421 compression

[Joejr915]

i have a 421 in 4mm 115mm longrod with blaster pistons. i have 17cc domes and have 210-215 compression. i think is to high. does anyone have compression readings with 18cc and 19cc domes. my alttude is about 1000 above sea level. i dont know what i need and where to buy at. i was looking for about 180-190 compression. please help thanks

[blanco25]

thats fine compression if you want to run alky and drag race. Its not going to be to reliable though. What kind of riding are you doing? I believe I have 18cc and im at 2300 feet and im at 180ish psi

[Joejr915]

I'm. Doing drag with 112 octance vp. I think that's too much compression

[blanco25]

call the guy in my sig kevin from herr jugs. have him cut you some domes, and give you some advice. But I have heard before people running compression higher than that before.

[krispy05shee]

To much compression can accually hurt you, causes the motor to work against itself, I run 21cc cut 9 degrees, my compression is around 160, squish is about 49 thou. id try a lil higher cc domes and get your comp down and see if you get any better results.

[Joejr915]

i have 19cc domes ordered thou wicked atv. hopefully these work for me i will post what i get to help others.

[sleeper06]

19cc will put you in the 190s,20s low-mid 180s

[firebanshee]

All that compression will def kill your over-rev,i use to rattle plugs loose with 18cc domes on alky, i put in 21cc domes and pumped about 180ish at sea level and my bike ran alot harder and ALOT more reliable. You should lower your compression and run more timing.

[dajogejr]

Couldn't agree with you guys more.

I like to stick to 165 to 185 Cranking compression and add timing, it's easier on the bottom end and...it's easier to adjust timing than it is compression.

 

As said, that much compression is killing overrev and top end. Shoot for 180ish. With your setup, probably a 20cc domes is what I would shoot for.

 

Are you flat dragging, hill shooting, duning, etc?

[Joejr915]

i got 180-185 ccompression.this is at 1000-1500 elvation. hopes this helps anyone else trying to build something.

[rubberneck]

Sounds pretty consistant, i kick 180 at sea level with 20s

[banshee332]

Gary I run 19cc cut domes in my cub. 175 pounds compression. Im going to bump it up to around 185-190 this year and see if it helps. The domes you had in it before was killing your topend. We run 500 feet. If those dont work let me know I can hook you up with getting a custom set cut for your set up.

[Wheelman Chassis]

i have redline alky domes ,19cc i pump 170 psi