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Topic: asked my question badly about timing

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asked my question badly about timing (1/4)
11/8/11 12:02am

theycallmered
Former Member
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, - Australia

Vette(s):
Second-month production Shark, this 1968E was built up by original owner into 1969 ZR1 (L88 body with LT1 engine) for Club Racing. Body styling is from Maglioli's 1968 L88 "Le Mans" racer

Joined: 10/27/2010
Posts: 54

I asked my question poorly about timing the LT1 circa 1970.

I had expected the Holley 4555's vacuum tube (front of base) to be ported, hence my orginal query. Now I suspect it's not ported vacuum, and the pic would seem to confirm? Would appreciate a second opinion on this.

https://www.c3vr.com/member_uploads/14801_14900/14820/BF23F_4555_assembled_(14)A.jpg

The red arrow indicates where my distributor is connected to the common hose, and the rectangle indicates the tube-in-carbie.

So: all my manuals being silent on the issue, am I right in thinking that timing is set with the vacuum line connected to the distributor? That would be new to me, being accustomed to Autolites and Webers with ported vacuum for the distributor, where the vac hose is disconnected and plugged for setting static timing.

In addition to a confirm or deny, wouldn't mind knowing the reasoning behind having both static and vacuum advance at idle (if that's the case)?

Cheers from Down Under.

(changed large image to link -aapple)

|UPDATED|11/7/2011 9:02:57 PM (AZT)|/UPDATED|

______________
1968E (2nd month production) convertible first registered California 1967 and a retired SCCA race car. It is still race prepped and built up as a '69 ZR1 (announced '69 but not built until '70); i.e., the L88 car with LT1 motor.

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Re: asked my question badly about timing (2/4)
11/8/11 12:09am

Adams' Apple

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Duncanville, TX - USA

Vette(s):
#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
Posts: 20128

That is full-time vacuum there...anything that is BELOW the throttle plates will be full-time vacuum....anything ABOVE the throttle plates will be ported.
The great debate continues...full or ported vac for distributors....the argument works both ways, as it really depends on the usage of the engine. Ported is best for drivers/emissions. Full is best for balls-out, don't give a crap about emissions...

You should, however, always disconnect and plug the vacuum when setting initial timing.

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Joel Adams
C3VR Lifetime Member #56
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(click for Texas-sized view!) NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

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Re: asked my question badly about timing (3/4)
11/8/11 7:32am

lukesvette

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HOWELL, NJ - USA

Vette(s):
1979, Targa Blue (72 Color), Pace Car rear spoiler, L88 hood, Dark blue factory interior, 525HP 406, HD 700R4, 370 gears,Steeroids, composite rear spring, TT IIs wrapped in T/A Radials.

Joined: 5/18/2004
Posts: 6812

Ditto with Joel regarding disconnecting the vac while setting up the timing. Leaving the vac connected will advance the timing while you are trying to set your baseline and figure when you want your advance to come in.

You'll be trying to advance an already advanced distributor... Wacko

Good luck! Big smile

Paul

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Re: asked my question badly about timing (4/4)
11/8/11 8:03am

Many thanks for the feedback. I've never even HEARD of any debate about ported or unported vacuum for dizzies; so I don't have a dog in that fight.

I'm just wanting to time my vehicle correctly so it'll start and run well.

I see that GM calls for the 70 LT1 to be timed with that hose plugged:

so I'll give it my best; though my engine won't even start with 14 degrees of crank-only timing (had to dial it back first). I'm not running the oem transistor ignition, but rather an hei; perhaps that's relevant? In any case, won't be doing more on this until my timing light is repaired or replaced.

Cheers!

______________
1968E (2nd month production) convertible first registered California 1967 and a retired SCCA race car. It is still race prepped and built up as a '69 ZR1 (announced '69 but not built until '70); i.e., the L88 car with LT1 motor.

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