oldcutlass

You need to run the highest octane available due to your engines compression.

sysmg

I agree. A high compression 10.25-1 Olds 425 will not run well on regular gas.

Firewalker

Now the shocker. Few engines from the factory or rebuilt are true 10.25 compression.

dragline

You can also try a 1 or 2 range colder heat range spark plug, My preference is no vacuum advance 15-18 deg. initial, 20 deg mech advance, total 36-38 deg. using different dist. spring combinations to get the best advance rate. Much easier to tune without the vacuum advance. Although your carb may be sufficient as far as cfm, steady part throttle surge or lean may require a larger primary jet. Small cams can create havoc with long stroke big blocks. Just curious, what country are you in?

Robert Zuijdam

Just a status update. The engine runs fine on 32º of total timing with premium fuel (RON 98) (USA 93).
I bumped up the total timing to 36º and noticed slight pinging. So I tried RON102 octane fuel (equivalent to 97 octane in USA) and pinging is gone. The car runs smoother and feels more responsive. The idle also picked up another 100 RPM.

Should I leave total timing at 36º or bump it up to 38º?
Is using a dyno the only way to know where maximum power and ignition timing meets?

I am from the Netherlands. Fuel is quite pricey here.

RON95 cost $6.75 per gallon.
RON98 cost $7.40 per gallon.
RON102 cost $8.43 per gallon.

oldcutlass

Did you limit the vacuum advance so your total with vac. adv. is around 50*? I'd run the ron98 with 34* total.

olds 307 and 403

Agreed, drop a couple of degrees and run the 93, better than the 91 I can get here. I also don't feel so bad about our high Canadian fuel prices, only pay $5.50 Canadian for a US gallon of 91.

Robert Zuijdam

I have the vacuum advance disconnected since it adds 22º of timing. That would mean 56-58º total with vac. adv connected, which I assume is too much.

Firewalker

Get an adjustable vac can for the distributor if you must, but it needs that vac timing for best mileage and it would hook it up to the intake vac. Then adjust the canister vacuum can timing down for less timing, if any ping.

Vacuum timing goes away when you get on it

oldcutlass

This is a great kit, just follow the instructions. The adjustable vacuum can only controls rate vs available vacuum. The springs will help you dial in your curve, and the stop plate will help you limit the vacuum advance.
https://www.jegs.com/i/Crane-Cams/271/99600-1/10002/-1

FStanley

Try a tank of 100 race gas see if it improves


also, wouldn't a Air/Fuel test help him out on if he is too lean or not??? rather then just guessing??? Just wondering if this could identify issue???????? thoughts from the group??????