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  • kry1300

    Sep 27

    well, regarding running 91ron fuel, stock ignition plate, 9 heat range plugs and retaining the airbox (in conjunction with my drag gearing and suspension set up) this netted an improved drag time of 11.32s (from 11.63 prior to gearing and suspension set up), but as expected retaining the same top speed over the line as previous of 185kmh, equating to a rwhp figure of around 100hp, possibly up to 105 as this figure is worked out on a race weight of 350kg’s but i expect my actual race weight is more like 375kg’s, i dont actually know my race weight as i havnet been in a position to measure it yet, but it would be a minimum of 350kg’s, so ive used this figure to work it out to date. actually, ill have to take my bike down to simms metal before i go to the drags this year and get a more accurate race weight, hmm, yeah.

    on the face of it, my tuning theories of obtaining 125rwhp the cheaper way have been quite optimistic.

    however, there are a few things to consider. first and for most, rwhp figures from the most popular brand of motorcycle dyno tune machine across the world are considered in many race tuners circles to be deliberately calibrated to deliver highly optimistic figures, wether this is generally from operator or machine error im not sure, however there is general concencus regards the general inaccuracies of this popular brand of machine to the point where true, or at least corrected, figures have been published for them, for instance, fj 1200’s in stock form are considered to produce around 120rwhp, but the corrected figure supplied is stated as 93-97rwhp, hence, considering this, im of the impression that the 125rwhp claimed by some on other sites for their xjr’s using what ive described as the ‘standard tuneup’ is likely to be one of these optimistic figures, imho.

    drag racers have generally always worked out hp figures using basic physics, in the form of hp calculators (essentially a calculation using mass, distance, speed and time), which is where my figure of 100rwhp has come from, if you consider the descrepency between the measured and corrected figures for the fj above, its possible that my 100hp is perhaps not far from others 125 in context, which actually bodes well for my cheap tuneup.

    secondly, its possible that i was getting some clutch slip when running my cheap tuneup as i proved i was getting slip when i went to the standard tuneup immediately after running the 11.32 from which the 100hp figure was worked out on, and thirdly, i have a suspicion that our NGK DPR plugs arnt much chop, or at least that i may have gone faster using the 8 heat range plug instead of the 9, which i may have the opportunity to prove at this summers drag tuning, so all considered i may not have been as far away from the average hp figures for the standard tuneup as it at first may have seemed. or maybe im the optimistic one, we may never know.

    speaking of hp figures, the legends race car engines (essentially being blueprinted fj and xjr engines) have figures advertised in the area of 150hp, but i believe that these are output shaft figures, and again the relatative accuracy of the dyno used comes into question, put this into perspective and again a figure that is not neccessarily to far from my 100rwhp is possible, if not probable, again, without back to back testing of engines on the same dyno machine in the same conditions, we will never know, in any case, we would only have a comparative difference between the engines, not neccessarily a definitive hp figure.

    a fella i chat with down the drags (who has run 9.50’s on a near stock busa) has also run 9’s on one those old original 80’s gixxer 750’s, he recons this bike only made 98rwhp, but it was light as fuck because thats what he concentrated on performance wise, his race weight would have been atleast 100kg lighter than mine, makes you think dont it.

    anyway, after fitting 36y’s, the 4 deg ig plate, 8 heat range plugs, running 98ron fuel, and a heap of testing and runs at the drags, i got my time down to 11.05 at 191kmh, so picked up another quater second and 6kph, which calculates a figure of 110rwhp, a decent improvement all considered (particularly cause im still running the airbox and my engine is internally (valve clearances aside) as the factory sent it out), and given me the scent of a 10 second pass, so this, ultimately, is what ill be shooting for this summer.

    ive got pod filters to fit, some larger main jets to go with them if i need em, but the other thing im interested in now is spark plugs, or at least wether our DPR plugs are a bit dodgy or not compared to the JR plugs ive now got.

    i recon i might just try these JR10B’s with the current tuneup (airbox still fitted) at the drags first, before fitting the pods, just to see what happens.

    so what have i learned, hp figures can be dodgy, and maybe spark plugs too, but also, maybe its about how you use it, as apposed to what youve got.

    time will tell.