Gen 6 Big Port Heads

Discussion in 'High Performance Modifications' started by 1980RS, Apr 4, 2019.

  1. 1980RS

    1980RS Veteran Member

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    I never have had a chance to play with any Square port heads in the past as they were either too expensive or I just never had an engine to use them on. I do have some 990's but I do not want to mess with them as they are virgin heads and my be worth something to someone some day. That being said I picked up 2 sets of 934 Gen 5-6 Big Port heads to see what they will go on the bench and may use them in a future project. What prompted me to get them is you can get head gaskets to use the heads on mark IV blocks. I was reading on Super Chevy that when they were using these heads on an old 454 HO engine that they tested 3 sets of heads. They used the factory ones, Merlin Sq. Port and a set of Merlin oval ports. Both sets of Sq. Ports were within 20hp of each other but when they bolted on the Merlin ovals you would think the low compression engine would shine, right?, well it lost "62"hp compared to both sets of the big port heads. Never saw that coming and Merlins are supposed to be better than 781's out of the box.
     
  2. Rich Schmidt

    Rich Schmidt Veteran Member

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    Don't worry about messing with the 990's,they never came on anything from the factory. They are an 89's and later service replacement heads.
     
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  3. 1980RS

    1980RS Veteran Member

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    Ya, I know they are a service replacement head. I did get the 934's bowl ported this week and will add new valves as GM ones weigh a ton. The valve job on these heads was horrible and the guy said they are ready to run. Every time I go with someone's work other than my own I am always disappointed in the results.
     
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  4. 1980RS

    1980RS Veteran Member

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    Got to put one of the 934's on my 468 today and I do have enough piston to valve clearance with the roller cam so the 10 to 1 Big Port engine project is a big go. Lot's of things to test out with this one.
     

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