Honda TRX ATV Forum banner
1 - 2 of 2 Posts

·
Registered
01 Honda 400EX
Joined
·
7 Posts
Discussion Starter · #1 ·
I am wondering what kind of hp gain will i get on my honda 400ex with weisco piston, stage 2 hotcam, full exuadt FMF Power bomb and big gun slip on, ported & polshed head.? I’ve already done everything mentioned but the stage 2 hotcam and port & polish the head. Am I looking at 50hp range? I’d also like to mention iits widened 6 inches
 

·
Super Moderator
Joined
·
4,356 Posts
Are you looking at increasing the HP to 50 or by 50? The engine has 28 HP as delivered from the factory and that is peak HP - Honda does not publish the dyno charts or specify at what RPM the 28hp is seen.

With extensive modifications to the crankshaft, bore, oversized valves and adding forced air induction you might double the HP to 50, but it would be a short lived engine as all reliability would have to be sacrificed to achieve that goal.

With the mods you have described the peak HP might be raised to about 35 at appx 6000 to 9000 RPM.

Now for an actual comparison, the BHP (braking horsepower) of a stock 400EX will be higher than the 28 crankshaft HP of the engine. So with gearing changes you might achieve 50 BHP at the rear wheels. Publish the dyno charts after you complete the build just to see how close you come to your goal.

For those interested here is some TRX400EX info:
Honda 400EX Specs
  • Years Made: 1999 – 2009 (was not manufactured in 2010 or 2011 and was reintroduced as the TRX400X in 2012 then discontinued altogether at the end of 2013) in 2005 the engine cases were redesigned and reverse was added, however no changes were made to the crankshaft, cylinder, head, cam or valve train.
  • Model name: TRX400EX
  • Engine : RFVC, dry-sump, 1-cylinder, 4-stroke (developed from the popular and reliable XR400R - while the engine cases were redesigned, electric start added and the kick start removed; the piston, cylinder, head and valve train were direct transplants from the XR400R
  • Displacement : 397 cc
  • Bore and Stroke : 85 x 70 mm
  • Carb : 38 mm piston-valve with accelerator pump
  • Cooling : Air-cooled
  • Starter : Electric
  • Clutch : Manual
  • Transmission : 5-speed
  • Final Drive : O-ring-sealed chain
  • Ignition : CD with electronic advance
  • Suspension Front : Independent double-wishbone with Showa shocks, 5-position spring-preload, 8.2 inches of travel Rear : Pro-Link fully-adjustable single Showa shock, with 9.1 inches of travel
  • Brakes Front : Dual hydraulic 174 mm discs Rear : Single 220 mm disc
  • Tires Front : 22 x 7-10 knobby radial Rear : 20 x 10-9 knobby radial
  • Honda 400EX Top Speed: 72 MPH
  • Length : 72.2 inches
  • Width : 45.3 inches
  • Height : 43.7 inches
  • Wheelbase : 48.4 inches
  • Honda 400EX Horsepower: 28 HP
  • Honda 400ex Seat Height : 31.9 inches
  • Turning Radius : 10.5 feet
  • Ground Clearance : 4.3 inches
  • Honda 400EX Weight : 375 LBS
  • Fuel Capacity : 2.6 gallons including 0.4 gallon reserve
  • Colors : Black, Red, Yellow
  • 1999 Honda 400ex specs were virtually unchanged through 2009
 
1 - 2 of 2 Posts
Top