repowering with 5.7L twins

[octowood]

I am repowering my boat, It has aq171 engines with 290 outdrives, I have bought twin
5.7 L engines for the project. I keep getting conflicting answers about whether the outdrives
will work. Any input would be appreciated.
Thanks

 

[RicardoMarine]

First...., double check the center-to-center spacing of the two AQ171's as to make sure that the 5.7L's will fit correctly.
This should be close to 33" or so, center-to-center.

Secondly........., your lower units will need to change from 2.15:1 to 1.61:1. No substitutes, unfortunately.
The transmissions will work just fine!
I believe that the 290 transom shields will accept the V-8 Y-pipes.
There should be no issues with the V-8 Flywheel Covers.... just make sure that the PDS splines are "fine spline".

Thirdly....., I'd suggest steering clear of replacement SBC engines that would be using the full dished pistons.


Your throttle cables (at the engine) will now Pull, rather than Push!



Have fun..... good project!

Edit:
If the spacing would pose a problem, and if your AQ171's are good, have you considered the Duo Prop lower unit addition?
This would require the 2.30:1 ratio, and are generally a bit less expensive on the used market (tougher ratio to sell).
The performance gain for a V-8 can be 25% to 35%..... and is not quite as great for the 4 cylinder engines, but none-the-less, there is a gain.
Food for thought perhaps!

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