Jeworks compression numbers and changing dome size???

[grezzmky]

I took the 35 domes out of my 4mm BB jetworks motor last year and went to 33s. I did not ride much last year and I put TL on at the same time so I cant say what it did... I did a compression check yesterday and only got 151 in each hole. Put a new stronger battery in today and got 180. took the (purchased used) 33s out and put the 35s back in and got 176.
The reason for the compression check in the 10 degree weather is cause I was talking to Art about an impeller yesterday and when we were talking about my setup he kinda freaked and said the 33s would give me over 220 lbs compression. and that they have special 34s cut for upgrading from 35s.

2 questions, What are other peoples compression with Arts motors?
and what should the difference be on 35 to 33 domes on 84mm slugs?

 

[grezzmky]

used 3 different gauges btw. Matco, new autozone, and 8 year old autozone

 

[Bobert540]

Were the new domes cut and did you check the squish? What octane has have you been running?

 

[grezzmky]

Im thinking maybe the "new" domes have been cut b4 I bought them. Have not checked squish yet. need to bring home some solider tomorrow. what should the compression increase be from 35 to 33 if they were really 33cc domes? Thanks everyone

 

[Big Kahuna]

Hard to say. Rule of thumb I believe is 7lbs per cc. But not sure if stroker and porting plus sexy height changes effect that or not.

 

[grezzmky]

What are "sexy height changes"??

 

[grezzmky]

Ive always ran

50/50 93 and 110 or 111

 

[OkaucheeMustard]

I took the 35 domes out of my 4mm BB jetworks motor last year and went to 33s. I did not ride much last year and I put TL on at the same time so I cant say what it did... I did a compression check yesterday and only got 151 in each hole. Put a new stronger battery in today and got 180. took the (purchased used) 33s out and put the 35s back in and got 176.
The reason for the compression check in the 10 degree weather is cause I was talking to Art about an impeller yesterday and when we were talking about my setup he kinda freaked and said the 33s would give me over 220 lbs compression. and that they have special 34s cut for upgrading from 35s.

2 questions, What are other peoples compression with Arts motors?
and what should the difference be on 35 to 33 domes on 84mm slugs?

I wouldnt be able to answer your specific q but can comment that your ring end gap at 10deg F versus operating temp will be pretty drastic. As im sure you know the rings will grow when you put fire on them.

 

[grezzmky]

Art says to start the motor and let it cool for 30+ min b4 doing the check.
I guess since no one else has any idea of the compression on one of Art's motors or what changing domes does ill check the squish and just figure this out on my own. Thanks for the responses I did receive.

 

[Bobert540]

Since Art built your motor he is your best resource. That is why you pay to have someone build your motor.

 

[ProSouth]

Are the 33 cc domes engraved?

 

[grezzmky]

Since Art built your motor he is your best resource. That is why you pay to have someone build your motor.

He said it should have 220 and it has 180 with fresh topend. so just a little stumped that's all.

 

[grezzmky]

Are the 33 cc domes engraved?

just the factory yam7633 just like the 35s say yam7635...
I put the 35s back in and got 176

 

[ProSouth]

sooo whered you get the domes? seems like they may be cut domes. Who bored the cylinder? was the piston to wall clearance correct?

 

[grezzmky]

sooo whered you get the domes? seems like they may be cut domes. Who bored the cylinder? was the piston to wall clearance correct?

SLIGHT groves on one small part of one piston so Art and Robert sold me some new slugs and JEtski Lou did a hone and put the new pistons in. he also measured the custom base gasket and called Chuckie (I believe) who sold him a thin spacer and two stock gaskets that added up too the same clearance. Knowing this now I am deff gonna check the squish next. looking for ADA head torque specs now...

 

[grezzmky]

the 35 domes came with the head installed in the engine from Art

 

[ProSouth]

SLIGHT groves on one small part of one piston so Art and Robert sold me some new slugs and JEtski Lou did a hone and put the new pistons in. he also measured the custom base gasket and called Chuckie (I believe) who sold him a thin spacer and two stock gaskets that added up too the same clearance. Knowing this now I am deff gonna check the squish next. looking for ADA head torque specs now...

so it has the spacer? i didnt think you needed it for a 4mm.

 

[grezzmky]

The spacer is really thin like might as well have just used 3 gaskets.. but that make since cause it only comes up 2 extra mm's right? how many thousands is that? how thick is a gasket?

 

[ProSouth]

2mm is like 80 thousandths, different gasket companies have different thicknesses

 

[grezzmky]

Right. Lou said he bought a bunch of gaskets trying to make the same thickness Art originally has with his custom gasket. Id have to say checking the squish has to be the next step right? I have some soider but nothing to measure it with other then maybe comparing it to a feeler gauge.