Stuck between cylinder heads

Discussion in 'High Performance Modifications' started by Justin79maro, Sep 11, 2019.

  1. Justin79maro

    Justin79maro Veteran Member

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    I do want to up the compression some if I go with aluminum heads but I don’t want to run such small combustion chamber sizes, and I don’t wanna change the pistons. Plus it’s a street car anyway lol
     
  2. G72Zed

    G72Zed Veteran Member

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    Totally understand, everything is a compromise, and a limit to certain mods.

    If your 385 is at 10:1 right now with a "0" deck with a 64cc chamber as you say, and looking at 5.5-6 thou per CC, you would need to shave the 64cc aluminum head approx. .016.5 to .018 to remove 3cc and hit 10:3 CR

    Or .025 to .027 to remove 4.5cc and hit 10:5 CR. So a basic flat mill will do in this case, that's if they pour at 64cc to begin with.
     
  3. Justin79maro

    Justin79maro Veteran Member

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    I always heard that if you run 11.1:1 or more compression you need to higher then 93 oct gas, the head guy told me 10.1:1 would be a maximum with iron heads I should go without detonation. Also does going from iron to aluminum with the same combustion chamber lower the compression ratio Bc it’s aluminum? Or does it just act like you have a lower compression meaning you can run say a higher compression on 93? That confuses me
     
  4. biker

    biker Veteran Member

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    I think the theory with aluminum is that it gets rid of heat more quickly than iron, and heat is one of the factors that contributes to pre-ignition. That goes for hot spots within the chamber as well. sharp edges or carbon buildup can create hot spots. Combustion chamber design is another biggie. If the heads create a good swirl with the incoming mixture, it is less likely to detonate. Static compression is a funny thing as the guys here have mentioned. Your combo may calculate at more than 10:1, but your cam timing may bleed off a good deal of pressure when running which will also keep things calm in the chamber. There is also quench area within the chamber that can be optimized to help avoid detonation.
     
  5. Justin79maro

    Justin79maro Veteran Member

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    What would be a good chamber design and how do you calculate quench? I’ve heard of people talk about it but never knew how to find it lol
     
  6. biker

    biker Veteran Member

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    There are smarter guys than me on here to explain their experience with quench, but it is basically the measurement between the flat top of the piston and the lowest portion of the combustion chamber with the piston at TDC. So, factors that affect this are the distance that your piston sits down below the cylinder deck height, and also the gasket thickness. Nice tight quench area increases swirl (turbulence) which helps mixture burn completely. Vortec heads apparently have a really good combustion chamber design for promoting complete burn.
     
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  7. G72Zed

    G72Zed Veteran Member

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    That's a fair and common general statement, I have tuned some cars with 9.8 CR with aluminum heads and good pump gas that would rattle themselves to death, and I have done mid to upper 10's in CR with Iron heads that are NOT detonation prone at all with the same fuel.

    It's all in the combo and tune up, there is allot more to it that just CR with a certain given octane rating.

    Ah, the old Al vs Iron debate, well, in my experience, with everything being exactly the same, it's the same volumes, so its the same SCR . But, it's called an "internal combustion engine" and not much static with a running engine, and heat is power, and aluminum does an amazing job of getting rid of the heat!! But, they are lighter, you need to know what the weight off the nose is worth. In some racing classes its worth allot, some other classes, not as much you would think.

    Looking at it like this, a typical SBC aluminum head gives a 35-40 pound weight savings, take a typical 3,750# Camaro running 12.10 @ 108, takes around 360hp ish RWHP, the same setup -50# gets you 12.07 @ 108.3 with the same 360hp, to get back that ET/MPH with iron heads, you need another 5 RWHP, not that difficult.

    Let's face it, most people like the look of aluminum heads, and It's getting more expensive to produce good quality cast iron heads, there heavy as heck, ugly to look at, costs more to ship, takes longer to port, and expensive to fix, if not impossible.

    I have 2 complete head packages I use for my engine for A-B-A-B R&D testing, after everything was done, I went back to my iron heads, even though the aluminum heads "beat" the old iron on every spec on paper, and the flow bench, but that's just me, your results may vary.
     
  8. G72Zed

    G72Zed Veteran Member

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    Google is your friend in this case.

    Great post by Biker, it's the one time that higher compression given with a tighter piston to head clearance actually lowers the the risk of detonation, win /win.

    I like the carbon hitting the head LOL.
     
  9. Justin79maro

    Justin79maro Veteran Member

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    Starting to think $1600 for aluminum heads vs $850 for iron with the same end result would be a no brained in that aspect lol. Basically just be spending double JUST for the material it’s made of. Unless you get cheaper aluminum heads lol like profiler instead of afr
     
  10. G72Zed

    G72Zed Veteran Member

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    Well, you already own the Vortec's, but you have to figure the porting costs in them vs new properly sized/prepped aluminum heads, it's to decide where to spend the money for the best return on investment. If you did your own porting, it would be a no brainer, work on the Vortec and try them out, that's the fun of testing stuff out to see what works.

    Personally, I would buy the Profiler's before the AFR's.
     

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