Freestyle I'm scratching my head at this one...........

tntsuperjet

tntsuperjet

Tntperformance-engineering.com
Location
Georgetown ca
Quinc said:
Then you have guys like @JetManiac running 210psi+ on pump gas with no issues.
Click to expand...
Ok here the huge mistake people make.
Stock Cyl running 230psi compression has the same compression ratio as a dasa at 165psi.
You always have to factor in the exh port height.
Cranking compression does not give you the whole story!!!!
You have to look at the compression ratio and the corrected compression ratio.
Because at cranking speed you have no trapping pressure so the pipe is not functioning.
Example a dasa with 195Psi cranking is 16to1 comp ratio valves closed.
Stock 62t at 195 psi is 11to1.
So basically a engine with short exh port will have a higher cranking compression then a eng with tall exh port with same bore stroke and some size.
But they will have same compression ratio.
Once the engine is running and the pipe factored in the tall exh port engine will be more affective at mid top rpm and your trapped comp will go way up. Low ported engine will go down.
So that being said anyone that thinks just because someone else runs 200psi on pump gas doesn't have any bearing on weather you can or not unless you have exactly the same setup.
Exactly the same means, same engine , exh, jetting, carbs, prop, nozzle, hull, air cleaners. So basically the only difference better be the paint job!!
Because just going from a 8/13 to 9/15 prop is enough to take the very same engine and detonate it to death!!
Here a example from another sport.
On my sled, if I go from a 68 gram weights in the clutch to 70 gram weights I go from a 125 main jet to 155 main jet to keep same exh has temps at wot.
Load requires fuel. No load no fuel needed.
Small prop won't use same hi speed jet as tall prop.
That is why reverse jetting works so well for many people. They use the fuel down low for tq and go real lean on top to get better revs because they run short prop with no load on mid and top.
Make sense??
 
senor

senor

There are to many variables in determining what gas should be used. The compression gauge is the worst tool in deciding this. Timing advance,timing retard,squish,squish band width,squish velocity all need to be factored in as well as choosing the correct heat range plugs.Even transfer port roof angles play a part in controlling detonation. I've ran as high as 245 on my snap on gauge on sub 800 cc motors on 87 octane pump gas. Not a race boat but for freeride and some boat chase fun.Also the water ingestion that most of these freestyle skis see leads to a lot of failures
 
Last edited:
air blair

air blair

you are the reason
Location
thumb, mich again
tntsuperjet said:
Ok here the huge mistake people make.
Stock Cyl running 230psi compression has the same compression ratio as a dasa at 165psi.
You always have to factor in the exh port height.
Cranking compression does not give you the whole story!!!!
You have to look at the compression ratio and the corrected compression ratio.
Because at cranking speed you have no trapping pressure so the pipe is not functioning.
Example a dasa with 195Psi cranking is 16to1 comp ratio valves closed.
Stock 62t at 195 psi is 11to1.
So basically a engine with short exh port will have a higher cranking compression then a eng with tall exh port with same bore stroke and some size.
But they will have same compression ratio.
Once the engine is running and the pipe factored in the tall exh port engine will be more affective at mid top rpm and your trapped comp will go way up. Low ported engine will go down.
So that being said anyone that thinks just because someone else runs 200psi on pump gas doesn't have any bearing on weather you can or not unless you have exactly the same setup.
Exactly the same means, same engine , exh, jetting, carbs, prop, nozzle, hull, air cleaners. So basically the only difference better be the paint job!!
Because just going from a 8/13 to 9/15 prop is enough to take the very same engine and detonate it to death!!
Here a example from another sport.
On my sled, if I go from a 68 gram weights in the clutch to 70 gram weights I go from a 125 main jet to 155 main jet to keep same exh has temps at wot.
Load requires fuel. No load no fuel needed.
Small prop won't use same hi speed jet as tall prop.
That is why reverse jetting works so well for many people. They use the fuel down low for tq and go real lean on top to get better revs because they run short prop with no load on mid and top.
Make sense??
Click to expand...
Priceless info. Thanks for spelling this out for us. This stuff here is why I still scroll through the X.


Air blair cell
 
badvinny

badvinny

Location
Saskatoon,SK
I had fouling probs for a while over a year ago, almost every weekend, BR8ES, they sort of cleared up and only one or twice last year (none this year yet), so I picked up some BR8EYA a couple days ago and surprisingly had a fouled plug on the old BR8ESs so in went the new EYAs. So far it seems to run great, maybe better but not positive, but very good for now. Dasa 1000 12mm, 32 degrees, Novi 48, RRP pipe
 
JonasOlson

JonasOlson

Location
Sweden
So.. Did we come up with a correct answer on these failurs..? Cuz I got one too..
This is what my Dasa 1200cc 7port looks like after 18h from brand new;
IMG_3121.jpg
IMG_3141.jpg
My ski setup is;
*Dasa 1200cc 7port 94mm (need to bore it up to 95mm)
*46cc head dome
*48mm Dasa Carbs
*MSD Enhancer
*160mm pump
*BR8es sparkplugs
*Running 98-RON pumpgas

My Dasa 48mm carb setup is;
Main: 130 1/2 turn out.
Pilot: 120 1-3/4 turn out. (Dasa told me that I need a 135)
Around 70m above sea level.
Around 20°C in air temp normally.
1/42 oil ratio (2.5% oil)

So basically.. My Builder tells me that the jetting is spot on the the Head domes is the right size for pump gas (46cc = 185psi). He tells me that he thinks that heat and dilatation made the piston ring clip the exhaust port and cause this, some how..

Dasa on the other hand tells me that the Pilot jet is way low and the the 46cc head domes equals 205psi and need racefuel and thats why the piston looking like it does. Keep telling me that detonation did this, but my eyes can’t see any detonation signs on the ”good" piston though..?

So im like in between and dont really know what to do..

I picked up some bigger Pilot jets and 48cc head domes today, but I dont know if its gonna solve the problem.. I guess the time will tell =/
 
Blue

Blue

Judging your cheapness
Location
St Cloud Florida
@JonasOlson take a better pic of the good piston so we can see the dome better. It looks very black but its hard to see. Also a pic of the domes. Are they black to??

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JonasOlson

JonasOlson

Location
Sweden
Here is some pics of the "good" piston and the domes;
IMG_3215.jpg IMG_3211.jpg IMG_3122.jpg

I have read some about the thing called "piston wash",
My piston wash aint looking that good though..
Or what do you guys think?

Then Detonation that Dasa claims be the reason, I cant see any detonation..?
 
Blue

Blue

Judging your cheapness
Location
St Cloud Florida
Its lean. Domes shouldnt be that black. Barely any wash on the piston. Richen her up.

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sneds

sneds

Location
Wasaga Beach
I've seen this before on here somewhere and thought it might help you.

fe9abccd586b59e90919c35f6bb92314.gif


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tntsuperjet

tntsuperjet

Tntperformance-engineering.com
Location
Georgetown ca
I have 6 Dasa pistons out of 4 different Dasa motors all have exactly the same damage.
It's 100% caused by detonation.
It brakes the ring land on the exhaust side then ring snags port and rips it up like you see.
Stop looking at 205 psi.
That's bull $hyz number that means very little in big picture.
Dasa runs 200+ deg exh port.
Mix that with 205 psi and that's 16to1 comp.
not gonna run on pump gas.

Your low speed jet is out 1-3/4 turns.
That means low speed circuit is lean and your flooding fuel on bottom end.
Take your low speed screws to just under 1 turn.
If it lean bogs u need bigger pilot jets
Low speed screws are only!!!!! For idle fuel adjustment.
Idle only.
So your 1-3/4 turn is giving u a pig rich idle and that's covering your lean big with residual fuel.
But when it's ramping down from high throttle settings it's deadly lean.
 
bach6177

bach6177

JonasOlson said:
So.. Did we come up with a correct answer on these failurs..? Cuz I got one too..
This is what my Dasa 1200cc 7port looks like after 18h from brand new;
View attachment 318665
View attachment 318666
My ski setup is;
*Dasa 1200cc 7port 94mm (need to bore it up to 95mm)
*46cc head dome
*48mm Dasa Carbs
*MSD Enhancer
*160mm pump
*BR8es sparkplugs
*Running 98-RON pumpgas

My Dasa 48mm carb setup is;
Main: 130 1/2 turn out.
Pilot: 120 1-3/4 turn out. (Dasa told me that I need a 135)
Around 70m above sea level.
Around 20°C in air temp normally.
1/42 oil ratio (2.5% oil)

So basically.. My Builder tells me that the jetting is spot on the the Head domes is the right size for pump gas (46cc = 185psi). He tells me that he thinks that heat and dilatation made the piston ring clip the exhaust port and cause this, some how..

Dasa on the other hand tells me that the Pilot jet is way low and the the 46cc head domes equals 205psi and need racefuel and thats why the piston looking like it does. Keep telling me that detonation did this, but my eyes can’t see any detonation signs on the ”good" piston though..?

So im like in between and dont really know what to do..

I picked up some bigger Pilot jets and 48cc head domes today, but I dont know if its gonna solve the problem.. I guess the time will tell =/
Click to expand...
With my motor I requested pump gas domes and got the jetting specs right from them and was running an MSD enhancer so I don't see how there could have been a setup failure
NovI 48's
135 pilot 125main 2.5N/S 115g spring 60 return jet


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