Too much timing?

[TJ's GMC]

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.

[ilvracn]

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

[Clyde]

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.

[George Bongert]

Originally Posted by TJ's GMC

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.

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, 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.

[David R Leifheit]

Originally Posted by Clarke

First of all, this is not my area of expertise, so I appreciate your feedback. Given the subject of this thread, I'd like to explain how I arrived at 16 degrees (in lieu of the factory spec of 7.5 degrees).

Many old timers I've spoken to over the years say they never use a timing light; they adjust the distributor (advancing the timing) until the motor starts to run rough (detonation), then back it off a little. (What's a little? I don't know? LOL!) I tried that with my 305 and it started running rough at 20 degrees, so I backed if off 4 degrees.

Correct me if I'm wrong, the engine achieves the greatest amount of power when the combustion process happens when the piston is at it's highest position (least amount of open area), just as the piston is starting on it's "down stroke". This is why when you advance the timing from factory spec, the engine idle increases. As you are reducing the amount of open area during the combustion process, the increased energy pushes the piston down, resulting in more power.

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.

[Clarke]

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.

[TJ's GMC]

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.

[George Bongert]

Originally Posted by TJ's GMC

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.

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%.

[TJ's GMC]

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!

[1969_CM2590D]

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?