RD400 drag race porting

[teazer]

Anyone got any advice on what can be done to get an RD400 closer to TZ750 porting?

I have an RD350 with 64mm bore TZ750A barrels and it's easy enough to ride, but I need more power.  I could fit a 3G3 Motrac barrel but that's still 347cc and close to 80HP and as they say too much is never enough, so I'm thinking that a full 430 with TZ porting has to be "more".

If I fit a 750D/E top end, it needs a 9mm spacer to account for the extra stroke and 115mm rods, but the piston rings fall into the inlet ports, so that isn't an optimum solution. 

Or I could use the hacked up set of RD400 barrels currently acting as a door stop, but that is even more complicated.  I would need to raise the exhaust port from 35.5 to xx.xmm down.  And then raise transfers from 51.5mm down to xx.xmm down.  Unfortunately there's not enough metal above the transfers without machining off fins and welding the roof of the ports up. That's a lot to take off and I can't use a 9mm spacer because the ring/s also fall into the inlet port.

Anyone built a big HP RD400 that would like to chime in?

[EE]

Because of the stroke difference you can't just transfer the TZ port hieghts to a 400. Try using the same ex port duration (or more) and degrees of blowdown from a TZ700 or 750 and see what you get for the 400 's stroke.

[teazer]

Thanks Ed.  That's actually what I did, so I went back and found an error in the data used for calculations.

I did use the 62mm stroke and 115mm rod and let the computer convert the port timings into port heights and opening/closing points, but there was an operator error so thanks for making me stop and check. 

Do you have a piston recommendation - single ring pro-light, by any chance? I found a YZ250 with the same TZ750 bore on Wiseco site that might work, but if the crown height is different, I can add that to things to be considered.

[racerclam]

Give me a call and we can discuss your porting dilema  702-858-9177 richstaylordporting.com

Rich