cam advance verse kncok

R

rarebit

New member
I installed a new roller chain. The old chain was rattling like a mofo. While I was at it I advanced the 422 cam 4 degrees :eek: :eek: :eek: (I know the 422 already has 4 degrees ground into it and it's supposed to be installed straight up so dont give me shit.) All I can say is that it has more low and mid power then it ever did. The ball bearing t66 spools up just as, if not faster, then stock turbo. The top end power doesnt seem to be hurting like I expected. It seems the whole rpm band has shifted down about 600rpm. Holy cow, what a difference. It's no joke.

The problems is, it has a tendency to knock now. I retearded the timing a whole 7 degrees and it still knocks a little. This has me scratching my head. I know the cam drives the dist. So, advancing the cam must advance the dist as well, right?

Say the old chain was streched enough to retard the cam 4 degrees. When I installed the new chain, and advanced the cam 4 degrees, that would be like effectiveley gaining 8 degrees cam advance. Would this advance the base timing 8 degrees as well? I haven't checked it with a timing light yet cause I don't have one. I speculate this is what is going on and I'm wondering if anyone can verify this is what's happening
 
S

Sy769

Donating Member
Changing cam position while leaving the distributor in place will change base timing.

Get a timing light and set base timing.
 
ed hess

ed hess

race or get outta the way
just curious since you made this change

you might be surprised to see what difference was made to your cylinder pressures from changingwhen the valves open and close.

ed
 
bigtime

bigtime

Sy-Ty Builder
ed hess said:
just curious since you made this change

you might be surprised to see what difference was made to your cylinder pressures from changingwhen the valves open and close.

ed
Click to expand...

You probably raised your dynamic compression resulting in the knock.
Just tune it and you will be fine. You don't *need* to have allot of timing
you only *need* what the engine wants. Every combination wants
something specific to itself
 
nightdiver

nightdiver

Active member
Even though it shouldnt knock,the diff in dynamic compression is small.
How much advanse do you run @ the upper area ?
I had 20* with the L35s and 98 oct gas
 
R

rarebit

New member
i run 20 degrees with the brodix heads 14-20psi. i think the base timing is off significantly after re-degreeing the cam. i can't find 0 degrees on the fluidampr.
 
R

rarebit

New member
Jeepers, batman. Up to 27*? The most I've ever been able to run without getting some knock was around 21-22*. I do run 91 octane though. What octane are people running to use 27*?
 
nightdiver

nightdiver

Active member
100 oct.
When i tried that it was just for a few minutes (with the L35s) and i couldnt believe the differense i saw....MAN that was power
Now the file that Mike sended me has 27* at the upper area....i wouldnt use anything else than 100 oct though
 
nightdiver

nightdiver

Active member
Advancing the cam will make the intake valve close sooner...this means closer to the BDC resulting more air in the chamber, so more low end torque and psi on the gage when you do a compression test
 
ghettosled

ghettosled

SYTY SUPERSTORE
those programs with 24deg + are on C16. 100 octane wont be nearly enough with 20+ psi.

find tdc with a piston stop and mark the balancer. make sure what you see on the damper with a timing light is what is showing in the computer.
 
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