What is your initial timing advance? Please explain any mods or other things that may have changed your timing needs. Also give your total advance and at what RPM if you have that info.

Thanks

 

Both the 390 I was running before and the FE446 I'm now running like a lot of initial advance. Both are healthy cams.

The idle gets better all the way up past the 30 deg BTDC, is that typical? Obviously, I can't run that way. I have not noticed any pinging at higher RPM with total advance in the 40 deg range. I'm guessing, it's at or past the BTDC lettering on the balancer.

 

Can't tell you what the total advance is, the balancer don't read that far. I've set the timing on all my FE's ( 3-4 390's and a 427) at 12 degrees initial. the 390's used a Cam Dynamics 296 degree .526 lift ( I'm foggy on those specs, been 20 years) the 427 had a Holman-Moody 310 degree, .515 lift solid grind. The Merc I have now has a mild Crane 272 degree Energizer. 390's had 10-10.5 to 1 comp and the 427 had 11-11.75 to 1 ( had it stroked at first)

 

When my vacuum AND centrifugal were frozen (and hadn't yet diagnosed the problem), I adjusted it where it ran best.
For best power and driveability it wanted 25-30* or more advance. BUT for fair idle and good hot restart I had to hold it to something reasonable. I think I settled for 25* fixed.

And, no, the balancer hadn't slipped, so that was the real number. I verified the marks with a dead-stop (home-made, plans in my FTE webpage).

Later, when I discovered the frozen vac. and cent. mechanisms, I repaired them and took it back to something more reasonable like 15*. Passing gear torque was *much* better after that.

With that timimg, I still had no knock. Remember that's with a pretty low compression with the piston tops sitting well below the deck. With my rebuild, I'm expecting compression in the range of 9.5:1, but with a slightly wild cam. Once it's up and running, I'll report back.

--Matt

 

I am running close to 11 to 1 compression on my 390...12 degrees is about all the initial I can run without pinging problems on 92 octane...I think it would like a little more for starting, but I would need to limit the total...d44hd

 

Here's the list of mods first:

Holley 750 on Edel performer 390, 292/292, 250/250@.050",.554/.554" lift Wolverine cam. CJ-sized exhaust valves, double springs matched to cam, 10.5:1 TRW forged pistons.1 7/8" long-tube headers to dual 2.25" (no crossover) exhaust. Total compression was "below 11" according to my machinst who did the grunt work of measuring the heads and pistons/deck height, head gasket, etc. Initially, it was a bitch. Too much initial advance and PING. Not enough, VERY bad idle (vacuum dropped below 9 inches). Never had a vacuum advance on it initially.

Motor is over 10 years old now, only about 5K miles on it. In the last 2 years, I put in an adjustable vacuum advance. The Holley 750 has a ported vacuum for vacumm advance, but it's vacuum at IDLE, less vacuum as you open the throttle. Obviously opposite of a Ford carb.

However, I adjusted the vacuum advance pretty stiff, and pumped up the initial advance to just under 20 degrees, and finally got 12 inches of vacuum. Open the throttle, and the advance DROPS so the motor doesn't want to rev up very fast, also keeps it from pinging. Plenty of low-end torque.

Now, I work on the dizzy. Two springs on the mechanical advance, one weak, one strong. The strong one has some play in it, so the intiial 5 or so degrees of advance is held with only the one weak spring. Then, the heavy one comes on, after that initial 5 degrees (or more). Disassemble dizzy, reconfigure for the 13 degrees instead of 18 degrees (26/36 crank degrees) total advance and put in two WEAK springs. Since both are already in tension, the initial 5 degrees or so advance I talked about above now comes on slower, because it's TWO weak springs holding it.

Overall, it all works out. Nice initial for idle, vacuum advance doesn't advance on startup, so startup advance is around 8 degrees. When vacuum comes up, the vacuum advance comes on up to 16-18 degrees or so. Good idle. Max advance is 35 degrees, around 3000RPM or maybe higher. Smooth idle with big cam. No pinging on 93 octane. Never tried anything else. Ever since I did this, it doesn't run-on any more either.

I would not suggest this method for anyone. I may find out in 10 years that I toasted the rings and valves because the dynamic cylinder pressure was so high. If you decide to do this, you might be able to work off manifold vacuum for the vacuum advance method I used. My Holley must be for a Chevy application, not sure of what it was for.

ak

 

With a cam like that and those pistons, your 10.5 to 1 comp ratio shouldn't have been a problem. The vacuum fitting I hook the advance to is the one on the right side of the main metering blockon a Holley. This source has no vacuum pull at idle, it only pulls vacuum when the throttle is opened. If yours was advancing at idle, then you used the wrong source. Run on ( deiseling) is usually caused by the idle screw being opened too far and letting too much air by the throttle blades.

 

The Holley has the same ported vacuum source as the Ford carb. What is happening is the idle speed screw is turned far enough to uncover the transfer slot and the ported vac is reading manifold vacuum thru the open throttle plates. There arew ways of modifying the throttle plates to allow the idle speed screw to be closed farther. I would bet adjusting the idle mixture screws is tough also, because the transfer slot is only partially controlled by the mixture screws.

 

You can drill small holes in the throttle blades to increase the air to the motor, while keeping the blades closed far enough to keep the transfer slots from being exposed. I also agree that, the throttle blades being open too far may have also been the problem.

 

Trust me, in my case, the ported vacuum is basically manifold vacuum. The idle screws do nothing to the ported vacuum (again, in my case). This Holley was a Chevy replacement, or whatever brand that needs vacuum at idle for vacuum advance.

Been there, done that...

 

There is no difference between a Chevy Holley( we're talking the square bore, not spread bores and even then they operate the same, just have different base plates and bolt patterns) and one for a Ford as far as the function. The only real difference in applications is the presence of the kickdown lever for Ford automatic transmission applications. If your idle mixture screws didn't respond , then that's another indication that the ldle speed screw and blades are open too far, thus exposing the transfer slots. When this happens the carb is operating in the intermediate circuit, this circuit is between the idle and main metering circuits. If you had closed the idle speed screw, you would have found that the idle mixture screws would have responded to adjustments. In addition to that, the vacuum port on the side of the metering block, would have had no 'vacuum pull" Like I said before, this port has no pull till the throttle blades are open. Get a Holley manual and read it, you will see where you were mistaken on your diagnosis of your problem. I've been fooling with Holleys for 20 something years now but when I first started messing with them, I didn't understand them either. I recently ran an 850 double pumper "Chevy " Holley on the 390 in my 68 Monterey and it worked fine, vacuum advance and all.

 

My idle mix screws work perfectly, and have no affect on the vacuum port I used. For all I know, it's the WRONG ONE

I know all about the normal ported vacuum operation. I have to go take a look now, because you've piqued my interest. It could very well be that I caught manifold vacuum...

ak

 

I didn't mean to say that the mixture screws had an effect on the vacuum port on the metering block. Having the ldle speed srew in too far and opening the throttle blades will uncover the transfer slots and thus, put the carb into the intermediate circuit, which the mixture screws have no control over ( they don't respond to adjustments in the intermediate circuit) . Having the throttle open too far, will also at the same time, create a vacuum signal to the port on the metering block, advancing the distributor, or starting to anyway. Hope this helps, I tried to be as clear as possible the first time, maybe I wasn't.

 

And I, in the middle of work, answered you without really reading what you were saying. But yes, you are talking about the typical "low-vacuum", "open throttle plate", Holley story. And the resulting workaround, drilling the throttle plates.

Been there done that. Now, with the advance setup the way it is, with a high initial at idle (and not during start), the idle is even better than it was, and, while the idle mix screws did work initially, they are much easier to control now.

Back to the root of it, the port I took off the Holley has what seems to be manifold vacuum. I've never checked it with a vacuum guage, but it works for me. I really have to check where I took it from. Where is the usual ported vacuum on the Holley 750 vac-sec? I'm pretty sure I took it off the right (passenger) front of the carb, underneath the fuel bowl.

ak

 

Just about all Holleys have that port, and yes it is manifold vacuum. Like I said before the one on the right side of the main metering block isn't exposed to vacuum till the throttle is opened. Not all Holleys have this port, the 850 I mentioned before doesn't have it. I had to use the one under the main bowl, but for some reason it doesn't advance the distributor at idle.