You want around 32 total degrees of advance with the vacuum advance disconnected. This is usually around 8 degrees initial and the rest coming from the centrifugal advance. Most will run ported vacuum for the vacuum advance. The problem with most stock distributers is, the full advance comes in far too late and a curve kit can bring in the centrifugal advance where your particular engine with mods makes the most power. The changing of the springs and tweaking of the adjustable vacuum advance takes some trial and error but will yield better overall performance. Hope that helps.

JEGS 40004: HEI Advance Curve Kit For 1974-1979 GM HEI Distributors - JEGS High Performance

Buy JEGS 40004 at JEGS: JEGS HEI Advance Curve Kit For 1974-1979 GM HEI Distributors. Guaranteed lowest price!

www.jegs.com

https://autosalesinc.pxf.io/c/40473.../2996090/35994?subid=autolinker&u=https://www.summitracing.com/parts/sum-850314

 

Much depends on your definition of 'slightly hopped up'. Initial timing was generally 4° on the 350's, and as cams get bigger that extends, with some seeing as much as 12°. But with a mild cam, 6°-10° is generally in the ball park.

Vacuum is set at idle (warmed) with the dizzy unhooked and adjusting the idle mixture screws very slightly (1/8th of a turn or less, each side) until you are getting somewhere around 15 or higher. Might also require idle screw adjustment to keep rpm down, timing adjustment, air bleed screw adjustment, can be a real pain going round and round to dial idle in, depending on what carb you have, as playing with idle mixtures can have a negative affect on initial transition to off-idle, pauses or loss of power etc.

 

I run 22 degrees initial on my 350. 38 total. I overthought the timing on it far too long. Just advance it until it pings, and back off a few degrees.

I can run my car at 36 degrees initial just fine if I pin the distributor weights closed. My car won’t even start at less than 18 degrees initial advance. My car seems to be a bit abnormal though.

 

Here is a good explanation of timing and vacuum.

Pit Stop: Chevy Won’t Run Without 30-Degrees Base Timing

Pit Stop: After a head-swap, a small-block Chevy Won’t Run right without 30 degrees of base timing. What could have gone wrong?

www.motortrend.com

 

Squag27, I recently went through the same dilemma. I had the distributer in my 1981 go bad. And what that meant, was it wasn't advancing any more. So I went to Autozone, bought a new one, and installed it. Like you, I wound up at 12 degrees initial timing, based on the antique timing light that I used. And that's were the timing is currently set. THE PROBLEM IS... I literally have no idea how much total timing I have because I simply don't know how much timing a "STOCK" distributer from Autozone adds. I have heard 18, 20, 22 and 24..... My best guess is it adds 20 degrees, putting me at the sweet 32 degree spot. I never set timing based on "highest idle". I set my carb adjustment screws that way, but not timing. Because my engine is a low compression motor, I am still fidgeting with 13 and 14 degrees initial, but that's not what I'm getting at... What I'm getting at, is that it sounds like we are both running stock style distributors, with basic vacuum advance. And 12 degree's initial timing with the vacuum line plugged and the motor at idle, seems pretty close. Just sayin'.

 

Sorry for the slow reply gents and I appreciate all the info.
So as I understand it in my specific case, the Holley Sniper EFI I have pretty much makes tuning an engine via vacuum impossible because the idle control valve is constantly adjusting to try and get the best idle out of it. At the same time it appears that the dizzy in the car had way too heavy of a spring in it as well. I set the car to 12 degrees initial but it basically stayed at 12 degrees and never increased with RPM. It still isn't right now but it shouldn't take too much more to get it right. I guess the other thing I'm dealing with is that the vacuum advance is hooked up to the Sniper's ported vacuum source and apparently it needs to be hooked up to manifold vacuum in order to actually work. It's all a bit complicated.

 

Most folks use ported vacuum to the vacuum advance and the stock HEI distributer springs are way tight and need lighter springs for any performance gains. Attached is the Jegs/curve pdf and it shows how changing the springs will bring in the centrifugal advance to the desired range depending on springs used. You can also use one heavy and slightly lighter spring to fine tune even more. A timing light that allows advance is also recommended and with the vacuum advance disconnected, you want about 32-36 degrees total advance which there are many variables that dictate the correct total advance. Hope that helps.

https://www.oreillyauto.com/detail/c/innova/tools---equipment/diagnostic-tools/test---tune/4887d9c7148f/innova-timing-light/inn0/3568?pos=2

 

I do have a dial back timing light already which has helped. The problem is that apparently the Sniper EFI's ported manifold is run differently than a traditional carb and in my specific setup basically does nothing for the majority of my driving conditions. That coupled with the fact that my engine runs no EGR or any other emissions junk means that I supposedly need to run it on manifold according to the gurus at Holley as well as multiple Hot Rod and Motortrend Magazine articles I've been reading on my rabbit hole of research about this.

 

You can run manifold vacuum to the vacuum advance, however, depending on driving habits, initial and centrifugal is where you find the most performance (WOT). The vacuum advance is for cruising RPMs, whereas, if you have a lot of static timing + manifold vacuum advance you may have too much total timing at those RPMs which can cause engine damage. Sounds like you are doing your homework which will pay off in the end. Good luck.

 

Thanks! Yeah for my day to day habits my RPMs are pretty low with the 6 speed manual I run so I don't really see the benefits of vacuum advance with the ported vacuum source.

 

I just want to jump in here again. When you say you're distributer isin't advancing.....that's the exact problem I had. AND....the reason I swapped distributers. In my case, when I was checking the timing with the light, I'd whap the throttle, and I saw the mark "move", but that's all. I replaced the dizzy with a new one and HOLY CRAP!!!!! That's timing mark went zipping when I hit the gas and it felt like a whole new engine! So I guess all I'm saying, is if this is happening;;;

I set the car to 12 degrees initial but it basically stayed at 12 degrees and never increased with RPM.

Then you may have the same issue I had, which was frozen advance weights???

Edit: And I just wanted to add....HOLY MOLY did I pick up horsepower!!!! Once the dizzy was adding timing like it's supposed to, what a difference in the way the car ran, for realz!

 

Yeah I've has the dizzy apart and the advance isn't seized up on it. I changed the springs and weights out and now it does advance timing but I still need to do some work to fine tune it.

 

I usually remove the vacuum advance and advance the initial. I get much better results that way. Since I know what's going on with the engine and I have a nice Hurst Autostick shifter on my TH-400, I don't need the vacuum advance. I do put a lot of work into the important part of the advance system, the mechanical Advance. Chevrolet put a lot of money and time into the mechanical advance systems on these cars. I am using the advance weights from a 1964 Chevelle 360 horse 327. They're perfect for my 1978, low compression 454 truck motor.

 

I used to use timing lights and the dwell meter and pretty much everything available back in the early 80's and had some good results trying to set everything exactly to spec. By the mid 80's I threw everything away. I found setting the timing by ear worked way better for me. I would twist the dizzy until the motor sounded right and go for a drive. After that I would push the advance up until I got some spark knock under moderate acceleration and come back home and back off a couple degrees and call it a day! Good luck finding your perfect settings!

Joe