Subject: [FlyRotary] Re: PP Timing

In a message dated 12/9/2007 4:32:22 AM Eastern Standard Time, lendich@optusnet.com.au writes:

The inlet timing would be the same ( 85 degrees) - but later, but not so late as to get into the compression stage, which might cause further issues.
 
I remember discussing this with someone (it might have been Lynn) but I can't remember what the negatives are with such a late PP.
 
Can someone put me straight on this again!
I hope I got those degrees right!
George (down under)

Port Timing

IO = Intake opens
IC = Intake closes
EO = Exhaust opens
EC = Exhaust closes

US Model First Generation RX-7
IO 32° ATDC
IC 40° ABDC
EO 75° BBDC
EC 38° ATDC

European Model Model First Generation RX-7
IO 32° ATDC
IC 50° ABDC
EO 75° BBDC
EC 48° ATDC

First and Second Generation 6-Port 13BPrimary intake (Part throttle/cruise)
IO 32° ATDC
IC 40° ABDC
Secondary intake (Part to full throttle)
IO 32° ATDC
IC 30° ABDC
Auxiliary high speed ports (Full throttle above approximately 4000 rpm)
IO 45° ATDC
IC 70° ABDC
EO 71° BBDC
EC 48° ATDC

Second and Third Generation Turbo 13B
IO 32° ATDC
IC 50° ABDC
EO 71° BBDC
EC 48° ATDC

Racing Beat "Street Port"
IO 25° ATDC
IC 60° ABDC
EO 84° BBDC
EC 48° ATDC

Racing Beat "J-Bridge Port"
IO 115° BTDC
IC 72° ABDC
EO 88° BBDC
EC 57° ATDC

Mazda Factory Peripheral Port
IO 86° BTDC
IC 75° ABDC
EO 73° BBDC
EC 65° ATDC

This information was copied from Paul Yaws very informative web site at:

WWW.Yawpower.com.

You cannot spend too much time reading on this site.

I could not get my mind around some of the numbers you cited. I am setting up a new house in Zephyrhills Florida, and will be building a new shop here as money becomes available. I have none of my stuff here, and had to refer to Paul's web page to see the open and close numbers. This is my wife's computer, and she has nothing about rotaries on it.
We will be in Ohio for Christmas and we will keep that house for summer time.

Of the 4 events called out in both piston and rotary engines, the intake port (or valve) in the piston case, closing point have the greatest effect on lower to middle range power. This also applies to the Pport engine. 

Note: that even the exotic high speed ports on the 6 port engine close at 70 degrees ABDC.
My Bridgeported engine closes at 80 degrees, techically, but is flowing very little at that point. (big radius and polish job on the closing line). Extending the closing point to gain HP higher up the RPM range is fine for a car, or an application where torque can be mulitplied by some sort of transmission, but the fixed loading of a propeller may not allow you to wind up to your ideal or near to your ideal power RPM. So a robust mid range is a must.

The side ported engines (even street ported) open the intake port After BDC. So exhaust dilution is nil. In the Pport engine, this is not possible. The big hole in the housing will be opening long before the exhaust port is closed off to any extent, and dilution is going to happen.

From this fact alone I deduce that the intake port should close just after 70 degrees. That the intake port should open as late as it is possible to build. The intake port would have a near rectangular shape, not far removed from a tall looking exhaust port. Even so, the round port may be flowing so poorly near the open and close points that very little  affect may be noticed. The top of the exhaust port I would leave stock. I would widen and radius the sides of the port. I would open the port just a bit early with a slight bow to the centerline, and a generous radius.

The idea here is to minimize overlap.

The Pport engine has the pointed rotor tip to open and close the port /vice the flat side of the rotor. The flow is uninteruped in effect, with the down side being that the flow is directed right out the exhaust port, producing the giant fireballs the racers love to generate.

The RPM where this shuts off is controlled by the overlap period.

Airplane engines operate in the low to middle of the RPM range of the engine.  My bridgeport idles at 2,200 RPM. The hint here is that automotive like closing points will produce the best airplane engines.

A poorly done Pport engine will massively outperform a side port engine. The Pport will be less happy with exhaust system problems. More thought to header lengths and muffler design. A function of overlap. Smaller header tubes rather than larger. Same exact length a must. Same angle into a collector. Longer rather than shorter.

The idea here is to have the port close before a reflected wave can get back to it.

The port numbers I could give you from home are from Mandeville modified housings that were used up to 10,700 RPM, and that data would probably be of no value.

Sorry.

Lynn E. Hanover

Thanks Lynn,

It goes without saying that I always appreciate your contribution. I may have to refer back to what you were saying to clarify some points.

I now understand the closing event has the most effect on the mid range power we need in Aviation (why is that? and why is your BP closing of 80 degrees flowing very little - there seems to be plenty of suction still going on?) and that closing event should not exceed 70 degrees ABDC. This is probably something you told me previously and I hadn't remembered ( or understood properly). However the Mazda Factory PP is 75 degree IC, perhaps allowing for higher HP at the higher RPM range. Whereas the Leman's engine seems to be about 70 degrees ABDC.

Secondly, the later the opening event the better ( I understood that one) because of overlap and contamination of the inlet charge at lower RPM. Now if we could just close it before we open it, we would be way ahead - but of course that is not possible, so the squat PP is the next best shape and timing.

 

So the opening later is better; but the closing later is not good! As we say in Australia - BUGGER!!

 

Anyhow there is another reference in your response which I don't quite understand and that is "So even with red lines at or above 8,000 RPM this modest port closing is more than adequate (this is understood). If I remember correctly (this becomes less likely with time) " Can you explain the last sentence about (less likely with time). Do you mean later openings gave better higher RPM, HP in the racing industry.

TIA

George (down under)