Timing is Everything - Team Camaro Tech
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post #1 of 24 (permalink) Old May 19th, 14, 04:33 PM Thread Starter
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Timing is Everything

I wanted to report that I have been putting many miles on the car and it is running incredibly well and has been a blast to drive. Put 140 on yesterday and got 11 mpg.

I do have one question for which I am seeking some advice.

Just as a refresher, this is a 496 BB and I have 18 degrees of initial timing, total of 38 + 12 VA.

As I said, it runs great, however, with only 7hg of vacuum at idle, if I pull away from a dead stop and don't give quite enough gas, the vacuum drops and the timing falls back to the initial and it is a pig. If I give it a little too much to avoid this situation, I spin the tires.

If I turn up the idle speed to try to compensate I have to deal with engine run on more often than not. If I give the initial, more advance, then i have to deal with limiting the mechanical advance on an HEI.

So, with all of that said, what are the thoughts on changing the VA can to one that will provide full advance (if there is one) at less than the 5hg that I have as the minimum on the current adjustable unit?

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post #2 of 24 (permalink) Old May 19th, 14, 05:07 PM
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Re: Timing is Everything

Assuming you are running full manifold vacuum, get a B-28 stamped vacuum can (VC-1810 part number). This will start the vac advance at 4" of vacuum, and be all in by 8"...

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post #3 of 24 (permalink) Old May 19th, 14, 05:46 PM
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Re: Timing is Everything

My Sister just picked up a B28 can for me from Autozone since no one in Canada sells them. My vacuum at idle is pulling 8-9" @ 16* initial, 36* total and my mixture screws are set where I want them. I can get 10" if I open up my mixture screws more but then it's too rich at idle. My OEM can in my 70 Z28 is a 201 15 and is only getting me an additional 3*. I haven't swapped it out yet but I know it will get me a better idle. All other driving conditions are fine for me with the stock can.

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post #4 of 24 (permalink) Old May 19th, 14, 06:56 PM
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Re: Timing is Everything

Quote:
I have 18 degrees of initial timing, total of 38 + 12 VA.
so
Intial of 18
20 degs in the cent
what rpms is the 38 degs all in at , no VA attached?
12 in the VA
Correct?
u also state its an HEI,, have u put more degs in the cent from the off shelf settings... HEI have a lot of VA, less Cent than non EGR engines.
Also NEVER go above 40/42 degs for intial+cent+VA without dialing timing/ AFRs in with a knock sensor you have 18 +20+12=50 degs

Also need to know at what vaccum the VA starts to activate and the vaccuum its all in at
This NEEDS to be done with a vaccuum pump without engine running.

u have a hestatition/ running on issue....
Both of these can be related directly to over advancing/ under advancing at low rpms and your mixture/ AFRs at these rpms

So next question... have u put the AFRs into ball park numbers and THEN set up your 'best' timing?

Also how wild is the cam duration/ overlap/ lifts... if quite wild getting to track specs u may require, more idle advance (intial +VA) and the VA MUST be all in at the idle vaccuum,

Without knowing the answers to these questions ANYTHING u do will be just hit n miss , trial and error stuff

38 is more than what modern head design and fuel will require
So 1st thing suggest is get that 38 deg down to 32/34 at around 3000/ 3200 rpms
That will then take the intial down to around 12/ 13 degs.
With the VA having 12 degs and intial of ASUMING it will be fully activated at that engine vaccuum.. this will give u an idle of 24 degs... which as I said before unless u have a track cam is way too high.

Next question are your mixture screws AND idle speed screws within the factory specs of around 1 1/2 turns +/- 1/2 turn?
If not u NEED to set your seconday butterflies so that they are.. and if not this is most proberly the cause of the run on and hestation because everything in the timing has been compensated to patch this error in carb setting up....this needs to be fixed , not patched.

My Spelling is not incorrect...it is creative

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post #5 of 24 (permalink) Old May 19th, 14, 07:27 PM
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Re: Timing is Everything

Quote:
Originally Posted by Steptoe View Post
so
Intial of 18
20 degs in the cent
what rpms is the 38 degs all in at , no VA attached?
12 in the VA
Correct?
u also state its an HEI,, have u put more degs in the cent from the off shelf settings... HEI have a lot of VA, less Cent than non EGR engines.
Also NEVER go above 40/42 degs for intial+cent+VA without dialing timing/ AFRs in with a knock sensor you have 18 +20+12=50 degs
It all depends on how you dizzy is curved. 12 initial and 25 cent (No VA attached) should work ok. +50 isn't a problem because this will only happen at cruise when not under load. When you open the throttle to accelerate the vacuum drops and advance drops to your all in # if your rpm is high enough to have full mechanical advance.

For most engines I go 12 + 25 all in at 2500-3000.

Your idle will be 24 VA attached and will immediately drop very close to initial when you step on the go pedal.

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post #6 of 24 (permalink) Old May 20th, 14, 12:24 AM
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Re: Timing is Everything

Quote:
+50 isn't a problem because this will only happen at cruise when not under load.
And u are saying detonation cant happen at cruise?
Which is exactly why LPG got a bad name back in the 70s and 80s with bearing/ valve rescission etc.
Detonation can and will happen at low loads ...it doesnt need to be auditable..Start dialing in engines with data loggers knock sensors , imap , tps o2....become a real eye opener... U can throw so much of the 'old school' concepts right out the window.

My Spelling is not incorrect...it is creative

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post #7 of 24 (permalink) Old May 20th, 14, 07:44 AM
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Re: Timing is Everything

If you're cruising at 60 mph it takes about 50 hp to maintain cruise speed.

If you're dizzy is curved to all in at 3000 you won't be all in at cruise speed unless you have pretty low gears. Even small pedal movement will drop vacuum and retard spark. Hard on the throttle will bring you back to initial plus mechanical at whatever the advance is at the current rpm.

Tuning with wide band is a great way to go as well as data logging. However for a lot of guys this is not practical.

The other terms you're tossing out such as TPS, Map, MAF and O2 are used in EFI setups not much for carbs

I'm not familiar with knock sensors that work with non computer controlled engines? When the knock sensors detect detonation the computer pulls timing. And data loggers are used extensively in the racing world but can be expensive.

Old school we would advance until detonation and back off a couple degrees.

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post #8 of 24 (permalink) Old May 20th, 14, 10:12 AM
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Re: Timing is Everything

The B28 can at Autozone is sold under the part # DV1810.

You can order it online and have it shipped to your house or the local store.

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post #9 of 24 (permalink) Old May 20th, 14, 04:28 PM
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Re: Timing is Everything

Quote:
If you're dizzy is curved to all in at 3000 you won't be all in at cruise speed unless you have pretty low gears. Even small pedal movement will drop vacuum and retard spark.
ok u are cruising with say a 308 diff around 2700 a 355 close onm 3000
Considering the curve is elipical and the top is close to horozonal then at least 90/95% of the cent is all in...say 2900 of 3100 rpms and 34 degs
So there is around 30 degs there
Now cruising with a bit of a cam at those rpms u will have 15 1/2 to 18 deg of vaccuum.
And considering the VA will be all in at something below 10 or 12
there is another 12 degs there
Now u are sitting right on the limits of the 40/42
Not have AFRs correctly set and increase speed a couple mph ....u are over into dangerous area...And the sad part is u will not know it untill something fails in the engine over time
This will then be blamed on the engine builder or part failure... NOT the tuning specs established when the engine was dialed

Quote:
I'm not familiar with knock sensors that work with non computer controlled engines?
u do not need a computer controlled engine to fit knock O2 imap or throttle position sensors....
Quote:
And data loggers are used extensively in the racing world but can be expensive.
No they are not.. this is the 21st century....the computers that put the man on the moon cost millions.. today we have more computing power in our smart phones
My data logger paid for its self just in the savings in fuel in the 1st 6 months
Quote:
The other terms you're tossing out such as TPS, Map, MAF and O2 are used in EFI setups not much for carbs
Really? any techo on a dyno will hook up these to your engine if they know what they are doing.. and if the dyno is too old then they will have a modest data logger like an innovate unit that will do all that... on non EFI, carbed, non computer engines.
This is the 21st century.

Power is efficiency... and so is economy which is why carbs have idle , cruise/economy and power circuits separately... and the dizzy also has power (cent) idle (initial+VA) and economy/cruise VA separately

Something so basic that most ppl just cant seem to under stand....

Quote:
Old school we would advance until detonation and back off a couple degrees.
yep.. keep in mind I have been messing around for over 40yrs now..
A note on that "old school" BS
Advance an engine and it sounds more powerful... put it on the track and it is slower... its like an optical illusion....something we stopped doing in the late 70s early 80s.
The best position is to retard ill withing a couple degrees there is a noticeable drop off in power (measured distance/stop watch) and economy.. then increase 2 or 3 degrees.

look we spend thousands building the engines ,10s of thousands on the car.. 1000s on the tools in the workshop, then when it comes to dialing the engine into the car we choke on a few 100 dollars for a data logger... but are quite willing to spend even more on a dyno tune which simply tunes to the best of what is in the current carb/ dizzy settings and stil not have the full potential.. usually not even close

I just dont get the above logic.. doesnt make even basic common sense... for a few 100 bucks.

And to clarify something else
Dailing an engine in...that is establishing the tuning pionts ... like the tuning specs in the workshop manual u tune the car to for best performace/ economy
Tuning an engine... that simply re setting , if required , the carb , dizzy to the specs established from the dialing in
or as most tuners do... set the engine to the best they can with the current carb/ dizzie setting in the engine.. which are usually way wrong... patching maybe a better term.

So ppl have a choice.
Spend a small fotune on the car... then at the end spend weeks and money making do with what u have.
OR
Spend a few 100 dollars, have a very nice tool in your arsenal in the tool box, and dial the engine in in the same manner as car manufactures do to get the ultimate performance/ economy

And get over the 'old school' "Im not interested in economy BS" dial the engine correct in and 'unfortunately' u get the dreaded "ecomomy " thrown in for free.
Old school tuning mid 14s 18 mpg to 21st century tools [email protected] mph and 18mpg to 32 mpg couple road trips and paid for the data logger.

I now use it with a couple m8 setting up their cars , and even on our old 1912 to 1951 vintage British technology cars.

Before simply ordering a given VA.. u NEED to estblish your best engine specs
The carb AFRs in ball park
The mixture/ idle speed/ butterflies sorted
Then find the best STABLE idle advance setting
The best total advance setting.
Then (if no knock sensor) adjust the VA vaccuum characteristics and the nuber degs in it and the cent to suit and stil be under 40/42 degs

ANY ONE of the above changes will change the vacuum characteristics of the engine which will most properly mean the VA canister u get will be the wrong specs.

How to change degs in the cent, change degs in the VA how to change the vaccuum start AND the vaccuum stop points in the VA I have described many times in these forums over the yrs.

If u cant be bothered to read (not skim) all of the above u have no interest in getting your engine to run as well as it could.

My Spelling is not incorrect...it is creative

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post #10 of 24 (permalink) Old May 20th, 14, 04:57 PM
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Re: Timing is Everything

Well I installed the B28 vacuum advance can and the car idles like crap, so bad it fouled all the plugs. At idle with the vacuum connected it gave me 34* of timing.

I couldn't adjust the idle mixtures screws and my timing and idle was not steady. The idle sounded like a pro charger engine, up and down with the idle. Initial timing with vacuum plugged is 17* and total advance is 37*. Full manifold vacuum is 8" Hg.

So I cleaned the plugs and swapped out the B28 can for the stock 201 15 can. Runs better the way I had it before the B28 can.

Mark 70 Z28 M22 3.73 Z21 Z87 - Lunati 20120121 Roller Cam

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post #11 of 24 (permalink) Old May 20th, 14, 06:10 PM
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Re: Timing is Everything

Quote:
The idle sounded like a pro charger engine, up and down with the idle.
The usual reason for that is the VA is not all in at the idle rpm vaccuum..What happens is the car fires up, pulls on the VA adding advance to the initial advance.. the idle speed increases as the advance increases... then the engine basically runs out of enough fuel , runs rough then slows down... the VA increases , the advance increases ands repeats.

A very similar situation can happen if cent weight are too light and swing out at idle rpms

I repeat
Quote:
Before simply ordering a given VA.. u NEED to estblish your best engine specs
The carb AFRs in ball park
The mixture/ idle speed/ butterflies sorted
Then find the best STABLE idle advance setting
The best total advance setting.
Then (if no knock sensor) adjust the VA vaccuum characteristics and the nuber degs in it and the cent to suit and stil be under 40/42 degs

ANY ONE of the above changes will change the vacuum characteristics of the engine which will most properly mean the VA canister u get will be the wrong specs.

My Spelling is not incorrect...it is creative

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post #12 of 24 (permalink) Old May 20th, 14, 06:13 PM
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Re: Timing is Everything

Quote:
Originally Posted by COPO View Post
So I cleaned the plugs and swapped out the B28 can for the stock 201 15 can. Runs better the way I had it before the B28 can.
Have you got a friend you can borrow a carb from so you can swap and see if that's the problem ?

That's what I would try first.

I don't like big cams, but all of my friends who run them use double-pumpers.

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post #13 of 24 (permalink) Old May 20th, 14, 07:04 PM
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Re: Timing is Everything

This sounds awefully familiar to what I was going through a couple years back...

How "steady" is the vacuum? if it is erratic, it couls be a wiped cam lobe, which will wreak havoc on trying to stabilize your idle...

My vacuum would bounce between 6-8, and would not "smooth" out---I Had two wiped cam lobes...

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post #14 of 24 (permalink) Old May 20th, 14, 07:40 PM
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Re: Timing is Everything

I don't think it's the carb cause my old solid lifter motor ran fine. The plugs look decent with the roller motor and stock can. After installing the B28 can and idling for 30 min trying to set it up the plugs were coated with black sticky crap.

Before installing the B28 can the car ran fine. It has 69 front jets and both power valves are 5.0 and the plugs are R45. The R43's were too cold. I leaned out the idle mixture screws to 1.5 turns out and have a vacuum reading of 8-9". When they were 2 turns out my vacuum was 10" and that's why I chose the 5.0 PV. I think they'll be fine running between 8-9" Hg. I have to recheck my vacuum readings with a new vacuum gauge I picked up.

I've dialed in 36* total advance with 16* initial. Using the B28 can, my timing jumps to 34* at idle. Way too much for this motor since my initial is 8* more than a stock LT1 with factory specs of 8*.

I can see it on the plugs and a bit of crap out of the tail pipes. After swapping the can back to the stock one, I don't see anything coming out of the tailpipes. Prior to the can swap my plugs looked good. Even though the stock can just gives me an additional 3* of timing, I can live with that. I could probably cut down the vacuum on the B28 can by rigging up an inline adjustable vacuum knob but why bother I'm thinking.

I have a 3310 750 Holley for my spare carb but it would need a kit if I was to try it but I know this 4555 orig carb, I've had it for 33 years and have rebuilt it many times and have been using it straight for about 20 yrs.

If it doesn't rain the next day or two, I'll take the car out so the plugs can get into their cleaning mode.

Mark 70 Z28 M22 3.73 Z21 Z87 - Lunati 20120121 Roller Cam

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post #15 of 24 (permalink) Old May 20th, 14, 07:44 PM
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Re: Timing is Everything

Quote:
Originally Posted by keithl1967 View Post
This sounds awefully familiar to what I was going through a couple years back...

How "steady" is the vacuum? if it is erratic, it couls be a wiped cam lobe, which will wreak havoc on trying to stabilize your idle...

My vacuum would bounce between 6-8, and would not "smooth" out---I Had two wiped cam lobes...
The cam is a Lunati Retro LT1 roller. I can get the vacuum pretty steady at 10" when the mixture screws are at 2 turns but I don't want it that rich, so with 1.5 out I get close to 9 but it will drop to 8 for a sec. I know how a car runs with wiped lobes. I've have 2 solid lifter cams. The 1st got me about 43,000 mi before wiping 3 lobes. The 2nd solid lifter cam got me 8700 mi with 1 wiped lobe while using the proper oils with enough ZDDP. This roller motor has about 3 hrs on it and runs well so far.

Lunati Hydraulic Roller Cam 20120121
Advertised Duration (Intake/Exhaust) 278/288
•Duration @.050" (Intake/Exhaust) 232/242
•Gross Valve Lift (Intake/Exhaust) .507"/.507"
•Lobe Separation 112
•Intake Center Line 108
•RPM Range 2000-6400

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Last edited by COPO; May 20th, 14 at 07:59 PM.
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