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Old 10-21-2018, 05:53 PM   #1
oemoilleaks
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Default b20 block questions

I am currently in the middle of building a b20 "performance" engine. Basically the goal is as close to 200hp I can get with a dual carb big bore set up.

But I was just doing some more research before I head to the machine shop and I came across a little note on brickboard about the '74 b20 blocks being the weakest.

Is this true?

The core engine I bought was a '74 8-bolt engine. I have another unknown b20 block on the shelf as well.

What would be the best way to have the blocks tested to see how porous the casting is?
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Old 10-21-2018, 06:45 PM   #2
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Can you post a link to the Brickboard article?

I am not aware of any issues with the 1974 blocks, but I have seen more ventilated 8 bolt bolt B20s (1974-1975), mostly being caused by broken connecting rods. I have seen a couple of 6 bolt engines with holes, but they were abused engines.

If you are worried, ask your machinist about sonic testing the block.
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Old 10-21-2018, 11:18 PM   #3
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Eric!

Sure thing here's the link https://www.brickboard.com/RWD/index...897&show_all=1

I hadn't heard this before so it threw me off my research track.

I was actually trying to find the appropriate dimensions/specs for a b20e head so I could have the machinist recreate it with the b20f head I'm using. I was also looking for new valves for the b20f head.
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Old 10-21-2018, 11:50 PM   #4
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Just have it sonic checked...they're not any weaker. That's just BB lore. Ask for data and information and they all run. The head needs to be reduced in thickness a lot. The specific dimensions should be measured as a volume for the combustion chamber not some other data. Valves - KG Trimning has larger exhausts. I've covered building here: http://calgaryvolvoclub.com/forum/vi...hp?f=12&t=2699 Useful head stuff here. http://calgaryvolvoclub.com/forum/vi...2227&start=315
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Old 10-22-2018, 01:21 AM   #5
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I'm with ^^^^, never heard of the 74 blocks being weak. Also never had issues with mine thus far, even punched out to 92mm, been running in that configuration for 20 years, 100k or so, and I don't drive it kindly. It's only at around 9:1 and sitting at 135rwhp, so your goal, done right shouldn't be too bad to attain.
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Old 10-22-2018, 09:39 AM   #6
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I've *heard* that later blocks, in general, are slightly more prone to core shift, but I really suspect it's a case of low sample size anecdotes.

That said, my even smaller anecdotal group never included any 8-bolt blocks, just a couple of B18's, a B20B, and several B20E's.

AFAIK a machine shop can do a sonic wall thickness check on the blocks as they sit, this would let you know if the core is shifted enough to matter.

There is some spurious information floating around on BB, like in that thread where someone mentions differences in stroke. They may have been confused by the differences in compression ratio, but that's all done with cylinder head chamber sizing, the strokes on all B18 and B20 engines are the same.

Since you're boring the block out anyway, it doesn't really matter which one you start with (6-bolt vs. 8-bolt considerations aside). Maybe take both in and have the one that seems to check out the best on the sonic wall thickness checks (most metal, and the most even on all sides of all cylinders).
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Old 10-22-2018, 10:46 AM   #7
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I was also not aware there was a forged B20 crank in 75...according to that thread.
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Old 10-22-2018, 11:10 AM   #8
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Even if there was (no clue really), I don't think it would matter. 200 HP N/A certainly isn't going to be stressing a cast crank or a forged crank, that's not what breaks on any vaguely sane engine builds.

Maybe when you're into the 'Swedish top fuel' 1000+ hp redblock builds that matters, but they're probably not using an old OEM forged crank then either.
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Old 10-22-2018, 11:27 AM   #9
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Hello Joe,

I found the thread to which you refer.

Once and only once have I seen a porous/cracked block. It was a block that came from our stock of used blocks and was not labeled so I'm not sure if it was a 1974 block. But ever since then, all of our blocks get crack checked before they are rebuilt.
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Old 10-22-2018, 12:25 PM   #10
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Quote:
Originally Posted by gsellstr View Post
I was also not aware there was a forged B20 crank in 75...according to that thread.
Pretty sure they are all forged. I've never seen a cast one...and I'm running a B21 crank in my B20 (which, of course, can't be done according to the BB).
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Old 10-22-2018, 03:56 PM   #11
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ok phew. I got worried since I had never run across that before.

I'll have the blocks sonic tested soon and see what comes out of it.
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Old 10-22-2018, 05:55 PM   #12
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Quote:
Originally Posted by oemoilleaks View Post
ok phew. I got worried since I had never run across that before.

I'll have the blocks sonic tested soon and see what comes out of it.

Well you could but...
How big are you planning on boring it? 92mm? OK do it..
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Old 10-22-2018, 07:37 PM   #13
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Well you could but...
How big are you planning on boring it? 92mm? OK do it..
Bore it? or Sonic Test it?
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Old 10-22-2018, 08:01 PM   #14
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Just have it sonic checked...they're not any weaker. That's just BB lore. Ask for data and information and they all run. The head needs to be reduced in thickness a lot. The specific dimensions should be measured as a volume for the combustion chamber not some other data. Valves - KG Trimning has larger exhausts. I've covered building here: http://calgaryvolvoclub.com/forum/vi...hp?f=12&t=2699 Useful head stuff here. http://calgaryvolvoclub.com/forum/vi...2227&start=315
Craig,

These posts are really thorough! I've been reading through them and will have a bunch of questions as soon as I get a mental grasp on them!

Specifically about the flow values of the porting for the larger KG valves.
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Old 10-22-2018, 10:47 PM   #15
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Quote:
Originally Posted by oemoilleaks View Post
Bore it? or Sonic Test it?
I's ax-ing you if you PLAN to bore it to 92mm? If planning that big..stock is 3.5" which is 88,9mm, then sure, sonic check it..If not that big, maybe not spend the money.
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Old 10-22-2018, 11:23 PM   #16
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Quote:
Originally Posted by John V, outside agitator View Post
I's ax-ing you if you PLAN to bore it to 92mm? If planning that big..stock is 3.5" which is 88,9mm, then sure, sonic check it..If not that big, maybe not spend the money.


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Old 10-23-2018, 02:06 PM   #17
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Quote:
Originally Posted by oemoilleaks View Post
I am currently in the middle of building a b20 "performance" engine. Basically the goal is as close to 200hp I can get with a dual carb big bore set up.

...

What would be the best way to have the blocks tested to see how porous the casting is?
Quote:
Originally Posted by John V, outside agitator View Post
I's ax-ing you if you PLAN to bore it to 92mm? If planning that big..stock is 3.5" which is 88,9mm, then sure, sonic check it..If not that big, maybe not spend the money.
I just assumed that he was going to bore it to 92 mm based on his question.
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Old 10-23-2018, 02:22 PM   #18
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AFAIK he's going to be using custom forged pistons that are 3.6" (91.44mm).
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Old 10-23-2018, 02:37 PM   #19
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How are you going to get 200hp? Forced induction ?
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Old 10-23-2018, 03:14 PM   #20
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How are you going to get 200hp? Forced induction ?
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Old 10-23-2018, 03:34 PM   #21
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How are you going to get 200hp? Forced induction ?
With 2.1 liters, your only real avenue to 200 HP is revving the piss out of it (and having enough I/H/E flow to support it).
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Old 10-23-2018, 06:38 PM   #22
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With 2.1 liters, your only real avenue to 200 HP is revving the piss out of it (and having enough I/H/E flow to support it).
I've got a heavy foot.
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Old 10-23-2018, 07:39 PM   #23
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Quote:
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I just assumed that he was going to bore it to 92 mm based on his question.
It would certainly make it easier to make a fun-er-er engine..Moar Torax.
but not significantly change things I would suggest..i just don't get too fixated on XXX.z HP
And i don't fixate on motor alone...I say you can't talk motor without referencing gear-set and final drive, since we don't drive engines around, we drive cars.
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Old 10-23-2018, 07:41 PM   #24
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Quote:
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With 2.1 liters, your only real avenue to 200 HP is revving the piss out of it (and having enough I/H/E flow to support it).
But John, you have to define what you think that means..

me I don't think 7000 is revving the piss outta sumpin..

8000 yeah

And whats I/H/E? for us nervous novices??
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Old 10-23-2018, 07:49 PM   #25
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Quote:
Originally Posted by John V, outside agitator View Post
It would certainly make it easier to make a fun-er-er engine..Moar Torax.
but not significantly change things I would suggest..i just don't get too fixated on XXX.z HP
And i don't fixate on motor alone...I say you can't talk motor without referencing gear-set and final drive, since we don't drive engines around, we drive cars.
True - cars are systems. No point mating 200 hp to a 2.90 final drive if you were thinking of having fun!

What car is this B20 going in? What are you using it for? Enquiring minds want to know!
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