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

[Glenn Quarles]

Guys, how much exhaust timing is too much on a .21? For, lets say a Sport 20 boat. I have been doing some reading and digging, and it seems that alot of guys, that i greatly trust seem to like the 183 range. But with further reading and digging, seems alot are running the 190 range, and some higher. How much is too much? When does it get picky on launch and hard to needle?

So you can see there are a bunch of opinions. I guess the only true answer to "how much is to much"....360* is for a fact too much!!!

GQ

 

[RodneyPierce]

LOL @ Glenn. Good answer :lol:

 

[Chris Wood]

there are alot of factors that go into motor work.. i know as i talk to my dad about it.. crank timing is one.. then you have total exhaust port area ect ect ect. i have learn what works for ME. not always works for everyone else. the best way is trail and error.

i do know that the BOAT has alot to do with what the motor will dole out in performace.. that i can say is for sure.

chris

 

[dwilfong]

For sure what will work on one setup will fail on another. But the best way to make a decision is to listen to every option and come up with your own answers. That is what makes this kind of discussion very important to new boaters.

David

 

[dwilfong]

On my .21 tether boat engines ive allways used T shaped or reverse top hat exhaust that is straight accross the full width so timing is the same accross the full width.Most specialist control line speed aero motors also use straight full width ports as well all be it at much higher timing than we use in tether boats. I find that 176 degrees exhaust & 123degrees transfer is the best for my motors & 26.5 degrees blow down. I find that the pipe bangs in much harder when it comes in with much more rpm. Allthough my timing my be considered relatively low in terms of other motors, In the same boat my motor is 10-12mph faster than a CMB RS7. Martin.

Martin

That is what I was thinking. That a wide port at top would give a good sharp pressure wave to the pipe. The pipe would have to be set up for this to work to its full potential. Any thoughts to pipe set up for this ex port?

David

 

[RodneyPierce]

I like to start good technical discussions like this one. It never hurts to hear from many of the respected racers/engine modders.

 

[Roxyflash]

Just ship the Motor to Steve Woods and be done with it.LOL:lol:

 

[RodneyPierce]

Roxy, sometimes thats not an option when your broke like me :lol:

 

[Jerry Wyss]

Roxy, sometimes thats not an option when your broke like me :lol:

So your sure you have 188* Ex port timing? Its not totally unuseable,, this is o/b right? TT engine, GO motor?

 

[camaroboy383]

perdy sure he is talkin about a go motor...

 

[RodneyPierce]

It is a GO 21, but I dont have it at 188. Its an IB motor for a sport 20 hydro. The head space was rediculous, something like .018 WITHOUT any shims. I have a fella turning me down a couple buttons, so I can tighten the space up to .006 or so. My exhaust timing is right around 186, transfers at 127, boost at 123, induction closing at 65 duration at 218. We will see how she runs on sunday

 

[Jerry Wyss]

It is a GO 21, but I dont have it at 188. Its an IB motor for a sport 20 hydro. The head space was rediculous, something like .018 WITHOUT any shims. I have a fella turning me down a couple buttons, so I can tighten the space up to .006 or so. My exhaust timing is right around 186, transfers at 127, boost at 123, induction closing at 65 duration at 218. We will see how she runs on sunday

ow,, yeah i did go back an actually read the first post again :blink:

Many engines come with rediculous headspacing,, thats what makes them so important to, at the very least Check! Far too many users don't even know what headspace is, let alone how much it is. I even heard of a Mac21 O/B that had .016" H/S an it Was Runnin' Strong!

I just heard all the Angels hit a note,,

Looks like you'll be "breaking-in on Sunday then?,, that sucks :lol:

 

[RodneyPierce]

this sucker is super tight too, Has the most pinch ive personally ever seen. Its going to take forever!

 

[hydro rob]

Good info here, I use the 7pt engine and havent begun to change the timings. I will be using different head buttons though....

 

[Jerry Wyss]

this sucker is super tight too, Has the most pinch ive personally ever seen. Its going to take forever!

The only thing that can take that tightness out is heat. I would suggest you build some in it by heavily restricting water or pulling it off altogether. Otherwise you'll just be running cold (with a rich needle setting) and water going thru too.

This a tough balancing act with an I/B,, you need to be rich but you can't be cold too.

Lotsa fuel is your friend, water is not, its a fickle sucka that will ruin your day.

 

[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.

 

[steve wood]

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

 

[John Knight]

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

Absolutely correct. An IB is NOT the same as an OB with a lower unit in the water as a heat sink.

 

[Chris Wood]

i am just curious to hear from andy and jack..

what are your thoughts in regards to timing when it comes to motor that uses a DOME piston vs a flat top.. i am under the impression the dome runs a higher compression ratio. also the exhaust open with that piston gives it a longer duration with the piston going up and down on the stroke. ( stays open longer and opens sooner )

I have heard good and bad with this set up.

your thoughts please.

thanks

chris

i am shocked nobody responded to this question i had.

 

[Andy Brown]

i am just curious to hear from andy and jack..

what are your thoughts in regards to timing when it comes to motor that uses a DOME piston vs a flat top.. i am under the impression the dome runs a higher compression ratio. also the exhaust open with that piston gives it a longer duration with the piston going up and down on the stroke. ( stays open longer and opens sooner )

I have heard good and bad with this set up.

your thoughts please.

thanks

chris

i am shocked nobody responded to this question i had.

Chris,

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