Opinions, dumb idea: Using vacuum canister + vac advance to avoid hardstart 38' - Page 2 - Hot Rod Forum : Hotrodders Bulletin Board
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  #16 (permalink)  
Old 06-03-2010, 04:51 PM
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What kind of starter do you have? With gear-reducted starters I dont even see this prob anymore, even on oval track cars with conventional headers after running at peak power for 30 minutes. I would stick with the locked mech adv if I had the timing setup you have and try to get some vac advance if you can, but if not its really not a big deal.. and get a better starter with big cables going to it.

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  #17 (permalink)  
Old 06-03-2010, 05:25 PM
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Quote:
Originally Posted by bubbahotep
my only loss the use of the vac advance for cruising light load since my vac can is just stuck at advanced fully?
That, and if the reservoir ever goes below the vacuum that is needed by the vac. adv. can to stay fully advanced, you will obviously lose timing advance until the vac. in the reservoir comes back up.

I had thought at first you were running a gnarly cam but a 236/242 @ 0.050" doesn't qualify for needing a locked-out advance dist., IMO.

If you set it up w/36-38 total timing all in by 2500-3000 RPM, w/as much initial timing as the engine "wants" (initial could be anywhere from 16 to 24, ballpark- the rest from mechanical), and use a vac. adv. as a vac. advance and have 10-12 in the can, the engine will run great for you. Use the timing retard to lower the initial for starting, like it was intended.

The ACCEL #31035 is an adjustable vacuum advance can for GM HEI that allows infinite adjustment to BOTH the amount and rate of advance. Comes w/instructions and tool.

To limit the amount of vacuum advance w/an OEM or some adjustable cans like the ADJUSTABLE VACUUM ADVANCE CAN KIT- Crane #99600-1: 99600-1 INSTRUCTIONS, you will need to physically limit the vac can's travel w/a VACUUM ADVANCE LIMITER PLATE- Crane #99619-1: #99619-1 INSTRUCTIONS.
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Old 06-03-2010, 08:46 PM
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Vac Advance

Hey Bubba, While your solution to your problem at hand is pretty clever. I think that FBIRD&COBALT can help you set up for an engine that likes alot of timing. I have dealt with two big blocks that liked the timing but the starters didn't. If you can't crank your sbc without an interrupt and a timing box, you really should consider a gear reduction starter. I cured both the big blocks mentioned with gear reduction starters. Back in my Mopar days, cranking big cam, high compression, high timing engines was never an issue due to the factory g/r starters with no interrupt or box. Big cable, big battery, g/r starter= easy start. Worked on my 454 motorhome too. Used a later model 350 g/r on it. On the other two I used Powermaster. Food for thought. olnolan
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Old 06-03-2010, 08:56 PM
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Starter is brand new MSD high torque with fat wires on both red and black. The wires are like 2 3/4" pipes. lol. They hardly bend at all, not too many strands inside and cost more than the starter if I remember

My reservoir wont get below the amount needed to maintain the vac advance. It is an adjustable vac advance can which supposedly can work as low as 5hg and seems to be somewhat true.

This 8981 MSD timing computer requires advance locked out at full in order to work. You give it your total timing and then I adjust my advance curve via a dial as well as my idle timing via another dial and the advance quickness via another dial. Its drawback is that its forcing me to start with 18' timing (after the 20' retard it gives).

Fbird is no doubt correct in everything and what he says about my hot hot start with gas mixture makes sense. I even installed a carb spacer thinking I had some percolation after the engine heated at shut off and caused the carb to dump gas. Didnt make a difference.

Engine never goes above 180-200' while running. Starter is 1" all around spaced from the headers, with the ignition switched "off" I can turn the motor freely so the starters not overheated. I can ALWAYS start the car. Just now and then I get that vrr vrr vrrrrrrrrr vrrrrrrrr.

OLDBOGIE - Ive had this thing at 50' idle and 50' driving around town at one time due to the dizzy slipping and never heard a ping. Must have been like that for months Id guess and I only noticed it when I felt I little stumble one day at idle. Possible there was just too much noise to hear the ping? That was years ago now though. Never sees more than 38 now and maybe 36 if I listen to Fbird
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Old 06-03-2010, 09:13 PM
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Ground Cable

Hey Man, You may want to check your ground cable if it only hard cranks on occasion. Also starter shimming. Ground battery to block, block to chassis with the two cables under the same block bolt, block cleaned to bare metal. Remove solenoid and shim starter so it can be hand operated in and out of the flywheel with a smooth action at three separate points around the flywheel(sometimes the ring gears have a little run out). I went through this on my 406 boat engine and on the 454 motorhome. More food for thought. olnolan

Oh, I forgot, the type of cable you are using isn't the right stuff for 12vdc if its super stiff and doesn't have many strands, you want as many strands as possible to improve current flow to the starter. May be another thing to consider. olnolan
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  #21 (permalink)  
Old 06-03-2010, 09:35 PM
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Starter is MSD 5095, I thought thatd be enough gear reduction. Tiny starter too. Starter gear is as perfectly spaced as I could see. Goes in and out freely, no binding, no twisting, spaced according to MSDs little piece of paper that came with the starter.

My Ground cable goes from battery straight to an unused hole in the starter aluminum mounting block and then theres 2 or 3 more going to chasis. But its NOT many stranded. I thought the many strands were more for audio and easier bends. And the + goes to the starter direct. Both are also the length of the car (battery in trunk). Fairly new Optimum battery too.

The carb, thanks to info from this board, was properly adjusted last year on the plates where I had too much "square" exposed. Things right at factory setting now with a good 900 or so idle rpm.
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Old 06-04-2010, 05:21 AM
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Bases Covered

Hey Bubba, Well if you're already running a gear reduction starter it sounds like you've got all the bases covered. Starter and grounding issues already mentioned by others here was just starting to sound like where your real problem was. olnolan
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  #23 (permalink)  
Old 06-23-2010, 06:30 PM
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Just an update: this was a failed idea with good intentions. Sure enough I was caught in traffic (ny) and on the brake at idle. After inching forward in traffic I lost all reserve vacuum from my canister which made the vac advance drop and then my "total" timing dropped so that dropped my idle timing and ka chugga ka chugga ka chugga. It was good throwing it into neutral but thats just not a fun driving experience. If I was just stopped at a light it was fine but the stop, inch forward, stop, killed it.

And yes it did wreck my phasing. I was past the firing by a good 1/2" I think. Way beyond the plug wire. Not good.

Now Im back to just 36' locked with the 20' start retard and using the msd 8981 computer to keep me at 28' idle timing. I'll do with the ignition "off" switch and be happy with that much.

Was worth a shot
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  #24 (permalink)  
Old 06-25-2010, 07:16 AM
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I think your problem is the 20 degree retard.10 would be better with 20 degrees the rotor is almost halfway between two terminals when it fires.It can fire the terminal ahead of it almost as easily as the one it is intended to fire so instead of 20 degrees timing retard occuring it can actually be 50 to 60 advanced if it fires to the wrng terminal.
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  #25 (permalink)  
Old 06-25-2010, 09:15 AM
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Barnym, that's an interesting possibility that makes sense. Up until I did this vac advance trick I think my phasing was off by the width of a full rotor tip at 38' timing too. My phasing was past the spark wire (my dizzy spins clockwise I thought) and my spark was always after the pole. So, that'd be even worse? My spark was technically already late but grabbing the correct terminal, add in 20' retard and I'm even later?

If I'm now phased perfect at 38' or 36' is 20' retard still an issue you think? I can, but never tried it, disable the retard feature but it's not adjustable. It's 20' or nothing.
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