Re: Too much timing?
 

These engines have super low compression so I don't think you have to worry to much about detonation with 16 initial. I heard that same saying from the old guys as well. lol Setting by ear I had mine originally at 4 degrees. Then I bumped it up to 8 and felt a nice increase....then 10 and felt little more, higher didn't seem to make All that much difference so I stopped. I'm considering the HEI from HEIDIZZY on ebay. I'm gonna try and do an acceleration video so we can do some comparing. Hopefully this weekend.

Re: Too much timing?
 

the factory setting of 7.5 degrees was made to be safe under all conditions. if your pulling a 10000 lbs load on a 90 degree day you may want to back the timing off a little. for normal driving 16 deg should be fine as long as you dont hear any pinging. more likely, low rpm high load. fuel will make a difference too, lower octane means you run less timing.
rick

Re: Too much timing?
 

Remember these engines were designed to run the low octane gas of the day which was 92 octane according to the owners manual, today this is high octane.

Re: Too much timing?
 

Greetings again to all following this thread!

Personally, I would stick pretty close to factory settings, and certainly nothing over 10 degrees advance. Given factory specs, you are already 2.5 degrees above what is recommended, and I don't believe you will damage your engine with it set at 10 degrees initial advance since it's not that big of a jump. However, there is one thing to consider in advancing initial timing too far, and that is kickback against the starter which can, and has resulted in damage to starters:goodluck:, such as a broken starter nose cone. This is something that must be considered no matter what engine you are working with. Again, I wouldn't recommend anything above 10 degrees BTDC.

Re: Too much timing?
 

First, the "old" method of adjusting until it runs good is, in my opinion, only valid for engines of our era. Once computers got involved with the engines, you lost control of the timing. What this method does do is take wear into consideration. As the timing chain stretches the timing does change.

Second, While you are correct, the most power should be gathered at top dead center, you have adjusted the firing to be 16 degrees before top dead center, meaning it is firing well before TDC. According to the information on Jolly's site, 450 RPM idle and 5 degrees BTC.

Is your engine old or rebuilt with all new innards? If all new then with that much advance (triple stock) I would suggest something is terribly wrong. If it is an old, worn, engine then it is possible that the wear is the reason for the advanced timing. Which suggests, to me, a rebuild will be in your future.

One thing people do need to do when working on an older engine is to not rely on the tools (timing light) but rather on what the engine is telling you. You can time it all day with the light, and it will run rough if it is really worn. I have seen "kids" get frustrated trying to work on non-computer all manual older systems. They can't even figure out how to set the points (which could also affect the timing).

Having said all that...
If it works for you at 16BTC, then that is good for you. You could be compensating for wear, or have something else going on. If you are confident that everything else is as it should be, then enjoy your truck.

Re: Too much timing?
 

My engine has 57K orig miles on it. A couple years ago, I gave it a complete tune up. The compression was really good and consistent within a couple psi between cylinders. Majority of the valves were within tolerance, a few were .001-.002 out of tolerance, so I dialed those in. The vacuum was/is 19 inches. It was running good before the tune up and still is.

It was after the tune up when I started experimenting with the timing and it seems to have a litte more power. I drive it one or two days a week all year ago and put the cheap gas in it wherever I need it. I do a lot of towing too. I've never noticed loss of power, pinging, or inconsistencies at any time year around. Therefore, I think it's okay, but based on the feedback I think I'll dial the timing back to 10 degrees. I was running it at 7.5 degrees before and it was fine too. I was just trying to get more efficency/power out of it.

Thanks again for all the feedback.

Re: Too much timing?
 

Your welcome! This has been alot of fun for me. lol The ol V6 has been running so good in my GMC that I've been needing something to do! haha! My engine is the same....mileage is unknown as it is Not the original V6 from that truck, but the compression was at 120-125 in all cylinders and the cam looked fairly good last I had the valley pan off. Put some engine restore in the oil and now I need to find some ZDDP for the oil and it should be good for, hopefully with the easy driving I'm doing, another 100,000. The oil was so dirty when I got the truck that I had to change it 3 times withing 40 miles before it was finally staying clean, but rather have clean oil than a flat cam or anything else.

Re: Too much timing?
 

Greetings TJ and all the other club members following this thread!

This has been a very interesing subject with a lot of good comments, and recommendations. Regarding the subject of a ZDDP additive for the oil, I would like to offer a suggestion. Amzoil Synthetic Motor Oil. I am running Amzoil Synthetic Oil (already contains ZDDP) in my 2001 Pontiac Bonneville (3.8 Litre V-6). My brother also runs Amzoil Diesel Synthetic Motor Oil in his 2001 Chevy 2500HD Duramax Diesel, and swears it's the best oil he's ever used. It's a bit more expensive, but I took into consideration the benefits of synthetic oil plus the added benefit of the ZDDP. I know some folks who say you can run synthetic basically forever, however, I still recommend following the manufacturers oil change schedule. One nice thing about some these newer cars (like mine) is that the computer will warn you that you need to change your oil soon. I change both the oil, and the filter (no sense in having clean oil in the crankcase when there's still dirty oil in the filter) when the computer indicates that there is 5% oil life left. Of course, after the oil has been changed, the computer has to be reset (very simple procedure) to reset the oil life countdown to 100%.

Re: Too much timing?
 

Have heard alot of good about Amzoil. Joe Gibbs oil is what my machinist sells for a good price. I have been using Rotella with no issues thus far. Plan to add the zinc at the next oil change which will be soon if I head to troutdale in the truck this summer. Now I gotta figure out something else I can mess with on this thing! haha!

Re: Too much timing?
 

I'm a little tardy on this post, but over this Labor Day weekend i finally got back to my '69 305E 2500. The truck has 41K+ on it with manual everything. Coming form Alabama it was one of the last pickups to have no emission controls. With all that in mind, it's incredibly simple and brings a whole new meaning to the term serpentine belt.

I did the 4412 swap with the 1937 adapter when I got the truck the truck a few years ago. It never would idle right often not holding an idle as well as a hesitation beast on giving it the gas. I get frustrated over time. As time went on, I realized I had misread the instructions for installing the carb and tightened things to ft/lbs instead of in/lbs. A few moths ago I ordered new gaskets for the adapter and carb for when I could get to it, putting off fears I might have warped anything.

Saturday, I put the new gaskets on and once the dry carb got gas, things improved over 1000%. Toning the idle down from what was probably 1000+ RPM, it held its idle much better at the specced 500 RPM.The truck idled for over a half an hour. In the driveway, I gave it the gas and it accelerated smoothly. I let i sit for a few hours and with a flick of the key it fired up. Same thing the next morning. So a lot of problems solved. It still had a slight miss, though, so today I timed it by by feel, turning the dizzy until things were much smoother and reset the idle speed.

With all that in mind, I took it into town for a road test. No stalling and a decent idle, but going up a hill under load there was hesitation. so I got back home and looked into setting the idle mixture. Holley says to use the manifold vacuum for that- so there was one error I'd been making. I have been using the ported vacuum on the 4412 fer setting it up- Holley instructs to use that, but just for the vacuum advance. The advance was checked a while back and was OK. I came across this thread which got me looking into using manifold vacuum for the advance. More to look at as time goes on.

With my non-emissions 305E what I've come across here and elsewhere on the net tells me I should be using manifold vacuum, not the emission controlled ported vacuum. I came across this post here http://www.hotrodders.com/forum/port...uum-95255.html and I'll copy one response below which was pretty enlightening. Comments?

Re: Too much timing?
 

Quote:
Originally Posted by badhabit
.DO NOT HOOK YOUR VAC ADVANCE UP TO NORMAL VACUUM--- this will cause the idle to race and really run flat, because your advance is all in at idle-- not as you accelarate.

This will only happen if you select the wrong VA can. Having full vacuum advance at idle will increase the VE, reduce the EGT's and make the idle smoother. A former GM engineer wrote a nice piece on vacuum advance:

Quotation thanks to JohnZ

As many of you are aware, timing and vacuum advance is one of my favorite subjects, as I was involved in the development of some of those systems in my GM days and I understand it. Many people don't, as there has been very little written about it anywhere that makes sense, and as a result, a lot of folks are under the misunderstanding that vacuum advance somehow compromises performance. Nothing could be further from the truth. I finally sat down the other day and wrote up a primer on the subject, with the objective of helping more folks to understand vacuum advance and how it works together with initial timing and centrifugal advance to optimize all-around operation and performance. I have this as a Word document if anyone wants it sent to them - I've cut-and-pasted it here; it's long, but hopefully it's also informative.

TIMING AND VACUUM ADVANCE 101

The most important concept to understand is that lean mixtures, such as at idle and steady highway cruise, take longer to burn than rich mixtures; idle in particular, as idle mixture is affected by exhaust gas dilution. This requires that lean mixtures have "the fire lit" earlier in the compression cycle (spark timing advanced), allowing more burn time so that peak cylinder pressure is reached just after TDC for peak efficiency and reduced exhaust gas temperature (wasted combustion energy). Rich mixtures, on the other hand, burn faster than lean mixtures, so they need to have "the fire lit" later in the compression cycle (spark timing retarded slightly) so maximum cylinder pressure is still achieved at the same point after TDC as with the lean mixture, for maximum efficiency.

The centrifugal advance system in a distributor advances spark timing purely as a function of engine rpm (irrespective of engine load or operating conditions), with the amount of advance and the rate at which it comes in determined by the weights and springs on top of the autocam mechanism. The amount of advance added by the distributor, combined with initial static timing, is "total timing" (i.e., the 34-36 degrees at high rpm that most SBC's like). Vacuum advance has absolutely nothing to do with total timing or performance, as when the throttle is opened, manifold vacuum drops essentially to zero, and the vacuum advance drops out entirely; it has no part in the "total timing" equation.

At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier in order to develop maximum cylinder pressure at the proper point, so the vacuum advance can (connected to manifold vacuum, not "ported" vacuum - more on that aberration later) is activated by the high manifold vacuum, and adds about 15 degrees of spark advance, on top of the initial static timing setting (i.e., if your static timing is at 10 degrees, at idle it's actually around 25 degrees with the vacuum advance connected). The same thing occurs at steady-state highway cruise; the mixture is lean, takes longer to burn, the load on the engine is low, the manifold vacuum is high, so the vacuum advance is again deployed, and if you had a timing light set up so you could see the balancer as you were going down the highway, you'd see about 50 degrees advance (10 degrees initial, 20-25 degrees from the centrifugal advance, and 15 degrees from the vacuum advance) at steady-state cruise (it only takes about 40 horsepower to cruise at 50mph).

When you accelerate, the mixture is instantly enriched (by the accelerator pump, power valve, etc.), burns faster, doesn't need the additional spark advance, and when the throttle plates open, manifold vacuum drops, and the vacuum advance can returns to zero, retarding the spark timing back to what is provided by the initial static timing plus the centrifugal advance provided by the distributor at that engine rpm; the vacuum advance doesn't come back into play until you back off the gas and manifold vacuum increases again as you return to steady-state cruise, when the mixture again becomes lean.

The key difference is that centrifugal advance (in the distributor autocam via weights and springs) is purely rpm-sensitive; nothing changes it except changes in rpm. Vacuum advance, on the other hand, responds to engine load and rapidly-changing operating conditions, providing the correct degree of spark advance at any point in time based on engine load, to deal with both lean and rich mixture conditions. By today's terms, this was a relatively crude mechanical system, but it did a good job of optimizing engine efficiency, throttle response, fuel economy, and idle cooling, with absolutely ZERO effect on wide-open throttle performance, as vacuum advance is inoperative under wide-open throttle conditions. In modern cars with computerized engine controllers, all those sensors and the controller change both mixture and spark timing 50 to 100 times per second, and we don't even HAVE a distributor any more - it's all electronic.

Now, to the widely-misunderstood manifold-vs.-ported vacuum aberration. After 30-40 years of controlling vacuum advance with full manifold vacuum, along came emissions requirements, years before catalytic converter technology had been developed, and all manner of crude band-aid systems were developed to try and reduce hydrocarbons and oxides of nitrogen in the exhaust stream. One of these band-aids was "ported spark", which moved the vacuum pickup orifice in the carburetor venturi from below the throttle plate (where it was exposed to full manifold vacuum at idle) to above the throttle plate, where it saw no manifold vacuum at all at idle. This meant the vacuum advance was inoperative at idle (retarding spark timing from its optimum value), and these applications also had VERY low initial static timing (usually 4 degrees or less, and some actually were set at 2 degrees AFTER TDC). This was done in order to increase exhaust gas temperature (due to "lighting the fire late") to improve the effectiveness of the "afterburning" of hydrocarbons by the air injected into the exhaust manifolds by the A.I.R. system; as a result, these engines ran like crap, and an enormous amount of wasted heat energy was transferred through the exhaust port walls into the coolant, causing them to run hot at idle - cylinder pressure fell off, engine temperatures went up, combustion efficiency went down the drain, and fuel economy went down with it.

If you look at the centrifugal advance calibrations for these "ported spark, late-timed" engines, you'll see that instead of having 20 degrees of advance, they had up to 34 degrees of advance in the distributor, in order to get back to the 34-36 degrees "total timing" at high rpm wide-open throttle to get some of the performance back. The vacuum advance still worked at steady-state highway cruise (lean mixture = low emissions), but it was inoperative at idle, which caused all manner of problems - "ported vacuum" was strictly an early, pre-converter crude emissions strategy, and nothing more.

What about the Harry high-school non-vacuum advance polished billet "whizbang" distributors you see in the Summit and Jeg's catalogs? They're JUNK on a street-driven car, but some people keep buying them because they're "race car" parts, so they must be "good for my car" - they're NOT. "Race cars" run at wide-open throttle, rich mixture, full load, and high rpm all the time, so they don't need a system (vacuum advance) to deal with the full range of driving conditions encountered in street operation. Anyone driving a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and fuel economy, probably because they don't understand what vacuum advance is, how it works, and what it's for - there are lots of long-time experienced "mechanics" who don't understand the principles and operation of vacuum advance either, so they're not alone.

Vacuum advance calibrations are different between stock engines and modified engines, especially if you have a lot of cam and have relatively low manifold vacuum at idle. Most stock vacuum advance cans aren’t fully-deployed until they see about 15” Hg. Manifold vacuum, so those cans don’t work very well on a modified engine; with less than 15” Hg. at a rough idle, the stock can will “dither” in and out in response to the rapidly-changing manifold vacuum, constantly varying the amount of vacuum advance, which creates an unstable idle. Modified engines with more cam that generate less than 15” Hg. of vacuum at idle need a vacuum advance can that’s fully-deployed at least 1”, preferably 2” of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can (15 degrees), but is fully-deployed at only 8” of vacuum, so there is no variation in idle timing even with a stout cam.

For peak engine performance, driveability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively. Don't ask Summit or Jeg's about it – they don’t understand it, they're on commission, and they want to sell "race car" parts.

Re: Too much timing?
 

I tried my engine(305E with a 600 cfm 4 barrel and modded magnum manifold) on Manifold vacuum advance and it would hesitate off idle after idling for so long. Thing is, weather on Ported or Manifold....both are useless under load. Under load your relying on the weights in the dizzy for advance. The vacuum timing only comes in while cruising at a constant set speed to aid in power and mileage. Therefore, not Enough or to Much can have an affect on power and mileage. Which is why I backed mine down to 8 initial and left it on Ported timing. I did do 12 initial once, but it felt like to much and didn't really make a difference, so I left it at 8-10. 4-6 is is factory for stock, but with the extra fuel I have found advancing a little helps. Also the addition of an HEI makes a difference in itself. That and hot wires and plugs will aid in power. I still need to open the plugs in mine a tad more, but I haven't as it runs like a top and I drive it Everyday...so if it ain't broke I don't fix it. lol If I had a dyno that would be something I would play with and get some paper results. :thumbsup:

Re: Too much timing?
 

TJ, when you decide to open up the plugs, I have found the correct plugs with larger gaps. I'm running AC-R44XLS6 plugs that take .060 gaps for HEI applications in my 478M.:upyes:

Re: Too much timing?
 

That's one big sparky! lol

Re: Too much timing?
 

Thank you for the wonderful write-up 1969_CM2590D. I think I will take your suggestion and go with manifold vacuum. What do you recommend I set the initial timing to? The factory spec is 7.5 on mine. And to be clear, I still set the timing with the vacuum advance disconnected, correct?

Re: Too much timing?
 

this is a 6+ year old tread
I just adjusted the timing on my 305E. I think I set the initial timing (yes with the vacuum disconnect) to around 10 degrees and then used the manifold vacuum. The advantage is that you get timing added to your idle after you start the engine, but you won't have hard start issues due to too much advance when it's turning over.