Ignition 101 - Page 4 - Chevelle Tech
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post #46 of 102 (permalink) Old Jun 18th, 10, 10:26 PM
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Matt
 
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Re: Ignition 101

Maybe I'm missing it, but which of the non hei vac cans is for a 66 396 325 h.p.? From the list it seems as though a few could work, but nothing specific. NAPA lists the following: vc1605 b9, vc680 b1, and vc1765 b20. Three entirely different cans.
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post #47 of 102 (permalink) Old Jun 21st, 10, 3:44 PM Thread Starter
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Re: Ignition 101

Quote:
Originally Posted by matt's66 View Post
Maybe I'm missing it, but which of the non hei vac cans is for a 66 396 325 h.p.? From the list it seems as though a few could work, but nothing specific. NAPA lists the following: vc1605 b9, vc680 b1, and vc1765 b20. Three entirely different cans.
Two thoughts...

First using factory specifications is only good if you have all of the factory specified parts that go along with the specification. So many of these cars have been modified over the years that factory specifications apply to very few.

Second giving a specific part number is like giving a man a fish. He may eat for a day but give him a fishing pole instead and he may eat forever (even if he DOES get sick of fish ).

That is why having the vacuum specifications on the advance cans is WAY more useful than year/model. You can measure your specific setup and choose the best matching advance can.

Steve
1968 El Camino, 402 with TKO
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post #48 of 102 (permalink) Old Jun 21st, 10, 4:38 PM
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Bill
 
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Re: Ignition 101

If you really, really, REALLY want the hot ticket street setup you'll pony up enough cash to get a F.A.S.T. setup and then you'll have an engine that runs like a brand new 2010 car. Except of course for all of the roller stuff and a hot cam and the 6" rods and all that.


Like this :

http://www.jegs.com/p/Comp-Cams/Fast...16335/10002/-1


Then the issue of fiddling with timing, vacuum advance and all of that arcane stuff from 30 years ago becomes a matter of hooking a laptop up to the computer in your car via a usb port and dialing up what how you want your cars engine to operate.

See? You CAN teach an old dog some new tricks!
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post #49 of 102 (permalink) Old Jun 21st, 10, 5:17 PM
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Re: Ignition 101

Quote:
Originally Posted by vrooom3440 View Post
Two thoughts...

First using factory specifications is only good if you have all of the factory specified parts that go along with the specification. So many of these cars have been modified over the years that factory specifications apply to very few.

Second giving a specific part number is like giving a man a fish. He may eat for a day but give him a fishing pole instead and he may eat forever (even if he DOES get sick of fish ).

That is why having the vacuum specifications on the advance cans is WAY more useful than year/model. You can measure your specific setup and choose the best matching advance can.
Well, the ENTIRE engine except for timing chain, adjustable vac can and carb is 44 years old. It has the original cam, lifters, dizzy etc. I was curious as to the original specs. It doesn't really matter anyway, I changed the whole timing curve to stop the WOT ping on pump gas. An oem can would probably rattle itself to death when set to factory specs. Just nice to know what it WAS.
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post #50 of 102 (permalink) Old Jun 21st, 10, 11:00 PM
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Smile Re: Ignition 101

Quote:
Originally Posted by matt's66 View Post
Maybe I'm missing it, but which of the non hei vac cans is for a 66 396 325 h.p.?
From the list it seems as though a few could work, but nothing specific.

NAPA lists the following:
vc1605 b9
vc680 b1
vc1765 b20.

Three entirely different cans.
Quote:
Originally Posted by Mexbkr View Post
I think I found the answer to whether I have the correct can installed. I looked up in Lars G. paper and found that the B1 starts at 8-11 and maxes 8 deg at 16-18 in. But the B20 , starts at 5-7 and maxes at 11-13. I have a 1967 327, non-hi Perf, with powerglide.

P/N............ID#......Application............Start s @ “Hg..Max Adv (Distr. Degrees @ “Hg.)
VC680........B1.......59–63 All Chev......8-11...................8 @ 16-18
..............................1966-68 327 exc. Powerglide

VC1765.......B20.....65 396 Impala Hi Per..5-7...............8 @ 11-13
...........................1966-68 327 Powerglide Exc. High Perf.

Does this sound right? replace B1 with B20?
The ... VC680 ..... B1 ..... "vacuum can" .... is listed as a stock 1967-68 396 can, for all applications ...

All 3 cans are listed as used in big block/small block applications, I did not see a 1966 396/325 listed ....

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Last edited by mr; Jun 22nd, 10 at 8:41 AM.
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post #51 of 102 (permalink) Old May 25th, 11, 11:38 PM
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Re: Ignition 101

Say you run the car on a dyno without vacuum hooked up.
You find 36 total to produce max power. Hooking up the vacuum again, will that effect power ? I mean, how do you know for sure itīs not adding a degree or two, even with very low vacuum in the manifold ? Especially on the top end, when vacuum signal may be starting to show.

If so, going to the dyno in street trim, running wot with vacuum hooked up is best ? And then if itīs adding a degree or two, you would compensate for that by finding the engine to produce most power at 35 (measured timing without vacuum hooked up) And, make sure to not do any adjustments to that vacuum can (or change it out) after youīve been to the dyno ??

What are youīre experiences ? Does having a vacuum can hooked up or not have any effect on total timing when going wot ?

65 Chevelle, ZZ502 with 11,2:1cr and 242/252 110 cam.
Th400. 3,73. 5200stall.
Best 1/8: 7,058 Best 1/4: 11,17 Best mph: 118,6 Best 60: 1,56
13.6mpg

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post #52 of 102 (permalink) Old May 26th, 11, 7:44 AM
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Re: Ignition 101

Not usually...

THe vacuum can doesn't start advancing until the vacuum reaches something in the range of 8 - 10" depending on the specific one. Doesn't do anything to the timing at an inch or 2.

There is no reason to unhook it at the dyno. Apart from it not making any difference, there is no logical reason to do so. You don't do that any other time; why would the dyno be any different? What good would dyno tuning bem if you did it with the car in a different state from when it's operating normally?
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post #53 of 102 (permalink) Old May 26th, 11, 9:11 AM
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Re: Ignition 101

Not saying it would, just curious when I set the ignition at 36 and then hook up the vacuum if Iīm really at 36 or not. But like you said, shouldīnt have any effect at 1-2" vacuum.

65 Chevelle, ZZ502 with 11,2:1cr and 242/252 110 cam.
Th400. 3,73. 5200stall.
Best 1/8: 7,058 Best 1/4: 11,17 Best mph: 118,6 Best 60: 1,56
13.6mpg

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post #54 of 102 (permalink) Old May 26th, 11, 10:11 AM
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Re: Ignition 101

Question:

If you had a initial of 18*...and then you hook up your can to manifold vacuum...and rechecked timing.....you ignition is now at 38*.....would that mean your can has 20* of timing in it?

Also if you had 36* at 2700...all in without the can hooked up.

Then you hook the can up and go for spin...you then have 56* at cruise?

So ....in order to get you magic number of 52* you would need 16* of vacuum on the can...and this would give you 34* at idle on the can off manifold vacuum.

Is this correct?

67 chevelle malibu / SS/ custom

Currently undergoing a metal work to remove all rust, if I ever get there.

Cant decide on prostreet or cruiser with a 4 speed.
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post #55 of 102 (permalink) Old May 26th, 11, 10:21 AM
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Re: Ignition 101

Sounds spot on with me Aaron !

Hereīs an alternative.. food for thought.
Almost locked out at 34 degrees initial + 2 mechanical = 36 total.
Now try run timed vacuum on top of that at 16 degrees.
You now have at idle: 34
Cruise: 52
Wot: 36

Funny how the numbers are looking very similar :-)

65 Chevelle, ZZ502 with 11,2:1cr and 242/252 110 cam.
Th400. 3,73. 5200stall.
Best 1/8: 7,058 Best 1/4: 11,17 Best mph: 118,6 Best 60: 1,56
13.6mpg

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post #56 of 102 (permalink) Old May 26th, 11, 10:33 AM
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Re: Ignition 101

Quote:
Originally Posted by Rokker View Post
Sounds spot on with me Aaron !

Hereīs an alternative.. food for thought.
Almost locked out at 34 degrees initial + 2 mechanical = 36 total.
Now try run timed vacuum on top of that at 16 degrees.
You now have at idle: 34
Cruise: 52
Wot: 36

Funny how the numbers are looking very similar :-)
I like like Remi!

Is that with ported vacuum?

I assume it is since you have 34* locked at idle and no vaccum increasing timing at that time.

67 chevelle malibu / SS/ custom

Currently undergoing a metal work to remove all rust, if I ever get there.

Cant decide on prostreet or cruiser with a 4 speed.
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post #57 of 102 (permalink) Old May 26th, 11, 10:58 AM
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Re: Ignition 101

Yes thatīs with ported vacuum.
I stole the idea from Joe, who probably stole it from someone else lol

Iīm running 24 initial - 36 total - 52 with full manifold vacuum though.
Havenīt tried the (semi-)locked out yet, will probably try it someday soon. Running the ported this way, you get almost no timing curve from the mechanical, but still hit about the same numbers. Since you donīt run vacuum at idle, timing will still be there when taking off and giving it some throttle, this way should give an increase in response. Compared to running full man vacuum and have it retard the ignition during medium throttle takeoffs.

I guess youīd have to watch out for pinging a little more down low though, but since running a lot of stall like you are, I donīt think you will be able to load the engine enough to have a problem without going up on rpmīs, and since youre going up on rpmīs you should be ok since the mechanical would already be in anyway...

Also one thing I noticed when my HEI was locked (read rusted to the point of being stuck over the winter) was that ignition was retarding about 1 degree per 1000 rpm, I read the reason for this is that while the ignition takes the same amount of time to produce a spark from signal, the engine travels faster and therefore the piston will have traveled further as the rpmīs rise, resulting in a retarded situation. I donīt know how guys go round this when going locked out ? Maybe the more high end ignition systems travels faster and therefore reducing the amount of retardation ? I was using the stock zz502 HEI at the time btw.

65 Chevelle, ZZ502 with 11,2:1cr and 242/252 110 cam.
Th400. 3,73. 5200stall.
Best 1/8: 7,058 Best 1/4: 11,17 Best mph: 118,6 Best 60: 1,56
13.6mpg

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post #58 of 102 (permalink) Old May 26th, 11, 1:39 PM Thread Starter
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Re: Ignition 101

The problem with fixing initial higher is this creates too much advance at cranking engine speeds. The charge fires off and creates too much pressure BTDC and trys to make the engine run backwards. For many Chevy engines this affect kicks in above about 18*.

Do not worry about the potential of a vacuum can adding a few degrees on top. First as already pointed out the vacuum cans usually do not add anything until some minimum amount of vacuum is present, and you are unlikely to hit that at WFO. Next is the vacuum advance compensates for pressure in the cylinder. As you hit the limit of engine breathing at high RPM the cylinder pressure naturally drops. This is why the torque curve begins to fall off. As cylinder pressure drops more advance can be used.

There are also dwell affects built in to the HEI electronics that tweak things a smidge as RPM increases. I do not recall off the top of my head the exact details.

Steve
1968 El Camino, 402 with TKO
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post #59 of 102 (permalink) Old May 26th, 11, 3:01 PM
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Re: Ignition 101

I know exactly what you mean Steve, I went thru a few starter gears last year, before I sat down and tried to grasp how to set ignition the right way. (from when it was locked) Still have a lot to learn, but the basics are starting to sink in. The fix for keeping my starter happy was mounting a switch for the ignition, I let the engine get up to good cranking speed and then flick the switch.
It makes starting a two hand job, but it keeps my starter happy and my car a little harder to steal.

I`ll stop worrying about the can causing an advanced situation on top going WOT. What does WFO stand for exactly ? Tried googling it and all that came up was some weather stuff and the seventh record from a band called overkill. lmao.

65 Chevelle, ZZ502 with 11,2:1cr and 242/252 110 cam.
Th400. 3,73. 5200stall.
Best 1/8: 7,058 Best 1/4: 11,17 Best mph: 118,6 Best 60: 1,56
13.6mpg

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post #60 of 102 (permalink) Old May 26th, 11, 3:28 PM
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Re: Ignition 101

WFO...wide fu**ing open

FWIW...wildman gave me a few tips that work real good for me! Using ported vacuum advance...I have 23 initial & 14/15 mechanical (bushing from 4secondsflat) gives me 37/38 total in by 2500 rpm's & no hard starts...then I use the crane adj. vaccum can set up to give me another 14 at cruise! My motor is happy as hell, no pinging or detonating & it's very responsive at idle & everywhere else aswell! I did change the way the crane can works though cause it kinda works backwards from how I thought it should work, as far as the stop goes anyhow
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