Builder Help/Compression Question

[munki63]

So Ive read a lot about domes and what i figured is that i should run 35cc domes on my ski BUT I went to a local race and I was asked what i was running so i told them I was running 35cc (185psi i think) and i was pretty much called an idiot for running such high compression in a 701, am i missing something, ill only run pump gas (93 octane), So i went out and bought 37cc domes, in fear of blowing my engine like i was told would happen, I would like some input from you guys, would it have anything too do with me being 2000ft above sea level.

Edit
Will there be much power difference between the too?

Thanks

 

[OCD Solutions]

Not sure what their problem is, I aim for 185 on my skis and run pump gas still with no issues yet. Perhaps it was just a bunch of dicks being dicks? :dunno:

 

[munki63]

What happens if you run too high compression and too low octane?
Also with the 37cc if i rev my engine up out of the water it will start to diesel...

 

[Matt_E]

You should be fine on an otherwise stock 701 with those domes on the highest octane pump gas. A drypipe might necessitate bigger domes because it revs higher, maybe that's why racers were giving you chit.
Your engine running away on 37cc domes isn't related to compression.

 

[munki63]

Your engine running away on 37cc domes isn't related to compression.

What would it be related too?

My setup;
Dual 44
B-Pipe(Mod)
Shark Fab Head
Blowsions Lighted flywheel
Bore+1mm

Adding this winter;
Porting
Delta Vf2 with reed spacer
Lightweight coupler

 

[Matt_E]

It's usually a sign of an air leak.

 

[steve-uk]

What would it be related too?

My setup;
Dual 44
B-Pipe(Mod)
Shark Fab Head
Blowsions Lighted flywheel
Bore+1mm

Adding this winter;
Porting
Delta Vf2 with reed spacer
Lightweight coupler

check your vf2's... like matt said .. air leak.. i had this issue all looked good, stripped my motor all the way down and wasnt until i removed the vf2's that i found the cages were loose... the screws seem to come loose on the vf2

 

[orangefinger]

You loose compression being in higher altitude, on my Blaster I run 33cc domes at sea level and 31cc domes at Altitude. at 5500 Feet.
There are opinions that differ ....

The engine is a 61x 82mm bore, ported, the compression reads arround 180/180 ...

 

[munki63]

What kind of power loss do you get from an air leak?

 

[Mark44]

you get a toasted motor.

Mark44

 

[rollin5150]

Correct me if I am wrong, but I believe you loose 15psi of compression for every 1000ft of elevation above sea level. I run 28cc domes on my ADA head. They state that I should have ~200 compression but I am right around 175-180.

There are other factors as well such a your rings and cylinders.

 

[stanton]

racers run wide open, we dont.

 

[Big Kahuna]

So Ive read a lot about domes and what i figured is that i should run 35cc domes on my ski BUT I went to a local race and I was asked what i was running so i told them I was running 35cc (185psi i think) and i was pretty much called an idiot for running such high compression in a 701, am i missing something, ill only run pump gas (93 octane), So i went out and bought 37cc domes, in fear of blowing my engine like i was told would happen, I would like some input from you guys, would it have anything too do with me being 2000ft above sea level.

Edit
Will there be much power difference between the too?

Thanks

Depending on how you ride you are borderline. I ran 185+ on pump gas but my ski was set up for flat water freestyle. At the beach that compression jumped up to over 190. But no WOT. Had this been set up for racing I would have run less compression or a mix. You were at the races talking to racers. They are going to assume that you ride like them. If you asked me at the races and I did not ask you what kind of riding you were doing then I would assume you were racing also. KABOOM.

 

[ryan]

i am running 215 on 93 pump gas WOT all day long. stock bore ported 701.

 

[Big Kahuna]

Is your timing turned back 90 degree's!

 

[munki63]

you get a toasted motor.

Mark44

From an air leak??

 

[OCD Solutions]

From an air leak??

Air leak = more air than fuel = lean condition = toasted motor. :bigok:

 

[Mark44]

I

From an air leak??

Yep.

Mark44

 

[tor*p*do]

It's usually a sign of an air leak.

or way too small jets/lean mixture

 

[munki63]

So back too the domes
i should be fine if i run my 35cc over the 37cc i just have to run 93 octane right