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Old 05-18-2023, 11:42 AM
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I could not agree more Cliff!
At least 3 out of the many Pontiacs I have had over the years a got a incredible steal of a price because the seller followed what every other jerk in the town he lived in told him to do and then the owner couldn't get the car / motor to even run as good as stock again!

So many people in this string are stating timing numbers at a given rpm without referencing if that timing was at part throttle of wide open.

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Old 05-18-2023, 11:53 AM
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Quote:
Originally Posted by Cliff R View Post
"This info may be new to new enthusiasts, not necessarily to old hawks who never really learned the principles of things but instead stuck to fallacies for 50+ years and can't learn anything new, or how things really works."

+1, 2, 3, 4, 5 and 6.

You can't read a single thread on any Forum about this topic without someone copy/pasting information they Googled up someplace and some of it isn't even accurate. Since I custom tune for a living and have for decades you'd think by now poor running engines would quit showing up with those POS aftermarket "high performance" spring/weight kits in them trying to get ALL the timing in right off idle, plus they have disabled the VA, but no, I still see them just about every single time one shows up. STOOPID, just stupid, but folks still buy into all that crap and think a well thought out V-8 engine build needs a super-quick timing curve and no added timing at light engine load for improved effciency.

I'm really not complaining here as following poor advice and making poor choices have kept my wallet full for decades. Even though I'm retired at this point I still get calls every single day where folks are having tuning issues, carb and distributor and can't get it sorted out, neither can their freinds, beer drinking buddies, local "gurus" and shops in their area that still work on these older cars.

The fix is ALWAYS the same when these vehicles show up for "carb work". I attack the distributor first, amputating the POS springs/weights and crap that was installed, put stock parts back in them, modify the VA to add the timing it should, and low and behold the carburetor problem is mostly or often completely fixed!........
Probably a lot of these guys are influenced by reading about the old royal bobcat tricks by milt schornack and crew ... but a faster mechanical curve on leaded gas in 1966 made a helluva lot more sense than with the stuff we have now!

  #63  
Old 05-18-2023, 01:37 PM
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Quote:
Originally Posted by dataway View Post
People need to come up with a uniform way to express their timing numbers ... something like.

Initial - mechanical - vacuum .. in my case 9-24-15

Then maybe two numbers for start - end rpm of Mechanical like (800-2900)

So my engine (YS-400) would be 9-24-15 (800-2900) ... doesn't tell the whole story by a long shot, but gives a basic idea.

Sorry, back to the OP's question.
Your notation suggestion is similar to what I use now. I have one of those Progession Ignition Bluetooth distributors. I store various "tunes" on my iPhone using their app.

I usually list the initial timing first, followed by vacuum (with a "V"), then the mechanical (with an "M"), followed by the "all in" engine speed for the initial + mechanical. Here's an example:

initial= 14deg.
mechanical= 20deg
vacuum=12deg
"all in": initial+mech (14+20) at 3200rpm
so, on the list it looks like this: 14-20m-12v_34@32k

It's easily distinguishable from any other tune I keep on the app and makes choosing easy.

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Old 05-18-2023, 03:35 PM
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Tips and tricks from yesteryear worked OK for them back in the day. Engine efficiency was NOT on their list anyplace so not much attention paid to tuning for "normal" driving, or that a vacuum advance is a load sensing device and doesn't detract from making power or running fast at the drag strip. Not their fault and I'm not meaning to bash any old timers in any way.

Even so we should be a LOT smarter about these things this day and age, espeicially considering how rare some of these engines and parts are, plus the cost of fuel. The days of using gas-guzzling carburetors and all-in timing curves right off idle should be far behind us, but sadly I still see the SAME EXACT CHIT being done to distributors today that they were one I was back in High School in the 1970's. WAY back then none of us really knew what we were doing, or if we were helping out these these engines. Even so every single one got an aftermarket intake, carb, distributor, or at a minimum some sort of cheap POS spring'/weight kit installed in the stock distributor. We also did STOOPID things to the engines when they were apart. Any SBC build got thick head gaskets when the factory used .020" steel shims on them, high volume/high pressure oil pumps that just robbed power, twisted off oil pump drive shafts and wore the distributor gear out 10 times faster. Then we installed a POS Zoom double roller timing set, what piece of bovine excrement that was. I could go on for hours here.

Anyhow, despite all the good information we have available to us today much of it sadly is still Googled up, learned from poor examples, blended together and regurgitated on the Forums. It amazes me that as much coverage as timing and setting up distributors get that folks still really do NOT undersrtand how these things really work or that adding some super quick mechanical advance curve does NOT eliminate the need for more timing at light engine load, etc.......

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Old 05-18-2023, 05:32 PM
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Quote:
Originally Posted by Cliff R View Post
Tips and tricks from yesteryear worked OK for them back in the day. Engine efficiency was NOT on their list anyplace so not much attention paid to tuning for "normal" driving, or that a vacuum advance is a load sensing device and doesn't detract from making power or running fast at the drag strip. Not their fault and I'm not meaning to bash any old timers in any way.

Even so we should be a LOT smarter about these things this day and age, espeicially considering how rare some of these engines and parts are, plus the cost of fuel. The days of using gas-guzzling carburetors and all-in timing curves right off idle should be far behind us, but sadly I still see the SAME EXACT CHIT being done to distributors today that they were one I was back in High School in the 1970's. WAY back then none of us really knew what we were doing, or if we were helping out these these engines. Even so every single one got an aftermarket intake, carb, distributor, or at a minimum some sort of cheap POS spring'/weight kit installed in the stock distributor. We also did STOOPID things to the engines when they were apart. Any SBC build got thick head gaskets when the factory used .020" steel shims on them, high volume/high pressure oil pumps that just robbed power, twisted off oil pump drive shafts and wore the distributor gear out 10 times faster. Then we installed a POS Zoom double roller timing set, what piece of bovine excrement that was. I could go on for hours here.

Anyhow, despite all the good information we have available to us today much of it sadly is still Googled up, learned from poor examples, blended together and regurgitated on the Forums. It amazes me that as much coverage as timing and setting up distributors get that folks still really do NOT undersrtand how these things really work or that adding some super quick mechanical advance curve does NOT eliminate the need for more timing at light engine load, etc.......
Oh my god your reading my mind.. Google it up ….LOL

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Old 05-18-2023, 07:03 PM
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Some other details about plugs really need to be talked about while where at it.

A plugs porcelain will self clean starting at 840 degrees up to 1600 degrees.

That’s a 760 degree temp spread that works .

If we consider that a safe full throttle exh temp is 1300 degrees then if your chosen heat range in the plug your running is in the ball park of being centered for what the plug can handle then you could very safely add 25% more Hp to your motor while keeping the same plug heat range you are currently running.

Yes, this assumes your air to fuel mixture is such that you never top 1300 degrees of exh temp.

So for example if you plug temperature range was pretty centered and you where increasing your motors output from 500 to 625 hp, then that same heat range should work for you if you don’t top that 1300 degree .

Now the tuff part, not all cylinders will make the same amount of exh temp!

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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs!
And he was not talking about 1/8 or 1/4 mile ETs!

1) 1940s 100% silver 4 cup tea server set.

Two dry rotted 14 x 10 Micky Thompson slicks.

1) un-mailed in gift coupon from a 1972 box of corn flakes.
Two pairs of brown leather flip flops, never seen more then 2 mph.

Education is what your left with once you forget things!

Last edited by steve25; 05-18-2023 at 07:10 PM.
  #67  
Old 05-19-2023, 05:02 AM
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In my opinion this topic, like many others gets all twisted up because WAY too many folks regurgitate information that isn't accurate in the first place.

No names mentioned here but I'll list a few things below that are commonly posted on this topic or I've seen before when this topic comes up.

1. My engine runs better with manifold vacuum to the VA vs ported vacuum. Well, that is not an accurate statement. Your engine may idle a little better, but anytime you push down gently with your right foot the EXACT SAME TIMING is added by the vacuum advance. It NEVER does anything different than a manifold applied source except doesn't add timing at idle or coasting to a stop.

2. I cured an overheating issue switching to manifold vacuum to the VA. NEVER once in all the years I've been tuning thousands of these vehicles has that ever happened. Not one single time, ever. A few times I thought initially an ill fated vehicle I was working on was going to get better with that swap but it was ALWAYS superficial and after driving the vehicle it continued to run hot/overheat just like I did before I switched over to manifold vacuum to the advance. Same reason as above, ported vacuum applies FULL timing when you are driving the vehicle just like manifold vacuum does. I suppose if you idled everywhere you went you may see some improvement in that area, but day in and day out vehicle operation I've never once improved cooling or cured a running hot/overheating engine with that move.

3. I swithced over to ported or over to manifold vacuum to the VA and cured a pinging issue. Once again not possible. The both do EXACTLY the same thing when your right foot is applied to the gas pedal, so someone please tell me how one causes pinging and the other doesn't? I'm all ears here because it completely defies all the laws of physics if you see the slightest difference one vs the other.

4. I get better fuel economy with manifold vacuum to the VA vs ported. How? Do you idle everywhere you go, because during all "normal" driving scenarios when the right foot is applied gently to the throttle they both do EXACTLY the same thing.

5. Here's the best one of all. I unhooked the vacuum advance and my car ran quicker at the track.....DUH? Any heavy or full throttle instantly reduces the vacuum that applies the VA to nearly zero. Even the lightest spring in a VA is WAY WAY WAY stronger than the vacuum your engine makes at WOT when you have equalized the pressure above and below the throttle plates. So it's not possible for the VA to have any impact one way or the other on your drag strip or full throttle runs.........FWIW.......

6. Last one. I'm not able to use VA because when I hook it up the engine bucks, kicks, and miss-fires in protest.
All of these engines will benefit from some additional timing at light engine load. The problem here is that most VA units were used on engines that either had very low initial timing settings from the factory (early higher compression engines) or they were later low compression smogged up engines and the factory added a BUTT LOAD of timing to them with the VA to get optimum timing during "normal" driving scenarios. Either way almost all VA units add TOO MUCH timing for many of these engines. That only gets worse when you make changes to your engine like increasing compression or using a tiny cam, or cam on a tight LSA which spikes cylinder pressure pretty high early in the RPM range. In almost all cases we simply have to modify the VA to apply LESS timing when we call on it. The source doesn't matter with this one, we just need to reduce how much is added at cruise RPM's to make the engine as happy as it's going to be and effectively burn a leaner mixture rewarding the end user with improved efficiency, more MPG's, less carbon build-up, etc..........

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Last edited by Cliff R; 05-19-2023 at 05:13 AM.
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Old 05-19-2023, 07:58 AM
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Quote:
Originally Posted by Cliff R View Post
In my opinion this topic, like many others gets all twisted up because WAY too many folks regurgitate information that isn't accurate in the first place.

No names mentioned here but I'll list a few things below that are commonly posted on this topic or I've seen before when this topic comes up.

1. My engine runs better with manifold vacuum to the VA vs ported vacuum. Well, that is not an accurate statement. Your engine may idle a little better, but anytime you push down gently with your right foot the EXACT SAME TIMING is added by the vacuum advance. It NEVER does anything different than a manifold applied source except doesn't add timing at idle or coasting to a stop.

2. I cured an overheating issue switching to manifold vacuum to the VA. NEVER once in all the years I've been tuning thousands of these vehicles has that ever happened. Not one single time, ever. A few times I thought initially an ill fated vehicle I was working on was going to get better with that swap but it was ALWAYS superficial and after driving the vehicle it continued to run hot/overheat just like I did before I switched over to manifold vacuum to the advance. Same reason as above, ported vacuum applies FULL timing when you are driving the vehicle just like manifold vacuum does. I suppose if you idled everywhere you went you may see some improvement in that area, but day in and day out vehicle operation I've never once improved cooling or cured a running hot/overheating engine with that move.

3. I swithced over to ported or over to manifold vacuum to the VA and cured a pinging issue. Once again not possible. The both do EXACTLY the same thing when your right foot is applied to the gas pedal, so someone please tell me how one causes pinging and the other doesn't? I'm all ears here because it completely defies all the laws of physics if you see the slightest difference one vs the other.

4. I get better fuel economy with manifold vacuum to the VA vs ported. How? Do you idle everywhere you go, because during all "normal" driving scenarios when the right foot is applied gently to the throttle they both do EXACTLY the same thing.

5. Here's the best one of all. I unhooked the vacuum advance and my car ran quicker at the track.....DUH? Any heavy or full throttle instantly reduces the vacuum that applies the VA to nearly zero. Even the lightest spring in a VA is WAY WAY WAY stronger than the vacuum your engine makes at WOT when you have equalized the pressure above and below the throttle plates. So it's not possible for the VA to have any impact one way or the other on your drag strip or full throttle runs.........FWIW.......

6. Last one. I'm not able to use VA because when I hook it up the engine bucks, kicks, and miss-fires in protest.
All of these engines will benefit from some additional timing at light engine load. The problem here is that most VA units were used on engines that either had very low initial timing settings from the factory (early higher compression engines) or they were later low compression smogged up engines and the factory added a BUTT LOAD of timing to them with the VA to get optimum timing during "normal" driving scenarios. Either way almost all VA units add TOO MUCH timing for many of these engines. That only gets worse when you make changes to your engine like increasing compression or using a tiny cam, or cam on a tight LSA which spikes cylinder pressure pretty high early in the RPM range. In almost all cases we simply have to modify the VA to apply LESS timing when we call on it. The source doesn't matter with this one, we just need to reduce how much is added at cruise RPM's to make the engine as happy as it's going to be and effectively burn a leaner mixture rewarding the end user with improved efficiency, more MPG's, less carbon build-up, etc..........
The above post tells you almost everything you need to know about vacuum advance and how it plays with initial and mechanical advance to make the engine happy. I have a 1971 Grand Ville in my shop right now with only one problem. It gets horrible gas mileage according to it's owner. He says it gets 8.5 MPG! It starts easily, runs silky smooth and drives just fine. He is sure the carburetor needs to be rebuilt and it was just recently done somewhere. I looked it over. Carburetor had some choke adjustments that needed a little attention but basically it seemed to be OK. Then I looked at the dwell and timing. Found it still had transmission controlled spark hooked up and of course it was not working at all. So no vacuum advance at all on this 4500 lb. low compression 455 sled. Today I will remove the distributor, bypass the TCS solenoid, braze a stop on the vacuum canister at 10-12 degrees. It has 22 degrees now with vacuum applied. I expect these changes to make a 10-20% improvement in gas mileage and get it to the 10-11 MPG. these cars got in the city. Doesn't sound like much, but at $4.00 a gallon, he will be happy. As Cliff explained, you have to understand how the whole system works and how to tune it for modern fuel. This engine had 12 degrees initial and 24 degrees mechanical advance @ 4500 RPM. 14 @ 2200 RPM. So light throttle cruise should be 36-38 degrees total timing. Very conservative but much better than the 26 degrees it has now. If he wants to get more serious about optimizing it later, I will check the jetting and it will probably need to go a little richer and put the dist. on the distributor machine and dial in the curve a little better. I have to balance customer budget with the results he wants.

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Old 05-19-2023, 08:31 AM
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Good plan. Total potential timing at cruise is right for what you are doing. I've tuned hundreds of older high compression engines to run on this new fuel and they ALWAYS like about 10-15 degrees additional timing at light engine load. They NEVER like, want or respond well to super quick all-in timing curves right off idle (many show up here that way).

Most folks do NOT understand the mechanical advance portion of tuning. These engines require a timing advance curve simply because we are bound by the laws of physics with these things. To accomplish complete/efficient combustion the timing must start sooner with increased engine RPM because we have LESS time to get it done as the cycles per second are increasing as well. With a very well thought out engine build, optimum compression, cam making good cylinder pressure, tight squish, etc you will NOT need a quick curve or "all-in" early. Well thought out engine builds will like LESS timing everywhere as they are more efficient. On the other end of that spectrum you have the guy who "lowered the compression for pump gas", then installed a cam on a tight LSA that bleeds off more cylinder pressure with it's added overlap, so it will LIKE, WANT, NEED, and RESPOND WELL to a LOT of initial timing, plus a really quick timing curve to help it be more efficienty at low engine RPM's.

It's just physics with these things, and ALL of these N/A engines end up with simliar if not near identical timing curves no matter what brand they are. It's all about CID, static compression ratio and cam events for the most part. Of course some engines are simply more efficient than others based on design, and some older varieties had HORRIBLE combustion chambers designed for emissions, so in those applications you may find yourself pouring more fuel to them, and throwing more timing at them to make them happy........

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Old 05-21-2023, 07:35 AM
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Default Tcs install

Can anyone tell me do you cap off second port on Tcs solenoid 1970 Pontiac 400

  #71  
Old 05-21-2023, 08:17 AM
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The problem with the 70 to 72 non 455 HO system is that if you disconnect it you get no vacuum advance at all,
The solenoid was fed full manifold vacuum so when you bypass the stock system you than want ported vacuum for the distributor for the best performance, but I forget if there is a ported vacuum port on a 70 to 72 carb be it 4 bbl or even 2 bbl.

The stock system provided no vacuum advance but in high gear, and even then the engine temp needed to be between 85 and 220F.
Below 85F and above 220 the system allowed vacuum advance in all gears.

And yes engineers consider 220f a ok engine temp.
That being said you could add a ported vacuum source to one if you know what your doing.

Not having it hooked up or running ported vacuum also means you may need to increase your base timing at idle .

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And he was not talking about 1/8 or 1/4 mile ETs!

1) 1940s 100% silver 4 cup tea server set.

Two dry rotted 14 x 10 Micky Thompson slicks.

1) un-mailed in gift coupon from a 1972 box of corn flakes.
Two pairs of brown leather flip flops, never seen more then 2 mph.

Education is what your left with once you forget things!

Last edited by steve25; 05-21-2023 at 08:30 AM.
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Old 05-21-2023, 08:45 AM
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The 71 Grand Ville I just finished yesterday, I bypassed the TCC system because it didn't function. I simply attached the vacuum advance to manifold vacuum. It runs just fine. I did limit the vacuum advance by brazing the slot closed some to allow 10 degrees of vacuum advance. Before modification, vacuum advance was 22 degrees. I agree with Steve that ported vacuum would have provided the smoothest idle, but this carburetor did not have a ported vacuum source. I didn't want to get into the carb as this was a customer car and I wanted to control the costs. With 12 degrees initial and 10 in the vacuum canister, the idle timing of 22 degrees gave it the very slightest change in smoothness. I backed the initial timing off to 10 degrees with a total of 20 degrees and added a 1/4 turn out to the mixture screws. This brought the idle quality back to silky smooth. Car runs really nice now.

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Old 05-21-2023, 09:32 AM
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i never noticed that big of a difference between manifold and ported. mostly just faster idle speed on manifold vacuum ... if i wanted to drop my idle speed without any real effort i would switch to ported.

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Old 05-21-2023, 11:33 AM
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To me In terms of factory carbs the size of idle air bypass passages in conjunction with the primary throttle plates being in the ball park to both have a good idle speed and no off idle stumble are rather limited to what they where designed for.
That being ported or full manifold vacuum.

I say this in terms of what the carb can do without screwing with the distributor.

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Wernher Von Braun warned before his retirement from NASA back in 1972, that the next world war would be against the ETs!
And he was not talking about 1/8 or 1/4 mile ETs!

1) 1940s 100% silver 4 cup tea server set.

Two dry rotted 14 x 10 Micky Thompson slicks.

1) un-mailed in gift coupon from a 1972 box of corn flakes.
Two pairs of brown leather flip flops, never seen more then 2 mph.

Education is what your left with once you forget things!
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Old 05-22-2023, 07:14 AM
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The "ported" vs "manifold" vacuum to the VA debates rage on. The problem with all the great info folks copy/paste or post on the subject is that most of it wasn't all that accurate right to start with. Then when you try to explain how it really works the folks posting the info very quickly get their panties all wadded up and start defending their information even when they have about as much experience with that sort of thing as I spent on the crapper this morning. Then if you try to update their info and bring them up to modern times they start using "famous" people as sources to just muddy the water even more.

These days I stay out of it for the most part. Tired of seeing the SAME long/lengthy articles copy/pasted on the Forums about how ported advance was only done for "emissions" and you are "stoopid" if you do it any other way, blah, blah, blah.

I guess folks don't realize that WAY back before emissions these high compression engines with tiny cams in them didn't have very much initial timing. Common to see zero, two or four degrees on the sticker when you raised the hood. Then look at the VA units they used. Most only added a small amount of timing to those really low initial numbers. The engineers knew that you couldn't run a butt-load of initial timing on those engines or they would "buck" the starter on a hot re-start, plus they idled best/most efficient around 14-18 degrees timing at idle.

So we come along half a Century later with goofy cams and lowering compression and the engine woln't idle for chit till the initial timing is well off the scale, so we give them 14, 16, 18 or even more initial timing. Then the same folks add another 20-30 degrees or even more via the VA hooked to a manifold vacuum source and SOB the engine starts acting like it's happy at idle speed but still BARELY producing enough vacuum for power brakes and to stay running at a stoplight. Maybe if you'd have made better choices for compression, cam events, overlap, etc the engine wouldn't need all that timing to be happy?

In any case IF you find yourself having to run a butt-load of timing on one of these engines at idle or anywhere else you just missed the cam choice some (late intake closing/too much overlap/compression too low or a little of all three). Not a big deal because EVERYONE wants to hear that "menacing" idle quality vs the engine sounding like a stock 350 in a 1987 Chevy half ton truck. It's cool, all good and I'm glad folks do all that because it has kept me completely BURIED in work for decades sorting out all that distributor and carb stuff.

Kind of intersting and funny but I had my scan tool on a 2011 Tahoe over the weekend. A good friend just bought it and it has a few issues, needed A/C charged and brakes all the way around, etc. I was running diagnostics and monitoring things. Fully warmed up and well heat soaked the ECM had base timing at 14 degrees. Never saw it go over 17 degrees at idle speed the entire time I was working on it. I guess the engineers that set up that deal didn't know what they were doing either as that engine was missing another 15-20 degrees of timing at idle..........FWIW......

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Old 05-22-2023, 09:02 AM
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Another great point by Cliff concerning factory computer controlled timing. No one of can argue that PCM controlled timing has greatly increased fuel economy and driveability. If you watch the timing curve with a scan tool on a GM truck for example, initial timing is very rarely over 20 degrees. Usually 15-18 degrees. In park or neutral, if you gently bring the RPM's up, you get a nice smooth curve peaking around 32-35 degrees at 3000 RPM's. Now if you actually drive the vehicle with the scan tool on, there will be situations where you may see 50-52 degree's. This would be during deceleration down a hill, float condition on the highway and so forth. As soon as you accelerate, the timing drops immediately into the safe zone, 38-42 degrees or so. If the knock sensor pics up some detonation, it will pull timing out 2-3 degrees at a time until it goes away. I have learned allot about how I want to try and mimic my non-computer curves to be more like the electronic ones.

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Old 05-23-2023, 04:14 AM
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That's EXACTLY what I saw driving the big Tahoe the other day. It stayed in the range you mentioned most of the time. At very light engine load a few times it went up near 50 degrees but immediately comes back to the "normal" range when engine load and throttle position were increased. I've always found this interesting and facinating as the curves the ECM uses are pretty much on par with how I've been setting up distributors for these older engines for decades, specifically the smooth/steady advance right off idle and settling in around 3000rpms or so.......

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Old 05-23-2023, 04:10 PM
uttergto uttergto is offline
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Cliff, I have been reading all of the responses on timing. I have several questions, they may be dumb but I can't find the answers. I have a 1965 original GTO, how do you check the vacuum advance, how many degrees it is advancing? I have set the initial timing at 10 deg. advanced and run the engine up until there is no more advance, this appears to be about 28 deg. total, is this correct? I can't find anybody with a Sun Distributor machine to run the distributor. Thanks.

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Old 05-23-2023, 04:28 PM
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steve25 steve25 is online now
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How is it that you know that you have 28 degrees?

Are you running a different balancer then stock which is scribed with degree marks?

Do you have a timing tape on a stock balancer ?

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Old 05-23-2023, 06:38 PM
mgarblik mgarblik is offline
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The easiest way to know where you are starting out is to buy or borrow a dial back timing light. A digital one is best like the Innova or Snap-on. One with a manual dial is OK but not as accurate in general. I just don't remember if a 65 timing cover just has the pointer for zero or an actual number plate. Either way, set your timing light for 10 degrees and start and idle the engine slow, like 600 RPM and see if the light flashes at 0. If it does, the initial timing is 10. If not adjust the distributor to 0 to give you the 10 you want. Then plug your vacuum advance up to manifold vacuum. Adjust your timing light back until you are at 0 again. Say the light says 30 degrees. That means your vacuum advance has 20 degrees vacuum + 10 degrees initial. Now unhook and plug the vacuum advance line. Hold the engine at various RPM's to look at the mechanical advance. I would do 2000 RPM's. Dial back the light to zero and read. If it says 22 degrees for example, you have 12 degrees mechanical advance @ 2000 RPM's. Do the same at 2500, 3000, 4000, 4500 RPM.s Now you have established a mechanical curve. You can go to 5000, but usually not necessary. Most factory curves are all in around 4500 RPM's. Takes a little time but that's all the info you need to develop a decent curve. Old engine like that on today's crap fuel, you will need to limit the vacuum advance to about half or 10-12 degrees.

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