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  1. #61
    Senior Member BasicQ's Avatar
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    Quote Originally Posted by EH179 View Post
    Basic, those quoted posts of yours are typical of what i remember reading years ago from Shrinker and Tuner...very clever guys.

    Do you browse the racingfuelsystems forum?
    Yes I do.

    They are from Shrinker but from what I think is a now a defunct forum called Motorsports village. I’ll send you the link to the whole thread if you want. Do you recall Shrinker came up with and manufactured his own carby design? I think the poor bugger passed away before it really got off the ground but you can still see what he came up with by googling Smart carb or something to that effect. An Aussie too.

    From all the sources of research I have done it’s those guys on places like racingfuelsystems that most correlate with what I see applied in the real world.

    Edit; don’t worry about googling, here’s the link

    http://www.smartcarby.com/index.htm


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    Last edited by BasicQ; 23-12-2020 at 09:05 PM. Reason: Add link

  2. #62
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    Motorsports village died when the owner and Tuner had a bit of a disagreement. Shrinker/tuner/Mark W were all around on the original Innovate forums which might still be archived somewhere.

    Racing fuel systems have a new forum if anyone isnt aware so go sign up!

  3. #63
    Do you ever leave? EH179's Avatar
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    Quote Originally Posted by BasicQ View Post
    Yes I do.

    They are from Shrinker but from what I think is a now a defunct forum called Motorsports village. I’ll send you the link to the whole thread if you want. Do you recall Shrinker came up with and manufactured his own carby design? I think the poor bugger passed away before it really got off the ground but you can still see what he came up with by googling Smart carb or something to that effect. An Aussie too.

    From all the sources of research I have done it’s those guys on places like racingfuelsystems that most correlate with what I see applied in the real world.

    Edit; don’t worry about googling, here’s the link

    http://www.smartcarby.com/index.htm


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    Yes, March, 2013.

  4. #64
    Senior Member BasicQ's Avatar
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    Default 750 Fuel Demon to 750 Street Demon

    Quote Originally Posted by guy incognito View Post
    Racing fuel systems have a new forum if anyone isnt aware so go sign up!
    Thanks for that, I read an indication from Mark W the forum would move but didn’t know it had and just found it.

    I’ll sign up now.



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    Last edited by BasicQ; 25-12-2020 at 11:44 AM.

  5. #65
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    Does anybody know Tuner's real name?

  6. #66
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    I'll have it somewhere from old emails and such, why do you ask?

  7. #67
    Senior Member BasicQ's Avatar
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    Default 750 Fuel Demon to 750 Street Demon

    Quote Originally Posted by GtoGeoff View Post
    Does anybody know Tuner's real name?
    Tuner, aka, Yeti, aka, Bigfoot

    aka, William Maley of Portland.


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  8. #68
    Senior Member BasicQ's Avatar
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    Default 750 Fuel Demon to 750 Street Demon

    Went for a drive today with the 850 down leg.

    This is one of the really early Mighty Demons that came out when Demon still had the Race Demon line. These early Mighty Demons had the main body of the non-removable venturi sleeve Race Demons with a calibration closer to the Speed Demon of the time. It bridged the sizable gap between the Speed Demon and Race Demons at the time. This carb has 1.562” venturi and 1.75” throttle blades. In the Race Demon line up it was designated 1000cfm and Mighty Demon 850cfm. One could only assume if the Mighty Demon was called a 1000 then they may lose sales to the target market and likewise calling the Race version an 850. Part of the Race Demon line up was an 825cfm with 1.425” venturi so it also wouldn’t make sense to market 825 and 850 together in that line up. Holley had the 1000cfm in the HP line with same venturi and throttle dimensions so that was the competition.

    So with it being an early Mighty Demon while the Race was still being sold it has a calibration a little bit different than what you get with a newer one today. The main difference is the older has .028” mab, pri MJ 85 and bottom emulsion .033” Newer have .031” mab, pri MJ 83 and all three emulsion holes .031”. Not a whole lot of difference but the ‘new’ specs emulate the Race Demon General Competition 1000cfm back in the day.

    So how did it drive? Well for starters I still haven’t drilled out the .031” emulsion and taped for removable yet in the metering blocks that came with the 750cfm. I was using the metering blocks from this carby that I had already done the modifications to on the 750 tune. The blocks that came on the 750 are on this carby. Only difference between the blocks on the two different cfm carbies from Demon was the IFR. I never really finished the tune on this carby and am now revisiting after a few things came to light on the 750 tune. I did however tap for lower IFR on the 750 blocks. So the calibration of this carby for today’s drive is as follows:

    Mighty Demon 850 down leg boosters
    Pri MJ 83
    Sec MJ 91
    Pvcr’s .059”
    From pv 6.5 rear blocked
    IFR .031” lower position
    IAB .070”
    MAB .028”
    Emulsion .031” blank .031” blank .031”
    Squirters pri 31 sec 31
    Pink cams pri & sec

    Having done some tuning on this carby already I knew there was no point going factory 85 pri MJ so I started at 83. Same for IFR. No point going through that test with .038” up high as I know the results already, Gina Rhinehart rich. IFR as low as .031”s should give me an indication of how far on the lean side it is and then go back up from there.

    So cruising at 60ks it was a tad rich at an average of .92/93 lambda but it soon leaned right out at 70/80ks, mostly 1.0 to 1.08 lambda. Then heading toward 90kp/h and up to and a bit over 100ks it flipped back to rich. Level highway .88/90 lambda average. Next step will be to go up a couple of sizes in IFR and reduce MJ to 80. I am thinking that will richen the transition fuel and lean out the mains a bit. From there take a look at air bleeds if needed to fine tune. Didn’t do a WOT test. That’s a Sunday morning in the secluded industrial area test.

    What sticks out like a dogs twig & giggleberries is the performance of what would be considered an over sized carby. My 383 has a single plane manifold and revs at 100ks is 3250rpm. Nailing it at 100 in comparison it out accelerates the 750cfm. If the butt dyno was lying to me the chirp on the newly laid hot mix on the Geelong ring road didn’t. In case you are wondering acceleration from lower speeds just as good.

    Report back with changes if rain stays away for the weekend.

    Can’t wait for Calder to open.


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    Last edited by BasicQ; 04-03-2021 at 04:52 PM.

  9. #69
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    Basic,

    A couple of comments.

    I think your rich 60km cruise is caused by the Idle Down Channel restriction being too big. It is the orifice that meters fuel and air to the transfer slot. A fixed orifice. In the original Holley book by Mike Urich, it is shown on page 30 in the lower photo as the 'channel restriction'.

    I think your lean cruise at higher speeds is on the main jet by then, so probably needs slightly larger MJ.

  10. #70
    Senior Member BasicQ's Avatar
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    Default 750 Fuel Demon to 750 Street Demon

    Quote Originally Posted by GtoGeoff View Post
    Basic,

    A couple of comments.

    I think your rich 60km cruise is caused by the Idle Down Channel restriction being too big. It is the orifice that meters fuel and air to the transfer slot. A fixed orifice. In the original Holley book by Mike Urich, it is shown on page 30 in the lower photo as the 'channel restriction'.

    I think your lean cruise at higher speeds is on the main jet by then, so probably needs slightly larger MJ.
    Is that the transfer slot restrictions in the pic? They are known to be a bit oversized in performance oriented carbies. I think they can be tapped for 10-32 for drilled replaceable restrictions.

    [img]https://i.ibb.co/3fKZJDp/EC978217-FFC7-4-DBC-8194-53-E2-A07-A29-E0.jpg[/img]

    My logic for dropping MJ size is how quickly or small a throttle angle change it took to go from 15.1:1 to 12.9:1 AFR. To me it was the mains starting and only transfer slot before that. I am also figuring that this larger venturi carb takes more to get the depression needed to get the boosters up and running compared to the 750 so mains are starting a tad later.

    What’s difficult to convey is that there is very little throttle to maintain these speeds. Using a throttle position sensor and logging the data would be the ideal way to do this type of tuning. Pin pointing changes would certainly be more accurate and an even more refined tune would be possible but I am not that ocd yet. Just looking to at least coarsely, with basic equipment have a better street strip type tune than generically provided by the carburetor companies.

    Thanks for your input Geoff, the transfer slot restriction could be a real possibility and I hadn’t considered it yet.


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  11. #71
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    Basic,
    I am not sure we are talking about the same thing?

    I was not referring to the actual T-slot in the carb bore. Is that what you are referring to? I was referring to the restriction that feeds the T-slot. It will be somewhere in the met block. I would expect it to be a pressed-in brass insert for more precision, not a hole drilled into the casting. Another name the Yanks use for it is the 'Economizer', because it controls the amount of A/F delivered to the T-slot, where much cruising is done. Hence the name Economizer.
    With T-slot length, emission carbs usually have longer slots [ leaner ] & perf carbs have shorter ones.

  12. #72
    Senior Member BasicQ's Avatar
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    Default 750 Fuel Demon to 750 Street Demon

    Not the best photo but are you talking about number 4 in the first photo? 19 is idle down well. It lines up with the indicated holes on the photo of the main body I put up. For metering blocks that don’t have a restriction that you described the holes with the red arrows are tapped to fit a drilled restriction. Second pic shows it done. Bottom pic is the Demon metering block. Just an open hole.

    [img]https://i.ibb.co/6m6Sxrf/899-A252-A-C604-4-B43-92-AB-E9-C9-C122-A075.jpg[/img]

    [img]https://i.ibb.co/qC6fqmt/D5777165-DFA6-49-E5-B65-B-C6236-EB8-C3-B3.jpg[/img]

    [img]https://i.ibb.co/GFT8LV3/ADF0-E7-C6-74-F6-4-B2-C-8095-BE6644-DD24-C5.jpg[/img]

    Are we on the same page?

    Actually, the more I think about it restricting the #4 hole in the metering block just restricts how much gets to the curb idle screw doesn’t it? It’s the slot that feeds the transition fuel through to the main body in those pictures. Are those economizer restriction fitted metering blocks a little different?


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    Last edited by BasicQ; 01-01-2021 at 08:08 PM.

  13. #73
    Do you ever leave? EH179's Avatar
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    I have no idea what Geoff calls the "economiser" channel?

    The transition slot, IIRC, is rather large in Demon carbs, and may need a restriction fitted, which nullifies whatever size the feed/economiser channel is.

    Basic, the first 2 photos don't work my end?

  14. #74
    Senior Member BasicQ's Avatar
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    Default 750 Fuel Demon to 750 Street Demon

    Quote Originally Posted by EH179 View Post
    I have no idea what Geoff calls the "economiser" channel?

    The transition slot, IIRC, is rather large in Demon carbs, and may need a restriction fitted, which nullifies whatever size the feed/economiser channel is.

    Basic, the first 2 photos don't work my end?
    [IMG]https://uploads.tapatalk-cdn.com/20210101/d97a109803f655e45c2a997a42da9225.jpg[/IMG]

    That work?

    [IMG]https://uploads.tapatalk-cdn.com/20210101/c897ae15fd29a196e8877271860fad09.jpg[/IMG]

    I’ll measure the t-slots on the Demons. Mark W would always say billet metering blocks have wider slots. Don’t recall if they are std Holley length though.

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    Last edited by BasicQ; 01-01-2021 at 08:29 PM.

  15. #75
    Senior Member BasicQ's Avatar
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    Transition slots measure ~7mm long (.275”) and .55mm wide (~.0216”).

    Anyone know std Holley dimensions?


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