78 L48 Ignition timing
Thread Starter
Burning Brakes
Joined: Aug 2000
Posts: 952
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From: Morgantown,WV USA
78 L48 Ignition timing
Hello,
I was hoping someone could suggest a good timing setting for a 78 L48 that is stock except for dual exhaust and an advance kit (replaced the springs with the middle level advance springs)?
I am looking to wake the car up a little, but do not want it so wild that it starts hard or heats up. The stock setting is 6* BTDC- anything better than that?
Dan
I was hoping someone could suggest a good timing setting for a 78 L48 that is stock except for dual exhaust and an advance kit (replaced the springs with the middle level advance springs)?
I am looking to wake the car up a little, but do not want it so wild that it starts hard or heats up. The stock setting is 6* BTDC- anything better than that?
Dan
Burning Brakes
Joined: Jun 2008
Posts: 1,086
Likes: 1
From: Michigan
Dan,
Read the timing sticky at the top of the C3 page. You can wake up the car a lot by following the instructions.
I have a curve that looks like "E" in the attached. "E" or "F" is fine. Mine is 13* base, with a 21* bushing giving me 34* total (with vacuum disconnected and plugged) and the springs noted give me the curve. All in is at 2500 rpm. This is an MSD HEI with a 6AL box set up.
The car starts easily, runs well and drives with a little more power than the stock stuff.
Read the timing sticky at the top of the C3 page. You can wake up the car a lot by following the instructions.
I have a curve that looks like "E" in the attached. "E" or "F" is fine. Mine is 13* base, with a 21* bushing giving me 34* total (with vacuum disconnected and plugged) and the springs noted give me the curve. All in is at 2500 rpm. This is an MSD HEI with a 6AL box set up.
The car starts easily, runs well and drives with a little more power than the stock stuff.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
Setting timing at "idle" is GM's way of meeting emissions standards and keeping warranty costs down. If the engines are de-tuned and don't make the HP they are capable of producing, there is less engine damage during the warranty period.
As mentioned, read Lars [Grimsrud's] paper on how to set timing for performance. Basically, you want to have as much timing advance as the engine can tolerate (without any pre-ignition...pinging) throughout the engine RPM range when at WOT. Lars recommends 34-36 degrees of mechanical advance for SBC engines. The actual amount depends on your engine, where you live, type of fuel available, yada, yada...
Timing at idle is just a 'resultant' of what it measures once you have the performance timing set. It should be in the 8-16 degree band when you get done. Then just set up the carb for best idle adjustments.
As mentioned, read Lars [Grimsrud's] paper on how to set timing for performance. Basically, you want to have as much timing advance as the engine can tolerate (without any pre-ignition...pinging) throughout the engine RPM range when at WOT. Lars recommends 34-36 degrees of mechanical advance for SBC engines. The actual amount depends on your engine, where you live, type of fuel available, yada, yada...
Timing at idle is just a 'resultant' of what it measures once you have the performance timing set. It should be in the 8-16 degree band when you get done. Then just set up the carb for best idle adjustments.
Burning Brakes
Joined: Jun 2008
Posts: 1,086
Likes: 1
From: Michigan
I think 7T1Vette means to say it is 34-36* total timing which is mechanical (centrifugal) + base (initial) BUT not including the vacuum advance.
From Lars:
TOTAL TIMING: the base or initial timing PLUS the full amount of the centrifugal advance equals the total timing. Although all aspects of timing are important, total timing is the single most important aspect that you need to be concerned about. When you read posts that people say “set timing to 36º” it’s the total timing they are referring to.
From Lars:
TOTAL TIMING: the base or initial timing PLUS the full amount of the centrifugal advance equals the total timing. Although all aspects of timing are important, total timing is the single most important aspect that you need to be concerned about. When you read posts that people say “set timing to 36º” it’s the total timing they are referring to.
