exhaust timing on a .21. How much is too much?

[RodneyPierce]

Jerry, I will be running with no water tomorrow, atleast for a few tanks. The water is getting cool enough here now, weathe rhas been in the low 70's for the last couple weeks. I gotta get some heat in this pig.

careful of no water on an inboard.you can destroy a p/l i a couple laps

Steve, I ran it this way last weekend, and she barelly got any heat in her. I ran it for a good 5 or 6 laps at WOT with plenty of fuel.

 

[hydro rob]

Yea Rodney is right, all mine have been super tight as well, when I ran mine for the first few tanks it barely got over 120 on the temp gun.

 

[Chris Wood]

How would a dome give a longer duration? And what do you mean by "the dome runs a higher compression ratio?

Hey andy,

well i could be wrong here, this is just what i was thinking.. with a flat top piston on the down and up stroke, when it comes by the exhaust port it should be the same all the way across the piston face.. on a dome piston, the outter part of the piston goes down the exhaust port sooner than the center of the piston. because of the taper on top of the face of the piston.. if i am making sence.

as for the compression ratio. on a dom piston i am under the impression that the clearance on the outter most edge is different from the center. unlike a flat top that is the same all the way across. i would assume then that the compression ratio is different from the center of the piston to the edge of the piston on a dome. is that correct?

meaning that if you set the head clearance say at .006 on the outter edge then the center may be say .003 or what ever that number ends up.

i could be all wrong on this also

chris

 

[mtruex]

How would a dome give a longer duration? And what do you mean by "the dome runs a higher compression ratio?

Hey andy,

well i could be wrong here, this is just what i was thinking.. with a flat top piston on the down and up stroke, when it comes by the exhaust port it should be the same all the way across the piston face.. on a dome piston, the outter part of the piston goes down the exhaust port sooner than the center of the piston. because of the taper on top of the face of the piston.. if i am making sence.

as for the compression ratio. on a dom piston i am under the impression that the clearance on the outter most edge is different from the center. unlike a flat top that is the same all the way across. i would assume then that the compression ratio is different from the center of the piston to the edge of the piston on a dome. is that correct?

meaning that if you set the head clearance say at .006 on the outter edge then the center may be say .003 or what ever that number ends up.

i could be all wrong on this also

chris

chris,

only thing that changes the duration is when the port closes, the shape of piston top has no influence..

also, you would not want to have less angle on the squish band than you do on the piston dome..that would be like running the squish angle the opposite way with a flat top piston, not good..

 

[Andy Brown]

Thanks for handling that Martin!

 

[steve wood]

Thanks for handling that Martin!

also, you would not want to have less angle on the squish band than you do on the piston dome..that would be like running the squish angle the opposite way with a flat top piston, not good..

the first 2 nova 35 plus motors i seen had a 3° angle on the piston and a 1 or 2° on the head,for a reverse squish!

 

[Glenn Quarles]

Friends, I always run a new motor WITHOUT water for the first runs (sometimes as many as 10 or 12 runs depending on the outside air temp). If you have the needle set nice and rich you will not be able to get the motor up to the proper running temp with water on it. I find that running the motor TOO cool at first actually causes more wear as the sleeve doesn't get enough temp to expand to the proper size.

On the .12 motors I do not run water at all most of the time (in my hydro).

Glenn

 

[RodneyPierce]

ran here today, and uploading video now to youtube. not bad. This vid was early in the day, so you can hear its pretty darn rich. Started leaning on it a little bit more towards the end of the day, and it really started to sing. its finally loosening up some!

 

[Jerry Wyss]

Friends, I always run a new motor WITHOUT water for the first runs (sometimes as many as 10 or 12 runs depending on the outside air temp). If you have the needle set nice and rich you will not be able to get the motor up to the proper running temp with water on it. I find that running the motor TOO cool at first actually causes more wear as the sleeve doesn't get enough temp to expand to the proper size.

On the .12 motors I do not run water at all most of the time (in my hydro).

Glenn

Well said Glenn, Perfect in fact!

 

[RodneyPierce]

here she is. Nothing to crazy. Ill have to get more video next time when its not so rich for break in.

 

[Jerry Wyss]

He sure doesn't look very "unlearned" to me

What method of heat check do you use Rodney? The Breakfast Cereal method, heat tag,

gun or "it runs hot enough with the needle right there" kinda deal.

 

[RodneyPierce]

the "it runs hot enough with the needle right there" method. LOL I just usually feel the head. If i cant keep my fingers on it for more then a couple seconds, etc. I do need to get a heat gun.

 

[RodneyPierce]

and yah old cod, what do yah mean "unlearned" :lol:

 

[Richard Dahlheimer]

Boat was running darn good for just break in. Thanks for posting the vid, Rodney. You did a great job with the vid of Mikes JAE also. Richard D

 

[RodneyPierce]

Richard, thanks man! Ill try and get more vid before the year is over, of it singing on the needle.