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Thread: Interesting/disappointing dyno result. Thoughts?

  1. #1
    Join Date
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    Default Interesting/disappointing dyno result. Thoughts?

    So my 5 year classic race project is neariy "completed" (are they ever really done?). After starting with a tatty old Strada the engine is now sand cast Corsa cases, 96mm Pistal pistons/barrels, Ti H-beam Pankl rods, balanced 851 crank for 926cc, with 748R heads and CR gearbox, OEM 851 throttle bodies, 1 piece Corsa air box/Corsa intake, ST4 based 45mm exhaust. I've installed a P8 ECU but realistically for no real benefit as an aftermarket Power Commander PClll USB is the only real tuning instrument. The P8 has a "916 + 50mm slip-ons" FIM eprom installed, and I gave the fuel pressure regulator a couple of extra turns prior to tuning

    So what would you expect on a Dynojet dyno?

    I am an uneducated but avid reader of Brad Black's dyno reports, so his 851/748R/916 reports are in the back of my mind: http://www.bikeboy.org/748r.html

    Bottomline? I was thinking 120rwhp, maybe a touch more. Basically a 748R with a few extra cubes. As you can see I was a tad disappointed:



    I'm not hugely hung up on numbers and I realise all dyno's are different. For comparison a 998 FE on the same dyno produced 130rwhp.

    Things that stand out for me are the lowly 7000rpm torque peak and the way it falls off a cliff after 10krpm. Given the 748R cams/heads (36/30 valves) I was expecting something that liked to rev +10krpm, where what I've got seems to build power like a 2V 900SS. For info Brad's 748R report showed a power peak at around 11krpm and peak torque at around 8700krpm.

    Is it gasping for air with the OEM 50mm TB's? Is the 45mm exhaust too small given the short duration high lift 748R cams? Is the timing wrong? Or am I being unrealistic in expecting more?

    Funnily enough, 5 years on and I'd never actually ridden the thing. But prior to heading to the dyno someone may have (hypothetically speaking, Mr Plod) given it a wee run through the Perth Hills. They didn't (hypothecally) rev it too much but they can (hypothetically) confirm it made an awesome road engine, pulling like a train through the mid-range.

    But where is the top-end?

    So I can't help feeling just a little underwhelmed, with a bike returning pretty much as I delivered it, save for a something a bit easier to launch off the line.





    Last edited by seven4nineR; 05-11-2018 at 08:06 PM. Reason: Too much beer, removed some rubbish and adjusted pic size

  2. #2
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    Default

    So after a quick skim through your post, the motor's a 926cc 748R.
    In which case I'd be very disappointed with the final figures.
    Years ago when I 1st started playing with the 4 Valve 851's, I had a looong chat with John Hackett aka JHP Tuning/ Ducati Coventry, now John's a BIG 851/888 fan and a guru when it comes to tuning Desmoquatro's for racing.
    He's built more British Championship winning Ducati's than anyone else out there.
    Anyway what John imparted to me was...
    "If you want to start making serious power you need a bigger bore Header system", then on the question what's best for the final cans 45 or 50 mm ID?
    He replied...
    "Go for 50mm you'll never notice what you'll lose in the mid range, but you'll notice the gain on the top end".
    I followed his advice 1st making my own 50 ID cans and then later fitting a full 50mm Spaghetti system.
    This's with the full 50mm Spag' system...
    1st effort made 110 rwbhp, 2nd 116 and finally after going for bigger 35/30 valves the motor made 128 rwbhp, all of these figures are for a 916cc motor with softer cams (T1's) than you're using so...
    I think it's your exhaust system that's strangling the life out of your motor.

    Steve R

  3. #3
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    Do not despair just yet. What’s your cam timing. Like when is everything opening and closing? I agree that maybe 50 mm wouldn’t hurt, but choking it that much doesn’t explain the torque. And the lift certainly isn’t the issue, so if we’re mine i’d be looking at moving cams around.
    Last edited by griff851; 05-11-2018 at 06:40 PM.
    Griff
    To infinity and.......

  4. #4
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    But wait there’s more. Port velocity. A 748 has a lot less volume per stroke than a 926. The only way it can fill the cylinder is to increase port velocity. If your port velocity is too high, the air going over the valve surface increases past .6 Mach. From .6 Mach onwards a little shock wave forms and starts to choke the valve curtain area and redirect flow into the chamber, and it could be slinging the fuel out of the mixture as well. It can be worked out mathematically what the ideal is. I take it you didn’t do much port work otherwise you would have said so.
    Now my blow bag spins out quit freely past 11500, seriously rapidly actually, in all but top. (gets there but takes a little longer) It only has 9.8 lift, but the 748 drop cam head ports were taken out by me a tad to slow the air down.
    Food for thought.
    Other thing to note, increasing a valve size, not any port work, reduces the Mach number over the valve surface, that’s all. So if you went to a 40 say, your max rpm would increase. But then you run into valve inertia issues. Have look at ducati development from our machines to the 1199r. They are no fools.
    Last edited by griff851; 05-11-2018 at 08:31 PM.
    Griff
    To infinity and.......

  5. #5
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    Thanks for the comments, both of your ideas have been rolling around in my head.

    I didn't build the engine myself. Seeing as there were 3 different iterations involved (Corsa cases, 748R heads/gearbox with 851 crank etc) I gave it all to a local professional, along with some suggested timing figures taken from Brad's website. I'll confirm what I gave them shortly.

  6. #6
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    Wink

    I think the head is the most suspicious part in the disappointing results.
    The standard 748R head is a disaster port flow wise and looking at your dynosheet it seems there's an airflow problem. I did tune my 851SP3 couple a years ago and had g-inlet cams (SP5) installed but didn't upgrade valve wise, so still 33/29. My dyno curve looked just like yours (few hp less), hitting 100 rwhp @ 8250 rpm and then almost horizontal up to 106 hp @10.500 rpm.

    Running out of breath because of the smaller valves at higher revs.

    So I decided to upgrade as well:
    95 mm bore (was already done previous tune)
    Bumped up fule pressure (3.7 bar, was already done previous tune)
    748R heads (36/30 mm valves), ported inlet and exhaust side
    748R cams
    Pistons valve pockets larger and deck machined to gain compression (less pocket depth)
    static compression 12.2:1
    carrillo rods
    S4 cases
    dynamically balanced and lightenend crank (being done by Kaemna right now)
    standard SP3 headers and termi cans (45/50 mm)
    higher flow injectors (4)

    Looks a lot like your combo, but I guess the port work on the heads could be the difference.
    I was hoping for 120 RWHP as well, but up till now I just have parts, not put together yet.

    I also visit Brad's website a lot, great info! I figured it would be wise to advance the camtiming 6 degr. to shift the powercurve to lower rpm, don't need peak power @ 11k. Hoping for 120 rwhp @10-10.5 k.

    Sorry for this long post, but as my combo looks a lot like yours I thought I'd share my feelings

    Regards,
    Jacco
    Last edited by jakepeewee; 05-12-2018 at 04:40 AM.

  7. #7
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    Righto, so I've finally made it up to the shed and had a rummage through the crate of left over 851/748R bits I received along with the built up engine. In amongst it were a few notes jotted down for the engine builder when I handed over the parts/engines to be built into the 926.

    I had a nagging fear I may have given the builder some bunky 851 info but I was relieved to see I had basically copied the 748R section from the cam timing section on Brad's website and noted/highlighted his recommended 104/108 settings: http://www.bikeboy.org/camtime4v.html

    If the cam timing is "off" it is nice to know that at least I didn't tell them to make it that way, lol.

    Rereading the great info on that page one of Brad's notes stands out: "Advancing the inlets gives more midrange and less top end (therefore implying retarding the inlets gives less midrange and more top end)."

    So this looks like a pretty good avenue for investigation. As an amateur, cam timing is a bit of a dark art but it looks like something I'm going become a lot more familiar with.....wish me luck!
    Last edited by seven4nineR; 05-12-2018 at 08:13 AM.

  8. #8
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    Quote Originally Posted by jakepeewee View Post
    I think the head is the most suspicious part in the disappointing results.
    The standard 748R head is a disaster port flow wise and looking at your dynosheet it seems there's an airflow problem. I did tune my 851SP3 couple a years ago and had g-inlet cams (SP5) installed but didn't upgrade valve wise, so still 33/29. My dyno curve looked just like yours (few hp less), hitting 100 rwhp @ 8250 rpm and then almost horizontal up to 106 hp @10.500 rpm.

    Running out of breath because of the smaller valves at higher revs.

    So I decided to upgrade as well:
    95 mm bore (was already done previous tune)
    Bumped up fule pressure (3.7 bar, was already done previous tune)
    748R heads (36/30 mm valves), ported inlet and exhaust side
    748R cams
    Pistons valve pockets larger and deck machined to gain compression (less pocket depth)
    static compression 12.2:1
    carrillo rods
    S4 cases
    dynamically balanced and lightenend crank (being done by Kaemna right now)
    standard SP3 headers and termi cans (45/50 mm)
    higher flow injectors (4)

    Looks a lot like your combo, but I guess the port work on the heads could be the difference.
    I was hoping for 120 RWHP as well, but up till now I just have parts, not put together yet.

    I also visit Brad's website a lot, great info! I figured it would be wise to advance the camtiming 6 degr. to shift the powercurve to lower rpm, don't need peak power @ 11k. Hoping for 120 rwhp @10-10.5 k.

    Sorry for this long post, but as my combo looks a lot like yours I thought I'd share my feelings

    Regards,
    Jacco
    Hi Jacco, absolutely no apologies necessary, I really appreciate the comments and info on your build.

    Yes, I read a bit about the poor 748R ports/heads. I was initially disappointed at what I read after investing in what I thought was a good way forward with the build, picking up a complete low km 748R engine for the price of a set of SPS cams.

    My 748R heads had quite a shocking "edge" at the entry to the valve seat so I spent a bit of time blending that and unshrouding the valves to suit the 96mm bore prior to fitting. I don't pretend to be a porting wizard but they should be at least a little improved....from everything I've read they couldn't be any worse, lol.

    Bottom line though, I can't help thinking a stock 748R makes significantly more power than an 851, so even with poor porting the rest of the combo somehow works reasonably well? So to have an extra 178cc's underneath the R heads for no visible gain doesn't quite make sense.

    Revving it a little harder wouldn't worry me too much for what is a purely race application. I found an old article on the Hobbsport bikes back in the day (http://www.ducati851and888.com/showt...ight=hobbsport) and the journey to making them competitive. It talked of revving them to 13500rpm! Even with a freshly rebuilt engine and "short shifting at 12000rpm" they were making 140hp.

    Those are crazy numbers, but I braced the frame to make the engine a less-stressed member, went for the H-beam Ti rods, and balanced everything to give a little mental comfort revving it +10000rpm. You have to laugh that the current setup falls on it's face about then.....D'OH!

    Good luck with your build Jacco, it should be a beauty.

  9. #9
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    You built a custom engine and poped in a stock 916+header eprom and hope it works? Get your injectors cleaned and get a custom map. (Easier said than done, I know.) 916 has different cams and ignition timing and that eprom is by no means optimal. Install some bungs in the header for o2 sensors and do it right. Power commander can only do so much.

  10. #10
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    Quote Originally Posted by freqrider View Post
    You built a custom engine and poped in a stock 916+header eprom and hope it works? Get your injectors cleaned and get a custom map. (Easier said than done, I know.) 916 has different cams and ignition timing and that eprom is by no means optimal. Install some bungs in the header for o2 sensors and do it right. Power commander can only do so much.
    I have bungs in each header which were employed during the tuning. PClll USB allows for mapping of individual cylinders, just like the P8.

    The eprom installed was just a base to get the thing running, and tunable. No run = no tune. You simply have to start somewhere. From there the aim of the game is to optimise the AFR, whether you do that with a gazillion dollar Motogp ECU or an old P7, if they both produce the same AFR they will make the same power won’t they?

    So with an AFR of near enough to 13:1 across the range I’m not sure what extra mapping and an injector clean will achieve.

    Agreed on the ignition timing but living in one of the most isolated cities on Earth my options are pretty much non-existent on that front. Happy to hear otherwise but for all of the Apps available these days we don’t yet have “Diall-a-chip”, lol. Realistically I don’t think the possible gains there explain my missing ponies.

    PC are a suprisingly powerful tool, with the 1098R version i have on the shelf able to run individual maps for both primary and secondary injectors, so 4 individual maps....which should get some SP/SPS folks thinking! My PC also has provision for a quickshifter, just plug it in and enable it in the softwsre. They even have an “accelerator pump” function to crisp up throttle response should you so desire. So not a bad bit of kit.

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