Mornin' all,
Have done my initial break in on this baby, but now I need to dial it in a bit. I have a slightly lopey cam and it's throwin me off a bit. I seem to have forgotten most of my early years of hot rodding skills from high school those 40 plus years ago, and now with a little more time and money available I figure I would give it another shot. Da Queen and her fresh, tight 383 will mainly be on the street...with a few "grudge night" runs when the challenge arises :)
Did some searches here on the site and found what looks to be some sage advice, but there is a statement I'm a little fuzzy on. It reads:
The stock GM HEI distributor has 20 degrees of built in mechanical advance.
Your 28 degrees BTDC at 1000 RPM more than likely has got the initial and some mechanical advance together because of the RPM.
With the engine fully warmed up and the choke fully open, dis-connect and plug the vacuum advance hose from the distributor. Bring the engine RPM up to 2500-3000 RPM. Assuming that the centrifugal advance weights and springs have reached the maximum mechanical advance at the above RPM range (this can be adjusted by lighter or heavier combination of springs), set the timing at 32-38 degrees. Do not exceed 40 degrees. What you are looking for is the maximum amount of timing with no pinging. At this point you can check the idle timing and just leave it at whatever shows up. Remember that because the idle RPM is above 800 that some mechanical advance will be added to the actual initial timing. Re-connect the vacuum advance hose. If connected to the full vacuum source the idle will go up as well as the timing. Leave the timing as is and lower the idle RPM to whatever you like. Even with your combo you should be able to get the idle in the 650-750 RPM range if the carb is adjusted correctly.
Now, regarding that pinging...am I to assume this means no pinging at the 2500 to 3000 RPM...or when I bring it back down to idle? I was unable to find a sweet spot for an idle anywhere near the 650 range, but I attribute that to the fact that I am running a Turbo 350...and this cam.
Any help / advice / tips are heartily welcomed...
Da Queen and I thank you
Chris
Have done my initial break in on this baby, but now I need to dial it in a bit. I have a slightly lopey cam and it's throwin me off a bit. I seem to have forgotten most of my early years of hot rodding skills from high school those 40 plus years ago, and now with a little more time and money available I figure I would give it another shot. Da Queen and her fresh, tight 383 will mainly be on the street...with a few "grudge night" runs when the challenge arises :)
Did some searches here on the site and found what looks to be some sage advice, but there is a statement I'm a little fuzzy on. It reads:
The stock GM HEI distributor has 20 degrees of built in mechanical advance.
Your 28 degrees BTDC at 1000 RPM more than likely has got the initial and some mechanical advance together because of the RPM.
With the engine fully warmed up and the choke fully open, dis-connect and plug the vacuum advance hose from the distributor. Bring the engine RPM up to 2500-3000 RPM. Assuming that the centrifugal advance weights and springs have reached the maximum mechanical advance at the above RPM range (this can be adjusted by lighter or heavier combination of springs), set the timing at 32-38 degrees. Do not exceed 40 degrees. What you are looking for is the maximum amount of timing with no pinging. At this point you can check the idle timing and just leave it at whatever shows up. Remember that because the idle RPM is above 800 that some mechanical advance will be added to the actual initial timing. Re-connect the vacuum advance hose. If connected to the full vacuum source the idle will go up as well as the timing. Leave the timing as is and lower the idle RPM to whatever you like. Even with your combo you should be able to get the idle in the 650-750 RPM range if the carb is adjusted correctly.
Now, regarding that pinging...am I to assume this means no pinging at the 2500 to 3000 RPM...or when I bring it back down to idle? I was unable to find a sweet spot for an idle anywhere near the 650 range, but I attribute that to the fact that I am running a Turbo 350...and this cam.
Any help / advice / tips are heartily welcomed...
Da Queen and I thank you
Chris