How do you set your timing to exactly 4 degrees without a timing light? Short of hooking your tongue up to the ignition system and blinking your eye real fast, you really can't. What you could do, is adjust the timing to the highest vacuum reading. But you would need a vacuum gauge
Here's the deal on timing using a vacuum gage. You don't aim for a particular timing mark, because you can't with only using a vacuum gage. You keep turning the distributor until you get the highest vacuum reading. Lock down the distributor and go drive the car. I did this on my pure stock family cars into the mid-70's. When I bought my first FI Toyota Camray in 1986, I went back to the timing light. My wife had a 1972 Impala 350, vacuum timing worked great on that car. I had a 1964 Belair 236ci 6 banger and it worked great on that car too. That was in the past years, I would do that now. You ever heard of guys that degree their timing, only to find out that it was different from what the factory said the timing should be. I never knew that could happen, I always though factory engines were "right on", that is not the case in a lot of engines, because there are + & - tolerance factors at play when you build "production engines". I used to NOT understand how an engine from front to back could vary in detentions. How some pistons at the rear of the engine were deeper in the hole than the front pistons. How does a camshaft bore be out of alignment. These engines are not precision made. That said, the modern engines (circa 2000 versions +) are more precision built because machining technology has improved a lot of the decades. Another good reason why engines can last 200,000 miles and much more if you maintain the engine. O'Ya, oil have improved a huge amount too. Vet
2 key things on modern engines: knock sensors and rev limiters. In the old days you could crank up timing and blow an engine in an afternoon. Same with rev limiters...sit in neutral and floor it. Another story: lady at work wanted advise in the 80s for a car for her son. One of the candidates was a 73 Century with 350-4. I checked it out and they got it. It was nice....buckets console, PW, etc. Son was not enthused....he wanted the Nissan 200SX. A week later I hear from her that he got a big ticket for speeding and she temporarily took car away. A few weeks later he blew the 350 up and got his Nissan......
More timing will give you a higher vacuum reading. I run my timing locked at 35*. It will idle in Park at 15", and 12" in gear. If you used a vacuum gauge to determine best idle vacuum, you would almost certainly end up with more higher RPM timing than you wanted. In the age of emissions control, the factory initial timing spec was far from being the best performance/efficiency wise. In some cases it left a lot to be desired. Have a look at the 1972 timing specs, Look at the 350, and the standard 455. 4*BTDC initial timing. Maximum mechanical advance of 16*, and 18* respectively. By my math, that results in total WOT timing of, 4+16=20*, and 4+18=22*, far below the 30-34* that results in best power. Curiously enough, the Stage1 engine was 10* initial + 24* maximum mechanical advance for 34* total WOT timing. I have often wondered if Buick did this intentionally to make the performance of the Stage1 engine seem better than it really was. A 1972 GS455 timed to factory specs wood be a slug compared to the Stage1 with way more timing.
^^^ You put enough load on at low RPM at or near WOT on the best tuned engine and you most likely will get detonation. Like or not, none of it is good. The knock/detonation/ping event creates an "echoing" sharp pulse. Think of it as a concussion. It is not OK to have occasional and continual light concussions. Even if you don't die the first few times or slobber on your shirt. Realize the manual states it the way it does to keep people from setting timing to eliminate "all detonation" and the greater problem that will introduce over the life of the car, than people occasionally operating incorrectly. That is not an "OK" to operate it to the point of ping. Many of us started with manuals and were told "don't lug the engine!"
Thanks Vet. Yes true. I found out that when i set my dwell at 30 initial was on approx. 2 BTDC. if i would set it later to 0 TDC (factory) it isn't the best of timing setting. So i have it set to 4 BTDC for better performance.
That is why Jim Weise ran my engine on the Dyno with Race fuel 110 leaded. I remember him telling me that the Dyno loads an engine more than anything you can do to it on the street. He told me the engine will run happily on Pump premium, but if I ever took it down the track, he advised mixing in some leaded 110.
To the first part of your comment: i guess you misread my question. I asked a question about how to set ignition timing exactly as i would do it with a timing light. I know that you can't do that with a vacuum gauge. But a question like this could maybe lead me to new info about this topic.
Larry, all I can say is I have a very mild Comp Cam, you have seen the specs. I get a max of 15 inches of mercury, just enough for the power brakes to function. On my pure stock card, getting 20 inches of vacuum was standard to get. I was floored to find I can only get 15 inches of vacuum with a mild cam with a LSA of 112. Vet
When you compare 2 motors that are built exactly the same but for the compression ratio the motor with less compression will also produce less ide vacuum. Idle conditions ( low rpm) and especially with as lean as can be had idle mixtures wil call for more initial timing then what's needed until once 1800 to 2000 rpm comes around. Basically lean mixtures burn slow so you need to start the flame earlier. This is where having the vacuum advance in at idle wil allow the added timing needed while not having so much initial advance that can make the motor hard to crank. The closer a motor is to having the minimum amount of compression needed for a given Cam, then the more the motor may need vacuum advance brought in at idle. Many folks are fully amazed at how much cooler there motor runs not just at idle with vacuum advance ( the needed timing for the motor) but also how much cooler the runs when cruising.
Since the engines were under warranty, GM would not advise doing something that would increase their warranty claims. Detonation under those conditions would be very short-term. GM used to call "light" detonation "The Sound of Economy"; especially in relation to the Vega. That poor thing--and the craptastic "Iron Duke" in it's non-computer-control years were such rattlers that GM just gave up. But they weren't the only engines that needed more help. They simply wouldn't spend the money needed to actually FIX the detonation, so they allowed light detonation which generally doesn't hurt anything. Light detonation being detonation at part-throttle, often about 1/3 throttle. The more the throttle is open, the heavier the detonation and the more destructive it is. Not possible. Not likely to be even close. And it's VERY likely that you'll have wildly-advanced timing by going for highest vacuum. Not using a timing light? Best you can hope for is to "static time" the engine by putting the crankshaft at whatever position you want the initial timing--let's say 10 degrees advanced--and then looking at the geometry of the distributor with regard to points opening/closing, or the alignment of the reluctor and pickup coil. Done properly, and with some experience, you'd get within a couple of degrees of "correct". Not a bad system for an emergency repair, out on the road somewhere. At home? CONNECT YOUR TIMING LIGHT and do it right. If you don't have a timing light, (and an automotive multimeter) don't open the hood except to check fluid levels. If you're not willing to invest in essential tools, you have no business "working on your car".
I agree 100% with you. But when your 13 and your uncle shows you how to tune a car with a vacuum gage and you believe he is telling you the truth. That's what you believe until it's proven to you he was wrong. Besides, at 13 I didn't have enought money to buy a timing gun and a multimeter, much less how to use them. Vet
With points and a dwell meter/timing light you do not need a mulitmeter. I use it but ofcourse not for setting my points distributor.
I’m still learning after breaking down Larry’s write up with timing. It seems simple until you bring running temperatures and vacuum numbers into the equation . Thank you to trunkmonkey for helping me personally with my car. I hope I can pinch for a new moog front end kit and tires. I’ve been trying to follow all the timing threads. Good luck. You’re in good hands here! following
At 16 no money and no idea , was shown a simple way to set timing , with timing marks aligned , a test light connected neg coil to earth , ignition on rotate engine back 1/4 turn then to forward till globe illuminates check marks, adjust dizzy rewind check repeat , reasonable accurate, but does not measure vacuum advance unless the value is known , I’m sure you have all done this
Set the timing marks to BTDC, number #1 plug wire with a spare plug grounded, turn on ignition and rotate the distributor until the plug fires, then "minor" back and forth a couple of times. Reconnect plug and fire it up. Usually dead on. No tools needed, keep a plug in the glove box. Matchbook for points gap. Get you home and help folks on the side of the road. (Funny how many people forgot to tighten the distributor or points.)
It's been decades since I've wasted time playing with "points". The concept you listed is right, but the actual procedure--I'm thinking--is a little off. You wouldn't rotate the engine (crankshaft) because that would screw-up your timing mark alignment. You'd be turning the distributor housing retarded/advanced not the crank. Align the timing marks as said. Connect test light as said. Ignition on as said. You would be looking for the light-bulb in the test light to glow, but the distributor movement is different. You'd need to bring the distributor housing deliberately retarded (points open, test light not lit-up) from the desired timing, and then advance it until the light turns on. This puts the points at the cusp of opening, since when they open is when the spark fires. When you're confident that the points are right at the moment of opening, tighten the distributor hold-down. Yeah, that would work, too. I've never done it like that.
