A good read, again. I don't suppose there's an easy way to find out what my vac can is rated at? Is the part/ID number on the can itself?

 

Yes. My HEI was originally in a 78-79 403 engine. It has ~16º mechanical advance, initial set to ~18º would give 34º total mechanical, then the factory vacuum canister had 24º on top of that for a possible 58º at high RPM cruise. That didn't seem to bother any of the 403s back in the day.

Yes, vacuum is always disconnected when setting the mechanical advance.

 

Yes, it is on the factory canisters. I don't know about aftermarket ones.

 

Google for the vac. Can will be your best friend. It's been done and guys post up findings. I forget but one of the. Nova sites has info posted . I just stopped running the vac advance but it's apples to oranges your combo and mine.

 

The extreme amount of vac advance was a smog thing. It affects tip-in throttle response and welding a tab on the vac unit only partially fixes the problem, depending on the vac unit. There is a chart that shows not only how much advance the units have, but when they start. The higher the start point, the faster they drop out when you stab the throttle, which will cause less pinging if you have any compression. With low compression it rarely matters. High compression gets tricky.

 

That doesn't make sense to me, so I wanted to ask if you typed that the way you meant to. Seems like a faster dropout would prevent pinging since there would be less advance.

If that is actually what you meant to type, then apparently I'm not understanding what's going on and need some more explanation of what's happening in that situation.

 

Sorry, I didn't proof read what I wrote. You are correct. The faster vac advance drops out, the better if pinging is an issue. Basically it stacks on top of total mechanical advance, so if you have 20 degrees vac plus 40 degrees mechanical at 2800 rpm cruise and you stab the throttle, it may ping unless that vac drops out really fast. This is where adjustable vac units are great. You're basically adjusting the spring tension. Or you need to carefully pick an existing unit, hopfully close to a 10" vacuum start point if you have lots of vacuum. 5-7" units are far more common.

 

I thought maybe you typed it backward as well. Thanks for the clarification. Alas, my can has no numbers stamped so I'll just be guessing. If it IS adjustable, anyone know the size allen wrench to use? Maybe I could stab it in there and get lucky.
If too high a rated can is my problem, would the pinging stop after a second after jumping on it? Although I'm not sure I could wait that out so i could know.

 

You could disconnect the vacuum canister and see if the pinging goes away.

 

Ah, now there's a thought. I'll give that a try if it ever quits raining.

 

Imagine trying to do this with a modern motor LOL!

 

Carbureted? It's kind of a PIA. The only carbs I have found with the exact correct linkage have the computer connectors. No good.

Z? Why are you messing with your perfect 68?

 

That was good advice. I did exactly that today. 22* initial, 22*-ish centrifugal and it detonated pretty clearly. So I backed off the initial to 16* and put the light springs back on. No pinging even with the vac can hooked. Acceleration could be better but it's running well. I have the replacement carb to try. I put it on when I first got it and it ran like excrement. Pulled it back off and put the 1st one on just to find out the replacement was missing the plug in the hot idle compensator. They were supposed to build it a little richer so I'll try it again.

On a side note, the leaking accelerator pump on the 1st carb stopped leaking when I pulled the filter out of it. Doesn't make much sense but there it is.

 

You can find the rating of your vac can by using a Mity-Vac. Pump and watch. When it starts moving is your first spec - typically 5-10" of vacuum. End point is when it stops moving, usually 20"+ on GM stuff. If you do this with the car running, you can see how many degrees of advance it offers by checking with a timing light. Then use a caliper to measure the distance the vac arm can actually travel, divide that distance by how many degrees advance you get, and you can weld a stop precisely where you want it.
The allen wrench is usually the smallest or second from smallest in a multi-pack set of SAE allen wrenches.

 

My late 70's carb had the same linkage as my 80's non CCC carb. 44 total is a lot, no wonder it pinged with vacuum advance.

 

Yeah, 44 is a lot. Back in the 80s I had my distributor set up for 40º total advance. Ran great but one time I got sideways in 1st and ran it to 5500 RPM. I had filled up with cheap gas earlier in the week and apparently one cylinder detonated, blasted a chunk off the piston and cracked the rings. Lesson learned.

 

I fabricated a steel "stop" back when I put the HEI in. It's limited to 12-13*. I checked last night and looks to be all-in by 3000-3300 (by ear).

I'll be honest; I've been looking for months (google images) and I can't figure out what the "exact" correct linkage looks like for the 200-4r. Any way you could post a pic? This is what I have as of now. It's close but the geometry isn't exact. I have to use a spring on the end of the TV cable or I can't get to WOT. TVez doesn't make an adapter for this linkage either.




As of last night I'm at 18* initial and 22* centrifugal so 40* total. But yeah, I hadn't thought about breaking loose. WOT shifts about 4k so I haven't tested higher than that. Does the trans need a load in order to shift? Or was it the speed at which it accelerated (because the tires broke loose) that caused it to rev that high?

 

I had the Dual Gate in 1st and was hanging onto the steering wheel with both hands while the car was going sideways. I don't let the trans shift by itself when I know the tires will break loose because in automatic it will shift to 2nd then bog once it gets traction. Sometimes it will shift to 2nd then quickly to 3rd, then back to 2nd. Better to keep full manual control in those situations.

 

Yeah, I haven't driven in the rain with the new posi. Makes me a little nervous.

 

3.90's in the rain. Not too bad but around sharp curves i could feel it skidding a bit as my posi unit is as tight as it gets.


drove in the rain to the track back in june.

 

That doesn't look like a very good day for running at the track

 

I have hit weather like that, pouring rain going to the track. Anyone who says the prairies are always dry should have been here the past 5+ years. Another reason why I will NEVER run drag radials on the street, bad weather comes unexpected all the time lately. I will get pics of my linkage soon, pretty that is the same as mine. I compared it against my "1708" first four numbers of the carb meaning it is a 80's non CCC 307 carb, from a 85 station wagon with a blown swirl port turd and it was the same linkage from what I could tell. That car did have a factory 2004R. Can you post a pic of your spring set up? Full throttle and good line pressure is also an issue for me.

 

We beat the rain and got to the track and it was dry. Wasn't a bad day at all lol. Well minus the 85 degree and 75 percent humidity. Still managed a 12.77.

 

What I described was on dry pavement, but yeah, rain, posi, and a lotta torque make for interesting driving.

 

It's been a wet season down here as well. I swear spring and early summer were dray as a bone. Figures, that's when the car was on jack stands
I'd very much like to see that pic when you get time. I'll get one of the spring straight away.

So you're saying 90 degrees and 95% humidity is better?

 

I don't know the compression rate of the spring but it must be pretty rigid to not kick in until the cable runs out of travel.

 

That spring is a pretty great idea. I need to try that!

 

I may also as well, I like max pressure but need full throttle for the track. What is that spring off any idea?

 

When I took the car into the trans shop to make sure all was good with my install and was complaining about not having WOT, he said "You know, they make a kit for that." But that doesn't look like a kit to me. I'll get some measurements but again, I can't really measure the compression factor. And I don't want to take it off. Every time I pull that barrel retainer it gets harder to put back on.

 

It looks to be 10mm long and about 8mm wide. Again, it shouldn't start to compress until the cable runs out of travel.

 

My guess is that it should be stiff enough you can compress it a bit, but probably not half way with your fingers, easily with a pair of channel lock pliers. As long as its a little stiffer than the pull-strength against the cable and softer than the adjuster on the TV cable, it should work. Any decent hardware store should have something that'll work.

 

Agreed. I would also manually rotate your linkage until the cable runs out of travel and eyeball the distance between the linkage and the stop to see how much more travel you need and chose a spring according to that.
Do any of you guys have the TV cable housing with the brass nut for adjusting it's length? There's plenty of info out there on how to get the pressures and linkage correct but nothing about this cable. If I shorten it ("it" being the cable housing, one slides inside the other) does it tighten the cable, loosen it, or just do nothing?

 

I have that style and it works OK. If you adjust, there is a change in how far it pulls.

 

So, shorter pulls more....I think.

 

I was sculpture supply shopping at Lowe's today and ran across this. The spring is slightly larger around and slightly longer but the compression feels good. Might be worth a try for $4 or so if anyone is looking to solve their tv cable/WOT woes.