Rotor/Crank Timing

[RodneyPierce]

thats why I run GO engines :lol: :lol: :lol:

 

[Jorgen Andersson]

Remember the old Pirelli advert? - "Power is nothing without control"

Jorgen

 

[Mark Leyde]

thats why I run GO engines :lol: :lol: :lol:

Hey Rodney Mums the word dude.

 

[Chris Wood]

thats why I run GO engines :lol: :lol: :lol:

lol no that would be because you are CHEAP and don't the real mccoy lol

 

[Steve Anderson]

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[dwilfong]

There you have it! BDC/65. Makes for a great race engine! Got to be careful on crank induction engines though, because the crank will get weak and there is not much room to work the case seal area.

I took two peoples advice to come up with this setup. Marty for the 65 ATDC and Dick Jones for the BDC opening. Pays to keep a open mind and listen to every one.

David

.....and Dick Jones got the BDC from me.

Marty, The early opening helps the torque. It becomes huge and it's really noticeable in the Monos pulling through the corners

Got to be careful in the rigger though it can KILL the launch.....but once you get the prop hooked up the torque comes alive.

The biggest launch problems are with the standard type drums, Picco, old CMB and New VAC so be careful about cutting on those drums in a rigger. That is why you'd see me load the prop in the water before launching the rigger back when I ran Picco and CMB. BUT once you get all of that extra fuel burning, you got Horsepower baby!

Not a problem with the Ruasian/MAC style drum....or crank induction engines.

So the intake systems that let the fuel puddle up will have a hard time on launch. this makes senses less velocity at low RPM fuel settles. It seams that the rotor timing will control the velocity at certain RPM. With a lot of duration the eng turns into a ram jet kinda. The pipe would have to match the system. Get it out with a wide angle and balance it with the same back angle.

Just thinking out loud.

David

 

[dwilfong]

It seems to me that later closing timing when coupled with high exhaust timing improves the rpm and over rev. We ran 72 degrees ATDC closing on a CMB 35 to get the over rev we needed from a SAW engine. However, everything needs to match. The time-area of all the ports has to be enough for the target power. Programs for time-area are widely available. As far as I know they all originate from Gordon Blair and were available on a CD with his book. More detailed advice was once sold as TSR port 2000. A description of it can be found here:

http://www.macdizzy.com/19896hopup.htm

Lohring Miller

Lohring check this out. Let me know what you think?

http://www.porting-programs.com/

David

 

[Tom Foley]

i have heard of great gains on the opening side of the rotor.. i cannot verify this but have talked to some people that say it is better to open the OPENING side.

but i have read in books that the closing side is where it is at.. so i will be waiting to hear on this.

chris

Stan Simpson built a Picco 45 bluehead with 30* BBDC/65*. That's a total of 275 degrees of duration. It ran 97 mph in the 45 SG in Oval trim and 107 mph in the same boat minus the turnfin. That was back in 1998.

Andy,

If I am understanding the intake housing of that Picco correctly the disc valve opening is in the draft of the big end of the rod? Probably the only style of intake that would allow an open timing that early?

Do you know if reversing the rotation of that engine resulted in less power, assuming the open/close timing are the same? The housing flow path looks like it favors the standard rotation.

These types of intake housings are definitely directional for flow .

 

[Steve Anderson]

.

 

[Nigtmare]

A picture so you guys can see what I'm talking about. Housing to the right looks to me like it was run reverse rotation?

Steve maybe that engine was run in a gear drive set up. I did that with my OPS and gear drives back in the 80's.

Nick

 

[lohring]

I can e-mail a spreadsheet that helps with calculations. This site won't let me attach it. It takes some time to understand it and I can't promise there aren't mistakes.

Lohring Miller

 

[Andy Brown]

A picture so you guys can see what I'm talking about. Housing to the right looks to me like it was run reverse rotation?

Steve,

I have never used BDC opening timing on that type of disc. My first experiences where with early CMB GranPrix engines with Zimmerman valves, then on Picco and CMB drums when they came out.

 

[Steve Anderson]

.

 

[Marty Davis]

A picture so you guys can see what I'm talking about. Housing to the right looks to me like it was run reverse rotation?

Steve,

I have never used BDC opening timing on that type of disc. My first experiences where with early CMB GranPrix engines with Zimmerman valves, then on Picco and CMB drums when they came out.

Andy:

Does the needle setting (leaner) help with the launchability problems? Low speed needle help?

 

[Andy Brown]

Steve,

With an open time of 30 BBDC there it still 30 degrees of transfer opening (with transfer timing of 120) for the crankcase to evacuate before the intake valve opens. The correct pipes will help the case empty more quickly. Lab testing in reed valve engines show that the reed begins to open just before BDC in many situations.

Something that could not happen if a vacuum did not exist in the crankcase.

Marty,

Leaner? Not reliably. Low end needle? I don't know.

 

[dwilfong]

Steve,

With an open time of 30 BBDC there it still 30 degrees of transfer opening (with transfer timing of 120) for the crankcase to evacuate before the intake valve opens. The correct pipes will help the case empty more quickly. Lab testing in reed valve engines show that the reed begins to open just before BDC in many situations.

Something that could not happen if a vacuum did not exist in the crankcase.

Marty,

Leaner? Not reliably. Low end needle? I don't know.

Let me see if I understand this correctly. The transfer opening late builds higher pressure in the case. so when it opens the high velocity going thew the port will pull a vacuum in the case early. So a early opening of the intake will draw air. that is if the pipe can scavenge the ex quickly enough to take advantage of the high velocity of the port flow.

David

 

[Jorgen Andersson]

Andy wrote:

Lab testing in reed valve engines show that the reed begins to open just before BDC in many situations.

I read about a bench test from a Minarelli reed 125cc engine, when the rpm was higher than around 16000 rpm, the reed never closed completely, it was open during the whole cycle.

Jorgen

 

[lohring]

Good engine simulation programs can answer a lot of these questions. They need actual dyno tests to confirm the findings, but have been pretty accurate. They take a lot of practice and a good understanding of engine concepts to learn. My favorite low cost (around $400) program is EngineMod2T. Contact Neels van Niekerk at [email protected]

Lohring Miller

 

[dwilfong]

I have bin thinking. :blink: Marty said that he tried a adjustable intake on one eng. But from the sounds of it it just changed the timing not the duration. This might account for the results. If you make a drum intake with a sleeve and adjust the opening time it might show some results. once up to speed you could change the duration. This could be controlled with a micro processor with RPM input driving a servo.

David

 

[Mike Larson]

Steve.... with the two rotor housings, i'm of the thought, picco made both marine and airplane engines..... hence the reverse rotation.....

I had quite a few of the old silverhead 45's at one time, and actually ran into the housing issue scratching my head.

I also had the dumb idea, that, the motor might be converted, reverse rotation to run as an OB, like the Lafluer conversions available...... of course i couldnt just flip the crankpin to the other hole in the disk.....

Steve Ball, knows this subject and the sought answers easily.... He did extensive work on my rotors, and the disks to make these old school motors rock. He'll surely give timing numbers and data found per the disk, and housing, as he helped me extensively keep the dinosaurs alive..... he probably still has pics of the fixtures he has to refine the housings and disk...... message him..... he's a cool cat, that, if youre willing to listen, he'll teach you...... good luck.... Mike