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AQ170 repower?

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keithskinner77

New member
Hello, I have twin AQ170's with volvo 280 outdrives. I went through the motors that have not been on the water in many years and with the help of some new stuff got them running what i thought was well until i hit the water then neither really wanted to run well or right. I know the history of these engines and parts and such. I have a whole other spare engine as well. These motors have a little over 500 on one and 600 hrs on the other. I am at an impass as to what to do with this boat this winter. I am debating getting these running but between the three carbs and the distributor i am not sure if i want to continue to mess with it. I am thinking about repowering with a chevy 4.3l due to the abundance of parts. Anyone have an idea as to what would be involved to do this? Obviously the exhaust has to be redone and possibly the mounts but what else or is it even possible? What power plants will bolt directly to a 280 outdrive without a bunch of making things work? Any info would help. Thanks in advance.
 
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keithskinner77 said:
Hello, I have twin AQ170's with volvo 280 outdrives. I went through the motors that have not been on the water in many years and with the help of some new stuff got them running what i thought was well until i hit the water then neither really wanted to run well or right. I know the history of these engines and parts and such. I have a whole other spare engine as well. These motors have a little over 500 on one and 600 hrs on the other. I am at an impass as to what to do with this boat this winter. I am debating getting these running but between the three carbs and the distributor i am not sure if i want to continue to mess with it.
I can't say as I blame you.

I am thinking about repowering with a chevy 4.3l due to the abundance of parts. Anyone have an idea as to what would be involved to do this? Obviously the exhaust has to be redone and possibly the mounts but what else or is it even possible?
For one thing, the engine mount stringers would need to be re-done as to accommodate the side engine mounts.
See below as well.


What power plants will bolt directly to a 280 outdrive without a bunch of making things work? Any info would help. Thanks in advance.
Most any engine that Volvo Penta used (in the AQ series), will work with a 280 drive.
If you are not after speed, any of the OHC 4s would work.
If you are after more speed, then you would want to use the 4.3L or 5.0L or 5.7L GM SBC.
The 335 series Ford (302 or 351 W) would also be a candidate.

However, you would need to check the center-to-center dimension between the stern drives for a V engine, since these engines will require a greater distance due to the width of the engines.

For a V engine, (since you have the single exhaust relief transom shields), and only if the center-to-center dimension allowed, you would need two of the AQ200B or AQ225B exhaust Y-pipes.

The 280 transom shield will allow the use of any AQ series flywheel cover (bell housing in the auto world).

Also, for a V engine, the lower gear unit would change from the 1.89:1 to the 1.61:1.
For the OHC 4, the lower gear unit would change from 1.89:1 to 2.15:1.

I would start with the center-to-center dimension.
Click to expand...
 
Thank you for the info, i know the motors will fit it will be tight but they will fit. And the exhaust should be fairly easy to figure out and hook up. My main concern is bolting the flywheel up to the outdrive and what may be needed to do this properly. Cant find any examples of someone doing this.
 
keithskinner77 said:
I have also read that the 1.89 gear ratio is okay to use with the 4.3l. Is this not the case?
Click to expand...
Willing to bet this works with a possible step up in pitch on the prop. Slightly different animal but I swapped a mercruiser 4.3 for a 5.0 in a 21 ft bowrider, kept the V6 ratio 1.81 drive ended up going from a 19" to 21 " pitch prop works just fine. I got a lot of advice that a gear change would be required, and I don't think you can prop your way around 2-3 gear ratio "steps" but one gear step seemed to work in my experince. That would fit that the gear ratio steps allow manufactures to keep props within the typical 17"-21" range (15-23 in some cases). Seems like each step is roughly 2" in pitch... only my observations.
 
keithskinner77 said:
Thank you for the info, i know the motors will fit it will be tight but they will fit. And the exhaust should be fairly easy to figure out and hook up. My main concern is bolting the flywheel up to the outdrive and what may be needed to do this properly. Cant find any examples of someone doing this.
Click to expand...

The engine's flywheel cover (bell housing in the Auto world) is what will mate up to the transom shield.
You can use the V8 flywheel cover on the 4.3L engine.
keithskinner77 said:
I have also read that the 1.89 gear ratio is okay to use with the 4.3l. Is this not the case?
Click to expand...

For a single engine application, the 1.89:1 would work.
For a twin engine application, you would most likely need the 1.61:1.


We can never prop ourselves out of an incorrect drive reduction.



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Last edited:
RicardoMarine;662133[COLOR=#0000ff said:
We can never prop ourselves out of an incorrect drive reduction.



.[/COLOR]
Click to expand...
Respectfully, in the real world example I gave I did just that. Boat performs perfectly and hits the cirrect WOT rpm.
 
Respectfully, in the real world example I gave I did just that. Boat performs perfectly and hits the correct WOT rpm.
Click to expand...


OK....... respectfully, allow me to rephrase that:

"we can never ultimately prop ourselves out of an incorrect drive reduction!"

From an engineer's perspective:
The hull determines the required engine hp/torque.
Once selected, the engine determines the final drive reduction.
Once that is selected, the way in which the boat is loaded helps determine the best prop pitch/diameter.

Operating altitude can be another factor.


As for the OP here, if he was running a single 4.3L, he could most likely use the 1.89:1 or the 1.61:1, depending on hull size.

Since he's going with twin 4.3Ls, I would suggest the 1.61:1 reduction.


That said, he could certainly give the 1.89:1s a try.




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