Aluminum heads and static compression

Discussion in 'Street/strip 400/430/455' started by matt68gs400, Jun 19, 2019.

  1. matt68gs400

    matt68gs400 Well-Known Member

    Is there a minimum compression to run aluminum heads? I know they typically run at higher compressions but what about guys that have 9.5, 9 or even less than that and just want to exchange their iron heads for aluminum?
     
  2. StfSocal

    StfSocal Well-Known Member

    There is no minimum compression for aluminum head as far as i know. I think why everyone says to run a higher comp is because they allow it. Aluminum dissipates heat better meaning that you can run high compression without fear of detonation. A lot of people slap on aluminum heads without touching the short block. If you do that you won't get all he benefits, but it won't be worse.

    Also combustion chambers could be less with aluminum heads so you might bump compression regardless, this of course depends on the iron heads that are being replaced.
     
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  3. matt68gs400

    matt68gs400 Well-Known Member

    Looks like 64-66 cc for the TA heads and 68 cc for the edelbrock.
     
  4. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    You can get away with more static compression with aluminum heads. As mentioned, they dissipate the heat of compression much faster. When I first put the Stage1SE heads on my exiting short block, Greg Gessler milled them .040 to bring my compression from 9.4:1 to 10.4:1. The chambers were at 59cc. I run 10.5:1 with a 230/238/112 cam and a DCR of 7.8 in my current engine. It runs quite happily on 93 pump gas.
     
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  5. matt68gs400

    matt68gs400 Well-Known Member

    Larry, i have a great idea. Get your stage 2 heads and sell me your stage 1 heads.:D
     
  6. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    I'd have to get rid of my MT headers and buy new headers. Not likely.:D
     
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  7. Bens99gtp

    Bens99gtp Well-Known Member

    The new header go on easier ;)
     
  8. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Yeah but I’d lose that awesome MT sound.:)
     
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  9. Bens99gtp

    Bens99gtp Well-Known Member

    Aren't you running through muffler most the time anyways
     
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  10. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Yeah, but you can hear them regardless.
     
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  11. Bens99gtp

    Bens99gtp Well-Known Member

    Guess I never paid that much attention b4
     
  12. matt68gs400

    matt68gs400 Well-Known Member

    What will you buy next?
     
  13. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    I’m done.
     
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  14. matt68gs400

    matt68gs400 Well-Known Member

    Ah, I see, I misread your post.
     
  15. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    My next project will be putting the A/C back in and getting it working. The evaporator box is in with new parallel flow evaporator. Gotta buy a new compressor and condenser and other parts along with hoses.
     
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  16. BQUICK

    BQUICK Gold Level Contributor

    I knew someone that put them on a stock 8.5 comp 1971 motor with 118 cam....not optimum by any means but it ran hard....ran on piss...
     
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  17. sriley531

    sriley531 Excommunicado

    I have aluminum heads with 9.3cr. No problems. Also gives a little extra wiggle room for nitrous.
     
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  18. matt68gs400

    matt68gs400 Well-Known Member

    Can I also increase dynamic compression with aluminum heads or just static?

    I’ve been reading that 7.5 to 7.8 DCR is best for pump gas, 93 octane. But can I get higher than this with aluminum heads?
     
  19. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    My motor is 7.8. Runs all day on Pump 93. My timing is locked out at 34* with 10* of vacuum advance. I wouldn't go higher than 8.0 or so. DCR will depend on the SCR and particular cam IVC. With an SCR of 10.5-11.0, the DCR should fall around that 8.0 sweet spot.
     
  20. matt68gs400

    matt68gs400 Well-Known Member

    Time to pull a head this fall and see what’s really in there for distance in the hole, bore, any porting, piston dish, etc. I’ve been trying to skirt around that, hoping I could make some reasonable assumptions. But if I’m wrong, I’ll be pinging away if I put on a shaved head or the wrong head gasket, with this cam I have in it now.
     

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