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Topic: Chicken or Egg?

in Forum: C3 Fuel, Emission Control, and Exhaust Systems


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Chicken or Egg? (1/9)
 11/13/08 3:54pm
SportivoGold Member
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San Pedro, CA - USA

Vette(s):
1971, LT-1, T-top, 4-speed (M21), Mulsanne Blue, 3.70 rear, mostly original (sidepipes). 2006, Daytona Sunset Orange Coupe.


Joined: 5/26/2005
Posts: 239

Are you ready for the dumb question of the day?
 
I need to set timing and mixture on my LT-1. I've seen the thread regarding the vacuum-method of setting the timing, and it looks interesting enough to try.
 
My (dumb) question is: do I adjust the mixture first (Holley; vacuum secondary), or do I set the timing first?Confused


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Chicken or Egg? (2/9)
 11/13/08 8:55pm
acplus
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, - Canada

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1972, 1980


Joined: 6/23/2008
Posts: 558

I usually do...Timing, then Carb, then timing, then carb... check timing, fine tune carb. The chicken.
John
Chicken or Egg? (3/9)
 11/13/08 10:18pm
Adams' AppleLifetime Member
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Duncanville, TX - USA

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#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


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Ditto...it ain't gonna all work out with just one adjustment on each. When you change one, it effects the other, so ya have to go back & forth a few times until i just don't get no better...then yer done.

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Joel Adams
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Chicken or Egg? (4/9)
 11/13/08 10:28pm
deeboy59
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visalia, CA - USA

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1981 red with silver interior,350(L-81), 350TH, glass t-tops, aluminium rims, 1980 Black/ Black int., 350 GM crate engine/350TH, 1976 black/ saddle int., L-82 w/headers, holly carb, Hypertech ignition


Joined: 10/27/2006
Posts: 641

Hey Joel, dose this method work for high performance setups(big block w/big cam/ carb) as well ,  especially if one did not know the specks on the cam etc. ?
Chicken or Egg? (5/9)
 11/13/08 11:56pm
Adams' AppleLifetime Member
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Duncanville, TX - USA

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#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas


Joined: 11/8/2003
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The vacuum method works for any type of engine. Granted, an engine with a big cam is gonna be a bit harder to read steady vacuum on, but the end result is still the same...you want the highest vac. reading you can get.
Big cams can also be a little sensitive to the rocker/lifter adjustments...a little looser, or a little tighter can make a huge difference, both in vac. readings, and performance.
Another thing if using the vac. method for timing...make sure there are no vac. leaks to start with!

For those who have never seen/heard of this method, check out these two threads on the subject....some very good info here!

Setting timing

I hate timing lights

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Joel Adams
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Chicken or Egg? (6/9)
 11/14/08 12:39pm
deeboy59
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visalia, CA - USA

Vette(s):
1981 red with silver interior,350(L-81), 350TH, glass t-tops, aluminium rims, 1980 Black/ Black int., 350 GM crate engine/350TH, 1976 black/ saddle int., L-82 w/headers, holly carb, Hypertech ignition


Joined: 10/27/2006
Posts: 641

Thanks Joel .  As usual,  "Your the Man"  !!Thumbs%20Up
Chicken or Egg? (7/9)
 11/14/08 2:04pm
corvette440hpLifetime Member
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Joel, thank you much for enlighting us who haven't see all of that info. Very, very interesting Clap

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Chicken or Egg? (8/9)
 2/13/09 1:21pm
F4GaryGold Member
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Grapevine, TX - USA

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1972 LT-1 convertible with factory air.


Joined: 8/26/2006
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I used this method on my 72 LT-1.  I had to back off the  advance just a little as it would ping at full throttle above 3000 rpm.  I have a newish MSD distributor and I haven't had time to play with the mechanical advance springs.  Also, an LT-1 probably won't get as much vacuum as a regular small block.  I think I got it to about 12-14 inches.  (That's what she said!Shocked). 

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Chicken or Egg? (9/9)
 2/14/09 11:28am
VetteSpecialties
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Mounds View, MN - USA

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70 LT1 coupe, 69 350 HP coupe, 69 390HP 427 coupe, 71 LS5 convert, 85 coupe, 93 coupe


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Please remember that the vacuum method only makes your engine run best at the RPM it was at when you set it.  Ideally, you would have your engine running under slight load at the RPM you most often drive, then set for best vacuum.  If your advance systems are both functioning well and properly calibrated for your engine, this will be close to the setting from doing it at idle.

Larry
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