OW31 Top End

[JR]

Hey All, Does anyone know if an OW31 Top End will bolt on to a RD 400 bottom end?

[m in sc]

wrong stroke but the pattern is the same

[JR]

Can R5 cases be used?

[m in sc]

yes.

[teazer]

Do you mean a genuine ex works 6 port with reed valves or just any TZ750 top end?  I have an early TZ750A top end on a set of RD350 cases with RD transmission and TZ waterpump and crank.  All TZ750 top ends have the same bolt pattern as an RD250/350/400.

[JR]

Yes Teaser, a reproduction 6 port with reed valves. Can a RD400 crank be built with 110mm rods?

[bitzz]

You can use 110mm rods
or a 5mm base gasket from Cometic... or 4mm and take the port change

[John Ritter]

Might want to consider the rod/stroke ratio if for street. You would be going from an already 1.85:1 to 1.77:1, no problem on a well maintained race setup. Just a thought.

[JR]

Would a LC setup like this be too hot for the street?

[teazer]

Not exactly the best set up for the street.  If you want to use the RD400 bottom end, keep the 115mm rods, use a lift plate and then work out what changes you need to make to porting to make that all work. 

6 transfers are better than 4, but you could usefully increase the reed area and use even larger carbs if you insist on using that top end. 

I fitted a 409-OO 64MM bore "TZ700" on an RD350 bottom end and it is really mild. For the street it would be best to port it to what you want in terms of port timings to get the time/are that matches how you plan to use it. You can use any of the commercially available software such as Bimotion or MOTA to devise targets and port dimensions to match those targets.

For the street, I think an RZ or Banshee bottom end with Athena 421 or CPI top end would make a lot more power.  You need an RZ transmission though.  Banshee ratios are not the best.

[Jspooner]

I have a TZ/RDLC motor in one of my street bikes and I love it. Runs awesome and makes really good power. If you are looking for power though I'd bet Teazer is right about using an RZ or Banshee motor, but in my mind there's just something about the "TZ" part of it that's just really cool.

[JR]

OK All, If I want to build a dirt drag engine for the 400cc gas class, 500 foot dirt track, can be 410cc max but 4 strokes can be 450cc. What's the best setup? Any and all opinions accepted! Joe

[m in sc]

long rod 375 setup id say.

but if you are working w a 400 setup, that limits a few things, so id either trade out the 400 lower end for a 350 one as the options get more spread out (375 setup, etc) or track down a set of air-cooled 400 cyls and have them ported to the moon.

[Jspooner]

I'd use the motor I have but only more heavily ported with 40 or 42 lectrons or a heavily built banshee motor at the max bore size and still be under the class limit, also with giant carbs.

[teazer]

I'm with JSpooner.  If I already had a solid 400 foundation, I would develop that as far as it can go with much bigger reeds and carbs and ports.

if I was starting from scratch I would seriously consider a built Banshee with say a 421 CPI or Athena top end or larger and build a motor that could make way more HP that a ported 400.

If I had access to a 6 port TZ350D/E top end, I would sit down and work out target port-time areas and then work out if a 62mm bottom end would work and where would the ports need to end up.

Either way, I would start by working out HP targets and work through what I would have to do to achieve them before I started to sink tons of cash into the project.  And if all budget becomes an issue as it does with all my projects, work out what you can do to a 400 to get as far as you need to go. Not a lot of point in sinking say $10 grand in a fully built banshee motor to win a $5 trophy and bragging rights.