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The intake ports are shaped differently. There should also be different casting marks on them, but I forget what those marks are. I haven't done actuall 3rd gen wrenching for several years. Take a look through the FAQ sticky. There's a lot of information there that can help with this. Between the FAQ sticky and prelude3g.com, you can learn everything you want about 3rd gen Preludes.
 

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Discussion Starter · #22 ·
The intake ports are shaped differently. There should also be different casting marks on them, but I forget what those marks are. I haven't done actuall 3rd gen wrenching for several years. Take a look through the FAQ sticky. There's a lot of information there that can help with this. Between the FAQ sticky and prelude3g.com, you can learn everything you want about 3rd gen Preludes.
Okay gotcha. If I did end up having a b21 head on my b20a5, what headgasket would I use? I ordered a b20a5 88-89 one.
 

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As mentioned, you will need to get a B21 head gasket if you have a B21 head mates to a B20 head. People hv made the mistake of basing it off the engine block cylinder bore, but it’s the bore onthe head side that dictates in this case.

Do a search for “PK3,” I believe that’s the code for a B21 head, which I have.

FYI, I have a B21 head mates to a B20A3 block, which was the carbureted block. I used a B21 head gasket, and knock on wood, it’s been running fine for the past two years. Radiator level stays the same and the engine burn about half a quart every four thousand miles, not bad.
 

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@ttcheung97 is right. Match the head gasket to the head, not the block. And like he said, the casting marks I referred to in my earlier post are PK3 for b21a1 head. A b20a5 head would be marked with PK2.
 
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