low vacuum??
Thread Starter
Burning Brakes
Joined: Sep 2005
Posts: 832
Likes: 0
From: Sarasota Florida
low vacuum??
what should the vacuum be for a sbc? my car is probably at like 12-13 hg at idle, but i was told it needs to be atleast 20 hg. if it needs to be higher, how can i tune my engine to get more vacuum?
Drifting
Joined: Oct 2004
Posts: 1,496
Likes: 1
From: Lafayette Louisiana
A stock engine should be higher. I can't say how high, but maybe 15-20"? Your cam, timing and carb settings all effect vacuum. Give some details and you will get more answers.
Mine is at 12-13 with a xe268 and 1.6 rockers, timing at 17 initial.
Mine is at 12-13 with a xe268 and 1.6 rockers, timing at 17 initial.
Last edited by kevinator80; Jun 28, 2007 at 03:39 PM.
Thread Starter
Burning Brakes
Joined: Sep 2005
Posts: 832
Likes: 0
From: Sarasota Florida
stock l-82 heads 1.94"/1.50"
224/234 cam
performer intake and 600 cfm carb
the shortblock itself is a crate engine gm goodwrench 270 hp
Former Vendor
Joined: Aug 2006
Posts: 76,656
Likes: 1,850
From: Jeffersonville Indiana 812-288-7103
St. Jude Donor '08-'09-'10-'11-'12-'13-'14-'15
Here is what we always called the old Fart Chart! Hope this helps you.
Engine Vacuum Old Timer Chart!
Steady 17-22 in hg = normal
Low but steady = late ignition, valve timing or low compression.
Very low = Vacuum leak.
Needle fluctuates as RPM’s Increase. = ignition miss, blown cylinder head gasket, leaking valve or weak spring.
Gradual drop at idle = excessive back pressure in exhaust system.
Intermitted fluctuation at idle = engine miss or sticking valve.
Drifting needle = improper idle mix, adjustment, carbs not synchronized, or minor intake leak.
High but steady = early ignition timing.
Engine Vacuum Old Timer Chart!
Steady 17-22 in hg = normal
Low but steady = late ignition, valve timing or low compression.
Very low = Vacuum leak.
Needle fluctuates as RPM’s Increase. = ignition miss, blown cylinder head gasket, leaking valve or weak spring.
Gradual drop at idle = excessive back pressure in exhaust system.
Intermitted fluctuation at idle = engine miss or sticking valve.
Drifting needle = improper idle mix, adjustment, carbs not synchronized, or minor intake leak.
High but steady = early ignition timing.
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Drifting
Joined: May 2005
Posts: 1,909
Likes: 6
From: Lake Arrowhead - Georgia > 72 Base Coupe & 74 BB Roadster
[QUOTE=kevinator80;1560871989]A stock engine should be higher. I can't say how high, but maybe 15-20"? Your cam, timing and carb settings all effect vacuum. Give some details and you will get more answers.
Mine is at 12-13 with a xe268 and 1.6 rockers, timing at 17 initial.[/QUOTE]
Identical numbers....same camshaft......454!
Mine is at 12-13 with a xe268 and 1.6 rockers, timing at 17 initial.[/QUOTE]
Identical numbers....same camshaft......454!