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Loft’s of guys use those adjustable vacumn cans, just remember that they do not limit timing only the rate of vacumn. Most of those cans I test on my sun machines pull in as much as 20 to 25 degrees of vac at the crank. So that is why LATech using the crane cam stop. It works that way.

But why bother with it, the vac can number I gave you only pulls ten degrees at the crank. No adjustments needed and it pulls in the vac low so you can get the benefits at idle. I have a stack of those adjustable cans under my sun machines, I just throw them in the bin.

If you do use it make sure that you set it up with the stop to limit the vac advance to 10 degrees.
 

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1967 400ci/TH400
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Sometimes the pinging can be due to the vacuum advance can. It can be something like an additional 20 degrees more with high vacuum and then when you nail the gas, the addtional advance provided for by the vacuum advance does not retract fast enough so you are relying on the full mechanical advance pluse whatever advance is being added by the can at that instant. With the carb wide open, the vacuum drops so eventually all that extra 20 degrees goes away and you are running on just the weights/mechanical advance - with the problem being the advance can did not react fast enough.

There are different vacuum advance cans you can try and I recall the one you may want is called a "B-26". It only had 10 degrees of total vacuum advance, but also begins to operate at a lower engine vacuum and works better with big cams/low vacuum.

The other thing you can do is get the distributor set-up using the springs to get your total 34 degrees (Initial/balancer + dist, weights) to be all in at a higher RPM like 4,000 RPM's or even 4,500 RPM's. This stretches the weight's advance out over a broader range of RPM, ie instead of 34 degrees at 3,000 RPM's, you might only have 26 degrees at that RPM which effectively is the same as retarding the timing, but the weights will continue to add more timing as RPM's increase until you get your full advance of 34 degrees at 4,000 -4,500 RPM's.

So a lot of experimenting with Initial timing, mechanical timing, and the vacuum can. Most of this has been covered quite a bit in other posts if you do a search for it. (y)
So dumb comment/question....i don' have an advance / vacuum can anymore. I'm using an MSD Digital 6AL to an MSD Blaster Coil to a "billet" / mechanical HEI distributor. The original distributor had a vacuum can....since I removed it, I just capped that vacuum port on the distributor. Am I missing something here?
 

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Ice, yes you missing some great benefits. What you are running we call a racers set-up. Racers often pull the vac can and say they don’t need it because we’ll they put the pedal down all the way and go. There is no vacumn at WOT. Of course even with a vacumn can affixed it does not work at wide open throttle, because…….there is no vacumn then.

Timing is misunderstood and so is vac advance. Vac advance is often set-up improperly and adds too much timing. But when set up correctly it is really magic for your street performance set up.

you cannot add 10 more degrees of timing to your total timing numbers say 36 degrees,…unless you do it with vac advance, because vac advance works opposite your Centrifigal advance. Vac advance is load dependent. And Centrifigal advance is RPM dependent. They work together when they should, say at light throttle cruise to give you 46 to 48 degrees of timing needed to burn that leaner mixture.

And they work opposite each other at WOT as vac drops out and you are left with total. And they cross in between delivering you the proper timing based on load, or demand.

With your setup at light throttle cruise you have very inefficient timing. The max you can get is your limit say 36. Race cars don’t do “Light Throttle Cruise” so they don’t care. But a street car does, say if you drive on a highway?….the vac adds 10 degrees here that burns that lean mixture very efficiently something you cannot achieve without it. It gives more power with a light pedal, a complete burn, cooler running and better gas mileage,…all with no top end loss of power since vac drops out as pedal goes down.

I have fixed lots of guys “Race dist set-ups” so they can really get the power and benefits from perfect timing. Whiz bang billet distributors with no vac advance seem-cool to lot’s of guys, and understandable on a track car only. But for street performance why give up all the benefits for no gain.

Also, that extra 10 degrees of timing can be added at idle by vac and keep your engine much cooler. With no vac advance racers have to run that base setting up high to try to get a great idle, vac advance let’s you get a smooth cool idle real easy.

I even seen a guy who welded the distributor to the top of the block, no vac advance. Makes adjustments harder……so it matters what the purpose of the vehicle is.
 

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Oh boy, i have some work to do; had a feeling I was missing something important. My car is a daily driver so have no business having a "racer set up". I still have the original distributor which is in pretty good shape and had modified it to use with the MSD Digital 6AL ignition box.....and it had a vacuum can. Will get the vacuum can y'all recommended and put the original distributor back in. I just need to find a good distributor cap that can handle HEI.

I'm a college visit with my daughter but will get to this next week....and keep y'all posted! Thanks!
 

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I've had years and years of experience with first-gen GTO's and here's the main issue: the 389's and early 400's had 'closed chamber' cylinder heads and a lot of compression. Because of this, they need 98-100 octane fuel to run well without detonation. The only way to avoid detonation without using the proper octane is to retard the timing to the point where performance suffers. If you run a real octane booster like Torco Accelerator or Octane Supreme 130 or race gas, your car will run just fine. I have to run race gas in my '65 GTO which has the original #77 64cc heads (milled slightly). No other way around it. On my '67 GTO, I could not run the 670 heads on pump gas, even with water injection, here in hot arid central CA. I ended up installing a set of later cylinder heads with 87cc chambers to lower the compression to about 9.3:1. It barely runs on the 91 octane fuel we have out here without detonation. These cars were designed for 100 octane fuel, and that fuel is not available at the pump any longer.
 

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@67GTONUT - i lived in the Bay Area before moving to Texas. Was fortunate to have a 76 Gas station that had 100 Octane racing fuel / Sonoco available....but at $8.99 per gallon before prices went up. I would run a tank of 15 gallons of 91 premium with 5 gallons of 100 octane....car ran well. Have 93 octane at pump in TX....but that's not doing it, even with a can of STP octane booster. Will try the 2 products above. Thanks
 

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Also try


VP Octanium

I was using Octane Supreme 130 but it got hard to find and expensive

the VP stuff works just as well
Thanks, just ordered some Octane Supreme 130 and Torco accelerator to give then a try....noted on the less expensive VP stuff - will try that too! Cheers, Carl
 

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VP makes racing fuel so likely their product works. The Octane Supreme 130 and Torco actually raise the octane by points, not tenths of a point like the worthless '104' and '108' junk sold at parts stores. Pretty much ANY 'octane booster' sold at a parts store is worthless. That has been my experience over the past 40 years. The OS and Torco actually work. And, sadly, for the early 389-400's that are running stock compression ratio, the only real way around detonation.
 

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@PontiacJim @LATECH @armyadarkness @Lemans guy - thanks to all of you for the help; i think i finally solved my "car won't start when it's warm issue". As usual, i think it was a multitude of problems that needed to be addressed. First and foremost, the car has had a parasitic drain issue since i bought it and i will spend some time figuring that out. In the meantime, i've applied "a hammer to a push pin" approach. Problems encountered:

1) The MSD ignition / distributor cap set up i had was poor quality - the "cheap" distributor cap just melted (i've got pics below) so I'm sure that didn't help
2) The MSD digital ignition 6AL system is extremely sensitive to voltage drops below 12V; with the voltage drain above and running 2 electric fans, electric fuel pump, Vintage Air/Blower, Hi-Torque starter and a pretty good size stereo, i'm using a lot of electricity driving down the road. My voltmeter gauge would drop to below 9V during cranking.
3) Vintage Air ECU kept needing to be reset; apparently MSD digital boxes put out a lot of line noise...and Vintage ECU is also picky about voltage drops....
4) Ordered the wrong MSD HEI distributor....bought the "RACE READY" one without the vacuum can....not a good idea per above!
5) Engine was pinging at low RPMs
6) Need to optimize timing curve

So here is what i did:
1) got the proper MSD distributor with a vacuum can
2) installed a noise filter for MSD digital 6AL power source
3) Installed a 2nd battery in the trunk with Stinger Relay activated by key ignition; this powers the MSD digital ignition and a couple of other things
4) Installed a 250Amp alternator
5) Installed a 2nd voltmeter so i can check voltage to MSD during cranking

Car now starts rights up, been doing so for 3 days whether it's cold, or has been driven around
During startup, voltmeter on cranking battery goes down to 8-9V, 2nd battery voltmeter stays above 12V
Bought some VPRacing/and Turco Racing Fuel concentrate....no more pinging!

Now need to replace valley pan gasket, and tune the timing curve. A bit overkill on the solution but it's working and since it's my daily driver, having a 2nd battery as backup is a good thing IMHO. I will send pictures after i've cleaned up the engine bay and wires in the car. I installed a bunch of switches and relays while i was testing different configurations.

Thank you all for your help and getting me back on the road. Driving my old 2006 Nissan Frontier isn't the same....

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@PontiacJim @armyadarkness @LATECH @Lemans guy

Here is an update to my timing challenge and other issues - I've learned a lot about timing and was able to try different bushings and springs to play with the timing. Found it challenging to change the bushings nuts, springs were pretty easy. Found a new distributor from Progression Ignition - https://progressionignition.com/; i've included a quick video below. Basically, it's an electronic distributor where you can change the timing and timing curve from an App on your phone. You can save multiple timing profiles and even change the timing while the car is running. In addition, it has a "lock" feature that acts as an engine lock to prevent theft. Pretty cool, and the same price as an MSD distributor. Happy with it so far.

As far as the coil voltage issue, I brute-forced the solution by putting in a 2nd battery, activated through a Stinger relay. Come to find out, I thought I was bypassing the voltage resistor wire.....turns out I wasn't. So I have an overkill solution but now have a 2nd battery backup. I have cleaned up the engine (a bit) and the trunk where the 2nd battery and stereo amps/subwoofers are. I'm trying out different things before I do a frame-off restoration in the future (who knows when). This is my daily driver so want to make it run smooth and comfortable. Next up are: installing a new Vintage Air blower and hoses, CVF serpentine belt system (which requires an 11 bolt water pump, so a new timing cover, and a new harmonic balancer), changing valley pan gasket, and passenger side exhaust manifold (frozen and leaking heat riser valve). Thanks for all the help!

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This should be a video of how it works in my GTO -
 

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Cameo Ivory 1967
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Glad you found something to simplify your problem. I do like those Progressive Dizzy's.

Yeah, you're not really changing a total timing bushing with the dizzy in the car... and who wants to pull the dizzy 4 times? As you said, daily driver, so I think you made a good choice!
 
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