Porting And Compression

[jsekula]

Running 22cc domes with a Coolhead, my compression is only 105 psi on both cylinders. My cylinders are Stage 3 ported and this is a freshly rebuilt broken-in engine. Normally 22cc domes yield around 145 psi and 19cc would take you to 181cc at sea level, an increase of 36 psi.

 

Sea Level 1000 2000 3000 4000 5000 Feet

16cc 217 psi 176 psi 170 psi 163 psi 157 psi 151 psi

17cc 205 psi 170 psi 163 psi 157 psi 151 psi 145 psi

18cc 193 psi 163 psi 157 psi 151 psi 145 psi 139 psi

19cc 181 psi 157 psi 151 psi 145 psi 139 psi 133 psi

20cc 169 psi 151 psi 145 psi 139 psi 133 psi 127 psi

21cc 157 psi 145 psi 139 psi 133 psi 127 psi 121 psi

22cc 145 psi 139 psi 133 psi 127 psi 121 psi 115 psi

Stock 130 psi 124 psi 118 psi 112 psi 106 psi 100 psi

 

Could one assume that if I went to 19cc compression would go up to 141 psi? How many psi compression can you run on pump gas (92 or 93 octane)? How much compression will a stock crank take?

[Leadfoot350]

After you port the motor you really can not use the compression test you are using unless you want to see if you have equal pressure. You will need to find out what your compression raito is but I am unsure how to do this. Also you can not run too much compression with an unwelded crank.

[Leadfoot350]

After you port the motor you really can not use the compression test you are using unless you want to see if you have equal pressure. You will need to find out what your compression raito is but I am unsure how to do this. Also you can not run too much compression with an unwelded crank. I have recreation porting done and my comp is 145 with 18cc domes.

[Big Blue]

on my ported cylinders i have about 140 on my compression with 20cc domes and the motor is not broke in yet.

[jsekula]

on my ported cylinders i have about 140 on my compression with 20cc domes and the motor is not broke in yet.

What elevation are you atl? About a 1000... What are you running for gas?