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Penta Faq

woodywhat said:
can 13mm rods be fited to replace 9 mm rods without changing the crank? do squirters need any crank mods or oilpump change? i have a aq171a and several 93+ parts is it viable to build a 16v 13mm squirter setup with the aq171a crank? ive head that mitsubisi rods and cranks can be modified to fit b23 blocks, dose anybody know witch models the parts come from?
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anyforseeable problem with an aq171a motor with 13mm rods and penta pistons and 8v kjet ,na in a 242 with m47s2 as a d/d or will the stock clutch fail/motor fail/run lean or somthing i havent thought off?
 
woodywhat said:
anyforseeable problem with an aq171a motor with 13mm rods and penta pistons and 8v kjet ,na in a 242 with m47s2 as a d/d or will the stock clutch fail/motor fail/run lean or somthing i havent thought off?
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K-jet with a 16v swap:omg: Why not use B234 LH2.4 or MS?!
 
sbabbs said:
My 1987 AQ171C has rear thrust. The A B and C is the key, A and B center thrust, C rear thrust same as 90 plus B230's. The 250's are also rear thrust as they changed to that naming about 1990. So any 151C or 171C or 250 has the 2.5L stroker crank and rear thrust.

I've read that the Penta blocks(Super Marine) might possibly be thicker cylinder walls(Like the R sport blocks). Way to check is measure the depth of the hole in the front of the block with the water pump off to the cylinder. If the hole is not as deep on the penta block, then it's got a thicker cylinder wall and can be bored out more.
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Thanx Sbabbs!

If i understand correct i can buy these parts and they will fit in my '93 B230 block.
 
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Ruben said:
K-jet with a 16v swap:omg: Why not use B234 LH2.4 or MS?!
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decided to go 8v when i looked at penta 16v head as it needs serious reco. plus the car is k-jet already and ime just looking to do a quick motor/clutch/gearbox change to see how it will be different. ime also looking for a 3.31 diff {rare as in oz} to see if the xtra stroke will improve fuel figures.
 
I went from a 2.3 to the penta 2.5 in my old 242, and torque increased dramatically. I actually ended up with n xntrx's penta bottom end, 90+ with squirters, for the rsi pistons and rods and used a stock 8v head with the ipd turbo cam, and a t3/t4 turbo. Mileage just depends on how youve got it tuned, your gearing, how you drive...i wouldnt expect to see an increase or decrease in the cruise state, however...if there is a difference it will go down theoretically to compensate for the displacement. If i did it over again? 2.5l all the way, no doubt, worth the 3mm stroke, hands down!

Mark
 
B230 w/DOHC head

The b230 in my 1992 940 is a slant 4 cylinder. Adding the b234 head is not what I want to do. Were the earlier (1988 +/-) 740 B230 blocks upright? which 740 motor will take the 86 mm penta crank?
 
Been browsing this thread for a couple of days. From what I can see, there is no shorter 'stock' rod out there that will allow a stock piston to be used with the 2.5 crank, correct? For a 16v setup, better to find a set of 2.5 rods and pistons and cut the reliefs.
 
The OHC redblocks were never upright, but you can convert them to upright mounting using the sump from a OHV (B18, B20, etc) redblock...and presumably custom mounts...maybe OHV mounts?

Any B200/230 redblock (and perhaps the older B19/21/23s? I don't know the bearing sizes...) will take the 86mm crank, but you need to match the bearing size / layout of your crank to the correct block. The earlier ones (85-87?) had smaller mains, and the thrust bearing was at the rear*. The later ones had larger mains and the thrust at the centre*. That's true for both the marine and automotive blocks, both in 80 and 86mm stroke guise. I've had 86mm cranks of both type in the past.

* I might have those back-to-front.

That's right David - the stock rods are all the same length, it's the pistons which are different. You *could* use a shorter rod, but a standard (or longer-than-standard) rod and a shorter pistons is a more desirable solution; to achieve a better rod-to-stroke ratio. The redblocks have honking huge pistons by modern standards as it is, so the opportunity to improve that situation should be grasped with both hands, IMO.

cheers

James
 
So here's the next question for the stroker brain trust: Can you notch 2.5 pistons for 16v head reliefs? Is there enough meat up there? Are the 2.5 slugs actually 3mm shorter, or is the piston pin higher? Anybody know?
 
If this is a concern why not just find the 171c bottom end?. I would imagine with the wrist pin being that much higher it would be a big concern. I'm no expert and this same question has crossed my mind as well.
 
I had a feeling I had it back to front...sorry!

Pass. I was under the impression that they shaved 3mm off the top of the piston, and I share the concern about there being enough meat left for "notching".

cheers

James
 
I bought one for $600 that only had 150 total hours on it. 1987 Penta AQ171C rear thrust. I sold the pistons to Norway...

I might have a pic. I'll look tomorrow.

Simon
 
Yeah, the 171(c or d) is the 2.5 16v. The 151 is the 2.5 8v. That came in a, b, c and d flavours. You only got the early-style cranks in the 151s (a and b versions, I think).

cheers

James
 
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