On the highway, I'm pulling in around 51-52 degrees total advance with no pinging or "trailer hitching" Autozone sells this "B28" vacuum advance under part # DV1810[/QUOTE] What do you mean be "trailer hitching". Low rpm surging feel?
My "Goodwrench" 350 with a cam installed liked 20 degrees initial. Everything else was stock except for the tri-power and lake headers. I used to live on a pretty long and steep hill. I'd go to the bottom of the hill, turn around and drive up the hill. I'd advance the timing until it pinged, then back off 2 degrees.
My Vortec 350 has 20° base timing and 16° in the dizzy, I then add 10° vacume advance for the road and there is no detination or hard starting. I use a 1405 Eddy that is modded with an LT4 hot cam and a Air Gap intake. Runs great and pulls to 6500 rpm.
The beauty of computer controlled engines is that the computer is constantly checking and making adjustments on the fly. Pushing the timing to just under knock territory. Being able to monitor combustion and instantly adjusting fuel mixture is a hot rodder's dream.
Sometimes when you have the timing too far advanced (more than 52 deg total), the car will jerk/chug with light throttle changes during high vac cruise speeds. It feels like you are pulling a trailer - like when you want to slow down, but the trailer pushes you. This is usually caused by too much centrifugal advance in a worn out dist or incorrect curve. What you really need to do is get your distributor "curved" for the cam & car specs - see reply #9 I can PM you the name of the guy who did mine. He only works on points-type delcos, & he installs high perf points/cond (no modules, etc).
No one has mentioned it, so I will. Before you adjust anything, make sure zero on the timing matches zero on the balancer. Find true top dead center. On my 2 327 engines, one was 3° off, the other was 5° off. my 2¢ .bjb
Ive been haveing this problem and have tried all sorts of stuff. It does it sometimes and other times not. Its a re-manufactured from a good parts place but i should probably get one from GMC bubba. Ive been thinking it was the carb though.
You can try a different vacuum controller to see if there's any change. Here are a couple of Autozone p/n's depending on your cam duration (delco points type - pre HEI): DV1808 (OEM # B26), cam intake duration @ .050" 218-224 deg. * starts at 5-7" Hg, 17-18 deg advance all in around 11-13" Hg DV1810 (OEM #B28), cam intake duration @ .050" 226-232+ deg. * starts at 3-5" Hg, 16-17 deg advance all in around 6-8" Hg. With a big cam (more than 226*) set your initial at 16-17 deg at 700 RPM (will be rough). Hook up the vac avance to a full time vacuum source & adjust your idle speed back down to around 900. When you hook it up to a full time source, you will get instant advance & the idle will come up to 1100-1200. Throttle response should be snappy This is all dependent on the condition of the mech advance. The mech advance needs to go no more then 35-36 deg @ 3000 RPM
Okay. I just got in from setting my timing at 8 degrees BTDC. After a test drive, she seems to have a little more pep. I'll drive her today and she how she acts on the open road.
I run a Stock GM Dist duel point Tack Drive from a Corvette No Vacumn the Dist has a 12 degrees Curve in it and I set my Timing at bet 36-38 327/300 hp Just my 3.5 cents
Like I said earlier, she runs fine. I'm just playing around and doing things that are pretty basic. Kinda like the "Free Horsepower" articles that Hot Rod magazine used to publish. Every motor has a sweet spot, I'm just trying to see what mine is without getting too involved.
Most HEI 350 distributors had 22 total mechanical around 4000 RPM. If that's the case the engine will need to be set at 13-14 degrees initial. Since you probably don't have EGR you might get spark knock at part throttle, you may want to try the Echlin VC 1843 advance unit. An advance tuning kit to get your advance in earlier would help a lot. The suggestion to make 3 additional timing marks at 10 degree intervals was great, then you can actually see where your advance curve is. PS; Pull the rotor off and make sure the advance pivots are not worn out, if they are they make repair kits. If not, put a dab of electrical grease on the pivot pins. PSPS; If you go to the hardware store you can probably find a nylon bushing that will fit over the vacuum advance rod, this will kill 2-3 degrees advance to help the part throttle ping.
I'd like to see points duel! Watch them take 10 paces , turn and fire . Maybe a swashbuckling sord extravaganza if they miss
While I'm here, I've had pretty good luck setting distributors up with around 12 degrees initial and 36-38 degrees total advance for a baseline on most small block and big block Chevys. It might not be perfect, but it's a good place to start.
Here is a chart for a Generic 75-80 SBC HEI, a 69 - 350 300 HP, and a typical Performance curve. To get 36 total we would have to set the initial at 14, 0, 14 respectively. OOps the scale didn't show up, 1 = 1200, 7 = 4200 RPM
You guys might laugh at my old school way of setting initial timing on an engine that has had some work done to it; but after changing heads, cams and piston type and size; who knows where initial timing wants to be? So my theory is why not give her what she wants and throw the timing light back into your tool box and get the vacuum gauge out and connected. Warm the engine to operating temp, set the idle below where centrifugal advance starts to come into play. Then rotate the distributor until you have achieved the highest and smoothest vacuum reading on the gauge. I then will usually retard the timing until I loose 1/2 to an inch of vacuum as long as it stays a smooth reading. After that then start on what you think your total timing should be by having the distributor curved. For a total timing somewhere just below a cursing or light acceleration ping. If your set up makes for hard hot restarts; because of the initial timing being so far ahead. Split the ignition switch and have a separate crank button connected to the starter. Get the engine spinning and then throw the ignition switch on. We used this method of starting the toilet bowl racer (stock car) but we were also running 30 degree initial timing and I was tiered of replacing starter end frames. Dan.
I would never make fun of something that works for someone but I don't think it's the best way to approach it. Actually if you could vary the advance under cruise load to the highest vacuum without spark knock that would be great. It would help you figure out how much vacuum advance to run under hat condition. There is a point in timing called MBT or Mean Best Timing. If we are plotting this at full throttle and you had some vacuum from a throttle restriction you could use it (Vacuum/Manifold pressure) as an indicator. Normally we use a dyno and would at several points in a curve adjust the timing to Maximum Torque. This would be MBT at this point. In some cases we can't run MBT because we are knock limited. The amount of retard would be called knock retard. Often with a tight squish and an efficient chamber we do not have to retard for knock at full throttle rich load. After plotting the MBT curve we can put this into the distributor. Now in a production environment allowance have to be made for all the different operating conditions and we are usually conservative. The "free HP" comes from moving up the timing to closer to the real Best Timing. Most performance 'curves' allow for less distributor advance and more initial. A locked out distributor would work fine above 3000 RP but of course complicates cranking and can have tip in knock. If the advance is all in at 2800 and you are running 36 degrees advance, be it 6 plus 30, or 10 plus 26, or 16 plus 20 there will be very little difference in performance because you spend almost no full throttle time under 2800. In that case make it easy on your starter and run a reasonable initial and then limit the advance to get the desired mechanical. A problem I see is people putting 22 degree advance HEI's in older cars and using the original timing that was designed for 28-34 degree mechanical distributors. To me, marking the balancer is free, and allows the OP to actually figure out his curve without a distributor machine. And since he lives in my area, I'd be happy to drop by for a beer and tune!
Update: Dropped by Fred's today to check out his ride. Checked the initial and it was at 6, took it to 4000, it was at 6, not good. Pulled the cap and rotor off and sure enough, the mechanical advance was frozen. We got out the universal fix (wd 40) and Fred worked it in for about 20 minutes until it was nice and free. The rotor button was in bad shape so we hopped over to the part store and got a cap and rotor. I had some light advance springs so Fred installed them and we buttoned it up. The Vacuum advance works but it is one of the smallest advance travel I have ever seen (turned out to be 6 at manifold vacuum 3000). All the advance was in now about 2800 so we set total at 36. This ended up with initial being 16. I think in the future he might want to get an adjustable vac advance. So he's got about 42 at cruise instead of 12, should pick up from his 15 MPG.
Listen if you don't have a timing gun that will tell you your total advance then make sure you get a timing tape attached to the balancer. Then you can see your total. Be conservative pump gas sucks now. Jay
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