• Hello Guest, welcome to the initial stages of our new platform!
    You can find some additional information about where we are in the process of migrating the board and setting up our new software here

    Thank you for being a part of our community!

Penta 2.5L B21ft?

swedishK

Design by Beefsma
Joined
Sep 10, 2008
Location
Soldotna, Alaska
I might have a line on a cheap aq151 possibly two, and was wondering if I?d run into any issues swapping the 2.5 block into my turbo kjet wagon. I?ve seen b230 heads on 2.1 blocks, so I?m assuming they?d go the other way as well? Will a mildly modified turbo kjet fuel system be adequate to keep up with 400 extra CCs? The motors have been sitting outside on a pallet for a bit, and will probably need a full rebuild. Is the extra displacement worth the effort?


Now I?m unsure if they?re actually 2.5 blocks. One has a 531 head and the other has what appears to be a 405. Both single carb. I did not see any AQ designation on the ID tag by the starter, however both tags start with the prefix 250A.
 
Single carb penta will have the A cam. The AQ151 is the 16V penta. You are looking at two types probably a pre B230 block one with the 405 head and a B230 based one with the 531 head. I think they may have also called them AQ130 or AQ131.

You may have to drill some holes for a sensor or two. But the block and head would work for a buildup. Or you could use the heads if they aren't engines with the longer crank throw. Make sure you check that number four exhaust port. My penta sourced 531 needed a good bit of welding to repair it from corrosion.
 
Single carb penta will have the A cam. The AQ151 is the 16V penta. You are looking at two types probably a pre B230 block one with the 405 head and a B230 based one with the 531 head. I think they may have also called them AQ130 or AQ131.

You may have to drill some holes for a sensor or two. But the block and head would work for a buildup. Or you could use the heads if they aren't engines with the longer crank throw. Make sure you check that number four exhaust port. My penta sourced 531 needed a good bit of welding to repair it from corrosion.

AQ151 is the 8 valve 2.5 liter stroker engine, essentially an early 250A. The AQ171 is the 16 valve 2.5 liter stroker, which became the 251A. In the early years, the number was the horsepower the engine provided. Case in point, the AQ255 V8 engine was not a 4.2 liter V8, but a Chevy 350 smallblock.
 
Probably the most valuable part on those is the crankshaft, they would both be rear thrust and forged steel and stroking on the shaft rods are stock, pistons have shorter crown for longer stroke. Should be able to get the crank out easily enough. Hard parts can be the boat exhaust manifold, but even if you break the bolts, still will come off. Basically you need to get the head off if you wanna put the short block in your car. All the boat motors I've ever had where like new inside, real clean. I've never seen a volvo penta redblock boat motor that had salt water running through it. They use a closed coolant system with a heat exchanger. The salt water would run through the exhaust manifold. That is the hardest part to take off, but if you don't need head, you can take off the head with the manifold still attached and just toss it. Cam should be a V cam, but all 250's I've seen had dual carbs and you said these only had single carbs, might be A cam then.
 
AQ151 is the 8 valve 2.5 liter stroker engine, essentially an early 250A. The AQ171 is the 16 valve 2.5 liter stroker, which became the 251A. In the early years, the number was the horsepower the engine provided. Case in point, the AQ255 V8 engine was not a 4.2 liter V8, but a Chevy 350 smallblock.

250c and 251c are all late rear thrust engines
 
Back
Top