TECH: HONDA TRX450 ENGINE BUILD STEP-BY-STEP HOP-UP
What parts are worth what power By the staff of Dirt Wheels
A few years ago Dirt Wheels did a story on an owner-built Honda TRX450 owned by life-long quad fan named Daniel Gonzalez. Gonzalez was so pleased with the build that he took every opportunity to wear the knobs off of that TRX. Some of the miles were in races, but most were acquired having fun on desert and mountain trails. When Gonzalez did his build, he boosted the power with bolt-ons, but left the engine stock and original from the factory.
After all the miles and hours, the engine was a little tired. Eventually, the valves tightened up to the point that the engine had difficulty starting. From experience we knew that shimming the valves is a band-aid and not worth the time. It was definitely time for an engine rebuild. The Honda had an exhaust, a Robl carbon fiber intake and jetting. When the engine was fresh, the mods popped the Honda up to about 46 rear-wheel horsepower. That’s a nice bump considering stock Hondas start out in the high 30s for rear-wheel horsepower. To make that 46 horsepower, the TRX would need to actually start and stay running.
Well, it was time to freshen the old girl up, keeping budget in mind (because we’re cheap), and we wanted more power for minimum dollars. We also wanted to keep it on pump gas (back to that cheap comment), as that is convenient for lots of trail riding. We chose to have CT Racing overhaul the top end for us. We have been impressed with its valve work, and we wanted to see what they could eke out of it. We needed a piston, so for just a couple of extra dollars we upgraded to a JE 12.8:1 piston. That compression is at the top of the food chain for pump gas, and CT warned that we would need jetting.
Valve-clearance issues indicate dirt or sand getting through the air filter. The Honda runs titanium intake valves, and titanium valves don’t do well with re-facing like a stainless valve, so we opted for a set of ProX titanium intake valves. For the exhaust side, since we were popping in new valves anyway, CT went up 1mm on the exhaust side to 31mm. That makes the valves the same intake and exhaust sizes as most of the CR450R dirt bikes.
CT Racing did its five-angle radius valve job on the intake and exhaust. The multi-angle valve job has zero impact on durability, but it lets the head flow more, and with more flow we could stretch out a little more horsepower for cheap. The difference in cost from a three-angle to a five-angle is $10 per valve. Durability on the valves is controlled by how wide the 45-degree angle is.
The 45-degree area is the contact patch where the valve meets the head. Wider contact areas last longer, and narrower contact areas can make a little more power. You are usually only going to see a narrow seat-cut on a Supercross or national race motor that is coming apart on a very regular basis. CT uses a Newen CNC valve machine. This allows them to do multi-angle and radius valve jobs by just programming.
The CNC valve job is so precise that no lapping is required. They can get a 100-percent valve seal without lapping. This is important when working with titanium valves, as they can’t be lapped. Lapping takes the coating off of the valves and significantly shortens the service life of the valve. CT Racing does valve jobs for many Supercross teams because of their capability.
With the engine freshened up, we expected the power to return to the 46-horsepower number that the engine made before. Instead, we were pleased to see that the numbers were actually higher at 50 horsepower. We didn’t expect the numbers to increase that much with a race-quality valve job and that high-compression CP piston.
CT used a custom-grind Web Cam for our project. This cam was developed to make good power as a bolt-on, so no aftermarket valve springs were required. This cam also starts very well. Some electric-start Hondas do not start well with some aftermarket cams. In addition to the starting, we wanted good bottom-end pull to get off the corners in tight situations. It still needed to rev and make good steam on the big end. Adding the cam jumped the power roughly 5 horsepower.
PUTTING THE PIECES TOGETHER
Typically, a Honda TRX450 makes around 50 rear-wheel horsepower with 32 pound-feet of torque with a pipe, cam and jetting. All said and done, we pulled out 54.28 rear-wheel horsepower with 35.28 pound-feet of torque. That difference is the compression jump and the valves and valve job.
To attain good horsepower numbers, you will need to run the lid off of the airbox. For CT to get the power they got for us, they went back to the stock airbox and utilized a Pro Flow foam air filter in the box. CT’s Web Cam, along with the valve job with 31mm exhaust valves and CT pipe using 14 discs, requires jetting. The CT pipe comes with jetting for a stock setup, and all we used was the titanium needle. We needed more fuel on the bottom and top. We ended up with a 48 pilot jet and a 182 main to get away with pump gas and the 12.8:1 piston. This is in the league of a lot of ported full-mod heads, and we did it on an el cheapo budget.
HOW IT RUNS
It may go without saying, but jumping the horsepower up over 8 ponies and adding 3 pound-feet of torque is easy to feel when you hit the throttle. Gonzalez reports that the performance is stout, especially from mid-rpm to full throttle. It seems happy on pump fuel. The bad news is that his rear tires will pay a price, but he’ll be smiling as they wear out.
PARTS AND SERVICES
CT RACING: (562) 945-2453, www.ctracing.net
CNC 5-angel valve job $192
Pro-X Ti intake valves $65 ea.
JE 12.8:1 piston $199.99
Web Cam $424.80
CT compete exhaust with jet kit $529.95