Does High Lift Cam Affect Vacuum/Lights?

[fine69]

Hi All,

I've been having problems getting my headlights to function. The lights turn on, and you can hear them trying to actuate... but they do not lift up.

I had installed the Edelbrock Perrformer setup, including a .510 lift cam, so the engine has quite a lope to it.

My question is --- with this high lift, is the vacuum therefore adversely affected, i.e., weaker? If so, does this sound like a likely reason the lights wont actuate? They worked fine before my rebuild. :confused

Thanks.

 

[Jack]

Quite simply ... YES on all counts!

If power brakes ... How are they?
JACK:gap

 

[Jack]

.510" must be Performer RPM ... not just Performer.

Edelbrock 7102 cam is a lot of flat tappet cam for a street 350 ... lotsa intake duration ... 'specially one so dependant upon vacuum.

valve lift .488"/.510"
duration @ 0.050" 234°/244°
ICL 107°
ECL 117°
LSA 112°

JACK:gap

 

[JOE BYRNE]

Hey fine69,

I did the Edelbrock heads and manifold minus cam replacement and have not had a problem with my shades other than they are a bit slower when coming up. Any idea what the vacuum is off your manifold??...just curious and actually unrelated to your headlight problem

 

[vett boy]

It had a little effect on my 69 but not a lot.Sounds like you might have a leak.

 

[fine69]

.510" must be Performer RPM ... not just Performer.

Edelbrock 7102 cam is a lot of flat tappet cam for a street 350 ... lotsa intake duration ... 'specially one so dependant upon vacuum.

valve lift .488"/.510"
duration @ 0.050" 234°/244°
ICL 107°
ECL 117°
LSA 112°

JACK:gap

Yes, you're right, it's a Performer RPM. My typo.

 

[fine69]

Hey fine69,

I did the Edelbrock heads and manifold minus cam replacement and have not had a problem with my shades other than they are a bit slower when coming up. Any idea what the vacuum is off your manifold??...just curious and actually unrelated to your headlight problem

Hi Joe,

Not sure what the vacuum is from the manifold - but it may be related to the light problem since I believe that's where it gets its vacuum... (?)

 

[fine69]

It had a little effect on my 69 but not a lot.Sounds like you might have a leak.

I'm going to order a vacuum hose replacement kit. I hope it's a leak, otherwise, I'm gonna be totally bummed out .... :cry

 

[JOE BYRNE]

Just wondering....I have a Q-jet that is rich and a carb guy asked me what my manifold vacuum was and I told him it was 22 hg off the manifold. He said it was high??? Not sure it's a bad thing....maybe he was high.

 

[JOE BYRNE]

Amazing how these cars will bum you out when something is wrong.

 

[GaryS]

Good answers to your question but your homework isn't complete until you measure the vacuum. Have you done a simple idle vacuum test to see what your vacuum is at idle rpm? Should take all of five minutes with a $30 vacuum gauge set up from Sears.

Gary

 

[JOE BYRNE]

Gary,

What should the manifold vacuum be. I took mine the other night and it is around 22

 

[waterboy1976]

I believe manifold vac should be around 14...

I have the same RPM manifold only I am running 1:6 rollers which makes my lift .544 @50........My lights and power brakes are working just fine....Maybe a little slower but brakes are great...

 

[JOE BYRNE]

why is mine so high...and is it hurting anything

 

[waterboy1976]

That question I can't answer....Im not sure if vac to high wold hurt anything....Im sure someone will chime in here....

 

[GerryLP]

why is mine so high...and is it hurting anything

Joe,

Technically speaking, a high vacuum signal is a sign of good engine health (i.e. the engine does not have bad by-pass, no intake leaks, valves are sealing when closing, etc...); however, one has to make sure that the engine is tuned to the specified timing and engine idle speed.

Having said that, I believe that when tuning the engine, it should be done to the setting at which one obtains the most vacuum signal. For example, on an adjustable carburetor, the idle mixture is set to the highest vacuum signal, then one checks the idle speed and re-adjust if necessary to the correct setting (i.e. 750 rpm on a manual transmission Vette). Timing? The same thing I double check it mostly because if I am starting from scratch with a initial timing of 12 Deg BTC, this will allow me to keep the engine running while I am adjusting the other parameters. So basically, the engine should idle at its best vacuum signal while set at its prescribed idle speed and timing.

GerryLP:cool

p.s. Fine69, perhaps you can tweak the idle speed a bit higher while monitoring your vacuum, and you get a sizable improvement on vacuum signal (remember to use a non-dampened Gage)

 

[JohnZ]

why is mine so high...and is it hurting anything

There's no way it could be 22" Hg. at normal idle rpm; what rpm was the engine at when you checked it?

 

[glen242]

Yes, you're right, it's a Performer RPM. My typo.

I am running a cam (CC XE274) with similar specs, but on a 383. Manifold vacuum @ idle is 13". For my 350 street engine w/HE268 cam and stock heads, I had 15-16" at idle.

That Edel cam seems a little much, on duration, for a stock or near stock build.

I have seen others complain that the Edel. Performer RPM cam was too much for a near stock street engine.

 

[JOE BYRNE]

Idle is at 900.....that is what they call for on a 73

 

[waterboy1976]

That Edel cam seems a little much, on duration, for a stock or near stock build.

I have seen others complain that the Edel. Performer RPM cam was too much for a near stock street engine.

I love that cam in mine......such a great lope.......kinda shakes the car at the stop light side to side........rump rump rump rump

although my engine build was far from stock.....