CBR900RR Fireblade Performance Modifications
Inside this Newsletter
Stage 1,2 & 3
Ride day update.
The Broadford ride day was held in November, though it did rain most of the morning it turned out to be a good thing because Steve Brouggy from Australian Superbike School spent that time talking about basic suspension set up in terms that everyone could understand and apply in the afternoon when it cleared up. There has not been any date set for the next one, but we will keep you up to date when they are confirmed.
CBR900 Hot up
This has got to be one of the best bikes to hot up because of the really good increases in horse power that is obtainable. The ports in the cylinder head are small in comparison to a ZX7-9 or GSXR7 making it more suitable for porting and gas flowing and is generally easy to work on from a mechanics point of view. Complete dis assembly of the engine for cylinder boring is not ideal but well worth the effort and money spent.
This job has 3 stages to suit your own needs and the size of your pocket when it comes to shelling out the bucks, and can be added to at a later date when or if you desire. The CBR900 is never going to be an R1 beater but it will certainly hold its own with the Stage 3 kit fitted and provide many hours of adrenaline rushing ball tearing fun.
Stage 1 consists of a Hindle complete exhaust system, Dynojet carb kit and K&N air filter. The dynojet setting does vary from bike to bike which is why we like to dyno them to fine tune the kit. If that isn't possible, or you're interstate then the recommended settings in the kit will get you very close to the mark.
This example shows a stock figure of 118hp before we started working on it, (stock power for a CBR900 varies from 110 up to 118 hp). After fitting above mentioned parts and tuning to suit it finished up with a peak of 124 hp but more importantly a good 5-6 through the midrange where it is needed most. See graph below
The other aspect of this Stage is throttle response and acceleration. This is the single most important test because it relates to what the rider feels on the road. Its all about how fast the carburettor slide lifts up when accelerating at full throttle. The quicker it lifts then the harder it accelerates, but if it lifts too fast then your left with a hole in the midrange, so its important to get it right. You're probably wondering why they don't make them like this from the factory and there's a couple of reasons for it. To comply for ADR requirements it must pass emissions tests and noise tests, both exhaust and induction which means they are limited to how far they can go with it.
The graph below is from the same bike before and after fitting these parts. Obviously to make more hp it has to burn fuel, so expect an increase in consumption, it's not huge depending on how you ride but those who measure their mileage will find an increase. Of course if your too busy riding it then all you'll notice is the extra power that's on hand.
The price for this kit including Hindle stainless steel pipe, Dynojet
carb kit and K&N filter, fitted, jetted and dyno tuned from $1995.00.
You can bring the price down by not fitting the air filter or jet kit,
you will still get a good result, but if you're really hungry for more
power then that is the go before you get to stage 2.
Big Skid kit Stage 2
Stage 2 includes all of stage 1, porting, flow testing, and setting the cam timing. The first thing is to remove the cylinder head, set it up on the flow bench and record the flow readings so we have a base to work off. This is a very time consuming process because the flow rating is tested at 5 or 6 different valve lifts which must be measured using 2 dial indicators set up on a hand made plate bolted solidly to the test head that will give the same measurement and consistency every time a test is carried out. Depending on how much money is available to spend these tests may be carried out on all cylinders, inlet and exhaust, with a total number of 40 to 48 tests all before any re-shaping even starts. Once the data has been calculated and correction factors factored in it's onto the job of removing any restrictions in the ports and valve area. It's really important not to get too carried away with the porting tool as it is easy to remove metal and difficult to replace, so careful testing is required all the way through the process. Once the desired figures are achieved final clean up, seat cutting and re seating is done and the head assembled. As you will probably now realise this is a time consuming job which at the end of the day the money available to spend dictates the time spent in this area. To get a good result 4 - 5 days full time will need to be spent.
Now we fit the head to the engine and measure valve to piston and squish clearances before surface grinding the head to bring up the compression ratio. It's very important to get this right as to much compression means it wont run on pump fuel or worse still pistons hit valves and drives valves permanently into cylinder head causing much embarrassment for engine builder.
Once we have a handle on all of that then the head is assembled one final time, clearances checked and fitted to the engine. Because we have altered the deck height adjustable cam sprockets are installed and the cam timing reset using a degree wheel and dial indicator. The final tuning work can now be done to make sure that all the hard work has paid off in terms of good usable horse power. Generally these bikes don't need much jetting work and will run very well without making any carb changes. The graph below shows the result. Stock we had 113 hp at the rear wheel, with the Big Skid Kit stage 2 fitted we have a peak of 127hp but more importantly a good strong improvement right through the rev range.
Skud Kit Stage 3
This is not for the feint hearted, expect to have the front end in the air more than it is on the ground and if yours is an early model it will need a good steering damper to keep it from spitting you off. As with the other 2 kits all that has been done to this point is used as well as a Big Bore piston kit in either 945cc or 970cc. You can chop and change things or use your own choice of pipe, carb kit, piston kit, or not use some of it at all if your budget's tight, but if you want the best dollar value for performance this is the way to go.
Complete engine strip down and inspection is required, especially in the main bearing and big end bearing department as the load to these bearings is seriously increased, if you have the balls to use the extra power that's on tap. If the mileage is really low then you can get away with not doing anything, but if you want to improve things then it should all be balanced including the crankshaft, conrods, and pistons. It's a waste of time only doing the crank if everything else is out of balance and so on. Balancing everything is not essential but it does improve overall responsiveness and smoothness and lessen the possibility of something going wrong. It doesn't increase horse power! While this is being done the upper crankcase half which has the barrel cast into it can be bored out to suit the over size piston kit. Then it's a matter of fitting new bearings if applicable and checking to make sure that we have the desired oil clearance and that the piston ring ends are gapped. Once everything has been done final assembly begins. You may wonder why I said final assembly? It's because the engine is assembled to certain stages a number of times to check running clearances and make sure that it wont self distract when its fired up. This is where a lot of hours are taken up, one engine will take one person from start to finish including everything talked about in these pages the best part of one and half to 2 weeks. Now can you see why it costs so much?
When all the blue printing and measuring is complete its pretty much straight forward assembly work, finishing off by dialling in the cams to spec. All that is required now is to put 50 kms or so on it to bed in valves and rings, or if it has had bearings replaced a couple 100 road kmís before the final tuning is done, after which we should have close to the results shown in the graph below. Peak horse power has gone from 110 in stock form to 135 hp but most importantly the midrange has been given a healthy 15-20hp right through the range, the 970 piston kit is even better again but that's another story. Price is from $3000.00 not including pipe and carb kit.
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