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  • #46

    Re: What blower heads for a sbc?

    Re: What blower heads for a sbc?

    You have an egg beater on your engine between the carb and those big runners. Don't sweat it. Be careful with cold starts, let it warm up a bit, you really should never have any backfires once it warms up.

    My fabulous web page

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

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    • #47

      Re: What blower heads for a sbc?

      Re: What blower heads for a sbc?

      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
      Head runner size should not really effect your vacuum at idle. What it does effect though is the velocity of air through the port at different RPMs and loads. The general rule of thumb is to keep velocity at less than half the speed of sound at WOT at peak HP rpm, when velocity gets much faster the head goes into what is referred to as "choke". When that happens flow drops off dramatically and the horsepower curve goes flat or even drops. If you go too big the other way you will not have an issue with choke, but at lower engine speeds velocity will be very low -- low enough that fuel will tend to drop out of suspension and throttle response is compromised.

      On big cubic inch SBCs it is hard to go too big on the heads, especially with a blower, but my preference is to keep heads just shy of the choke point so I have killer throttle response and good driveability. A friend of mine put a Procharger F1R on a 383 SBC engine I built with AFR 195 heads. I expected the engine to really have choke issues and as a result have a flat power curve. Well it didn't -- it put down 650 HP to the rear wheels at only 5800 RPM. We haven't tried reving it higher yet due to a valve spring problem, but it went 9.93 at 136 mph in a 3600 lb car.

      Hope that helps.

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      • #48

        Re: What blower heads for a sbc?

        Re: What blower heads for a sbc?

        Well I have done a lot of reading on this subject-NOT.

        I love the fact everyone posting has got hands on and not basing it off of he said she said. Been reading this thread like a good book. lol

        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 regardless of detonation? (again, see the oft-repeated story posted above by Mike)

        Well, my thoughts are just like when you run alcohol, there is no real HP advantage form running it until you up the compression, then you see the advantage over gas and how much cooler the motor runs. When we run aluminum heads vs iron heads, we can round robin between races easier, the heads cool down faster.

        Now here is something interesting, when we ran a 468 with 990 iron head motor on 12:1 comp with C14 race fuel, we could run up to 52 degrees total timing and still pick up speed, after that point, it fell off on power. Now we were at 2700ft attitude when we did this. We then bump the motor to 496 with Hell Fire rings, Brodix heads and put in 17:1 comp. Ran it at 40 degrees on C16 race fuel but never bump the timing to see were it falls of on power. On nitrous we back off the timing. Difference=On the motor passes the 468 ran 8.76 vs the 496's 8.80. On nitrous the 468 ran 8.27 vs the 496's 7.76. Both with the same nitrous unit set at 200 shot in the same digger weighing in at 2150lb including driver and at 2700ft. Now form follows function-the cam in the 496 was a nitrous cam and its advantage was not seen until we hit the button. Did the 496 make less power yes and no. Apples to oranges

        Now we are planning on going blown, we have been told that it is better to use iron heads on iron blocks and aluminum heads on aluminum blocks, better head gasket seal, less prone to blown head gaskets. What are your thoughts?

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        • #49

          Re: What blower heads for a sbc?

          Re: What blower heads for a sbc?

          Interesting point about gaskets, seems the OEMS went to graphite head gaskets to deal with the different expansion characteristics of iron blocks and aluminum heads.

          My fabulous web page

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

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          • #50

            Re: What blower heads for a sbc?

            Re: What blower heads for a sbc?

            I've run 12 psi boost on big blocks with Fel-Pro gaskets and 20 with Cometics, both with aluminum heads and iron blocks. Guys do the same at more bost than that. I doubt there's much to worry about.

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            • #51

              Re: What blower heads for a sbc?

              Re: What blower heads for a sbc?

              We ran copper gaskets, but some guys running a blown SBC into the 6's at the same 2700ft had a head gasket problem and they solved it by switching to iron heads. We will try aluminum heads until we have a problem, if we have any problem at all.

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              • #52

                Re: What blower heads for a sbc?

                Re: What blower heads for a sbc?

                The problem doesn't show up on normal cars until they have a lot of miles on them, long after the stuff we build would have blown up or worn out or been taken apart to see how things look or get new parts.

                My fabulous web page

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

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                • #53

                  Re: What blower heads for a sbc?

                  Re: What blower heads for a sbc?

                  I've run 12 psi boost on big blocks with Fel-Pro gaskets and 20 with Cometics, both with aluminum heads and iron blocks. Guys do the same at more bost than that. I doubt there's much to worry about.
                  Yep, Fel-Pro #1003 head gaskets, 368 ci, 10.5:1, 68" Hg (~18 lbs.), iron block & alloy heads, 1400 hp. Whats not to like?







                  There are very few people in this world who's opinion I value, you are not one of them.

                  300 in 1999

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                  • #54

                    Re: What blower heads for a sbc?

                    Re: What blower heads for a sbc?

                    I've run 12 psi boost on big blocks with Fel-Pro gaskets and 20 with Cometics, both with aluminum heads and iron blocks. Guys do the same at more bost than that. I doubt there's much to worry about.
                    Yep, Fel-Pro #1003 head gaskets, 368 ci, 10.5:1, 68" Hg (~18 lbs.), iron block & alloy heads, 1400 hp. Whats not to like?







                    Got to love it.

                    Anything special done like an O-ringed block?

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                    • #55

                      Re: What blower heads for a sbc?

                      Re: What blower heads for a sbc?

                      Brodix heads and put in 17:1 comp.
                      What is this a diesel? :o
                      Escaped on a technicality.

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                      • #56

                        Re: What blower heads for a sbc?

                        Re: What blower heads for a sbc?

                        Got to love it.

                        Anything special done like an O-ringed block?


                        Nope, been do'in it like that for years. It's a bow tie block & a set Dart 23 degree heads because that's what I had laying around at the time. If you saw the stuff I use to run my Bonneville program you'd sheit.
                        There are very few people in this world who's opinion I value, you are not one of them.

                        300 in 1999

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                        • #57

                          Re: What blower heads for a sbc?

                          Re: What blower heads for a sbc?

                          Got to love it.

                          Anything special done like an O-ringed block?


                          Nope, been do'in it like that for years. It's a bow tie block & a set Dart 23 degree heads because that's what I had laying around at the time. If you saw the stuff I used to run my Bonneville program you'd sheit.
                          cool

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                          • #58

                            Re: What blower heads for a sbc?

                            Re: What blower heads for a sbc?

                            Brodix heads and put in 17:1 comp.


                            What is this a diesel? :o
                            We plan to run alcohol eventually. We also want to go FI and are leaning towards a blown BBC motor. We are going to build another short block. If we stay gas we will go 10.1 with nitrous and if we go alky we will go 12.1 no nitrous.

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