360 Tune Up
Thanks for the challenge, guys. I had already checked this distributor and since it was new, I ASSumed it was ok. After mapping the centrifugal advance curve, I plugged in the vacuum line to find that the diaphragm was open. No vacuum advance. So, I'm starting over literally. Fortunately, I had another distributor and mapped it. I also returned the Edelbrock 1406 to base #1 tune.
The 2nd distributor has the following map.
- Idle (750 rpm) 7 degrees
- 1000 rpm - 12 degrees
- 1500 rpm - 24 degrees
- 2000 rpm - 26 degrees
- 2500 rpm - 28 degrees
- 3000 rpm - 31 degrees
- 3300 rpm - 34 degrees
The vacuum canister on this one has 15 degrees of advance. I get 17-18" of vacuum at 750 rpm and 22" at 2000 rpm. Vac advance is hooked to manifold vacuum.
The lack of vacuum advance would explain the higher temps cruising under load at 2400 rpm or so. Correct? It is supposed to get hot this weekend. So, I plan to do some more temperature testing. I have a new electric fan coming today and hope to get it installed tomorrow. Mileage tuning may have to come later.
What is the recommended amount of total centrifugal advance and the recommended total of vacuum advance? Is 34 BTDC about right?
Thanks for your help!
Plot your numbers on a graph with rpm along the bottom, and degrees advance up the left side. Be sure to NOT include the vacuum advance numbers.
IMO your D has too many degrees of centrifugal, and not enough idle. but the 34* at 3300 is about right.
At your cruise rpm of 65=2240, it looks like the current cruise timing is 27+15=42 and that is at least 10* not enough. And that is partly where your lack of fuel economy is. That engine should run on 87 full-time. It just needs a split timing curve, more idle-timing and less at 2500 but a bunch more at cruising, and the Vcan has to drop out as fast as possible;factory cans are adjustable..
What a lotta guys don't realize is that you can't run a automatic timing curve on a manual trans car.......... because there is no convertor slip; the engine is married to whatever gear you are in .
The
AX-15 ratios are 3.83-2.33-1.44-1.00-.79od. with 3.55s, the road gears are
13.60-8.27-5.11-3.55-2.80
Here's one problem I see, correct me if I'm wrong;
at 32 mph, you sorta have to be in third gear to cruise at 2010rpm, at 26+15=41* timing, which is not a problem. But when you roll into the throttle, even just the 26* may be too much. never mind the 15 more in the manifold operated Vcan. And most especially if it doesn't drop out fast enough. And so there is your can of marbles. There is no fluid coupling, so the engine is stuck in rattle-mode.
So what do you do? Downshift right? and now the rpm jumps to 3250 and timing is 34@WOT . On a high compression engine this will be fine. But in your Stock long-block with an advertised 8/1 Scr, it may be too much, and so back to sack of hammers rattleing.
And controlling or trying to control detonation by running rich or cold is not the cure for this.
The cure is to fix the timing.
Lets look at 750 rpm in first gear.
Now the timing is 7+15Vcan=22* which is fine at no load..... but the only way to make it idle is to close the throttles too far which promptly dries up the transfers, and introduces a tip-in stumble, and a cold-idle problem. So you gotta not do that.
So forget about trying to make the engine idle on some pre-conceived amount of timing;in your combo, it does not matter one iota what the idle-timing is cuz the only time you will ever drive at 750 rpm is in a parade on account of with your combo 750 rpm is 4.5mph.
So the proper way to start your tune up is to set the Transfer-slot exposure to about square at the very least; then back up the timing to whatever gets you the idle-speed you want. then adjust the mixture screws to best lean idle. Of course the PCV system has to be functioning,the Vcan hooked to ported vacuum, and the metering rods have to be staying down. If you have fudged with them, put the stock ones back in, and the stock MJs as well.
If your cooling system is rock solid, and you are operating mostly at one elevation, then I recommend to run as hot as you dare, unless the pistons lock up when you shut it off.
If you are running fresh cold air, now you are all set to start tuning. The idle parameters have to be established before you start anything else. And once you have chosen a minimum cooling system temperature, your tune will be locked to it, meaning if you start too hot, and have to back up, then only your idle-tune may still be OK.
Ok so, now that the idle-tune is established, you can proceed
more coming; oops lost in cyber space
