ANOTHER timing thread...sorry guys...

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Jun 23, 2012 | 06:34 PM

#41

KevinK

Thread Starter

Drifting

Joined: Jun 2007

Posts: 1,404

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From: Ansonia/NYC CT

Quote:

Originally Posted by 63mako

You have 15 initial, 19 mechanical for a total of 34 @ 2700. All good. You also have 19 vacuum at idle. Add them together your at 53. That is surpassing the 52 max recommended. (there is your ping above 2700 in neutral) You say your vacuum goes from 12-13 at idle to 20 @ 3000. If your vacuum advance is continuing to add vacuum you may be well surpassing 53 degrees causing your ping in neutral. This should not affect ping while accelerating but could cause ping at cruise if your vacuum advance continues to advance past 19 degrees, again your surpassing 53 degrees total with advance. Solution is to limit vacuum advance to about 16 degrees for 50 total with vacuum. You have efficent heads that allow 34 degrees total so I would drop the total with vacuum to 50 degrees to be safe.

This is a quote from Lars:

"How much centrifugal advance (“total timing”) is in effect at cruise rpm? If the distributor has very stiff centrifugal
advance springs in it that allow maximum timing to only come in near red-line rpm, the vacuum advance control
unit can be allowed to pull in more advance without the risk of exceeding the 52-degree maximum limit at cruise. If
the engine has an advance curve that allows a full 36-degree mechanical advance at cruise rpm, the vacuum advance
unit can only be allowed to pull in 16 more degrees of advance."

You want your vacuum can to start @ 2HG below idle vacuum and pull 8 distributor degrees at 2 HG below your max vacuum.
A VC1675 also known as a B13 vacuum can will start advancing @ 9-11 HG and get maximum 8 distributor degrees (16 crankshaft degrees) @ 16-18 HG.
This is perfect for your combination. It is the vacuum can used on:

1968 327 Camaro Powerglide
1968 327 Impala AT
1968 307 AT
1968 302, 307, 327, 350 Camaro, Chevy II
1970 350 Camaro, Chevelle Exc. High Perf.

If you can't find one go with
VC680 Also known as B1 Starts advancing @ 8-11 HG with a total of 8 degrees distributor advance (16 degrees crankshaft advance) @ 16-18 HG

Used on:

1959 – 63 All Chevrolet
1964 Corvette exc. FI
1964 Impala, Chevy II
1965 396 High Perf.
1965-67 283, 409
1966-68 327 exc. Powerglide
1967-68 All 396
1969 Corvette 427 High Perf.
1969 396 Exc. High Perf.
1969 Corvette 350 TI
1969-70 302 Camaro
1970 400 4-bbl
1970 396 High Perf.
1970 Corvette 350 High Perf.
1973-74 454 Exc. HEI

Buy one, they are cheap. Leave your initial and mechanical as is, replace vacuum can with the one above, your golden.

I already have a guy out and about looking for one, for me, per Lar's papers. That's why I fiddled around a little again, to try to drop the total timing...just to tide me over, sans pinging, till I can get my hands on, and figure out how to install, a new vac can. Thanks for the list of cars I can find it on...that will help me out. It was either that, or I was gonna go with one of those adjustable ones. I took it for a drive, no ping (that I could hear) under load, no ping at highway cruising, either. Feeling kinda confident, I took her to one of my little spots, and launched it from 2,500rpms, and man, did I have **** eating grin on my face or WHAT! Spun the tires (275 Eagle F1s) in first to the point that I had to let off a bit, chirped them pretty good in second, and then 3rd and fourth we just sorta blah. But with 3.08 rear gears and a stock four speed, that's not bad, right? On that note, however, just as I was pulling into my driveway, after about a 5 mile drive from my little "drag strip", first gear made a little grind. Face palm.

Jun 23, 2012 | 06:51 PM

#42

63mako

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Joined: May 2005

Posts: 10,674

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From: Millington Illinois

St. Jude Donor '08-'09

Quote:

Originally Posted by KevinK

I edited my post. If you have HEI those won't work.

Jun 23, 2012 | 06:51 PM

#43

scottyp99

Le Mans Master

Joined: Mar 2008

Posts: 5,948

Likes: 72

From: Oxford MA-----You just lost the game!!!!

Kevin, your 'vette is a '76, right? Does it still have the original HEI distributor? I don't remember if you posted what you have or not, but, just FYI, the HEI distributors use a different vacuum can than the older points style distributors. Here is a newer copy of Lars' vacuum advance paper, which includes performance oriented HEI vacuum cans, down at the end of the paper.

http://www.corvette-restoration.com/...c_Adv_Spec.pdf

I used a VC1838, which ended up giving me 16 degrees of vacuum advance, but my engine pulls 20" of vacuum at idle, so you may need to use one of the others listed.

Oh, and Mako63, listen to this........BONK!!!!.........that was me smacking myself in the head for not realizing that an engine with no load will produce full vacuum!!! Derrrr!!!!

Keep the shiny side up!

Scott

Jun 23, 2012 | 06:56 PM

#44

scottyp99

Le Mans Master

Joined: Mar 2008

Posts: 5,948

Likes: 72

From: Oxford MA-----You just lost the game!!!!

D'oh!!! Mako, you beat me to the click!

Kevin, just go to NAPA and buy one, they are cheap, like less than 20 bucks.

Keep the shiny side up!

Scott

Last edited by scottyp99; Jun 23, 2012 at 06:59 PM.

Jun 23, 2012 | 07:01 PM

#45

63mako

Race Director

Joined: May 2005

Posts: 10,674

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From: Millington Illinois

St. Jude Donor '08-'09

Quote:

Originally Posted by scottyp99

Keep the shiny side up!

Scott

Hei performance choices are more limited. VC1838 is probably best for Kevin also if his is HEI. Or this:
http://www.summitracing.com/parts/PNX-D9006/

Last edited by 63mako; Jun 23, 2012 at 07:09 PM.

Jun 23, 2012 | 07:07 PM

#46

KevinK

Thread Starter

Drifting

Joined: Jun 2007

Posts: 1,404

Likes: 1

From: Ansonia/NYC CT

Seems like the one I want, then, is VC1838...it's a slight drop from the one I have, the VC1853. I'm not sure, but I'm pretty sure, that was the one I told my buddy to look for (he tows cars, and has "hookups" at junk yards)...I sent him an email with the part number I got off of Lars's vac advance page. I can check later, make sure he's not out and about looking for the wrong thin. Oh, and yes, it's a stock replacement HEI distributor from Accel. I was going to get an MSD dizzy, but it wasn't in the budget, and folks told me the stocker was well up to it, if set up properly.

Jun 23, 2012 | 07:29 PM

#47

63mako

Race Director

Joined: May 2005

Posts: 10,674

Likes: 122

From: Millington Illinois

St. Jude Donor '08-'09

"Budget build" is what hotrodding is all about. I used to run 12's is a 67 camaro that I had $1000 in but hundreds of hours scouring through junkyards and swap meets, days grinding on old 186 heads, swap meet intake and old holley that needed everything. Piecing together a dual exhaust system out of junkyard headers with pipes from old buicks and oldsmobiles with big motors and single exhaust, Removing the inner fenderwells, bumper brackets and bumper ect . It ran as well as the combination of parts I could scrounge could possibly run and got me to work and school every day. Broke a motor mount and busted my distributor cap into pieces powershifting. Ripped out half of the plug wires. Ended up taking my sock off, putting the pieces in place, tying the sock around the cap to hold the pieces together and put the 4 wires with the terminals ripped off in the holes after bending the inner wire around the outer part of the wire and shoving it in the cap holes. Fired it up and drove it home. You do what you can with what you got.

Jun 23, 2012 | 07:40 PM

#48

KevinK

Thread Starter

Drifting

Joined: Jun 2007

Posts: 1,404

Likes: 1

From: Ansonia/NYC CT

Never had anything like that, but I put a lot of time and love into my 150 dollar vortec heads, lol. Only thing I DIDN'T do, that I wish I had known about, was to grind down the seats for the springs, so I could have run a more substantial lift cam.

I drove this thing home from where I got it with a coat hanger holding the drivers side exhaust pipe on. I also had to unplug a cylinder and drive it home once on 7 cylinders, as I ignited a spark plug. That was pretty fun. Ran well for 7 cylinders, to be honest. Didn't really even notice, idled smooth.