| Upgrading the 4V Guzzi Twin First things first: Why would anyone invest in upgrading their 4-valve 1000cc Guzzi engine to 1225cc? Well, if you are interested in a bike with a tremendous horsepower/torque, and truly improved acceleration, this is for you! As an owner of a Ghezzi & Brian Guzzi (@440 lbs. with a tank full of gas, ready to ride), which is noticeably lighter than a Daytona or Centauro, and which the G&B frame could easily support more horsepower� I went searching for a way to build a higher horsepower 4V engine. In my mind there were two well-known tuner/builders for the 4v Guzzi engine, both offering quality and knowledge: Dynotec in Germany, and RaceCo in England. After some research, I concluded that the most reliable motors were the German-built Dynotec versions, and they are also Moto Spezial fuel injection tuning specialists. Very handy because I also wanted to remove the Weber/Marelli ignition system, due to the limited space aboard the G&B Supertwin. One look at the dyno-chart differences between the 4V 1000cc and the 1225cc engine (see diagrams), made me decide this would be the best way to go. This diagram shows a Centauro 1000cc with crossover, Mistral cans, K&N air filter and EPROM -vs- a Centauro 1225cc with the same modifications. Dyno-chart of the 1225 with cam. The 1225cc engine is modification is very involved, starting with the replacement of the original 90mm cylinder/piston with forged 100mm pistons. Valve enlargement is next on the list, from 33.5/29.5mm up to 35/31mm or 36/31mm (or you could go up to an impressive 39 mm as the Dynotec racebike, but this is best for race use only). The 36/31mm valves require a complete reconstruction of the head�s combustion chamber, so it is a very expensive modification. The intake and exhaust ports were flowed, and the Guzzi valve guides must be replaced with higher quality versions. Most 4V Guzzi motors (Daytona RS/Centauro) utilize Carillo rods, stock � which are high quality pieces that do not require replacement. The standard Guzzi cam followers must also be replaced by higher quality pieces. This is extremely important to note, since the coating on the followers occasionally have been known to start to fail between 15,000 and 20,000 miles (on the Daytona RS/Centauro), and if the problem is not caught in time then camshaft replacement is a must as well. Cylinder Heads before and after: 33.5/29.5mm vs. 35/31 mm Camshaft replacement was next, and depending on what you want, you have several available options. You could keep your original camshaft of the Daytona RS/Centauro (which have a highly different specs - have a look at the dyno-graphs). Or, as I did, you could also replace them for more midrange and top-end power (I chose a custom made cam by Dynotec, not shown). I wanted to keep the engine as reliable as possible, so the motor assembly (crank, rods, pistons and flywheel) were completely rebalanced. This is an absolute must, or you�ll drastically reduce the engine�s life span. The Daytona RS� flywheel is already light (opposed to most all other Guzzis of this vintage), so we did not touch it. We just made sure it was balanced properly with the other engine parts, as noted above. A Sachs Racing Clutch was used to deal with the higher engine power/torque. We used the Daytona RS gearbox, though we reinforced it due to reports of some failures with the 1225cc engine. A shank inside the main hollow gearbox axle was added in order to deal with the increased torque. A �deep-V� Moto Spezial 4.2-gallon oil sump replaced the original pan, which also allowed removal the oil cooler since I didn�t have enough space anyway. The oil pump was also replaced by nitride treated reinforced version. The stock starter is capable of starting the big-bore, so no real need of a replacement� but I decided to use a Ducati Superbike unit (smaller & cheaper than the Guzzi one) with great success� this will start the engine on the first push of the button. Ok, now it's time to talk about how it feels to ride it... I must say that I am very impressed with the engine�s torque. In first and second gear the bike easily wheelies, even in fifth gear it is tremendously stronger than before. Synchronized RPM/transmission downshifts become more critical, as the bike will lock the rear wheel even while downshifting from 5th to 4th gear! You must really be careful when running in the rain� one of the inconveniences of a 96 ft.lbs./@6300 rpm engine. Riding the mountains roads, as I do most of the time, I instantly noticed less gear-changes then with my �normal� (ehr...well, sort of) Daytona RS. This motor�s strong suit is it�s sub-6000 rpm midrange, with 3500 rpm still on top to use. As of writing this article the 3500 break-in miles are complete, so now I�m enjoying spinning the motor to its 9000 rpm indicated redline. Acceleration is tremendously stronger then before, with so much more power everywhere, even below 6000 rpm! To give you an idea how well it performs, while on the track I was able to out-accelerate the Aprilia RSV1000R and Ducati 996/998s. You can probably imagine what happens when the Guzzi accelerates past their stronger "Superbikes". To be honest, in the beginning my focus was more for midrange power, not just more top end as the Daytona RS had enough power up there for me. The new 1225cc engine has good acceleration from as low as 2500 rpm, even in 5th gear (though it and I prefer to stay above there). The acceleration becomes stronger at 4000 RPM, and even stronger at 6000 RPM, and on and on�!!! Fuel consumption for the first 1500 miles was purposely set-up rich, but once past the 3500 mile break-in, the Moto Spezial injection system has allowed me to tune the system, and I am now up to @30 mpg during �spirited� riding (much more quickly than authorized). The Moto Spezial unit (includes: odometer, tachomoter & injection system). This whole project has been very expensive� but given the results, I have no regrets. Jean-Marc � zebulon<at>supertwin.org Supertwin.org |
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