pattern the same?

The engine's bellhousing flange IS the Same,.........<br />But,..........<br />That's the ONLY Thing that's the Same,.........<br /><br />So,.....<br />The Answer to your underlying Question is,..........<br />NO,..... You Can't just bolt in a V8,+ Go........<br /><br />It Won't Work........

 

[Johnqpubiam]

Re: Can I replace my tired OMC 3.8L V-6 with a Chevy 350

I realize the motor mounts, exhaust, etc., needs to be changed to adapt the larger motor, but is there something that I don't't see (until I pull the motor) from the flywheel back that won't allow for a conversion? Thanks.

 

[jimmbo]

Re: Can I replace my tired OMC 3.8L V-6 with a Chevy 350

is the 3.8 a Buick engine or a Chevy? Bolt patterns on the bell housing are different.

 

[Lou C]

Re: Can I replace my tired OMC 3.8L V-6 with a Chevy 350

Looking at www.dougrussell.com in the OMC parts diagrams section, I see they used both the 3.8 and the 4.3 in 1985. Now if I recall right, the 4.3 is a cut down Chevy 350, and the 3.8 was a cut down Buick 350. However, I also seem to remember that Buicks had the distributor in the front, whereas the diagram for the 3.8 shows it in the back, like all the Chevy small blocks. I'd check to see if both engines used the same part # for the bellhousings, but even then it is not a guarantee that it will all fit. It is almost always easier to replace what was there to start with, because you also have to deal with the exhaust system, Y pipe, etc.

 

[Bondo]

Re: Can I replace my tired OMC 3.8L V-6 with a Chevy 350

If the Dist. is in the Rear of the motor,.....<br />It's a Shortened 305 Chevy..........<br /><br />If the Dist. is in the Front of the motor,.. It's a Buick,+ Nothing is going to Fit.........

 

[whywhyzed]

Re: Can I replace my tired OMC 3.8L V-6 with a Chevy 350

OMC quit using the Buick V6 in 1974. <br />But, back to the question: - Your V6 outdrive ratio is 1.71:1, a 5.7 V8 powerplant requires a ratio closer to 1.5:1 in order to keep you in a viable prop pitch range (17 to 21 inch pitch).<br />Unless your 3.8 is in a 3 ton boat or something, you'll need to change drive ratios.<br />An aftermarket gearset for re-ratio is about $1200. Add another $500-800 for labour to swap and preload bearings (very specific and expensive OMC shimming tools required).<br /><br />If you DO go V8, you may need to get the rear-riser OMC manifolds or else there may be clearance issues with the selectrim hydraulic rams.