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-   -   Budget 12A SP build (https://rotarycarclub.com/showthread.php?t=12975)

rxtasy3 01-09-2011 09:57 PM

tim, the wear on the oil control rings look really good, can reuse. if u reuse all the seals and springs associated with the rotors, they all should remain with/be put back where they came from. good luck with ur first build and hope it turns out to be a good running/long lasting engine. i myself only have 2 builds(same engine) under my belt and hoping to do more in the near future. so far have bout 80k on the 2nd build.

t_g_farrell 01-10-2011 09:25 AM

Micheal thanks for the comment on the oil control rings. Unfortunatley I
didn't keep the parts sorted as to what rotor they belonged to because I
thought I wouldn't be able to use the original rotors :banghead: Now it
looks like the original, lighter rotors can be used. I'll just make sure
everything is within tolerances when I put it back or replace it. The hard
parts are all so new that none of them show any wear at all. Especially
when compared to the other engine I tore down which was beat to death.

I think I'm going to do the street port by porting the secondaries fairly
aggressively and leaving the primaries pretty much stock except for
smoothing the area near the edges of the port openings a bit for better
flow. I've been doing a lot of reading on nopistons which has been very
educational. I want to maintian as much of my low end as I can but get
a good bump in hp once I hit the higher rev ranges. The exhaust ports
haven't decided on yet but I'm still reading.

Heres one question on the exhaust porting. Do you port the inserts at all or
just get close the edges of the end of the insert and shape it out from there?

NoDOHC 01-10-2011 07:28 PM

I usually pound them up as much as possible with a punch and hammer (until they are tight against the housing) and then polish them to 600 grit or so (minimizes radiative heat transfer from exhaust gasses, improves flow, makes slightly louder).

Constantly increasing cross-section is your friend for the exhaust.

For the intake, don't bring the port up any more than you absolutely have to if you intend to keep some semblence of low end. Raising the far edge (furthest from the housing) gives much greater performance improvements than raising the near edge and you can raise the far edge quite a bit without changing the port timing.

t_g_farrell 01-27-2011 01:22 PM

So are you saying for the exhaust you want a megaphone or cone shape with
no bump or waist in the middle? In other words you don't want anything thats
like a venturi on the exhaust.

It looks to me like if you follow the angle and contours of the stock insert
and carry that onto the housing as you port you end up with the classic
D shaped exhaust port. Good idea ?


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