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Lee,
With as many 13Bs operating in what seems to be exquisite comfort at 5500 rpm, is
there any compelling reason not to go to 7000 or so now that Tracy has a 2.7 PSRU
coming online? Do you think that additional 1500 RPM would have a dramatic effect on
engine life?
By 38 mm chokes do you mean the primary and secondary induction butterflies?
The figures you provide indicate a very nearly linear relationship between RPM and
HP. If that is so, it would seem that a street ported 13B operated at 7000 rpm would
yield about 177 HP and peripheral ports at the same 7000 rpm would yield about 237
hp. Does that sound right to you?
What kind of "epoxy" would one use to block up the side ports if one installed
peripheral ports?
With all that power (presumably from NA rotor housing, what's the exhaust like? As
bad (hard to tame) as a street ported Turbo housing?
I've seen pictures of bridge ports, and they look hideously difficult to do since you
have to leave "corner" of the housing there (presumably to prolong apex seal life?).
How much fuss and bother would peripheral ports be to machine? Do you have to
penetrate the water jacket or anything radical? It must be really difficult or have
a LARGE downside because I haven't heard from anyone who has them.
Is it safe to presume that the ~ 0.5 BSFC will hold pretty constant across the
various port configurations?
Inquiring minds need to know :o) ... Jim S.
Lehanover@aol.com wrote:
> In a message dated 12/13/2003 2:54:30 PM Eastern Standard Time,
> barrygardner@mindspring.com writes:
>
> > If I decided to get more ambitious in my porting, what are the lowest idle
> > speeds one can get with a semi-or full bridgeport? Or am I really best off
> > sticking with what Racing Beat calls the "streetable" port job?
> >
> The idle can be whatever speed you want, but it gets pretty jumpy under 800
> RPM. With a big street port, there is little change at all. Overlap between
> intake and exhaust is close to stock. A bridge port makes a big change in
> overlap and intake open time. So, it is real jerky under 1,800 RPM. The periphery
> port is about the same.
>
> I would start with the street port. A big well done street port is good for
> 229 HP with 38 MM chokes, at 9,300 RPM. If you use that for a while, and want
> a bit more, you can go back in and bridge port it and go up to 250 HP at 9,500
> RPM. Then if you still want more, epoxy the ports and runners shut and put in
> a periphery port for 300+ HP at 9,300 RPM.
>
> At speeds that you could use with a PSRU you would have (about) 165 HP-185 HP
> and 220 HP. Your HP may vary. My bridge ported 12A has 245 HP at 9,400 RPM
> breathing through two 38 MM chokes and still has 170+ HP at 6,500 RPM.
> You will have much better breathing so you should have more HP at 6,500 RPM.
> Calculate the torque for these outputs. Multiply the calculated torque value
> times the PSRU ratio. Compare that torque figure with the published torque
> figures for production aircraft engines. Notice the rated HP of the engine with
> similar torque figures.
>
> Close your eyes, and imagine leaving Sun&Fun vertically.
>
> Lynn E. Hanover
>
> >> Homepage: http://www.flyrotary.com/
> >> Archive: http://lancaironline.net/lists/flyrotary/List.html
--
Jim Sower
Crossville, TN; Chapter 5
Long-EZ N83RT, Velocity N4095T
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