Performance Upgrades from other Bikes
RZ350 or Banshee pistons are a far superior piston than the stock pistons.
Of the cast pistons OEM are arguably the best, the Vertex, then Pro-X
Of the forged pistons Wossner, then Wiseco
The center tab at the bottom of these pistons must be removed thought (very easy),
And Vertex must be trimmed a bit if used in an RD400.
For Racing Bigbore Topends (66mm and up)
1980 IT/DT 175 pistons or Yamaha Blaster Pistons. Either piston is 5-6mm shorter than stock and requires machining the top & bottom of the cylinder to compensate for the height. The blaster pistons also have a 10deg piston dome instead of the RD/RZ/IT/DT 15deg so it does require reccutting the cylinder heads (but if yourdoing a bigbore you need to recutt the cylinder heads anyway)

The Crankshaft
For High HP applications Shot Peening the connecting rods is recommended
2T2 rods are the best of the OEM rods

Big End Bearings
I used TZ750 big end bearings in my landspeed bike but there were less options then.
93310-422BO “They look better than stock, and even better than Wiseco silvered equivalents. They are TZ125 big end bearings” Coyote
Suzuki RM125 bearings 09263-22060 “They are silver, flat cages, good bearing life and last much longer” Lyn
Suzuki RM125 RG500 Wiseco part number is B1047 Chuck ‘Supertune” Quenzler
“A common upgrade on the 73-80 TZ250/350’s (and also RD350/400’s) is the Suzuki RG500 big end bearing” Fondseca

Piston Pin Bearings
Kawasaki JS440 jetski 13033-3005

Crankshaft Main Bearings
10 ball ignition side outer bearing NTN BL305NR
11 ball ignition side outer bearing NSK BL305N
73-80 TZ250/350/750 outer roller bearings part number 93310-00012

Exhaust Flange Gaskets
76-78 US spec cylinders use Suzuki 14181-01D00 They have a larger I.D.

Clutch Friction Plates
“1981YZ250H,1983 XS400, 1986 FZ600S, 1992 FZR1000D. XS400 plates work especially well” Dave
“FZR1000 friction plate have about 40% more surface area” M in SC

Clutch Steel Plates
RZ350 (more surface area than RD400)

Straight Cut Primary Gears
I’ve heard that HB used YZ490 parts to do this conversion
TZ350 (Takes a little work)
Banshee/RZ aftermarket straight cut primary gears

Dry Clutch
TZ250/350. Use the clutch and primary sidecover. This requires a longer mainshaft, but the stock TZ mainshaft has a higher first gear than the RD’s and is part of the main shaft so you can either run the TZ transmission with higher first gear and close ratios or get a special mainshaft from this company: http://www.yamaha-tz-classicracing.de/uk/teile_getriebe.html that allows you to use an RD transmission with the TZ dry clutch parts. The TZ dryclutch cover does not come with a provision for a kickstart mechanism but I have seen several of these covers modified to use a kickstarter.

Transmission
It is highly recommended for racing that you get your transmission undercut by a company like R&D Motorsports. R&D also does transmission micro polishing and anti friction coating.

“According to Yamaha service bulletin 259 any spinning gear should have between .003” to .005” side play for maximum efficiency. Too little clearance and it will bind, too much and the gears can pop out of engagement causing the dogs to become rounded. Select the proper size shim and install it so the spinning gear is moved toward the sliding gear that engages it. Sizes are 20.2x33x.5,.6,.7,.8,.9, and 1.0mm (137-17427-00-05). And also 25x34x.3 and .5 (168-17428-01-03)” Lyn

Reeds
-TDR RD and RZ single petal fiber reeds, if your extensively modifying your stock reedcages ask for the Harry Barlow cut.
-1986 YZ125S reeds. “These are a 3-petal reed cut one petal off to fit your stock cages. Part number 55Y-13612-00-00” MBSteve
-Another option is the 93-2012 YZ85 reeds and trim them down just slightly at the front. These are a single petal reed but thinner than the TDR petals. Part# 4ES-13613-00-00

Reedcages
Your options are:
-Modify your stock reedcages, this works great for 80% of the RD’s out there, Stock cages are good for up to 70hp.
-RZ350 reedcages
-V-Force replacement cages for the RD reedcage which also fit the RZ500, and YZ85. Part number V382A (Use AG472A stuffers) Afhaldeman
-RZ350/Banshee V-force replacement cages
-Or my favorite stock YZ85 reedcages with either stock reeds or TDR racing reeds part# 88-EE
Anything bigger than this and major surgery to your cylinders or replacing the whole intake reedbox is required.

Intake manifolds
RZ350 are a nice improvement and allows you to use an intake crossover tube or boost bottle.
Tz750 intake manifolds P/N 409-13565-00 are discontinued but TZ Mike does make very good quality reproduction manifolds.

Racing Ignitions
-Motoplat
-PVL
-ProFlo (No longer available)
-TZ250/350
-MZB
-MZB also makes a CDI ignition with lighting
-If you just want to eliminate your points which is ALWAYS an improvement Vintage Smoke makes a DYNA ignition kit that bolts right on.