Power Difference from 35cc domes to 33cc

[dpenta13]

Going to be assembling my motor this week.

Its a 61x cyl with 64u cases. New SBT crank, Ported 735cc cylinder from JM. And a Thrust Girdled Head with ADA domes.

I have 33cc domes coming for the setup.
I am a little nervous on running that compression. I want to keep it reliable.

Just wanted to hear if anyone has a similar setup and has ran both 33cc and 35cc domes and can give me there opinion on reliability and if the power gain is worth limiting my WOT time

 

[clouse22]

Personally I would just go with the 35cc domes if your doing WOT runs....but I would ask JM and get his thoughts.

 

[eastcoastjumper]

I rode with the 33cc domes using pump gas on a jet maniac 735 and then switched to 35cc domes when i rebuilt the motor. Truthfully I didn't notice a power difference. These aren't top end ported cylinders. Definitely felt a lot more responsive and low to mid pull increased, but up top it still feels like a "701".

 

[Freakrider]

Personally I would just go with the 35cc domes if your doing WOT runs....but I would ask JM and get his thoughts.

35cc domes is approx 185lbs compression and should be safe on pump gas

IMO 33cc domes (200lbs compression) is pushing it with pump gas

The 15lb difference in compression isn't worth the risk to me....but I may be wrong

Don't forget he has 83mm pistons with 735 so 35 cc domes equals 205 from my experience.

 

[tomski]

I would use the 84mm domes in 35cc or 38cc with the 83mm piston.

But that is up to you.

 

[eastcoastjumper]

Don't forget he has 83mm pistons with 735 so 35 cc domes equals 205 from my experience.

i might have a crappy gauge here but i'm reading 180 psi at sea level on a hot motor. 83mm pistons, 35cc ada domes, blue ported top end. fresh build. i had 205-210 with the 83mm pistons and 33cc domes on an older blue ported top end.

 

[clouse22]

Don't forget he has 83mm pistons with 735 so 35 cc domes equals 205 from my experience.

That's right my apologies.....i forgot my 701 was on 84mm bore which used 760 domes

 

[Freakrider]

i might have a crappy gauge here but i'm reading 180 psi at sea level on a hot motor. 83mm pistons, 35cc ada domes, blue ported top end. fresh build. i had 205-210 with the 83mm pistons and 33cc domes on an older blue ported top end.

I use a good craftsman tester and a hot motor will test out at lower numbers.

 

[dpenta13]

JM said i should be ok with the 33s if I limit my WOT time and to do a compression check before and after break in and go from there.

I just wanted to see if anyone noticed a good difference going to the 33cc domes from the 35.

But if the gains not really worth it i will probably go with the 35s and see exactly were im at for compression.

Anyone have experience with 34cc domes. Never heard anyone use them but ada has them on there website.

 

[BruceSki]

If you want to trade 33's for 35's I have two new 35's in the package here. I also have two used ones.

701 domes

 

[dpenta13]

I would use the 84mm domes in 35cc or 38cc with the 83mm piston.

But that is up to you.

By 84mm domes your refering to domes for a 760 motor correct?

When you increase engine displacement but keep the dome size the same does compression go up or down?

 

[Freakrider]

By 84mm domes your refering to domes for a 760 motor correct?

When you increase engine displacement but keep the dome size the same does compression go up or down?

Up.

 

[Freakrider]

701 domes max out use is 83 mm bore.

 

[tomski]

Increase

 

[dpenta13]

Ok freakrider thank you for the info.

I thought increasing displacement dropped compression because of tge larger area in the cylinder.

Good to know the correct info. Is it due to more air and fuel volume in the cylinder.

 

[dpenta13]

What do you guy think i want to be at for compression to run pump gas (93 octane) and not have to worry about the amount if WOT?

I think i will run 35cc for break in maybe then test compression an decide were i go from there? opinions?

 

[ToddW]

I know this is an old thread... but any updates?

What compression did you start with, what did you end up with?

Did you notice the 20psi compression difference if you tried the other domes?

Just curious, as I could really tell the difference going from stock up to around 180, was curious if going up another 20psi would be really noticeable.

 

[dpenta13]

Ended up just using the 35s never put my 33s in, the compression last i checked was around 185 i believe

i can post an exact number this week when i bring the ski home

35cc domes on 93 pump with my other mods i run it WOT for days no problem