Timing & Gas Milage

[BigBird05]

Per the 72 service manual, The TCS temperature switch is located in the right hand cylinder head between the number 6 and number 8 cylinder exhaust port, The switch is a two - position single terminal control which provides a path to ground for the cold override feature feature, when engine coolant temperatures are below 82 degrees. The off or neutral position is maintaned at coolant temperatures above 82 degrees.

[burnin oil]

To limit all timing confusion. The curve is important but the max timing is the critical point. You need to get the full timing weight advance and adjust the dizzy so it falls between 34-36 degrees for a stock head ( not vortec) motor. This is their happy place. From there you can let the idle fall where it pleases. If the idle timing (ie base timing) is not to your liking then a recurve is needed. If max timing and base timing are good to go then feel free to play with the timing wieght springs to dial it in. Odds are you will end up with either the factory spring or the kits heavy spring and a medium spring.


Beyond the above you have no control of the timing curve other than changing wieghts or making limiters in the advance plate for the timing wieghts or a different vac advance canister. The vav advance canister part number does give clues on the amount of vacuum needed to get a set amount of advance. Crane cams makes a limiter to adjust the vac advance but I never had much luck with it. The problem was the different cans has different internal springs and diaphragms so the vac canisters advance wasn't linear. They work somewhat but it's easier to just buy another can that does what you want. Changing cans also makes the advance smoother versus the crane limiter.


PS. Stop buy the house and I will teach you more than you ever wanted to know about anything with wheels. Besides learning a good mentor is paramount in this hobby. Find someone who will explain everything before even touching a wrench and you will be light years ahead in the game. Honestly 20 years of self learning can be surpassed in a 15 minute conversation with a car guy. Those of us who have done this for a lifetime forget the learning curve when talking to the new guy. We just need grounded from time to time. We are here to help each other and learn from time to time. Perspective is also a great teacher.

[burnin oil]

Do you have a link on that dizzy from the manufacturer? It resembles a computer controlled unit but has vac advance. Interesting to say the least

[Rich72C10]

https://www.topstreetperformance.com...stributor.html

Not much info - I think it’s a dead end cheapy. But i have ordered a pertronix igniter Ii

[burnin oil]

Interesting. Says it has mechanical advance. I didnt see it in the pic. On a traditional HEI the wieghts are above the star looking pieces. Those are the reluctant wheel. But under the rotor button. Y you pic it looks like a small cap from a points distributer with that style of rotor button. Definatly not an over the counter HEI setup.

You said that you had a spare ignition module. How many electrical connections are on it 4 or more? 4 is standard HEI and the one with 7 (from memory) is computer controlled.

[Rich72C10]

Just 4.

[HO455]

Originally Posted by Rich72C10

Hi Andy,

"I didn't want anything I couldn't get at a local parts house if I was on the road."

Ya, that one statement rings true for me, which is why I really dislike my current Top Street Performance JM6701 distributor. Though what outweighs the GM HEI for me is that I cannot stand the look of it, I really can't. There might be time I'll reach a point where tying out the PerTronix ends up being a PITA that I'll be forced to a GM HEI or even back to points (but I'd have to be really pissed off and frustrated).

I actually have an extra module for the TSP distributor in my glove box, I got it months ago. I just did not expect to find the Vacuum Can not holding vacuum the other day. I think it is holding enough vacuum to operate but no telling how long it will hold up.

Your basic Pertronix unit installed in an early cast iron distributor will be a very good set up. The cast iron distributors run truer than any later GM units (included HEIs) as they have bigger bearings and the machining tolerances were tighter. Which means less spark scatter and a smoother idle and cruising.
The beauty of using the Pertronix is after completing the conversion you can put the parts you removed in a zip lock bag and stash it in the glove box and if the Pertronix ever fails you on the road, you can reinstall the points and get home.

[burnin oil]

I would follow HO455s advice here. I have never seen that module before.

[Rich72C10]

Summit Racing has already shipped my new PerTronix Ignitor II (D100700) - I'll have it on tomorrow (seems it is shipping from Ft. Worth).

[68 P.O.S.]

Oh, eye candy That's a nice looking piece

[Rich72C10]

that is what she said .....

[Rich72C10]

So here is their charts for the spring and advance limit. Silver seems to be the default. I think I should go with Copper? Or is it best to stick with the Sliver?

They don't say what the default is for the advance limit ... thoughts on that?

[68 P.O.S.]

Looking at the chart, the distributor has 24 degrees of advance in it, which is good. You want it fully advanced in the 2500-3000 rpm area. The copper springs fully advance too early, and the silver ones fully advance too late. I would put one copper and one silver in and check it with a timing light to see what you get. Should be about 2750 rpm, which would be perfect.

For the advance limiters, it depends on what you want your initial timing to be. You can use no limiter and your initial timing works out to 36 (total timing) – 24 (distributor mech adv) = 12 initial timing. Or you could use the #10 limiter and get 36 – 20 = 16. Up to you, some people find their engine likes higher initial timing, others don’t. Being your engine is a mild build, I would probably keep it with no limiter, but test both out and see what the engine likes more.

[Rich72C10]

well, at least what you are saying is what I was thinking - need full/all in around 2500~3000! Thanks for pointing out that I should try one copper and one sliver!

Right now my engine seems very happy with 12° initial timing.

Edit:
It has arrived - pretty cool seeing that I just ordered it last night! The doc that came with it are a bit different from what you can download, which is a shame. It calls out Silver/Copper for what I was thinking I needed and what 68 P.O.S. suggested :-)

[68 P.O.S.]

Awesome, that's some shipping Let us know how the install goes and what you think of it vs the old one.

[ChevyRacefan]

Any time you change the cam, you need to change the timing curve.

[Rich72C10]

Sorry no updates on the install yet. But I have the truck prepped in the Garage and got the timing mark dead balls on 0°. Man its cold outside here in Texas - that is just not right LOL

[ChevyRacefan]

Originally Posted by Rich72C10

Sorry no updates on the install yet. But I have the truck prepped in the Garage and got the timing mark dead balls on 0°. Man its cold outside here in Texas - that is just not right LOL

Check TDC with a coat hanger wire in plug hole.
The chevy balancer outer ring can spin on the rubber and move the timing mark .

[Rich72C10]

Well, lets hope that did not happen! Though my main check was to get the new rotor lined up perfectly on reference mark I made before I removed the old distributor.

I suffered the cold garage and got it installed!! Though if you get your wires off by one slot on the distributor the engine will absolutely not start LOL!

Looks like I am getting the full range now with this new distributor. Stayed with 12° initial timing @ 650 RPM idle (no vacuum connected). I did moved to the ported manifold vacuum on the front of the carb, since that is what the Pertronix instructions said to use, so I'll stick with that for now. I know when I have it on manifold vacuum I have to adjust the idle down because the initial timing pops right up when it is connected to the Vac Canister on the distributor. I suppose that is right, since I am getting timing advancement straight off the bad at idle.

Power seems real good, no ticking or oddness at idle or during my drive. On my test drive around a few blocks she got me home perfectly fine - so I guess I did it right ;-)

[Steeveedee]

Looks like a well done installation! When I worked as a mechanic, the boss' kid installed a new distributor but failed to tighten the hold-down clamp. When I came in the next day, he told me that the starter failed when he tried to restart it after it "stalled'. What had happened is he seized the engine. Time for a rebuild. When I pulled it apart I realized why it acted like the secondaries weren't opening- the cam was going flat. I was a lot faster after the rebuild.

[Rich72C10]

LOL - yes that tie down is important. A bit ago I bought a cool distributor wrench, makes it easy to loosen & tighten! On my first drive in truck at the rebuild at my brother's it started to run like crap about 1/2 a mile away - I didn't think I'd make it back to his shop. It ended up he also forgot to tighten the hold-down clamp. He then told me, good lesson, don't do what I did!

Okay, girls are pretty worthless. I figured I'd have my daughter rev up to 35k by moving 500 RPMs at a time. By the time she got to 25k, she bailed and ran back inside and said never to ask her to ever do that again. So I got her mom out there. She couldn't figure out how to keep a real good lock, 15k was the worse for her. When we were done, she said she was freaked out too and her palms were all sweaty - YUCK!

Anyways, it seems to be following the copper/silver advanced chart, with all in around 25k

PS: another bit longer test drive. Off the line I totally can peel out longer and she really smokes the tires (or tire as in my case). I popped on/off I35 a few times and there really seems to be more power between 60~80mph. Lower speeds it feels like more as I am nailing it through 30 on up (as the engine reaches ~40k RPMs before the TH350 downshifts). I swear she is shifting better (engaging more to higher RPMs). Though all this nailing the gas peddle to the floor is No bueno for MPG but sure is fun to go Zoom Zoom LOL

[geezer#99]

Originally Posted by Steeveedee

Looks like a well done installation! When I worked as a mechanic, the boss' kid installed a new distributor but failed to tighten the hold-down clamp. When I came in the next day, he told me that the starter failed when he tried to restart it after it "stalled'. What had happened is he seized the engine. Time for a rebuild. When I pulled it apart I realized why it acted like the secondaries weren't opening- the cam was going flat. I was a lot faster after the rebuild.

How did the engine seize from retarded timing?
Just curious.

[geezer#99]

[QUOTE=Rich72C10;8879521

I know when I have it on manifold vacuum I have to adjust the idle down because the initial timing pops right up when it is connected to the Vac Canister on the distributor. I suppose that is right, since I am getting timing advancement straight off the bad at idle.

Power seems real good, no ticking or oddness at idle or during my drive. On my test drive around a few blocks she got me home perfectly fine - so I guess I did it right ;-)[/QUOTE]

If you need to adjust the idle too much with the adjustment screw you could uncover the transition slot and waste fuel because it’s idling on the power circuit. And you might get a slight stumble at first.
Using manifold vac helps sometimes.

[Steeveedee]

Originally Posted by geezer#99

How did the engine seize from retarded timing?
Just curious.

The distributor popped out of the manifold, disengaging from the oil pump. He was running high enough RPM before that to have it grind to a halt. Blue rod caps FTW.

[Rich72C10]

I also got in the mail today the replacement Vacuum Canister from TSP. This thing won't hold vacuum either. I have to keep pumping just to get near 15 - I think it leaks more then the one on my TSP distributor!

The Pertronix I pre-tested to 15hg can it held that for well over a hour. I guess I am glad I went with a new distributor.

With the Pertronix I am getting ~17hg (up from ~15hg) vacuum when the engine is running at idle. So I ganged a good 1~2hg with the new distributor.

I also swear my oil pressure is running to normal levels of my stock gauge - before I'd always seem to be at the 2/3 to near H mark on the oil gauge (especially before warm up). Though I haven't any clue why a new distributor would make a difference with the oil gauge readings. Kind of scares me that the oil gauge reading pattern changed. Though it's not like it is ever reading to the L mark (far left) of the gauge.