RD 350 transfer port cleanup

[Dvsrd]

Regarding squish band, combustion chamber shape and head geometry in general: I follow a retired Swedish diesel tech, who is repairing and building 50-125 cc two strokes, and testing them on his home built dyno. IIRC, he tested a 50 cc engine with an 80 cc aftermarket higher power cylinder, power in the 11-13 hp range. He tested two different heads with the same volume, and found a significant power increase. If you are able to understand Swedish, check out "Tvåtaktsmeken" on YouTube.

[RDnuTZ]

Wow. Reducing squish makes sense to me from the standpoint of raising compression, but I NEVER would have considered that a stock head isn't truly centered. It all makes sense though. Talk about some delicate machining work with a little wizardry!! I've tried reading 2T Tuners Handbook, but I feel like you need an engineering degree to understand half of what's being said. If you have any other resources, please point me in that direction! Thanks, Marc. Very very cool stuff.

here's a picture of stock T500 from another Mark thread. Notice the off-center plug hole and oval dome shape.

[SmokeAddicted]

That's so cool!! The overall concept makes sense, but to achieve the optimal spark/head position must involve some intimate knowledge (and math/physics)of any specific 2T engine. Explains why I see "Chuck" mentioned so much in performance threads. Very cool stuff.

I found A Graham Bell's book for free online 

[Dvsrd]

As the tread has wandered off into heads and squish, I wonder why many Suzuki two stroke heads had no squish area. Mark's T500, the GT750 and some PE and RM engines are of this design.
Not that Yamaha was much better, as the squish clearances mostly were too big to do much good.

[Dvsrd]

Btw, has any of you any experience with redirecting the secondary transfers to a more forward direction on RD's? According to Kevin Cameron this worked well on TZ750, Jan Thiel is also promoting it (aka "the leaning tower")

[sav0r (CL MotoTech)]

The lack of squish on those models was because they weren't attempting performance. Or at least, weren't trying to compete necessarily with similar displacement engines on power.

[m in sc]

mmm. i think it was an 'its good enough' design at the time. they were aiming for reliability, then performance.  a reliable 2t 500 twin from them was a big deal at the time. i think that motor was designed around 65-66 with of course, heavy influence from early 60s MZ design.  either way, it somhow works but its super dated. only bike ive ever had that pinged at idle.   

[Dvsrd]

mmm. i think it was an 'its good enough' design at the time. they were aiming for reliability, then performance.  a reliable 2t 500 twin from them was a big deal at the time. i think that motor was designed around 65-66 with of course, heavy influence from early 60s MZ design.  either way, it somhow works but its super dated. only bike ive ever had that pinged at idle.   

I seem to remember that the T500 was roadraced back in the 60s/70s, often in a Seeley frame?
I guess the engines were modified quite a bit for that use...Btw, is the T500 just like the 380 and 750 triples, just one pair of transfers?
(Although much better shaped transfer ducts, at least on the 750, than on any RDs, due to the pretty clever rotated cylinders)

[m in sc]

it was.

[1976RD400C]

I know I mentioned it before, but there was a Canadian that would show up at the club races in NH around 1980 with his tricked out T500. He could enter it in the RD modified class, where anything goes for engine and brake mods. He would blow the doors off all the RDs, and there were lots of them. I remember one weekend he showed up late and was pacing around in the pits, a bit upset, and in his French accent saying, "no practice, no practice". Well, it didn't matter, he won. 

[m in sc]

period ad.

[Dvsrd]

Was it really capable of a 13.20 quarter mile? That couldn't have been much slower than a H1/ Mach III?

[m in sc]

the 1st couple of years w the 34mm carbs, yup.  later not quite but close. they're stronger than most people think.  nowadays a lot of old guys fart around on them but they go pretty good. my previously stock 500 ran about the same as my 78 kz650. let's keep in mind , these were actually made to compete with British 650s & 750s, in particular, the Nortons. look at the lines of stockers  proportions. its very Norton ish in stock trim.

[RDryan]

Was it really capable of a 13.10 quarter mile? That couldn't have been much slower than a H1/ Mach III?

Ha, I was curious as to how it compared to the 69' H1 and google AI gave me an answer that the H1 was quoted to be running 12.2 seconds at 118 mph in the quarter mile. So a second slower I guess. 

[m in sc]

yup. the h1 def is a quicker bike, no doubt. but TBH ive had a few and really dont want another