Ignition Timing Help Needed
Thread Starter
Racer
Joined: Jan 2020
Posts: 388
Likes: 117
From: Tacoma, Wa
Ignition Timing Help Needed
I bought a 1979 L48 with an unknown performance cam, and an edlebrock intake and carb.
heads are cast iron and probably stock. Stock exhaust system with flowmaster mufflers. Running on 89 octane. Stock distributor.
I want to recurve the distributor for a couple reasons:
I don’t know if the previous owner ever did, it was never mentioned.
I want to learn. I bought this car to learn about old school hot rodding.
Question 1: Should I mess around with the carb and retune it first? Or set the timing first?
Question 2: How does octane effect timing? If I run 92/93 can I set the timing more aggressively?
Question 3: With unknown cam specs, what would be your best guess for intial and total timing. I’d rather be on the safe side than have the engine predet.
Question 4: What kind of recurve packages do you recommend?
I do plan on putting headers and dual exhaust on this summer, so I will be redoing all of this.
Any help is appreciated
heads are cast iron and probably stock. Stock exhaust system with flowmaster mufflers. Running on 89 octane. Stock distributor.
I want to recurve the distributor for a couple reasons:
I don’t know if the previous owner ever did, it was never mentioned.
I want to learn. I bought this car to learn about old school hot rodding.
Question 1: Should I mess around with the carb and retune it first? Or set the timing first?
Question 2: How does octane effect timing? If I run 92/93 can I set the timing more aggressively?
Question 3: With unknown cam specs, what would be your best guess for intial and total timing. I’d rather be on the safe side than have the engine predet.
Question 4: What kind of recurve packages do you recommend?
I do plan on putting headers and dual exhaust on this summer, so I will be redoing all of this.
Any help is appreciated
Last edited by Cmurray79; Apr 12, 2020 at 05:16 PM.
Le Mans Master
Joined: Oct 2010
Posts: 6,922
Likes: 839
From: melbourne florida
2023 C3 of the Year Finalist - Modified
You may not have to worry about compression unless more than the cam was changed. Email Lars for his timing papers and follow them and ask him about your quadra jet set up he's the expert on those carbs. Good luck. Happy Easter.
Race Director
Joined: Nov 2006
Posts: 13,151
Likes: 7,765
From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
2024 C3 of the Year Finalist- Modified
2022 C3 of the Year Finalist - Modified
Cruise-In VIII Veteran
You have a lot of "Unknowns " going on there.
a stock L48 has dished pistons and large volume combustion chamber heads. = Low compression.
you fuel choice has more to do with compression than anything else.
Timing for a "Hot" cam and high compression is way different than a standard engine. Timing for a mild cam with low compression is different still.
things you can do. Run a compression test on all 8 cylinders. That should at least give you an idea of what is going on in the combustion chambers. Put a Vacuum gage on it when idling . Adjust your low speed mixture screws to get highest vacuum at Idle. What is it? 17-18 inches of vacuum?? Pretty much stock cam. 9 inches of vacuum??? Pretty big cam in a L48. Get your compression readings and vacuum readings and post your findings on here.
then we can give you more advise on which way to go.
a stock L48 has dished pistons and large volume combustion chamber heads. = Low compression.
you fuel choice has more to do with compression than anything else.
Timing for a "Hot" cam and high compression is way different than a standard engine. Timing for a mild cam with low compression is different still.
things you can do. Run a compression test on all 8 cylinders. That should at least give you an idea of what is going on in the combustion chambers. Put a Vacuum gage on it when idling . Adjust your low speed mixture screws to get highest vacuum at Idle. What is it? 17-18 inches of vacuum?? Pretty much stock cam. 9 inches of vacuum??? Pretty big cam in a L48. Get your compression readings and vacuum readings and post your findings on here.
then we can give you more advise on which way to go.
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
If you wanna learn ... you can measure your cam's lift, duration, centerlines and overlap/Lsa ... then you'll know what it is.
some everyday hand tools along w/ cheap dial indicator, magnetic holder, degree wheel will do it.
Get some Lars insight & instruction. Find just which edelbrock carb you have (model #) ... some based on carter afb, others Qjet based. Don't assume.
some everyday hand tools along w/ cheap dial indicator, magnetic holder, degree wheel will do it.
Get some Lars insight & instruction. Find just which edelbrock carb you have (model #) ... some based on carter afb, others Qjet based. Don't assume.
Thread Starter
Racer
Joined: Jan 2020
Posts: 388
Likes: 117
From: Tacoma, Wa
If you wanna learn ... you can measure your cam's lift, duration, centerlines and overlap/Lsa ... then you'll know what it is.
some everyday hand tools along w/ cheap dial indicator, magnetic holder, degree wheel will do it.
Get some Lars insight & instruction. Find just which edelbrock carb you have (model #) ... some based on carter afb, others Qjet based. Don't assume.
some everyday hand tools along w/ cheap dial indicator, magnetic holder, degree wheel will do it.
Get some Lars insight & instruction. Find just which edelbrock carb you have (model #) ... some based on carter afb, others Qjet based. Don't assume.
I believe its a Carter style Edlebrock
Thread Starter
Racer
Joined: Jan 2020
Posts: 388
Likes: 117
From: Tacoma, Wa
Run a compression test on all 8 cylinders. That should at least give you an idea of what is going on in the combustion chambers. Put a Vacuum gage on it when idling . Adjust your low speed mixture screws to get highest vacuum at Idle. What is it? 17-18 inches of vacuum?? Pretty much stock cam. 9 inches of vacuum??? Pretty big cam in a L48. Get your compression readings and vacuum readings and post your findings on here.
then we can give you more advise on which way to go.
then we can give you more advise on which way to go.
Last edited by Cmurray79; Apr 12, 2020 at 06:41 PM.
