Stock zen rpm and pipe lengths?
 

Been tweaking on my thunderboat and was wondering what others are using as pipe length on the stock zen/257 combo. My pipe is a CC with a 2" band. I am at about 13" right now from the face of the head. Also, what is good rpm for this engine to run? Just want to make sure I am not looking for more rpm than should be expected. Finally, what type of tachs are out there to use on these motors. I have a borrowed sendec right now, but need to get my own.

RE: Stock zen rpm and pipe lengths?
 

The pipe length for me is 11-1/2" for mod motors, it's the best length for the RPM, yours will work fine if you run the boat for fun. This is a stoker RPM info from Hanson, it says 3.8hp@15000rpm with the turned pipe.

http://www.bhhanson.com/Marine%20Eng...uct%20Line.htm

http://www.rocketcityracing.com/prod...0&item_id=1269

RE: Stock zen rpm and pipe lengths?
 

Thunderboat rules require that the motor is completely stock except for the 257 carb. I am looking for rpm and pipe length info for this particular combo.

RE: Stock zen rpm and pipe lengths?
 

I would push the pipe up short and she should pull at least 14,500 rpm.

RE: Stock zen rpm and pipe lengths?
 

Use a Tach to find out the highest rpm for your compo that from 13" to 11-1/2" of the pipe length.

RE: Stock zen rpm and pipe lengths?
 

I run 295mm (just over 11.5") on my modded engine with a zero band pipe, and 285mm (11.25") on my stock zen with a zero band pipe.

RE: Stock zen rpm and pipe lengths?
 

Where are you measuring from? Exhaust port flange or cylinder centre?

G

RE: Stock zen rpm and pipe lengths?
 

I measure from the exhaust port on the engine, along the center line of the pipe to the join of the 2 cones of the pipe.

I'm not sure why my close brackets in my above post appears as winking smileys though?

RE: Stock zen rpm and pipe lengths?
 

No idea - thought maybe you were in Christmas Winkey Smiles mode. Seems short, 340mm as a start point works for me, shortest I go is 325mm.


Happy days,

Glenn

RE: Stock zen rpm and pipe lengths?
 

I started long (320mm) & kept shortening until I lost speed out of the turns, then lengthened it up 5mm. It's about the same as the other guys at my club running the same pipe. Some are longer, some are shorter, depends on who's modded engine they are running. The way it's set up now I have excelent speed in the straights & the turns & is set slightly longer than the guy who modded the engine & built the pipe thought it would end up at.

When I ran the Bonzi pipe (1" band) on my stock engine I had it set longer, but the pipe I'm running now is far better than the Bonzi one. With the Bonzi pipe I was recomended to start at 12 1/2" which is about 317mm, that's even shorter than you would go. Do you measure form the exhaust port or the plug?

Cheers
Jason

RE: Stock zen rpm and pipe lengths?
 

Hi Jason,

same as you, from the exhaust port flange on the motor down the centreline of the pipe to the fattest part of the pipe.

You are of course correct, different motors, set ups, props are all going to make a difference, and we are no doubt using different pipes too.

Your set up process is exactly the same as I use, works well for me to get it as good as possible.

Glenn

RE: Stock zen rpm and pipe lengths?
 

engines run different in different climates :)

RE: Stock zen rpm and pipe lengths?
 

Set your pipe length between 11-1/2 to 12" as most people do.

RE: Stock zen rpm and pipe lengths?
 

Go on rub it in - coming to your Summer now - I know, still, it is above freezing here at the moment so that's good.

Glenn