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  • #31

    Re: What blower heads for a sbc?

    Re: What blower heads for a sbc?

    Or they could play with different fuels instead of different compression ratios.
    That sounds reasonable. My first thought was take an Iron head setup that pings on 87 and see if simply bolting Aluminum heads on it eliminates the pinging.
    Build an iron headed engine on the edge of detonation. Hold it at peak torque on the dyno. Then raise the water temp until it detonates.
    Repeat test with identical aluminum heads.
    Head that makes it to he highest water temp before detonating is keeping the combustion charge the coolest.

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    • #32

      Re: What blower heads for a sbc?

      Re: What blower heads for a sbc?

      Yeah, you did prove some things, you just didn't answer the question we're talking about in this thread.

      Combustion chamber design has come a long way in the past 30 years, eh?
      My fabulous web page

      "If it don't go, chrome it!" --Stroker McGurk

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      • #33

        Re: What blower heads for a sbc?

        Re: What blower heads for a sbc?

        I don't know about 10.9 compression on pump gas with iron heads; but I run just under 10:1 compression with iron heads on pump gas, mostly 89 octane. The cranking compression on the 383 came out to be 195 to 210.

        My 70 Caprice with it's stock 10.25:1 compression also seems to run OK on 89 even with the AC on without detonating.

        I may have tuned these cars to run on gas, so I may not getting full power potential out of them.
        BS'er formally known as Rebeldryver

        Resident Instigator

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        • #34

          Re: What blower heads for a sbc?

          Re: What blower heads for a sbc?

          Yeah, you did prove some things, you just didn't answer the question we're talking about in this thread.

          Combustion chamber design has come a long way in the past 30 years, eh?
          Well, if it's true that aluminum moves the heat away, and that they can therefore take another half point in compression, would you not therefore presume that aluminum would make less power at the same compression ratio reardless of detonation? (again, see the oft-repeated story posted above by Mike)

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          • #35

            Re: What blower heads for a sbc?

            Re: What blower heads for a sbc?

            Or they could play with different fuels instead of different compression ratios.
            That sounds reasonable. My first thought was take an Iron head setup that pings on 87 and see if simply bolting Aluminum heads on it eliminates the pinging.
            Build an iron headed engine on the edge of detonation. Hold it at peak torque on the dyno. Then raise the water temp until it detonates.
            Repeat test with identical aluminum heads.
            Head that makes it to he highest water temp before detonating is keeping the combustion charge the coolest.
            That's what we did, but only up to 190 degrees.

            Comment


            • #36

              Re: What blower heads for a sbc?

              Re: What blower heads for a sbc?


              No one is addressing my comment about water jackets, either. Take a look. It's my thought that aftermarket heads, in general, don't have nearly the cooling detail as most OE heads. Plus the decks are thicker, etc, so the supposed heat-transfer qualities of aluminum versus iron are not usually an A-B comparo because there are other factors in the mix.
              That is a good point Dave.

              You know, I built an AFR 195 headed (the older 195s, not the eliminators) SBC that just will NOT stay cool. AFR decks are thick and just looking at the inlet water ports you can tell there is less room for water flow. I'm tempted to rig a test fixture next time the heads are off the car and see how many GPM I can put through the heads with a garden hose and a pressure regulator set to say 12 psi. Just block the rear manifold inlet and fix a hose to the front. Then let the water blow out the bottom holes into a plastic tote on a scale -- kind of like flowing an N2O setup, just on a larger scale. Crude, but it could be telling if I can compare two different head castings.

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              • #37

                Re: What blower heads for a sbc?

                Re: What blower heads for a sbc?

                I disagree that I did not prove anything. It may have not been a COMPLETE test to the point of detonation. However, it does address arguments of "iron heads make more power because they retain heat" (per Bill Mitchell, and per Dynoroom's anecdote above). Also, if I told you I was running 10.9:1 and 185 psi cranking compression on iron heads, you'd almost certainly reply that it would likely not run on pump gas without detonation. But it did...at full timing.

                No one is addressing my comment about water jackets, either. Take a look. It's my thought that aftermarket heads, in general, don't have nearly the cooling detail as most OE heads. Plus the decks are thicker, etc, so the supposed heat-transfer qualities of aluminum versus iron are not usually an A-B comparo because there are other factors in the mix.
                I have ran a PILE of engine w/ iron heads and 185 cranking compression w/o a single problem on pump swill.. Most people run more timing in an engine then it needs, anyhow.. They just create detonation for no reason... I run them and add timing until I see no increase in power, then I back it down a couple deg. and away we go! I have seen some engines that need the high side of 30 deg and some that barley want a little over 30 total...

                David, I feel you have a point about the iron heads having more cooling capacity and less material between the coolant and the heat.. With that said, I still feel the aluminum head is a better option, but thats just me. I have NOT done back to back tests w/ the same identical head in ferrous and non ferrous.

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                • #38

                  Re: What blower heads for a sbc?

                  Re: What blower heads for a sbc?

                  Well, if it's true that aluminum moves the heat away, and that they can therefore take another half point in compression, would you not therefore presume that aluminum would make less power at the same compression ratio reardless of detonation? (again, see the oft-repeated story posted above by Mike)
                  Good point, and I don't know the answer. I would expect that a change that gets it into detonation will be more important than a change that makes you lose a bit of efficiency. You still have an interesting question to answer if you ever have the opportunity.

                  I also think that chamber shape is more of a concern than head material. And what's the weight difference worth in hp?

                  On the cooling jacket thing....OEMs are very concerned with material costs and vehicle weight, aftermarket is not nearly so much. Heat travels very slowly thru iron, compared to aluminum.
                  My fabulous web page

                  "If it don't go, chrome it!" --Stroker McGurk

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                  • #39

                    Re: What blower heads for a sbc?

                    Re: What blower heads for a sbc?

                    Maybe the best of both Worlds would be coated chambers w/ aluminum heads..

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                    • #40

                      Re: What blower heads for a sbc?

                      Re: What blower heads for a sbc?

                      Or they could play with different fuels instead of different compression ratios.
                      That sounds reasonable. My first thought was take an Iron head setup that pings on 87 and see if simply bolting Aluminum heads on it eliminates the pinging.
                      Build an iron headed engine on the edge of detonation. Hold it at peak torque on the dyno. Then raise the water temp until it detonates.
                      Repeat test with identical aluminum heads.
                      Head that makes it to he highest water temp before detonating is keeping the combustion charge the coolest.
                      That's what we did, but only up to 190 degrees.
                      oh, I was thinking along the lines of 230 to 250 degrees... of course you need a pressurized cooling loop to do that..

                      Comment


                      • #41

                        Re: What blower heads for a sbc?

                        Re: What blower heads for a sbc?


                        Well, if it's true that aluminum moves the heat away, and that they can therefore take another half point in compression, would you not therefore presume that aluminum would make less power at the same compression ratio reardless of detonation? (again, see the oft-repeated story posted above by Mike)
                        This is were people keep going astray:
                        1) Theory says that the low heat transfer rate of iron should make an iron headed engine more efficient than an aluminum headed engine.
                        2) Efficiency (is this context) is fuel in divided by power out. Higher efficiency does not automatically mean more power.

                        DF, did you accurately measure BSFC during your Iron vs Al head tests? If so, did you detect a difference?

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                        • #42

                          Re: What blower heads for a sbc?

                          Re: What blower heads for a sbc?


                          Well, if it's true that aluminum moves the heat away, and that they can therefore take another half point in compression, would you not therefore presume that aluminum would make less power at the same compression ratio reardless of detonation? (again, see the oft-repeated story posted above by Mike)
                          This is were people keep going astray:
                          1) Theory says that the low heat transfer rate of iron should make an iron headed engine more efficient than an aluminum headed engine.
                          2) Efficiency (is this context) is fuel in divided by power out. Higher efficiency does not automatically mean more power.

                          DF, did you accurately measure BSFC during your Iron vs Al head tests? If so, did you detect a difference?

                          More temp in the chamber is more pressure which is, in theory, more power.

                          BSFC was the same.

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                          • #43

                            Re: What blower heads for a sbc?

                            Re: What blower heads for a sbc?


                            This is were people keep going astray:
                            1) Theory says that the low heat transfer rate of iron should make an iron headed engine more efficient than an aluminum headed engine.
                            2) Efficiency (is this context) is fuel in divided by power out. Higher efficiency does not automatically mean more power.

                            DF, did you accurately measure BSFC during your Iron vs Al head tests? If so, did you detect a difference?
                            More temp in the chamber is more pressure which is, in theory, more power.

                            BSFC was the same.
                            Well, since we've thoroughly hijacked this thread... I'll continue.
                            Granted, more temp in the chamber after ignition is more power, in theory.
                            However, the argument that Al heads reduce detonation sensitivity is based upon the Al sucking more heat out of the 700 degree combustion charge prior to ignition (i.e. quench). Thus, when looking at the combustion charge temperatures prior to ignition, the the Iron headed engine will have the hotter charge, and in theory, be more efficient.

                            Now, theory is for Scientists and I'm an Engineer... If Iron heads were measurably more efficient or powerful, everyone in NASCAR would run them, or they be illegal.

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                            • #44

                              Re: What blower heads for a sbc?

                              Re: What blower heads for a sbc?

                              I may have tuned these cars to run on gas, so I may not getting full power potential out of them.
                              I do that, my T-bird at 10.5:1 runs great at 6500' elevation on 91, but by 3000' I have to start backing timing off. I can get it to live at sea level with 91 but it runs like a dog compared to thinner air and more timing. Up here I some times will back the timing off some to run 85 octane to save money.

                              As for theory, I've always figured power can come from the temperature difference between the air temp and the combustion temp. Colder the air(denser) and hotter the engine (expanding the denser air) as long as there isn't detonation more power.
                              Escaped on a technicality.

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                              • #45

                                Re: What blower heads for a sbc?

                                Re: What blower heads for a sbc?


                                This is were people keep going astray:
                                1) Theory says that the low heat transfer rate of iron should make an iron headed engine more efficient than an aluminum headed engine.
                                2) Efficiency (is this context) is fuel in divided by power out. Higher efficiency does not automatically mean more power.

                                DF, did you accurately measure BSFC during your Iron vs Al head tests? If so, did you detect a difference?
                                More temp in the chamber is more pressure which is, in theory, more power.

                                BSFC was the same.
                                Well, since we've thoroughly hijacked this thread... I'll continue.
                                Granted, more temp in the chamber after ignition is more power, in theory.
                                However, the argument that Al heads reduce detonation sensitivity is based upon the Al sucking more heat out of the 700 degree combustion charge prior to ignition (i.e. quench). Thus, when looking at the combustion charge temperatures prior to ignition, the the Iron headed engine will have the hotter charge, and in theory, be more efficient.

                                Now, theory is for Scientists and I'm an Engineer... If Iron heads were measurably more efficient or powerful, everyone in NASCAR would run them, or they be illegal.


                                Actually there are some very good points being made which helps me make my decision. I would like to find out more about the relationship of the intake runner size to vacuum signal. I run about 14 inches of vacuum in the plenum. With a larger intake runner will my vacuum signal decrease? Isn't that a function of the cam overlap? What will it affect as I transition from vacuum to boost? Is it going to be lazy? I run mechanical secondaries which doesn't make a difference for secondary opening but what about a strong signal to the venturies? So how much runner is too much runner? I really despise backfires on a blower. ;D

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