why very high vacuum?
Thread Starter
Racer
Joined: Jan 2013
Posts: 302
Likes: 2
From: Sayville New york
why very high vacuum?
can not understand why this engine has a steady 24" of vacuum at 750 rpm.steady needle and checked with another gauge. engine 408" sbc , hyd.roller cam with .541 lift intake and exhaust,231/241 @.050, LSA 112. CR 10.5, AFR 195,air gap ,holley 750 hp,1 7/8" headers with msd ignition.so much vacuum headlight doors remain open (with all new hoses,canister,etc.)and only shut after engine is shut down and i can manually close.
Race Director
Joined: May 2006
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Is the issue you have the high vacuum or the doors not closing?
where are you taking the vacuum reading?
The door problem is related to the red and green lines, I assume you have a 71, in the lower part of the diagram below it has nothing to do with your vacuum readings.
http://repairs.willcoxcorvette.com/w...schematics.pdf
where are you taking the vacuum reading?
The door problem is related to the red and green lines, I assume you have a 71, in the lower part of the diagram below it has nothing to do with your vacuum readings.
http://repairs.willcoxcorvette.com/w...schematics.pdf
Last edited by MelWff; Feb 20, 2017 at 11:51 AM.
Safety Car
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From: Austin Texas
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too much vacuum is not keeping headlights up, more likely leak or failing vacuum valve.
I have never seen an engine pull 24" of vacuum, vacuum is direct result of timing setup.
I have never seen an engine pull 24" of vacuum, vacuum is direct result of timing setup.
Race Director
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From: Long Island
Engine Vacuum can be determined from how the cam was degreed. Timing of the distributor, valve lift etc.
When you downshift to slow the car, If I remember right the vacuum will spike. So the vacuum system should see a spike and the headlights don't open.
I would think that the high vacuum would not affect the operation of the headlights - unless the switch is by-passing, the over-ride is pulled, a hose is plugged or the hoses are not connected properly.
I would check the vacuum at the control valve as a start. Especially the control line.
Race Director
Joined: Sep 1999
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From: Plano TX
Headlights are up whenever the small diameter control hose that goes to the relays between the headlights does not have vacuum.
With engine running, disconnect the small hose from one of the vacuum relays, put another hose on it and suck a vacuum on that hose.
If headlight closes your problem is a vacuum leak in the control circuit. .If it doesn't close the problem is the relay.
With engine running, disconnect the small hose from one of the vacuum relays, put another hose on it and suck a vacuum on that hose.
If headlight closes your problem is a vacuum leak in the control circuit. .If it doesn't close the problem is the relay.
Thread Starter
Racer
Joined: Jan 2013
Posts: 302
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From: Sayville New york
the vacuum reading is taken directly from intake manifold at rear of carb.i install two new accumulators,two relays all new hoses. timing is 18 degrees initial ,36 total at 2500 rpm and 52 degrees with distributor adj. vacuum connected at 3000rpm.cam is set 2 degrees advance.after you shut headlights one stays open until you turn engine off and close with hands (manual) right now crazy 24 " of vacuum has me stumped.engine has 700 miles on it .also i checked compression while warm and "buried the gauge". engine starts on 1/4 crank turn actually explodes with instant start shuts off instant feels more like a diesel engine and power is incredible but why this vacuum? i have 11 corvettes three BB never saw any thing like this.in all honestly this c-3 would beat my 427/435hp 1967 coupe by three or more car lengths in 0 to 60 drag race.you would think this fairly aggressive cam would be in the 16 to 18 HG area of vacuum.i feel something is wrong forgetting the lights for now.
Last edited by Captain bob; Feb 20, 2017 at 03:16 PM.
Team Owner
Joined: Jan 2006
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From: Crossville TN
My guess is that your vacuum gauge needs calibration. New engines might produce 22" Hg. And too much vacuum is NOT a problem. The headlight actuators use vacuum to OPEN and to CLOSE the headlamp buckets; the higher, the better.
If they won't close, either the vacuum actuators or [more likely] the vacuum relays are malfunctioning.
If they won't close, either the vacuum actuators or [more likely] the vacuum relays are malfunctioning.
Thread Starter
Racer
Joined: Jan 2013
Posts: 302
Likes: 2
From: Sayville New york
i don`t know how that over-ride under the steering wheel works or even why you need it i guess i should try to find a owners manual.is the wheel in the middle suppose to be fully turn clockwise or counterclockwise in normal usage .?
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Race Director
Joined: Sep 1999
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From: Plano TX
The override does the following:
Push in: vacuum goes through the override and to the headlights.
Pull out: The port connected to engine vacuum is blocked. The port to the headlights is open. Result: Headlights go up.
You use it to clean the lights for instance. Reason GM put it there was because people used to drive C3s in the winter and you were supposed to leave the lights up all winter so they didn't freeze shut.
Push in: vacuum goes through the override and to the headlights.
Pull out: The port connected to engine vacuum is blocked. The port to the headlights is open. Result: Headlights go up.
You use it to clean the lights for instance. Reason GM put it there was because people used to drive C3s in the winter and you were supposed to leave the lights up all winter so they didn't freeze shut.
Thread Starter
Racer
Joined: Jan 2013
Posts: 302
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From: Sayville New york
both buttons are in the in position (thanks zwede makes sense now; ok two buttons left and right head light and wheel in the middle was once the wiper over-ride now disconnected due to long hood)
Team Owner
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Thread Starter
Racer
Joined: Jan 2013
Posts: 302
Likes: 2
From: Sayville New york
easy mike every day is a learning day with these corvettes. my friend ask me to buy a c-3 so i found a 1969 convertible with hard top and every option made except top engine, you name it then i saw this ridiculous rear window defroster cut into the rear hatch (ugly) anyways nice car, no rust $16,000 with 350/350hp engine .unmolested car with A/C he ask me about those same buttons / wheel under steering (i have a idea relating to lights and wipers but don`t know exactly
Race Director
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you do have the correct carburetor base gasket for whatever is under the air cleaner?
with engine off and primary and secondaries wide open you see no restriction from gasket looking down the throats?
that 18 initial contributes a lot to your vacuum readings
with engine off and primary and secondaries wide open you see no restriction from gasket looking down the throats?
that 18 initial contributes a lot to your vacuum readings
Thread Starter
Racer
Joined: Jan 2013
Posts: 302
Likes: 2
From: Sayville New york
MelWiff i just checked holley carb. primary and secondary butterflies at WOT. both are perfectly clear. i have been around chevy engines for 55 years and i have only witness a engine sound like mine 30 years ago.a 66 vette 431" BB that Zull had built for door slammer class. CR was 18 and wot set for 11,000 rpm with two speed powerglide. change bearings every 11 runs . anyways it sounded the same way when engine toggle switch was switched off the engine sounded like it instantly seized.24HG.vacuum bothers the hell out of a old man cannot figure this out especially with this cam.BTW. when lunati cam was installed "straight up" as purchase she showed 4 degrees advance with a 2 foot dia. professional degree wheel so the" master" purchase a million dollar timing chain,cam sprocket,crank sprocket from Germany with EIGHT keyway notches for advance/retard and he back off factory 4 degree advance to 2 degrees .i wonder?
Last edited by Captain bob; Feb 21, 2017 at 12:51 PM.
