compression test & compression ratio

[MILO]

i'm working on getting my 4 mil, HJR ported motor back in and running. i'm waiting on a clutch kit from Jeff @ FAST to close it up and finish things off. should i do a compression test before firing it up or wait till it has been run a little first? i know that normally you do it with the motor warmed up but i'm unsure what gas i'm going to run yet. Kevin at HJR told me to run min. 110 octane with my setup and i'm sure i can get either 110 or 112 from a local guy. should i just go with the 112 to start to be on the safe side?

 

also how do you calculate the compression ratio? it sounds like that is as much or more important than just compression test results in determining what octane fuel to run. and should i run a hotter plug or just stick to the B8ES that i'm running now.

 

MODS:

PC pipes & silencers

pro flow foam filter - no lid

v3's

noss head - custom cut 20 cc stroker domes

4 mil long rod stroker

bored .020 - wiseco 795's

.050 squish

+5 timing advance

HJR aggressive trail port (dune port)

about 1200' elevation

 

 

 

 

 

[2001Stroker]

Your static compression (engine not running) is going to be about 10.4:1. You need to call Kevin, and get the port duration. You need that for the Dynamic compression (engine running). Plus the rods stretch a little bit while it's running. 93 octane is good up to 10.5:1, at sea level, and 0 degrees of timing. With your dynamic compression ratio, +5 timing (which is actually 22 degrees advanced at 1000rpm), you're going to need about 104 octane. If you can't find that, 110 will do just fine.

[tidos76]

3.5 gal 110oct + 1.5 gal 91oct = 104.3 octane