VM-30's or PWK-28'S

Started by Brad-Man, February 16, 2025, 11:55:41 AM

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Brad-Man

I almost asked this question in the current thread about VM-30's, but decided against it because if someone did a search for the topic it would be here.

I already have genuine PWK's for a Kawasaki I bought over 13 years ago for $85 ea. from one of the online parts dealers that is now gone.

I purchased them because of the easier to tune and better gas mileage standpoints

The question I have now is - do they flow as much air as the VM-30's due to their flatslides?

Would the VM's be better on street ported engines?  Think EE's stage 1.5 or 2...
Toys don't make the man - Man makes the toys.
1974 RD350
1975 RD350/400 project
1985 BMW K100RS

m in sc

here's a nugget to gnaw on. I went from vm34s to tm32s on the lc hybrid and saw basically zero loss. I'd go w the pwks .

Yamanatic

Either carb you mentioned will flow numbers beyond the demands of virtually any RD350 or RD400 except maybe those with TZ/TR top ends and/or 10,000 rpm redlines; in real world street riding, max-flow will be seldom if ever reached anyway. Since most riding is done in the mid-rage, smaller venturi carbs will give the most tractable and responsive performance, and may actually lower the power-band threshold - mixing is best at maximum velocity and proximity to the fuel source at the floor of the throat, which occurs at partial throttle settings.

Just my seat-of-the-pants opinion :vroom:
Warren



   
Of Course It's Gonna Make Some Noise - There's GAS Exploding In There!

m in sc

^exactly.  circuit velocity plays I to it a lot for tubability as well. my motor iss pretty ridiculously built and the redlvlimiter is actually set to 10.2k. but I also know you can get 70 hp thru a set of vm 28s. ;)

teazer

Just to add to the comments, some years ago Olav Aaen tested flow rates and HP of flatslides compared to round and found 2 things.  Size for size flats flow slightly more. In addition he found that HP rose by more than the flow difference.

So I would expect PWK28s to be a better option than VM30s as long as they are jetted correctly.

Mark, how did you find that jetting changed with flats versus round slides?

m in sc

main jetting went down a tad, i think i was at 350s or so now at 330-340. not much.

teazer

That makes sense with a stronger signal across the needle jet.  Thx

Brad-Man

Thanks all!

You have validated my thinking - and choice of carbs.

Toys don't make the man - Man makes the toys.
1974 RD350
1975 RD350/400 project
1985 BMW K100RS