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290 outdrive fitment

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basspro207

New member
I have a 1970 307 ci GM mouse motor bolted to an OMC "stringer" set-up. I have just purchased a 1989 Imperial boat with a 4 cyl volvo with a 290 outdrive. Will I need a different "bell housing" for my GM in order to bolt up the 290? I know I will need to remove the old stringer and glass in the transom to prep for the 290 outdrive. Thank you!
 
You've got some work cut out for yourself, but you are certainly on the right track if you love the boat.
You'll need the following:
1.61:1 ratio lower unit.... the 2.15:1 4 cylinder lower will not work no matter how many props you try. Trust me!
Volvo Penta GM V-8 flywheel cover (bell housing in the auto world).
GM V-8 exhaust Y pipe.
AQ series Volvo Penta style exhaust manifolds and risers.
95mm exhaust hose.
Engine mounted sea water pump.
GM V-8 front engine mounts.
Morse 33C throttle and shift cables.
Throttle/shift unit that is 33C capable.

The 4 cylinder transmission is the same gear reduction... so no issues there.
 
Ricardo,
Thank you so much! The guy is giving me my money back for the boat with the 4 cyl. package. I will look only for a gm V-8 block from now on. Could you explain to me why at first you say the 2.14:1 ratio won't work but then say later that "The 4 cylinder transmission is the same gear reduction... so no issues there." Are they not the same? What are you calling the transmission? Is it the ratio of the gears in the "bullet" that is 2.14:1 and the transmission located in the upper housing? This is my first dealings wuith these outdrives and ratios and such. Sorry to seem like such a dummy. Lastly, if I stay with only a v8 package, do I definately need the 1.61:1 or are there otheres that will work if propped correctly? Where can I find the ratio on the outdrive?
Again, thank you so much for your input
 
basspro207 said:
Ricardo,
Could you explain to me why at first you say the 2.14:1 ratio won't work but then say later that "The 4 cylinder transmission is the same gear reduction... so no issues there." Are they not the same? What are you calling the transmission? Is it the ratio of the gears in the "bullet" that is 2.14:1 and the transmission located in the upper housing? This is my first dealings wuith these outdrives and ratios and such. Sorry to seem like such a dummy. Lastly, if I stay with only a v8 package, do I definately need the 1.61:1 or are there otheres that will work if propped correctly? Where can I find the ratio on the outdrive?
Again, thank you so much for your input
Click to expand...
It's all pretty much there in my first post.

Transmission = upper unit.
This is where the gear selection is made. With exception to the DP E transmission, all AQ series transmissions are of the same reduction.
This means that you can use a 4 cylinder transmission behind a V-8 and visa-versa.

Lower unit = the lower unit, or the bullet section as you called it.
Yes, this is where the "Over-All" ratio change occurs with this drive.

Ratio vs prop change! NO.... prop thrust dynamics do not usually allow for a prop pitch change to correct an incorrect ratio.
The engine determines the over-all ratio.
The 4 cylinder ratio is the 2.15:1 refered to as the D in a PZNR #
The V-8 ratio is the 1.61:1 refered to as the B in a PZNR #
There is also a 1.89:1 ratio refered to as the C in a PZNR #, and was used for the old inline 6 cylinder engine and for some V-6's.

If you remove the propeller and remove the ring anode, the ratio will be stamped into the aluminum prop shaft bearing carrier.
Wire brush the area, and it should expose the numbers.
This number will be good if no one has changed the gear set and forgot to re-stamp the carrier.

.
 
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