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Penta swap questions

E

EmmitJSwan

New member
Joined
Jul 8, 2024
Hello!
I have been looking into swap options for my 91 940 turbo instead of building the b230 in it. Before you drop the ol ls swap in this thread, I already have an ls and want to do something different. I also have a b5234t3 that would be cool but I’m unsure of the complications of that swap. I’ve heard some people chatting about a penta 2.5l swap and am very curious about it. What is the power limits of these engine? How straight forward is the swap? Are there variations between the engines? Thank you!
 
OVERDRIVE said:
Any Penta motor you find will need to be rebuilt, if not just straight parted out and turned into soda cans.
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+1, unless you come across some NOS, never run Penta, they were almost all run at 5,000 rpm for several hundred straight hours and then put away wet after being on saltwater. It's very hard to find one that doesn't have a lot of cylinder head rot.

The swap itself is straightforward but what kind of power are you looking for? Even with the extra displacement, V cam and 531 head, an AQ151 is still going to make less power than even the stock turbo B230 in your current car.

Turn up the boost and you're knocking on the door to 200 horsepower.
 
fatcatbestcat said:
+1, unless you come across some NOS, never run Penta, they were almost all run at 5,000 rpm for several hundred straight hours and then put away wet after being on saltwater. It's very hard to find one that doesn't have a lot of cylinder head rot.

The swap itself is straightforward but what kind of power are you looking for? Even with the extra displacement, V cam and 531 head, an AQ151 is still going to make less power than even the stock turbo B230 in your current car.

Turn up the boost and you're knocking on the door to 200 horsepower.
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The scope of this project is much more than that. HE341, 1200cc injectors, and big cam. I’m building a big power red block and am just curious if they have anything nice in them. I’ve heard forged crank and pistons thrown around
 
My 2 2.5 pentas happen to be low hours, but by far I love my turbo 2.5l. The na swap is going to be starting next week in my GF's 242, easy and everything bolts in, it's great
 
EmmitJSwan said:
I’ve heard forged crank and pistons thrown around
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The 2.5 does have a forged crank, but it doesn't matter. The cast crank is strong enough for anything you're hoping to build. The rods are the same, the pistons are cast but have 3mm less compression height. I'd take a worked over 530 over a standard marine 531.
 
mopar318 said:
You have an LS swapped Volvo already? The original post did not make that clear. You aren't going to be happy with a b230 after a good running LS swapped car. 16 valve turbo cars are fun, though.
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Not to a Volvo but I’ve already done an ls swP
 
OVERDRIVE said:
The 2.5 does have a forged crank, but it doesn't matter. The cast crank is strong enough for anything you're hoping to build. The rods are the same, the pistons are cast but have 3mm less compression height. I'd take a worked over 530 over a standard marine 531.
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Are they 9mm or 13mm rods? They came with either the 531 or the 16v right?
 
Pietercc said:
My 2 2.5 pentas happen to be low hours, but by far I love my turbo 2.5l. The na swap is going to be starting next week in my GF's 242, easy and everything bolts in, it's great
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What do you have done? How does it feel compared to stock?
 
EmmitJSwan said:
Are they 9mm or 13mm rods? They came with either the 531 or the 16v right?
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Depends on the year for the rods, though they are the same rods as the 2.3L b230, so you can swap them. Mine had the 9mm but I swapped them for 13mm. I did a LH2.4 swap at the same time, with chips, and going down the drag strip with stock boost it went as fast as my car last year with 10-11psi. Now with the SAAB apc hooked up again if I hit 10-12psi it makes enough power to slip the clutch in 4th. At stock boost I was as fast as @AnthonyHardy2 and his t6 swapped 242 (though badly tuned) running more boost. Once I get an M90 I plan throwing a 19t in with a modified apc pushing 16psi. My expectations for the NA are for it to have 160 With a slightly decked head and t cam (since it will have an auto behind it), maybe a bit more. The 531 from my turbo car went to @spock345 as it had a burnt valve, but the 531 on the NA is clean enough to use in an NA application.
 
Pietercc said:
Depends on the year for the rods, though they are the same rods as the 2.3L b230, so you can swap them. Mine had the 9mm but I swapped them for 13mm. I did a LH2.4 swap at the same time, with chips, and going down the drag strip with stock boost it went as fast as my car last year with 10-11psi. Now with the SAAB apc hooked up again if I hit 10-12psi it makes enough power to slip the clutch in 4th. At stock boost I was as fast as @AnthonyHardy2 and his t6 swapped 242 (though badly tuned) running more boost. Once I get an M90 I plan throwing a 19t in with a modified apc pushing 16psi. My expectations for the NA are for it to have 160 With a slightly decked head and t cam (since it will have an auto behind it), maybe a bit more. The 531 from my turbo car went to @spock345 as it had a burnt valve, but the 531 on the NA is clean enough to use in an NA application.
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I'd be surprised if the NA 2.5 hits 160hp. I am guessing 130-140 and about the same torque assuming everything is in tip top shape. Which is a pretty sweet spot to be in for daily transport in a 240.
 
Pietercc said:
Depends on the year for the rods, though they are the same rods as the 2.3L b230, so you can swap them. Mine had the 9mm but I swapped them for 13mm. I did a LH2.4 swap at the same time, with chips, and going down the drag strip with stock boost it went as fast as my car last year with 10-11psi. Now with the SAAB apc hooked up again if I hit 10-12psi it makes enough power to slip the clutch in 4th. At stock boost I was as fast as @AnthonyHardy2 and his t6 swapped 242 (though badly tuned) running more boost. Once I get an M90 I plan throwing a 19t in with a modified apc pushing 16psi. My expectations for the NA are for it to have 160 With a slightly decked head and t cam (since it will have an auto behind it), maybe a bit more. The 531 from my turbo car went to @spock345 as it had a burnt valve, but the 531 on the NA is clean enough to use in an NA application.
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Did you resurface the flywheel? What clutch
 
spock345 said:
I'd be surprised if the NA 2.5 hits 160hp. I am guessing 130-140 and about the same torque assuming everything is in tip top shape. Which is a pretty sweet spot to be in for daily transport in a 240.
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Carbed they are rated at 146. I figured tunned fuel injection and a mill of the head could at 15 HP. But that's me being wishful.
 
Pietercc said:
Carbed they are rated at 146. I figured tunned fuel injection and a mill of the head could at 15 HP. But that's me being wishful.
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Also consider that it is gonna be a bit worn and some of that power will have escaped over the years.

What EFI really is gonna get you is more usable power. I always read the old reports of EFI or mechanical injection making 10-20hp more than the carbureted versions of cars is because it is much more efficient, more closely maintains stoichiometric mixtures, and therefore can pass emissions with a better tune on it. With the boat motors they didn't quite care as much about passing emissions testing.
 
An untouched 160 and a T cam with 9% more displacement might get you a couple of hp's more. Increasing the CR might also bump it up a little. With more pumping volume, it will make peak power lower than the same top end on a 2.3.
 
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