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Old 11-22-2021, 06:52 PM   #1
The Holiest Man
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Default Advice: B21f / 530 Head +T build

Greetings, friends
I have a small project I'm working on, and figured I would heed the advice of the elders who have done this before me.
I pulled the 57k mile B21f out of my '78 242, I have a slightly ported 530 head that I would like to put on it, then +T it.
From the information I've found scattered across the internet, I've learned that the CR is 8.5:1, making this a good candidate for boost. My questions are:

1.) Would the stock rods and pistons be capable of holding 20-25 PSI?
From what I'm finding on previous threads, I'm seeing some people say they have, and it's no issue since the pistons are cast from the factory, but I'd like to make sure again.

2.) Head gasket. I've seen a lot of debate over which headgasket to use in this instance. From what I understand, a Cometic B21f MLS head gasket is that way to go. I'm seeing on their website that they come in a variety of thicknesses. Does anyone have input on what the "best" thickness would be, for my application? I'll be the first to admit that I do not know all the science between headgaskets and CR, I just know that it changes it.

Those are probably my 2 biggest questions as of right now. I'm sure more things will come up in the future, I'll update the post as needed.

OR

Do I not make things unreasonably difficult for myself, and just find a late model B230ft, swap my nice head onto it, and plop it in and call it a day?

Cheers!

Last edited by The Holiest Man; 11-22-2021 at 07:00 PM..
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Old 11-22-2021, 08:01 PM   #2
Marvelous3
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The compression ratio is achieved from a dish - or lack there of - in the piston.

Your 530 head isn’t going to drop the compression down from 9.8(I think):1 to 8.5. With that said, you can still throw a good amount of boost at a higher compression engine. Your rods and pistons will be fine. Changing the pistons and rods though will let you lower compression, if that’s what you’re after.

Either w cometic or oe Volvo gasket will work just fine
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Old 11-23-2021, 04:30 AM   #3
VB242
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You'll have to figure out the timing cover, I think STS machining makes an adapter with the timing mark on it. You see when you put the newer head on the old block. I cut back the newer backplate for the B230 timing cover to make it work my B23 block and 530 head. You should CC your head to verify the chamber size to determine your true compression ratio unless you know the whole history of the head and how many times it's been cut.
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Old 11-23-2021, 04:41 PM   #4
dl242gt
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With a good tune an early 8.5:1 B21F should be ok with boost but I'm not sure about 20psi. But you'll have to make sure it's a good tune with those cast pistons. The different thicknesses of the cometic head gasket will let you adjust the clearance so you can accomplish the tight squish to help you burn the gas well. I second the suggestion for the STS timing plate.
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Old 11-23-2021, 08:55 PM   #5
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You'll be fine at 20psi with the proper tune and fuel delivery.

Last edited by VB242; 11-23-2021 at 09:01 PM..
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Old 11-29-2021, 08:28 AM   #6
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You should be fine with 20 psi. I am running 29psi on my b21ft.
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Old 11-30-2021, 11:01 AM   #7
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and to clarify I am also running e85. plenty of cooling going on. I also am still tuning so it hasn't seen track time yet.
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