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Old 05-07-2012, 08:32 AM   #1
smithy
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Default 531 vs 405

Is there any advantage in using a 351 head over a 405. the ports looks the same. The combustion chambers look a bit different. I haven't cc'd them to check if they are the same size. The reason i ask this question is that i have a 405 head but i have found a 531 that is cheap.
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Old 05-07-2012, 09:05 AM   #2
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I don't know of any hard evidence, but the 531 is reputed to have a slightly more centered spark plug location. Also, most 405 heads are BCP, and the 531 should be a SCP head.

Other than that, really no difference to speak of.
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Old 05-07-2012, 10:14 AM   #3
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Aren't the 405 heads setup for Kjet injector locations? I know the 531's are not. That would be the biggest difference i could think of.

from what i remember the 405 and 531 have very similar flow characteristics. I dont know if i would bother changing from one to another but if its cheap enough it might not be bad to get as a backup head.
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Old 05-07-2012, 10:44 AM   #4
towerymt
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-SCP vs BCP (all 531 = SCP, 405 could be either)
-spark plug location in the 531
-k-jet holes
-a need for head mounted dizzy? only 531 can accommodate
-b21/23 block or b230? t-belt cover backing plates differ, as do valve covers, but you can still mix and match heads to blocks.
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Old 05-08-2012, 02:43 AM   #5
woodywhat
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Quote:
Originally Posted by smithy View Post
Is there any advantage in using a 351 head over a 405. the ports looks the same. The combustion chambers look a bit different. I haven't cc'd them to check if they are the same size. The reason i ask this question is that i have a 405 head but i have found a 531 that is cheap.
thanks
grab the531 head and deshroud the valves, skim the head.5mm. you didnt say which 405 you have 78-82 or 90-93 mods ime guesing 78-82 witch is big/w/p and if its not seeping, ide leave it on until you decide to rebuild the engine. meanwhile seach for a penta block {2.5l} to go with your tweaked 531 head and a good m47 alloy box.
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Old 05-08-2012, 02:45 AM   #6
woodywhat
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Quote:
Originally Posted by towerymt View Post
-SCP vs BCP (all 531 = SCP, 405 could be either)
-spark plug location in the 531
-k-jet holes
-a need for head mounted dizzy? only 531 can accommodate
-b21/23 block or b230? t-belt cover backing plates differ, as do valve covers, but you can still mix and match heads to blocks.
late 405 90-93 with blank k.jet ports run head dizy.
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Old 05-08-2012, 10:32 AM   #7
towerymt
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Originally Posted by woodywhat View Post
late 405 90-93 with blank k.jet ports run head dizy.
what? never heard of such a thing. On what block? In which car?
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Old 05-08-2012, 11:10 AM   #8
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Pretty sure it came in euro cars, maybe australia got it too. My dad had a '90 (I think it was a '90) 740 that had a 405 head on it in the UK. May not have been stock, but it looked original. It had been on there a long time anyway, and it ran on LH 2.2 as well, the kjet ports were not drilled out. Theres some real mixing and matching and oddities in different markets..
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