170psi or 185 psi domes????

[aqua]

Will there be much of a difference between the two domes(170 or 185). 91 octane is the highest you can usually find around here. which would you go with. thanks

 

[yamaslut]

Will there be much of a difference between the two domes(170 or 185). 91 octane is the highest you can usually find around here. which would you go with. thanks

170psi... I run 185psi and I'm right on the edge of race fuel... I run a 50/50 mix or 93 octane and 100 AVGAS... It will run on 93 only though

 

[Kny21]

170psi... I run 185psi and I'm right on the edge of race fuel... I run a 50/50 mix or 93 octane and 100 AVGAS... It will run on 93 only though

I thought 185psi you were still able to run on pump gas, no? Just thought you need 93 octane....

 

[Matt_E]

Nick, aren't you on an 84mm bore? I think on that larger bore, you are indeed on the edge of race gas.
But if I am not mistaken (and that's more than possible) 185psi on a smaller bore should be okay for pumpgas.


Maybe Paul or Chuckie could chime in here.

 

[Jr.]

There are several factors that make up the octain requirments of a motor. it's not just compression. Timing & ignition plays a very big factor.
As well as the carbs & tuning. Nicks motor is built for the higher requirment. The bore doesn't really factor in, in his case.
On a limited boat, 185 is about as high as you dare go on pump gas.
This is one of those subjects you can literaly write a book about.
Do a search, this is discussed several times & if memory serves me, there was some very good info posted.

ski ya, Paul

 

[aqua]

would it be ok for 91 octane though.....if not i would probably have to add a little bit of octane booster to each tank to bring it up a bit....i am not sure that i would want to do that.

Nick, aren't you on an 84mm bore? I think on that larger bore, you are indeed on the edge of race gas.
But if I am not mistaken (and that's more than possible) 185psi on a smaller bore should be okay for pumpgas.


Maybe Paul or Chuckie could chime in here.

 

[aqua]

thanks paul. i am starting to lean towards 170 since it seems to be so close to the race gas border line. gas is expensive enough as it is.

There are several factors that make up the octain requirments of a motor. it's not just compression. Timing & ignition plays a very big factor.
As well as the carbs & tuning. Nicks motor is built for the higher requirment. The bore doesn't really factor in, in his case.
On a limited boat, 185 is about as high as you dare go on pump gas.
This is one of those subjects you can literaly write a book about.
Do a search, this is discussed several times & if memory serves me, there was some very good info posted.

ski ya, Paul

 

[Jr.]

Stay away from octain boosters, they don't work!!!
If you are looking to raise the points of regular fuel, you will need to blend it like Nick does. If you have a local airport near, get 100LL AV-gas & blend it 50/50 You will be safe to go to 185, otherwise use the larger domes & stay at 175

 

[Don 79 TA]

total wieght, water temp, tunning, timing, comp, sometimes plugs and plug gaps help too, gas quality, etc... all play a role in determining what psi you can run as well as how long to hold the throttle open as well as what gauge you use to measure the psi

as a precaution you can always heat coat the pistons, that has shown to add detonation resistance and heat reduction in motors, especially 2 cycles

since i am usually in cold water here, i run higher octane
her sxr runs 185psi, but again she's not the type to hold the throttle open all the time, plus has the ada head which adds slightly better cooling

my sj, i use coated pistons, and high octane (more for just s precaution)

 

[SUPERTUNE]

If all things are set up right for freestyle riding...most superjets will run on 185 lbs. compression. All my set-ups work very well. However it does depend on jetting, plug heat range, timing and curve, and Please use ADA heads as they have very good squish ratio's.

 

[cambo au]

to the best of my knowledge it would be fine to run 185 if you are doing freestyle ie:short bursts on the throttle however it would be a different story if you are holding wot for long periods? this is just the basis i put my motor together with

 

[waxhead]

i am running 185 psi in my ported race ski with a type 9
i am using pump fuel
however i am back to 15 degrees timing up top

 

[Matt_E]

I run ADA 35cc domes on an 82mm bore with heavy FS porting - works out to 170psi. (Domes are rated 185psi)
I run premium and have no issue whatsoever. I can do WOT runs, too.
Timing is retarded 19deg on top to be safe.

 

[Frosty]

MAGOO ported 701cc (81mm bore)
35cc domes - ADA
stock ignition - protec modded cdi set to 9,000 rpms
stock timing
B-pipe
38mm oem carbs, oem intake reeds and airbox

comp tester showed 185 psi/cylinder - consistantly over seval different tests

I run 93 octane pump gas and not one problem, not even with WOT runs.

:biggthumpup:

Although, I do keep my WOT runs to a minimum anyway...

 

[yamaslut]

my setup:

Magoo Big Bore kit (84mm) Pro-x piston
Magoo freestyle porting.
ADA head w/ 35cc domes 185psi.

It rips sooooo hard and smells so good on AVGAS... I wish I had the cash to run it all the time... Like I said i my first post. It will run all day on 93 octane, but I like to run AVGAS just to be safe..

btw - I am still so amazed at what a good port job will do for your motor... It's like night and day..

 

[FL-cracker]

[/QUOTE]btw - I am still so amazed at what a good port job will do for your motor... It's like night and day..[/QUOTE]

So tru!:woot: That is the experience I have had with 4 stroke Dirt bikes as well!

 

[Matt_E]

:biggthumpup: Yup.

Of course, anything better than that horrible Yami stock port config is an improvement.
My amateur port jobs are proof of that.

I can't imagine what a pro-port job feels like.

Anyways, thumbs up to AVGas....love that smell! :arms:

 

[yamaslut]

:biggthumpup: Yup.

Of course, anything better than that horrible Yami stock port config is an improvement.
My amateur port jobs are proof of that.

I can't imagine what a pro-port job feels like.

Anyways, thumbs up to AVGas....love that smell! :arms:

it's leaded too...:hail:

 

[Frosty]

I am still so amazed at what a good port job will do for your motor... It's like night and day..

Hell yeah, I am very pleased with Pauls porting. In fact, I have a spare 61x cylinder in need of resleeving... I think I'm going to resleeve that to an 84mm bore next winter... and have Paul port that for me too. :Banane01: :Banane01: :Banane01:

 

[yamaslut]

Hell yeah, I am very pleased with Pauls porting. In fact, I have a spare 61x cylinder in need of resleeving... I think I'm going to resleeve that to an 84mm bore next winter... and have Paul port that for me too. :Banane01: :Banane01: :Banane01:

you can't go wrong w/ his porting.... good choice