72455

Helped a buddy with setting the timing on his '74 Nova tonight, and he called me later and said it really woke it up.

So that got me to wondering about my '72 U code Supreme. While I've been happy with its performance in the 3 years I've owned it, I've always wondered if there was something more. Current setup is. 030 over with a W30 cam, Holley 770 Street Avenger and Edelbrock Performer intake with Hooker headers and HEI ignition. Tranny is TH400 with a 2800 stall converter. Rear gearing is 3.08 limited slip. She gets sideways off the line, but doesnt pull hard on the top end. Mind you, when I'm cruising around 60-70 and "blip" the throttle, she'll put you back in the seat, but that may be because I'm right in the sweet spot of the torque band. If I hit it hard at highway speeds and stay in the gas, it just kinda climbs, but she's not real "snappy". I've never checked the timing since I've owned because I just figured since it ran the way it does, the timing was good, but is it?

I also need to know what my timing should be set at, and which vacuum line needs pulled to set the timing. We didn't do this in my buddy's Nova because he has an Edelbrock EFI system. And what exactly does "full advance" mean? I've done some research, and seen numbers like 30 deg or 36 deg full advance, but dunno what that's all about.

Or, based on what I've said about she runs, does it sound like the timing is fine? Like I said, I've never checked it in three years, so I'm really curious.

oldcutlass

Read these 2 links, this applies to all V8's not just Chevy
Timing101_1 (camaros.org)

by Lars Grimsrud (metroli.org)

Dynoking

The second link (by Lars) is a good read with information that I’ve never seen before. Thanks for the reference!

72455

I clicked the links but they're not working.

Vintage Chief

Each of the links works fine for me.

Greg Rogers

I threw the books and specs out the window. I had a HEI on my 71 350 and set it at 12 degrees as the manual said and it was terrible, took it for test drives and found that 20 was about right for that "smog type HEI". Since then I switched back to the original points type dist and again stared at 12- terrible! So I just set it as much advance as possible and drive it until it pings then set it back until pinging barely stops. Course then you may have too much total advance which I did, but keep messing with it and you'll get it... Good luck!

deadeyejedi

Sounds like it runs pretty well to me . Likely the nova woke up because the timing was way off . You can drive yourself crazy with this timing thing and in the end won’t feel much different . It’s one thing if you’re trying to pick up 1/10ths of seconds at the drag strip but on the street it will be hard to notice any tiny changes .you can pull the vacuum hose off the distributor and plug it, then check your timing to see where you’re at and go from there . IMO enjoy it ! being pinned back in the seat at 70 mph ain’t a bad thing 👍

72455

I wondered about the Nova being way off...seems like that was the case. If I decide to at least check mine, what should it be with everything hooked up, and with the vacuum hose off?

olds 307 and 403

If you want top end, I would not go past 38 with the vacuum advance unplugged. Watch how quickly it comes in for rpm. Another thing that happens, HEI distributors add another 4 or 5 degrees of timing over 4000 rpm. I made a psychical stop by tapping in the advance base and using the bottom of a bolt adjusted till I got the maximum mechanical advance I wanted.

72455

Is that 38 BTDC?

72455

So I checked the timing and it's firing at 38 with everything connected, and the 38 is lining up with the bottom notch on the timing tab...does that sound about right?

oldcutlass

You need to read those 2 links. To be blunt, the above tells us nothing specific. What is your initial timing and rpm at idle without vacuum advance connected? What is the total timing and at what rpm does it stop advancing without vacuum advance connected. Subtract your initial setting from the total which will tell you how much mechanical advance is built into the distributor. Then do the same tests with the vacuum advance connected and note those results. This will be your initial and total numbers with the vacuum connected.

The timing mark on the balancer will line up with the tab depending on what type of timing light you have and how it is set, if its adjustable.

Amplitude

I know this was just a question about timing, but it sounds to me like your problem isn't all ignition related. Plus I'm ignoring my work and like to type up overly detailed posts for some reason.
Your car should really still be pulling strong up to at least 5500 I would think. I'd wager you have multiple issues, ignition just being one of them. I'll bet your secondaries either aren't properly jetted, or the vacuum module isn't setup for them to open fully or perhaps open at all. That kick in the pants might just be your accelerator pumps, but not the full power of the actual secondaries themselves. I believe the Street Avenger carbs have only ever been sold as vacuum secondary, I remember reading in more than a few places where people have reported that they always seem to come with way too heavy of a spring. So, they may not be fully opening, could be jetted too rich, or could have a linkage improperly adjusted. I doubt they are jetted too lean, or else you would've really noticed some other symptoms after having the car for 2 years.
So, I have a bunch of recommendations for you. Firstly with carb tuning, you have two really good options for checking the jetting on the secondaries. Or you could do both for good measure. Option 1 isn't as convenient, takes some knowledge and wrenching on the side of the road: Learn how to really read spark plugs (the ground strap will also tell you allot about your timing), do a full WOT pull for as far as you dare on the streets of Mexico with a fresh or at least a cleaned set of plugs, and shut it off right at the end. I prefer the second option which gets you more immediate data without burning yourself, and you can immediately act upon it: get yourself a wideband Air/Fuel ratio gauge. If you can get one that logs Vacuum and RPM as well, that makes it even easier. Being able to get the propper and most power out of your timing also depends on your carb tuning to make sure you don't go lean, and then you can also work on top-end power by looking at your AFR at WOT. Sounds like you should have your power valve and transitional response pretty close. But you never know. There is always more power to be had, and more to be learned. I was lucky and picked up an AEM FailSafe Wideband Air/Fuel gauge BNIB for $150.
I just have my gauge mounted with double-sided adhesive in a cheap GlowShift brand swivel pod in front of my shifter on my center console. I didn't have to drill any holes, just tapped into a few wires, a vacuum line, and had the exhaust shop weld a $7 bung into my exhaust just after my header collector. In reality, for the most accurate reading, it should actually be mounted in the collector about 3 inches forward of the flange. But the in this application, the difference will be minimal.
Here are a couple other units that do the same thing as what I have. You can watch them real time, or they can save logs as your drive around. They can also be setup to trigger a warning light if the car should start running dangerously lean at High RPM. This could be a simple LED, a shift light that you already have, or cut power to your radio... Whatever you want it to do, as it's just an analog contact closure output. But you don't have to leave it installed all the time. You can just buy a cheap one that only monitors Air/Fuel, and doesn't record anything. Just install the sensor into the exhaust when you want to use it for tuning, run the protected cable through your door jamb, and just make sure to be safe watching the numbers go by, or have a friend there to help. You can also just T off of a vacuum line, and temporarily rig your normal vacuum gauge inside the car.

Innovative PSB1
Zeitronik Zt-2
FAST Wireless Bluetooth enabled Wideband
FAST Single Sensor System with full display and logging


Just remember it's all a package. Monitor and gather all the data you can, prior to starting to inspect and tune one system at a time.

With timing you typically want to adjust the counterweight springs set so that the mechanical advance is all-in by 3000 RPM. 35 deg of total timing advance seems to be seems to be about average. Some people go up to 38, while others seem to hover around 32. Depending on the slip in your 2800 stall, you might want just a little bit stiffer combination of springs so that your timing isn't all there until 3200. If you can, also adjust your Vacuum advance to ensure you aren't stacking mechanical on top of Vacuum advance during WOT. Change the springs to change your curve, and the bushing to change the total mechanical advance. Or ditch the HEI for a locked out distributor and put on an ignition box like the MSD 6AL-2 Programmable, then you can easily dial in your own timing curve and total advance. Some of the CDI boxes can even monitor boost or Vacuum and compensate for that. One of the easiest ways to dial in your timing and find out what your total advance is, and where it comes in at, is by using a dial-back timing light. Innova has a couple digital models with LCD readouts that also tell you engine RPM. So, as you increase engine RPM, you just keep adjusting the advance in the timing light so that it reads 0 on the factory markings. Look at the readout, and that will tell you what amount of advance you had to add. If you do this in 500 RPM increments, you can easily create a table a plot a graph of your timing curve.

Also checkout this distributor
https://progressionignition.com/


Here is another really cool option to control your timing. It also includes an anti-theft lockout feature.

Mechanical advantage and torque multiplication is typically the cheapest way to increase performance. Have you thought of doing a deeper rear gear and an overdrive. You could do a Gear Vendors Under/Overdrive, a modified 4L60E, or stay analog with a 200 or 700R4. The key to longevity in those is correct adjustment of the TV cable. From my understanding, that's what kills them.

One thing you didn't mention, was if any head work had been done? Remember, the flow numbers are pretty bad, heck, the same heads were used on both big and small blocks. That should tell you something right there. With an engine being an air pump, breathing through a straw isn't going to help anything. Also, a more modern and more agressive cam profile would really help.

Now, I don't have a 455. I'm running a 67 400 with big bore and short stroke. It only has a mild cam, headers, and the wrong carb on the stock intake. But it continues to pull until I run out of the ***** to spin it any higher. Even though I've heard tales that they'll go up to 7,000RPM. I'm shifting around 6,000.

72455

Thanks for the info. Now that I think about it, she actually does pull pretty strong through the whole RPM range. I know I've wound it up to 100 mph before I backed off and she was still asking for more, so I think I'm ok.

Amplitude

You can thank Newton's 3rd law for why it feels like it does. Going WOT from a part throttle cruise causes a rapid change in your momentum. Unless that same arc of continued acceleration can be sustained, it may feel like it isn't performing like it should and has fallen off.
All that being said, I would still look at you timing, and work through you carb tuning using a wideband or just a Vacuum gauge and reading plugs. I guarantee there was a fair bit of both power and efficiency left on the table when the carb and distributor were installed. We're only talking about maybe a weekend of check, testing, and tweaking.
Lots of videos and articles all over the internet on how to do these things.
Summit actually has a really good series of older videos posted on Youtube that go over the basics of how the carb actually works, some common mistakes, setting idle, picking the right power valve, tuning with the accelerator pumps, adjusting the vacuum secondaries, and picking the right main jets. It's actually really interesting, and you can see where there is a ton of opportunity for increases in both HP/TQ and MPG.