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Thread: Interesting/disappointing dyno result. Thoughts?

  1. #11
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    Quote Originally Posted by seven4nineR View Post
    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)."
    and just before that it says "Next - a generalisation."

    but if it is at 104 i'd say that's too advanced for the capacity.

    this one was at 114 - http://www.bikeboy.org/996SPS.html

    i don't think it'll need much different ignition advance curve, unless that eprom is different to the std. they generally didn't change it much (at all) back in those days, and a 916 p8 eprom usually goes out the top around 39 degrees. a couple of degrees either way will make fuck all difference. might be worth see if it's stupid all the same.

    the 853cc 748r i did is here. same 104./108 cam timing - http://www.bikeboy.org/853rstuff.html

    your torque peaks amazingly early for a 4v. a std 996 peaks similarly around 7k and again at 8 ish, but it's low for a 926.

    i'd get someone who knows what they're doing to look at the heads.

    or piss those high mufflers off with those long pipes. see if that helps. it's a long exhaust. i don't think 45mm headers are too small, and i've seen st4s make easy 120 through a std header set, but 45mm pipes that long out of the cross over to the mufflers strikes me as not good. i'm sure a good spag system would be better. steve's is a non cross over system with a short link pipe from memory. maybe try something like that. cut the st4s front header same length as the rear header and start going up in steps until you get to 50mm and go at that into the mufflers.

    you could bore the bottom of the throttle bodies out to 48.5mm or so. 46.5 is std from memory. that's nearly 9% more flow area. how big are the inlet manifolds under that? then again, the 853r i did had std 44mm outlet diameter from memory. don't recall now. it had 45mm headers too, into a 45/50mm half system.
    Brad The Bike Boy

    www.bikeboy.org

  2. #12
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    Brad,
    My bike, 851SP3, is 95 mm bore and 907 cc.

    As I wrote I am fitting 748R heads and was thinking advancing the cams (104/108 in stead of 110/102) like you did with the 853R you tuned, would be a wise thing to do for my bike. Do I understand you correctly that you're saying that with bigger capacity bikes this will be too much advance?

    So it's perhaps better to keep the original 748R cam timing because of the 907 cc capacity, or somewhere in between?

    Your insight is really appreciated!

    Jacco

  3. #13
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    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.
    Brad The Bike Boy

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    Sorry for maybe stating the obvious and I do not wish to insult people here who are clearly far more experienced than I will ever be at engine tuning............but I would start at the beginning and make sure I was getting enough air into those injector intakes...............have you tried taking that sock of an air filter off and running without to see what the difference will be ???. The airflow into them cannot be as Ducati intended..........A lot of development went into the diameter , length and shape of the intakes.........and then you go upset everything with the sock. Then try lifting the tank and see if there is any difference. Most racing engines have just a gauze to stop small children and animals being sucked into the intakes. My guess is there is a few HP there especially in the top of the rev range...................or have I missed something.

    I think the idea is to get the air filtered first , have too much and let the intake do its job......................
    Last edited by dudlington; 05-13-2018 at 12:06 PM.

  5. #15
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    worth trying, but i doubt a pipercross would make much difference. maybe the shape of the 851 trumpets if it still has them.
    Brad The Bike Boy

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  6. #16
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    Quote Originally Posted by brad black View Post
    and just before that it says "Next - a generalisation."

    but if it is at 104 i'd say that's too advanced for the capacity.

    this one was at 114 - http://www.bikeboy.org/996SPS.html

    i don't think it'll need much different ignition advance curve, unless that eprom is different to the std. they generally didn't change it much (at all) back in those days, and a 916 p8 eprom usually goes out the top around 39 degrees. a couple of degrees either way will make fuck all difference. might be worth see if it's stupid all the same.

    the 853cc 748r i did is here. same 104./108 cam timing - http://www.bikeboy.org/853rstuff.html

    your torque peaks amazingly early for a 4v. a std 996 peaks similarly around 7k and again at 8 ish, but it's low for a 926.

    i'd get someone who knows what they're doing to look at the heads.

    or piss those high mufflers off with those long pipes. see if that helps. it's a long exhaust. i don't think 45mm headers are too small, and i've seen st4s make easy 120 through a std header set, but 45mm pipes that long out of the cross over to the mufflers strikes me as not good. i'm sure a good spag system would be better. steve's is a non cross over system with a short link pipe from memory. maybe try something like that. cut the st4s front header same length as the rear header and start going up in steps until you get to 50mm and go at that into the mufflers.

    you could bore the bottom of the throttle bodies out to 48.5mm or so. 46.5 is std from memory. that's nearly 9% more flow area. how big are the inlet manifolds under that? then again, the 853r i did had std 44mm outlet diameter from memory. don't recall now. it had 45mm headers too, into a 45/50mm half system.
    Sorry Brad, didn't mean to take what you said out of context, that line just jumped out me and seemed to fit my "symptoms".

    The exhaust was a complete schmozzle to be honest. Trying to find someone to make a nice job of marrying up the ST4 headers to the Arrow cans was a lot harder than I thought it would be. I eventually found a guy who repairs/restores expansion chambers and his work is like art in metal, absolutely stunning. We had a chat, sounded very promising, so I handed over the bike with some Phil Aynsley photo's (http://www.philaphoto.com/imageLibra...lbum=106&pos=2) but what I got back looked sorta like some headers from a BMW boxer had been adapted on to the crossover...very wide and very weird. Turns out he hadn't worked much with straight tube, which would have been nice to know beforehand! He did a fair amount of re-work tucking everything in and readjusting but in the end neither of us was a happy chappy so I just added it to the list of things I would do myself at a later date and dragged it home.

    I knew the 748R was a revvy lil' bugger so I also had this article in mind when I was talking to the guy welding it: https://motodna.net/exhausted-motogp-exhausts/. So I was trying to recreate the long lines of the Corsa spag systems only in 45mm (after reading your 40mm OEM vs 45mm ST4 vs DP 50mm test.) which would keep the torque peak lower, but given the bigger tubes than OEM 851 I didn't expect to see much difference to be honest.

    From the article above I took it that the header length is the critical number. Once the pipes hit the crossover each slug of gas from the the single 45mm header pipe is effectively split into 2 x 45mm pipes, so my thinking was that after the crossover (barring any major obstruction) is almost negligible resistance compared to the headers, particularly as the gas cools and contracts. That was my "logic" anyway, but could be completely wrong.

    As you say: double up on the earplugs, remove the cans, and run it up again with a 400mm shorter system.

    There's also my previous agricultural looking single system for a quick comparison.

    Quote Originally Posted by brad black View Post
    i don't get the obsession with 748r heads.
    I'm not sure about Jacco, but my arrival at 748R heads just seemed like good value. On paper the modern cams, big valves, instant compression boost makes good financial sense....until you read about the poor porting....bugger! The fact I got a CR gearbox and shower injection was a bonus. I can't run the shower injection in Oz but I could in NZ where/when I bought the engine so that was my original plan.

    It is a bit of a pain in the arse at the moment, but it's early days, and it's all good learning. No-one said learning was enjoyable.....(insert heavy sigh here)

    Quote Originally Posted by dudlington View Post
    Sorry for maybe stating the obvious and I do not wish to insult people here who are clearly far more experienced than I will ever be at engine tuning............but I would start at the beginning and make sure I was getting enough air into those injector intakes...............have you tried taking that sock of an air filter off and running without to see what the difference will be ???. The airflow into them cannot be as Ducati intended..........A lot of development went into the diameter , length and shape of the intakes.........and then you go upset everything with the sock. Then try lifting the tank and see if there is any difference. Most racing engines have just a gauze to stop small children and animals being sucked into the intakes. My guess is there is a few HP there especially in the top of the rev range...................or have I missed something.

    I think the idea is to get the air filtered first , have too much and let the intake do its job......................
    I know exactly where you are coming from with this, I thought long and hard about filtration. Pipercross don't have a bad reputation (these were supplied by Ducati Coventry/JHP), and this filter is actually the 748/916/996 unit so should flow 120hp easily enough without strangling it. The trumpets actually sit inside little air pockets with a foam pad between the TB's giving the filter it's shape. Different style I know but my 749R/999RS makes 168rwhp with Pipercross filters, only revving to a conservative 11.5krpm (rather than the 13.5krpm intended for the engine in WSB), so the foam itself can't be an issue and the big 926 filter has far more surface area to suck through than the 2 x small filters on the 749R/999RS. Again, could well be wrong but that was my thought process.

    (see pic's below of why I couldn't not run some filtration: I nearly cried when my 999RS engine inhaled a small screw)





    Not sure about "a lot of development went into the diameter, length and shape of the intakes" the poor flowing OEM corrugated "hoover tubing" doing a U-turn into the back of the airbox, and the tiny airbox itself would seem to contradict that statement! Sorry, not having a crack, just having a laugh.

    Still, it would be interesting to remove the Pipercross filter as you say and make the comparison.

    The tank is not sealed at all, and the wiring loom prevents fitment of the bottom carbon "plate" under the steering head frame so there should be plenty of airflow, even without ram air.

    I do wonder about the OEM 851 trumpets though. The flare is minimal at best, nothing like the later models. I'm not saying they are my problem but they definitely leave room for improvement.



    I'm heading away to work for a few weeks tomorrow so nothing will be happening in a hurry, but I really appreciate all the comments.

  7. #17
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    Seven4nineR

    Not sure about "a lot of development went into the diameter, length and shape of the intakes" the poor flowing OEM corrugated "hoover tubing" doing a U-turn into the back of the airbox, and the tiny airbox itself would seem to contradict that statement! Sorry, not having a crack, just having a laugh.

    With regards to your statement above...........just to clarify I was talking about the racing engines , not the crappy system of getting air into the engine on the road machine. That is an absolute abortion !!!. The racing air inlets are at least an attempt to force more air in than necessary. You can still fit a Headlamp (I have on 2 of my road bikes made this conversion as they have big engines) so I do not understand why the factory did not adopt this. On my SP4 project at the mo I will leave off those vacuum hoses as they are shit in every way and look terrible and just run an open topped air box with K and N filter.

    The open system with the gauze is exactly what they did a lot on race engines , max air but small chldren , animals and SCREWS will not get sucked in. What is interesting about your photos is the screw seemingly kept it shape during the squashing between piston and head as there are loads of perfectly screw threaded impressions..............
    Last edited by dudlington; 05-14-2018 at 03:29 AM.

  8. #18
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    Quote Originally Posted by dudlington View Post
    Seven4nineR

    Not sure about "a lot of development went into the diameter, length and shape of the intakes" the poor flowing OEM corrugated "hoover tubing" doing a U-turn into the back of the airbox, and the tiny airbox itself would seem to contradict that statement! Sorry, not having a crack, just having a laugh.

    With regards to your statement above...........just to clarify I was talking about the racing engines , not the crappy system of getting air into the engine on the road machine. That is an absolute abortion !!!. The racing air inlets are at least an attempt to force more air in than necessary. You can still fit a Headlamp (I have on 2 of my road bikes made this conversion as they have big engines) so I do not understand why the factory did not adopt this. On my SP4 project at the mo I will leave off those vacuum hoses as they are shit in every way and look terrible and just run an open topped air box with K and N filter.

    The open system with the gauze is exactly what they did a lot on race engines , max air but small chldren , animals and SCREWS will not get sucked in. What is interesting about your photos is the screw seemingly kept it shape during the squashing between piston and head as there are loads of perfectly screw threaded impressions..............
    Yep, all good comments.

    I actually wish I'd never been offered such a good deal on the intake and airbox, it was the signpost that sent me down the rabbit hole. It seemed a waste to have a near-stock engine underneath it and that was the point which things went off the rails and weeks turned into years.

    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....)

    I'll definitely be removing the filter for a run up the road. It is too easy to do not to confirm/rule out the obvious. Plus you've gotta hand it to the crews back in the day, arriving at solutions through trial and error rather than computer simulations, and you can't argue with the performance they screwed out of these old tractors.

    That screw bent 3 of the 4 valves and chewed up the seat of the other but it did make it out. But I couldn't see the lil' fucker making it up the vertical section of the exhaust. so i went hunting...sure enough there it was, hammered into a pretzel. It was all i could do not to hurl it across the paddock outside the shed but it is a good reminder, even if I would rather forget. Don't let anybody tell you Ducati's are fragile though, the bike never missed a beat with the RS rockers strong enough to open/close the bent valves. It was only the smashed up spark plug that stopped it firing on 2 when I went to start it for the next session that signalled a problem. Classic "electrical problem" haha.
    Last edited by seven4nineR; 05-14-2018 at 08:47 AM.

  9. #19
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    Quote Originally Posted by seven4nineR 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.
    Last edited by nine16; 05-14-2018 at 09:17 AM.
    '01 996R, '94 888 SPO Ltd, '88 851 Adamo racebike, '91 ZX-7R K1 homologation, '89 NSR250 MC18r5k, '01 Derbi GPR50/75, '71 CB450/500 cafť.

  10. #20
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    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.
    Griff
    To infinity and.......

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