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What blower heads for a sbc?

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  • squirrel
    replied
    Re: What blower heads for a sbc?

    Or they could play with different fuels instead of different compression ratios.

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  • Eric68
    replied
    Re: What blower heads for a sbc?

    Originally posted by squirrel
    Interesting test, but as you said you didn't really prove anything because you didn't maximize compression ratio for the fuel used.

    Exactly. Like Dave said -- they didn't find the point of detonation. That would be an expensive test (and maybe impractical) to do because you would have to spend some time on a dyno (maybe a chassis dyno) and keep pulling the engine in order to mill heads, swap pistons, etc

    If by chance the commonly accepted position that aluminum heads can take another 1/2 point of compression safely holds true, then the aluminum head would clearly have the power advantage, 1/2 point should be worth about 7 HP in an engine like the one tested as I recall.

    By the way, I remember reading that article when it came out and I LIKED IT A LOT. Good stuff there -- I can't tell you how many arguments that test put to rest LOL

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  • squirrel
    replied
    Re: What blower heads for a sbc?

    Interesting test, but as you said you didn't really prove anything because you didn't maximize compression ratio for the fuel used.

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  • Freiburger
    replied
    Re: What blower heads for a sbc?

    I did not test the point of detonation, which was perhaps the fatal flaw. But I fairly well showed that there was no power difference, at least not in our test sample:

    http://www.carcraft.com/techarticles...est/index.html

    Please read the caveats at the end of the story prior to your critique.

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  • Dynoroom
    replied
    Re: What blower heads for a sbc?


    Someone needs to show me the hard data that shows that you can run more compression and/or have less detonation with aluminum heads. I know, I know..."they reject the heat more quckly." I'm not convinced. Compare the water jacket on an aftermarket aluminum head to one on an OE iron, too


    No proof but...............

    Lets go back in time..... back to the 60's...... ahhh muscle cars.......
    Remember when it was said aluminum heads on the 427 gt40's Ford's lost power on the Le Mans engines? Same was said of the 427 Chevrolet's with alloy heads. So what did everyone do? They pulled the aluminum heads off and installed iron heads. But what did we find out later? Just add a couple degrees more timing and/or 1/2 point or so more compression and the power comes back.
    This is due to thermal efficiency... the ability to remove heat from the chamber at a "faster" rate than iron.
    So any testing needs to be A-B-A testing to prove if there is any benefit to alloy heads. JMHO.

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  • squirrel
    replied
    Re: What blower heads for a sbc?

    I don't think it's a matter of rejecting heat, it's that aluminum is a much better conductor of heat, so the temperature difference between combustion chamber and coolant passages is lower on the aluminum head. This means that the chamber surface does not get as hot in the aluminum head, so there might be less heat transfer from the head to the air, and less tendency to detonate.

    If you set up an engine with both aluminum and iron heads with the same chamber shape and size, optimized mixture and timing, and found that they both detonated at the same fuel octane, then I'd say you made a pretty good case that the idea that aluminum heads are more detonation resistant, is wrong. Is that what you did?


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  • Freiburger
    replied
    Re: What blower heads for a sbc?

    Someone needs to show me the hard data that shows that you can run more compression and/or have less detonation with aluminum heads. I know, I know..."they reject the heat more quckly." I'm not convinced. Compare the water jacket on an aftermarket aluminum head to one on an OE iron, too.

    BTW, I've tested this, albeit on the dyno and not in a car. But we did a lot of hot sweeps and steady-state chamber soaking to try and prove something. And couldn't.

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  • squirrel
    replied
    Re: What blower heads for a sbc?

    Cost is probably the main one, and on a small block chevy that should not be much of a deterrent.

    The weight of the blower doesn't help things, so running aluminum heads just to help lighten up the engine is a good idea. You can run a bit more compression with aluminum heads, which is nice, but keep in mind that you might get "the bug" and go for more boost...so it might be wise to leave the compression a tad low, so as to not cause detonations problems down the road if you swap pulleys for more boost.

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  • ljfen
    replied
    Re: What blower heads for a sbc?

    Thanks for the replys. I like the idea of an aluminum head especially when it comes to detonation. But what are some of the cons of an aluminum head? Cost of course but anything else?

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  • revolutionary
    replied
    Re: What blower heads for a sbc?

    Good flow numbers on boosted application make a GREAT deal of difference. I like to give my customers the old 'hose theory' when talking about porting their turbo/blower heads. Put your thumb over the end of a hose and turn the spigot on. The water company has made sure that there is X amount of pressure in the line and on down into the hose - lets call it 20psi for example. With your thumb almost completely covering the hose end, a small mass of water will likely shoot out to feed your plants - consider this your stock heads under 5psi boost. Now remove your thumb from the hose end and the mass of water exiting will greatly increase even with the hose pressure remaining constant - consider this ported heads nuder the same 5psi boost. That extra mass of fluid - gas and air in our engine - is what will make more power.

    You can even take it a step further if you can consider that by removing your thumb from the hose and even with LOWERING the water pressure - or boost in your engine -it is possible to still get a larger mass of water - or air/fuel mixture - out of the hose by allowing it to flow more.

    As for using a flowbench, it is really just a comparator and has as much relevance in n/a and boosted applications. We're just comparing cfm under a pressure differential. During an engine's cycles the pressure differential varies greatly so measuring at a steady state like 28inh20 shouldn't mean anything anyhow. We just use it to see if we are making any improvements over the previous iteration.

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  • squirrel
    replied
    Re: What blower heads for a sbc?

    Originally posted by JeffMcKC
    your pushing not pulling the air, this is why boosted cars out run N/A cars with the same head.
    You can't pull air....all you can do is make a hole for it to go into. n/a engines have the atmosphere there to push air into the hole the pisont makes, blown engines have the atmosphere pushing air into the (bigger) hole that the blower makes, then the blower pushes the air into the hole that the moving piston makes.

    But thanks for the replies, I think you wound up saying the same thing I said, even though you went about it a different way. He needs the best flowing heads as he can afford, basically.

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  • Eric68
    replied
    Re: What blower heads for a sbc?

    I agree with Jeff. Get a big head, but within reason.

    A couple points here -- while the blower pushes air into the cylinder it does not pump it out. The engine pumps it out which results in pumping losses. So get a head with a GOOD exhaust port to minimize pumping losses.

    By the way, the better a head's intake port is, the less resistance to flow there is with or without a blower. Good flowing heads will make more power 99% of the time and this holds true whether you run a blower, nitrous, or are naturally aspirated.

    I would not go hog wild on intake runner size either. A huge, oversized port will be lazy on the street when the engine is not making boost. Since you are not making boost most of the time I would suggest that you do NOT ignore streetability with respect to port size.

    Specific recommendation for you here. Take a look at the Edelbrock Victor Jr heads. They have 215cc intake runners and a big exhaust port that flows very well. You can get them with just the valves (no springs or retainers) for right about your target price range.

    For springs, make sure you add seat pressure above and beyond what you need for the same cam in a "naturally aspirated" engine to account for boost pressure on the backside of the valve (trying to push the valve open). I recently had to upgrade springs on a friends 383 SBC due to valve float. When I did the math (area of the back of the intake valve times boost pressure) I found he needed 45 psi MORE spring pressure. Problem cured.

    Hope that helps.

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  • JeffMcKC
    replied
    Re: What blower heads for a sbc?

    This is turning into the out trick your self club real fast Eddie is right to a point, and that is the MAX Effort point, which this guy is no where near. :

    Guy, get on EBay and buy yourself a big runner head aluminum ( this will help with detonation) and you wont spend a ton on porting, the velocity will be OK, your pushing not pulling the air, this is why boosted cars out run N/A cars with the same head. You will need a Blower Cam to get the right valve events. A blower will calm a big cam down.

    Your headers will be a cork, the money you did not spend on porting can be used there.

    When you open the air flow up boost is going to drop, but more air is getting in to make power if you close the valve right.

    Don't Chase your tail on the Max Effort theory guys that wont make 20 Hp diff at 6000 RPM, if you where talking 35-50 lbs boost I would give you a different way, but your stock rods and fuel will limit your boost.

    By the way, if my Blower only puts out atmospheric pressure, I am getting a new one, 30 lbs of boost going past the intake valve is not atmospheric pressure, this is why its called boost. :-[



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  • squirrel
    replied
    Re: What blower heads for a sbc?

    That's right, cold is like dark, and vacuum....it's the lack of the thing you're really talking about, which is heat, light, and pressure.

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  • TheSilverBuick
    replied
    Re: What blower heads for a sbc?

    Originally posted by squirrel
    The way I see it, there is no such thing as a vacuum, there are only different levels of absolute pressure.
    Talk to any academic Chemist or Physicist and they'll say the same about Cold. There is no cold only differences in heat.

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