I have a lot of experience messing with engines and only do things I think will give me a visible result on the Dyno. Tuning an engine is not rocket science ,but it does require extreme degrees of patience , especialy when it's an engine you've never done before. All the results I have gained have been by trial ,error and destruction testing .I have an engineering background but no formal qualifications ,so I have to do it the hard way.The days of shaving metal from conrods & rocker arms & then giving them a good polish has gone ,engine's these days are built of top grade ,lightwieght materials that are made to tight tolerances ,that can't be matched in the garden shed.If you want to improve on crank & rods ,you have to go the titanium route which few can afford to take and until someone gives me the're bank account & says help yourself ,I'll stick to top end work .I tend to use engines that have been well run in say 5k miles so they are nice & loose.
The ZXR400 Kawasaki has been my most succesful result so far ,apart from my 450hp drag but that had a turbo and loads of nitrous oxide which tends to make big hp's gains fairly easy.Most circuit racers are looking for 5/10hp if there're lucky just to give them a slight edge.This sort of gain is not easy to achieve on a small capacity bike like the 400 , if you get a good one you might see 60hp rear wheel on standard bike, if it's a jap import probably 55hp .Our's was 72hp after tuning .Note there are some monstrous Hp claims made for these bikes ,so beware.Tuning an engine is really about bringing together the right collection of bits and pieces that work together.For instance there's no point in doing all you're engine work & then bolting an exhaust on the bike which wrecks the mid range power delivery ,so you can't drive out of corners.
Most people start with an exhaust & jet kit ,buy the best if it's available Acropovich exhausts as seen on nearly all world superbikes are well made & light ,beware makers who claim large hp increases as these will have bigbore downpipes & reduce mid range.The ZXR is one of those bikes you can't get an acropo for so I used an italian titanium road system with a race can .The micron race system works well on the ZXR .Race cans have little effect on performance as long as they are well made & light ,it's the downpipes that control engine performance.
Choice of jetting can be difficult ,different manufacturers kits work better in different situations .It's mainly the needle that's the problem they're never perfect ,usualy slightly to rich or to lean in the mid range once you've adjusted the top end.On the ZXR with no air box or with lid removed ,I found the dynojet needles were reasonable ,if you drop them to the lowest setting .I use 108/110 dynojet mains withh the aircorrector hole blanked.Idle 2.5 turns from fully in.The can ,airbox & exhaust should see you upto 63hp.Make sure you have the 32mm carbs ,also check bellmouth rubbers for shrinkage as they can get down to 26mm ,not much use to a 32mm carb .I make my own bellmouths .
Next it get's expensive with cam ,compression work & head flow.There is only one possible cam choice for the ZXR as nobody else does one ,that is Kent cams regrind of the originals (it can only be done to euro bikes cams as there's not enough metal in the jap one's).You will also need adjustable cam sprockets ,which we make, so you can set the cam timing .You will also need shims a lot thicker than standard ,which again I have to make.
The porting is quite simple but time consuming ,it involves cleaning the steps away from the back of the valve seats ,knife edging the intake dividers & matching the intake rubbers to the ports.Japanes cylinder heads a very good already so you're just tidying up the casting.
Compression & squish ,you need to bolt the whole thing together so you can measure vavle to piston & head to piston clearances .On the ZXR you can remove the base gasket & skim 0.5 mm off the head .Now you're upto 66/68hp.
As you can see it's a longwinded process for quite small gains & the cost is mainly in the man hours ,though from what I've told you here you can have a go yourself if you like .I have seen some ZXR engines with lightened cranks ,I was unable to measure any difference this might have made on the dyno .It is supposed to help the engine spin up quickly ,but it can also cause the engine to loose inertia making starts harder.
There were quite a few more tricks involving race airbox mods ,ignition and more severe engine work ,but they are alot of work for the last few hp's .
Aprilia RSV/R .First of all you need to remove the restrictor from under the airfilter & cut the restrictor out of the original can .Many bikes are sold as full power but I've still found the restrictors in them.
The first thing that was supposed to give a power gain was the acropovich can & big bore titanium side pipe ,there was a considerable wieght saving over the standard can , but much to my amasement I saw no power increase and if the acropovitch does'nt give a power gain it's almost certain that no other make of can will .I have also tested bigbore downpipes they give a couple of top end HP's but create a nasty glitch in the mid range .2 into 1 into 2 give a slight increase all the way through , but it's heavier & alot more expensive.
Next on my purchase list was a power commander ,on the Aprilia this only adjusts the fuel delivery ,it would have been nice to try a bit more ignition advance as this is usualy good for a few hp's .I will probably make some sort of ignition advancer for my bike .I don't have the facility to rewrite chips as yet ,which is why I went for the power commander.I have dynoed a few bikes with modified chips ,the ones that have been done properly are smoother than standard ,but they are in the minority .The power commander delivered a couple of top end hp's and got rid of a slight glitch at 6k rpm .So that gave me 112hp to go racing .
I have now been inside the engine & have raised the compression to 13:1 & done some port work , the end result was a general gain of 3/5hp without damaging reliability ,also the bikes standard starter motor can still cope .
Yamaha R6 is another bike I've had a fair bit of time to play with .I have seen 2 engines built by a quite famous tuner drop valves due to use of excessively strong valve springs ,this is fine if you intend to rev the engines harder than standard & happen to be a factory team who rebuild the engine after every race ,but I have found the standard valve springs more than strong enough to prevent valve bounce .the standard inner valve springs are prown to failure ,but will usually last a season & usually give a slight loss of power warning before failure.Apart from the valve train these engines are strong .
The original standard carb set up of these bikes can be very rough ,I've seen really rough power curves when they have been untouched .The first big power gain is the fitting of a race can or acropovich system for this you need to rejet ,the only jet kit to use on the R6 is the Factory kit (by this I mean the brand Factory rather than a genuine Yamaha item) .The standard air filter is as good as anything else ,on the race bike we run no filter just the wire mesh in the airbox to keep the gravel trap out.The standard cams in these engines have long duration this tends to damage the bottom end performance .I put kent cam regrinds in my engines they seem to work well .I have not tried the yamaha kit cams due to the high cost ,but they don't look as though they would be any better.
I do the usual
port cleaning work ,skim the head for a bit more compression & for all that
I get a gain of about 9HP over the original bike(which starts at 98Hp).The power
delivery is very smooth and gives really good corner driveability . I have a
few more little ignition & carb mods I do & also bigger rad to aid cooling
which gets a bit marginal at times.Here are dyno charts for before and after
.The standard bike shown in red was the best standard one I ever had on the
dyno , some were as low as 92Hp , but they all had a power curve as rough as
Suzuki 1200 Bandit .I've done alot of rejet's for cans on these bikes and know that you can get some ridiculous horse power from them usually at the expense of` rideability ,but I recently got around to tuning my buisiness partner Phil's bandit ,he had already cut the restrictor wire , fitted a race can ,K&N filter in airbox and a dynojet stage 1 kit.This lot works well together , stick to the 104 main jets and you get a nice even 5HP all the way and much crisper throttle response for bigger wheelies .Now I thought it would be nice to tune the engine so there was no loss of bottom end as he rides on the road all the time .So the engine got a set of kent reprofiled cams ,compression hike and port clean the results can be seen on the dyno chart.
I kept the original airbox ,downpipes and stage 1 jet kit so the engine would'nt loose it's nice bottom end driveability and the result surprised me ,as you can see there's hardly any change upto 6krpm and then it takes off .These engines still seem to suffer from top end oil starvation even though the oil pump is massive ,so fit an external oiler kit which we can supply and use good oil .I've also seen a few gearbox failures mainly second the wheelie gear .These engines are commonly dragraced so there are some serious tuning goodies to be had ,most of this is fine if you intend to drag race but can easily ruin a very tractable road bike.