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That's a really valid point mark.  It comes down to what we enjoy about our bikes and how and when we ride.

I had a VFR750 Interceptor at the same time as the RZ but I kept the RZ because it wasn't as fast or as competent because I didn't need to be riding fast around Chicago. The better we make our bikes, the faster we want/need to go to stretch them and ourselves and that inevitably is a road we have to get off before we get hurt.

I have a Ducati that I lusted after and rebuilt and customized and set up carefully and now it's almost done, I think I'll just keep the RZ and sell the Duc. 

Whenever I get nostalgic about the 500 I remember my talks with the old racers.  They would easily agree the 350 was a much better bike.

That 500 motor is amazing and is very neat+original but the riding setup on those bikes was terrible.  One of the few bikes out that there would feel twitchy yet refuse to go around corners.

NS400R was another dissapointment.  Had 3 and would rather have my RZs.  I ultimately found hte TZR250s were the most fun i've ridden so far.

My son had an RZ500 for a while and tried really hard to like it, but the handling sucked, brakes were so-so and power was lacking.  He sold a 120hp 900, so that was understandable. It was hard to get them to make much more power but a guy in Australia Russel Malley IIRC did a sterling job of letting a lot more ponies out of the stable.

I did borrow a friend's NSR400 for a weekend and it was a lot of fun to ride around winding country roads and infinitely better than the garage load of RD400s we had back then but it was too smooth and needed a few more horses to make it interesting. I am glad I had a chance to ride it but don't regret not buying it.

I bought mine in 93 and still have it.  Bought and built many other bikes but that's the only one I actually ride (not very often though). It came with Spec2 pipes and a Corbin seat and nothing much has been changed since I bought it other than maintenance items.

I'd really like a big bore (Cheetah) top end and modern forks and wider wheels, but mine is so close to stock I'd hate to mess with it.

But to your question: An RZ is faster than an RD, handles better, is stone axe reliable.  There is no comparison, the RZ is so much better.  Air filters disintegrate after about 10 years 

Compared to a modern bike, an RZ is slow and doesn't handle well but that's easy to fix and even stock, they are a barrel of fun and the sound as it goes through the gears is pure TZ to my ears.

I also have a shop full of GT750s and can't decide with the latest one whether to make it a monoshock, cafe racer with Gus Kuhn style tank and seat or build it stock to sell.  And of course I should sell the Phat Trakka to clear room for the GT750 drag bike, but that's another story.

i was referring to the hobbyist planes more than anything, piston props. But still. trends on the data will show up vs the o2, and if a head temp is used as well. whos looking at the gauge in this MC application to write a map? (efi) this would all have to be data logged.

Exactly. 

Flew in a small plane years ago in the evening climbing over the mountains with a full load and they did a great job of keeping the motor from melting as it struggled with a full load.  Unfortunately the gauges were all visible and EGTs were waaay up there and the headers could be seen glowing brightly.

The pilot would nudge the mixture or what I assume were timing levers ever so slightly to balance the need for altitude against the need to keep the thing from melting. Imagine if that motor had seized at 8,000.  We would have been stuck up there for ever. 

What we are looking for is usable information.  Masses of data is not the same thing.  And it has to be information that we know how to interpret and do something with.

As Mark mentioned, steady cruise where there's enough time to read a gauge and enough knowledge to know how to interpret the information, then it could be useful. I plan on adding EGT probes on my next drag race bike to see what temps get up to but there's no way I could read them at over 100 PMH, let alone do anything about it.

fJ6 were used in RD400E and F in Australia and I think Canada, so you could check the parts list and see if your dealer can get a pair or see if they are available in either of those countries as a Yamaha part.

They are leaner than say 5L1 used in C/D models and richer that 5I4 used in RD350s.  The closest Mikuni needle I found is 5DP7 which is a little leaner and may require larger needle jets or different air jets to get the fuel slope right.

You could measure your OEM needles every 5mm and compare the dimensions to keyster to see how close they are. To do that you can use an optical comparitor or just take a piece of paper and mark a line every 5mm.  Then make sure to tart at the very top in the same place and measure the diameters.

A simpler but less numeric way is to use a set of vernier/digital calipers and close them most of the way up on a needle and then slip the other needle in beside it. If the second needle is smaller diameter it will slide further through the jaws and if it's fatter it will sit higher.  It's fiddly but easy to see if one needle is thicker or thinner than another at any point along its length.

A few thoughts:
Piston engined aircraft do indeed rely on EGT readings but they are basically operating at fixed throttle for hours at a time and only make small changes to any control in flight. Motorcycles are the opposite end of that spectrum especially in traffic.

Where an EGT does make sense is on a race bike or on the dyno.  The same with a wideband O2 meter.  On the street the guage would be up and down like a kid on a trampoline and almost impossible to read and even harder to interpret.

I ran wideband O2/Lambda/Air:fuel (call them what you will) on a drag bike via a data logger where the throttle was wide open for the whole run and even at that, the variations were interesting.  On an LSR bike, that data would be useful and potentially so in real time. On a road racer, EGT gauges are useful to glance at down a main straightaway which is one of the few times the bike is wide open and for long enough to read.

EGT might be more useful to anyone with long straight sections of road and few LEOs where they could see what is going on, but the best power can only really be mapped on a dyno and then log EGT and/or mixture at peak power as a reference to compare to when jetting for changing weather at the track.

According to the rules we can go to 850cc. Right now we are like one overbore over, I forget what that comes out to, but I believe we are under 800cc. Anyways, we started the topic of building a second top end as a result of the displacement we have left on the table. Our current one works very well, and the cylinders are plated. So we want to keep it as is. So if we were to do it, the idea is to bore to get closer to 850cc, port, maybe do reeds, and consider a head design. Once the machine work was done on the cylinders we'd probably get them plated again. We are happy with our current head work, performance across the cylinders has been great, but the head gasket situation remains precarious. As you well know. The head design would mostly be to solve the head gasket issue, not particularly there to help with performance, though I suppose that goes hand in hand.

I didn't realize the bores were plated.  That sounds like a good idea. Stock liners are a little thin and not centrally placed, so going larger may require new liners and if so, might as well go with aluminum (plated) liners.

Head gasket leaks are an issue with those motors and I believe one cause is the uneven stud spacing.  And using inserts tends to exascerbate that. Brett DeS bolted his inserts to the top of the block with a ring of smaller bolts on his big bore motors to stop the leaks.

Heat management is quite a challenge because you need more (as in additional) cooling at low speed.  High air speed helps when going fast, but at lower speeds there's less air flow and more heat to dump.

I would try an electric water pump tied in to a thermoswitch. The stock fan switch should work or get a lighter switch.  Current draw might be high so that would potentially need a larger battery or maybe a separate battery for the pump with a relay. 

The problem with a larger impeller is that it pumps even harder (bigger power loss) at high revs and you have sufficient cooling capacity at top speed already.

What about air flow across the radiators?  Is there a way to improve low speed air flow without adding drag at higher speeds? Time to build a wind tunnel.......

What work do you need and what parts?

You mention the 115mm crank, and fitting a 400 trans, but do you need ignition and porting and bead blast and carbs rebuilt etc or could you do some of that yourself.

Engine building typically takes a lot more time that is charged for.  If you stripped and cleaned the cases and other parts that could reduce the time an engine builder has to take.

For example, simple things like cleaning the crankcases, getting the mating faces flat, countersinking all the screw holes etc take time for a builder, but you could do those at home with a little support.  And that applies to side covers and so on.  Take your time on jobs like that and farm out machining and porting if you feel up to it.

I saw an invoice of Chuck's on line recently and his parts bills were fair but he gave away his labor. He charged minimal amounts for things that just eat time.  As a hobby that's fine to support the sport, but it's hard as a business building motors for people like us. 

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.

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?

Cycle World tested F1, Toomey, Stock and Canadian pipes and they did indeed recommend Canadian pipes for the street.

For a stock looking bike they would be a neat way to go.

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Back when I weighed a little less than I do now, I was talking to some vintage race guys and concluded that eating lots of fiber and taking a decent dump before a race was the equivalent of about $2,000 of Ti hardware. 

I never did sit down to do the math on that one, but the conversion rate seemed about right.