Carcinogen
1/2 ton status
And aluminum?
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.
Timing advance question
- Thread starter Stephen Carter
- Start date
Don't remember that. I guess the power of Google would tell us. But I am on my phone and hate searching with it.
Stephen Carter
Registered Member
I did some searching. Apparently it's the same used in the 4bbl 3rd Gen fbody. Runs outta steam around 5-5.5k.
Carb sounds too big.
I put a big carb on mine once. Ran like hell.
Hard to start, and just didnt run right.
Put the 650 back on and tuned it and it was much happier. And mine is a 400 sbc.
I put a big carb on mine once. Ran like hell.
Hard to start, and just didnt run right.
Put the 650 back on and tuned it and it was much happier. And mine is a 400 sbc.
Carcinogen
1/2 ton status
Aren't Edelbrocks vacuum secondaries though? It was my understanding that it was near impossible to oversize a carb with vacuum secondaries, that's why the quadrajet was put on almost everything for a while.
Stephen Carter
Registered Member
I think they are. I was thinking about ordering a rebuild kit and the calibration pack that has all the Jets and rods in it and just lean it out a bit.
My guess is that your stock engine won't last at 5k for very long and may have a hard time getting there.
You could spend some time tuning that carb to get it close. You are at 700 feet in elevation so that will help. At 7000 feet where I live, it would be tough.
What are you using the truck for?
You could spend some time tuning that carb to get it close. You are at 700 feet in elevation so that will help. At 7000 feet where I live, it would be tough.
What are you using the truck for?
Stephen Carter
Registered Member
I think the most I've gotten it to was 3200 lol.
I'm just driving it as a daily at the moment. After I get a proper front driveshaft, some light wheeling. I mean it's got a 6" lift and 35s on it so I'm sure it could go places I'm not willing to go lol
I'm just driving it as a daily at the moment. After I get a proper front driveshaft, some light wheeling. I mean it's got a 6" lift and 35s on it so I'm sure it could go places I'm not willing to go lol
Stephen Carter
Registered Member
I'd like to thank everyone for their assistance in this whole timing thing. Finally got it all sorted out.
Settled at 8* at idle w/o vacuum advance. (as per the moroso timing kit instructions), With vacuum advance, the timing goes up to 30* at a 700RPM idle. So far, she is running like a champ, almost feel like a whole new motor lol.
Thanks again ya'll!
Settled at 8* at idle w/o vacuum advance. (as per the moroso timing kit instructions), With vacuum advance, the timing goes up to 30* at a 700RPM idle. So far, she is running like a champ, almost feel like a whole new motor lol.
Thanks again ya'll!
How did it idle at 30*?
Bit higher than what EFI ran/runs (20-25 seems about right) but again, on vacuum, that is meaningless when you step on the gas.
Bit higher than what EFI ran/runs (20-25 seems about right) but again, on vacuum, that is meaningless when you step on the gas.
Stephen Carter
Registered Member
Actually idles well, has a small miss for about 5 minutes after it starts, but other than that it's golden.
30 degrees is a lot of timing for idle. Make sure you check to see what your maximum (all-in) timing is. Here's why-Your mechanical advance maxes out at around 22-23 degrees added to your initial timing, and an unlimited vacuum can will add about another 20 or so (or about 22 in your case, assuming the mechanical timing advance isn't kicking in at idle). 8+22+22=52 degrees of total timing, which is going to be a bit high for most SBC engines. Opinions vary, but 34-36 total advance is usually a good place to start on total timing. Some engines (like Vortec-head SBCs) make best power even lower, around 32 degrees. It can be a bit higher on modified engines. Ultimately, I've seen people run varying timings based on how the engine behaves, just don't want you to run into any issues, and you don't want to mask another problem with timing advance. As dyeager said, typical idle rpm with manifold vacuum hookup is going to be in the 20-25 degree range depending on your initial advance. If you want to continue running 30 degrees at idle, you may want to get a vacuum advance limiter (Crane makes one) that limits how much vacuum advance your can will provide. They have multiple settings depending on your preference.
If the parts are out there, and someone is willing to do it, "high" advance at idle and proper advance for mechanical SHOULD be doable, just doesn't seem many people want to mess with it.
Really killing two birds with one stone that way....high advance cleans up idle (so it stinks less, and idles smoother) while relying on mechanical advance when accelerating. If you could knock it down to 20* at idle, and whatever your engine likes at cruise, you'd be in good shape. Additionally, if you can knock base timing down due to the vac advance (and ramp mech. advance up fast enough) you'd have easier starts with less load on the starting circuit.
Challenges with that could be making sure vac advance comes off fast enough, and ensuring that it doesn't ping under cruise conditions from too much advance.
Really killing two birds with one stone that way....high advance cleans up idle (so it stinks less, and idles smoother) while relying on mechanical advance when accelerating. If you could knock it down to 20* at idle, and whatever your engine likes at cruise, you'd be in good shape. Additionally, if you can knock base timing down due to the vac advance (and ramp mech. advance up fast enough) you'd have easier starts with less load on the starting circuit.
Challenges with that could be making sure vac advance comes off fast enough, and ensuring that it doesn't ping under cruise conditions from too much advance.
