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Thread: Interesting/disappointing dyno result. Thoughts?

  1. #21
    Join Date
    Nov 2007
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    Augustinusga, the netherlands
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    117

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    Quote Originally Posted by brad black View Post
    i don't get the obsession with 748r heads.

    you need to think in terms of inlet closing point more than centreline. centreline is just a mathmatical number, inlet closing is what changes how the engine acts. also exhaust opening. i wouldn't use a 748r exhaust cam if i had something better, and possibly not a 748r inlet either.
    Well Brad, I was never obsessed with 748R heads.
    Initially I bought bigger valves to fit in my original SP3 heads, but then I just happend to run into these (empty) 748R heads. I was told that these heads could be an excellent base for my project if the intake and exhaust ports were optimized. I also liked the idea of not meddling with my SP3 heads. And then I was told that the 748R cams would be better cams than the G-inlet and A-exhaust cams I was planning to install. New architecture cams: shorter duration and bigger lift. I know people like the SPS (T1?) cams, but this is what I went for. Also because of the positieve reports about the 853R (engine character) I read, these cams kind of appealed to me.

    So it got a bit out of hand. Next was the S4 cases I wasn't planning to do (but hey, with these 748R cams the motor is gonna rev, mind your cases!). And then the carrillo rods I also never intended to buy, but hey, when you're doing al this stuff it gotta be perfect.

    I hope it will al work out, but am scared I will eventually be somewhat disappointed, hearing all these things about the 748R heads ands cams.

  2. #22
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    Oct 2013
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    Belgium
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    The only thing I'll say against the race intake is the turning radius turns into something akin to a super tanker. Our "main" track down here has been closed to bikes due to safety concerns so we are now using a shorter/tighter track and I am seriously worried about getting around the tight hairpin. How ironic to go through all this shit just to have to bolt the old airbox back in. (and my wife wonders why I drink....)

    Well on one of my bikes with the racing inlets I have 30mm offset yokes and can get the ignition lock to work.........however the other bike with racing inlets has the 25mm offset yokes and that is definately tricky sometimes. Nearly been caught out a few times.
    Both these bikes with racing inlets run home made air boxes of a similar design. Max volume utilising the underneath of the tank also , largest vertical K and N filter possible and undisturbed inlets. First bike (1036cc) turns 165 Hp at the rear wheel and 130 Nm. The second bike (1198cc) turns 166 HP at the rear wheel and 139 N/m........The importance of getting air in cannot be understated especially at the higher RPM or on the larger engines.

    Get that sock off !!!!
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    Last edited by dudlington; 05-14-2018 at 03:55 PM.

  3. #23
    Join Date
    Apr 2013
    Location
    Perth, Australia
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    Quote Originally Posted by nine16 View Post
    Not to sidetrack things too much, but how are you securing the front of your tank since there are no slide-in receivers and you can't reach inside with the 1 piece airbox?

    FWIW, I don't have much to add as far as your tuning dilema, but I noticed your short-lipped 888 velocity stacks. On my build, I'm using ST4S throttle bodies (w/bored green injectors) and 996 stacks. Used the 996 ones instead of ST4S because I had the clip on, stack-covering filters. They aren't supposed to be the best for performance, but as noted here, I don't want screws or anything else finding its way into my motor.
    The front of the tank is just secured as per normal via the screw down pins. The sides of the airbox comfortably flex enough to sneak in the socket head allen screws and then let the sides relax back into position. I've made some small cut outs which allow the sides to fit past the heads of the screws.

    Yes, the OEM 851/888 throttle stacks bug me too. I'd happily change them out if I could find/make something better but it's a question of time at the moment. Unfortunately we're stuck with the OEM TB's for the class as the original injection system is mandated by the class rules. I could go the dual injector TB's as per back in the day but cost is a big issue on that sort of relative exotica.


    Quote Originally Posted by griff851 View Post
    Cycles to failure boys. Something to consider at 10000-13500.
    I looked at the period and what the WSB guys were doing. Thereís a period of open air box to semi pressurised, as the factory boffins struggle along the power chase. They knew a positive pressure is a good thing but getting it in without disturbing laminar flow is a bit of an issue. They had all sorts of things. Variable geometry velocity stacks etc. tank up off the frame, have a big intake at the front of the tank, donít have a big intake at the front of the tank, lots of stuff. By the time the 748 hits the market, they are well on the way.
    Now just because the velocity stack on a 748 works on a 748 doesnít mean youíll get the advantage automatically. The air box allows it to work.
    Iíve also read that a good velocity stack Vs. a hole was worth 4% increase in power in a still air environment.
    Yet more to consider is intake overall length will effect how much torque you develop. There is cool stuff like reverberation going on with pulses that have optimal harmonics. So lengths of things become important. You just need to make sure you going forward not backwards, changing and modifying things.
    Yes, there is some interesting info around on intake stacks. It has always "done my head in" that nearly everything you read seems to point to longer stacks being better......only for Ducati to steadfastly produce short stacks for their race bikes, and not just the older stuff. They must know something but it seems to contradict common theory and practice.

    Quote Originally Posted by dudlington View Post
    The only thing I'll say against the race intake is the turning radius turns into something akin to a super tanker. Our "main" track down here has been closed to bikes due to safety concerns so we are now using a shorter/tighter track and I am seriously worried about getting around the tight hairpin. How ironic to go through all this shit just to have to bolt the old airbox back in. (and my wife wonders why I drink....)

    Well on one of my bikes with the racing inlets I have 30mm offset yokes and can get the ignition lock to work.........however the other bike with racing inlets has the 25mm offset yokes and that is definately tricky sometimes. Nearly been caught out a few times.
    Both these bikes with racing inlets run home made air boxes of a similar design. Max volume utilising the underneath of the tank also , largest vertical K and N filter possible and undisturbed inlets. First bike (1036cc) turns 165 Hp at the rear wheel and 130 Nm. The second bike (1198cc) turns 166 HP at the rear wheel and 139 N/m........The importance of getting air in cannot be understated especially at the higher RPM or on the larger engines.

    Get that sock off !!!!
    Hooly dooly, what a couple of honeys! Love the black frame/wheel look, looks very tough, quite menacing. Great numbers too. If testing shows my sock to be a noose around the things neck I'll definitely be looking to follow your lead on the filters, thanks for sharing the pic's/info.

  4. #24
    Join Date
    Jun 2007
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    Bris Vegas
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    General rule, short runner length high rpm reduced torque, long runner length more torque lower rpm. I can explain it if your interested. Just PM, don’t want to bore anybody, it’s not as complicated as people think. It involves, a piece of garden hose and water, a room with a door and window and pouring a beer. Neither is cam timing, just looks like it when you first come up against it.
    Last edited by griff851; 05-15-2018 at 06:34 AM.
    Griff
    To infinity and.......

  5. #25
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    Oct 2013
    Location
    Belgium
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    I,m up for the beer thing .............................

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