351c vacuum reading - Vintage Mustang Forums
 
Thread Tools
post #1 of 10 (permalink) Old 05-24-2019, 09:55 AM Thread Starter
Senior Member
 
josephqatarcarguy's Avatar
 
Join Date: Feb 2017
Location: Qatar
Posts: 334
351c vacuum reading

hey, im getting a vacuum reading of 14 at idle, is this low?as rpm increases the reading goes up .... 351c 2v with edelbrock intake and comp cam 256H camshaft... car starts up and runs real smooth ... there is a slight engine vibration.

Also im losing engine oil... no visible leaks/smoking, could it be the intake is leaking internally?


but the car runs/drives real good.
josephqatarcarguy is offline  
Sponsored Links
Advertisement
 
post #2 of 10 (permalink) Old 05-24-2019, 10:20 AM
Senior Member
 
Blues Power's Avatar
 
Join Date: Mar 2010
Location: LI NY
Posts: 4,734
Garage
too many variables to tell if its good or bad

my bone stock 351C 2V with 110K on the clock. my timing at 9 BTDC
vacuum is 20 in park and 17 in drive

when RPM increased the vacuum should go down

my vac gauge is connect to the ported carb port not direct manifold and I have that vacuum tree thingy on the water pump disconnected.

1970 Mach 1 San Jose built Dec 23 1969. Marti 1 of 7. Purchased in 1987. Original family owner of the power train
351C 2v FMX.


1993 GT 13,000 miles, Built 2-12-93 Bought 8/3/93 Auto, 3:27 Axle, cloth, sunroof, AC. Unmolested all original car. Purchased new 8-3-93. still has the factory windshield fluid.
Blues Power is offline  
post #3 of 10 (permalink) Old 05-24-2019, 10:42 AM Thread Starter
Senior Member
 
josephqatarcarguy's Avatar
 
Join Date: Feb 2017
Location: Qatar
Posts: 334
my timing is at 12 Initial
32 Total



Quote:
Originally Posted by Blues Power View Post
too many variables to tell if its good or bad

my bone stock 351C 2V with 110K on the clock. my timing at 9 BTDC
vacuum is 20 in park and 17 in drive

when RPM increased the vacuum should go down

my vac gauge is connect to the ported carb port not direct manifold and I have that vacuum tree thingy on the water pump disconnected.
josephqatarcarguy is offline  
 
post #4 of 10 (permalink) Old 05-24-2019, 10:47 AM
Senior Member
 
Blues Power's Avatar
 
Join Date: Mar 2010
Location: LI NY
Posts: 4,734
Garage
that seems way low
should be 6 initial for factory
. my engine likes a little more.

and 38 total

you need to get your dizzy checked out and calibrated,

1970 Mach 1 San Jose built Dec 23 1969. Marti 1 of 7. Purchased in 1987. Original family owner of the power train
351C 2v FMX.


1993 GT 13,000 miles, Built 2-12-93 Bought 8/3/93 Auto, 3:27 Axle, cloth, sunroof, AC. Unmolested all original car. Purchased new 8-3-93. still has the factory windshield fluid.
Blues Power is offline  
post #5 of 10 (permalink) Old 05-24-2019, 10:50 AM
Senior Member
 
Hemikiller's Avatar
 
Join Date: Jun 2002
Location: Killingworth, CT
Posts: 8,625
Garage
256H is a very small cam for a 351C - 206/206 @ .050" , .468/.468 lift - vacuum reading should be higher at 12* static timing.

I see no reason it shouldn't be able to manage up around 18" of vacuum, but that also depends on static timing and how you have the carb tuned. If you have tweaked and tuned it and the BEST it can manage is 14", you definitely have something going on, whether it's worn rings, bad valves seats etc.

As far as the oil loss, it could be pulling it from under the intake. If you have a friend follow you, let off the gas at 30-40mph and downshift to second. If it puffs a bunch of gray smoke out the tailpipes, then you have either an intake leak, or your rings are giving up the ghost.


Quote:
Originally Posted by Blues Power View Post
too many variables to tell if its good or bad

my bone stock 351C 2V with 110K on the clock. my timing at 9 BTDC
vacuum is 20 in park and 17 in drive

when RPM increased the vacuum should go down

my vac gauge is connect to the ported carb port not direct manifold and I have that vacuum tree thingy on the water pump disconnected.
Vacuum gauge should always go on manifold vacuum, ported vacuum is 0 at idle.


Quote:
Originally Posted by Blues Power View Post
that seems way low
should be 6 initial for factory
. my engine likes a little more.

and 38 total

you need to get your dizzy checked out and calibrated,
Agree his total timing is low, but let's focus on the oil consumption/low vacuum issue, as distributor calibration/total timing has nothing to do with idle vacuum readings.

Nothing worthwhile is ever quick, cheap or easy, those that can't do, complain

71 Mach 1

HOLLEY TECH PAGES
FORD OE TACH HOOKUP FORD OE TACH HOOKUP w/MSD (pg 7)

Last edited by Hemikiller; 05-24-2019 at 10:57 AM.
Hemikiller is offline  
post #6 of 10 (permalink) Old 05-24-2019, 11:05 AM
Senior Member
 
Blues Power's Avatar
 
Join Date: Mar 2010
Location: LI NY
Posts: 4,734
Garage
yeah i meant the dizzy can not the gauge. post fixed.

1970 Mach 1 San Jose built Dec 23 1969. Marti 1 of 7. Purchased in 1987. Original family owner of the power train
351C 2v FMX.


1993 GT 13,000 miles, Built 2-12-93 Bought 8/3/93 Auto, 3:27 Axle, cloth, sunroof, AC. Unmolested all original car. Purchased new 8-3-93. still has the factory windshield fluid.
Blues Power is offline  
post #7 of 10 (permalink) Old 05-24-2019, 11:05 AM Thread Starter
Senior Member
 
josephqatarcarguy's Avatar
 
Join Date: Feb 2017
Location: Qatar
Posts: 334
I will have a friend follow me and try that mate , just a question how come the car runs brilliantly..pulls hard ... starts right up .... no issues except the oil consumption?
Quote:
Originally Posted by Hemikiller View Post
256H is a very small cam for a 351C - 206/206 @ .050" , .468/.468 lift - vacuum reading should be higher at 12* static timing.

I see no reason it shouldn't be able to manage up around 18" of vacuum, but that also depends on static timing and how you have the carb tuned. If you have tweaked and tuned it and the BEST it can manage is 14", you definitely have something going on, whether it's worn rings, bad valves seats etc.

As far as the oil loss, it could be pulling it from under the intake. If you have a friend follow you, let off the gas at 30-40mph and downshift to second. If it puffs a bunch of gray smoke out the tailpipes, then you have either an intake leak, or your rings are giving up the ghost.


Quote:
Originally Posted by Blues Power View Post
too many variables to tell if its good or bad

my bone stock 351C 2V with 110K on the clock. my timing at 9 BTDC
vacuum is 20 in park and 17 in drive

when RPM increased the vacuum should go down

my vac gauge is connect to the ported carb port not direct manifold and I have that vacuum tree thingy on the water pump disconnected.
Vacuum gauge should always go on manifold vacuum, ported vacuum is 0 at idle.


Quote:
Originally Posted by Blues Power View Post
that seems way low
should be 6 initial for factory
. my engine likes a little more.

and 38 total

you need to get your dizzy checked out and calibrated,
Agree his total timing is low, but let's focus on the oil consumption/low vacuum issue, as distributor calibration/total timing has nothing to do with idle vacuum readings.
josephqatarcarguy is offline  
post #8 of 10 (permalink) Old 05-24-2019, 11:26 AM
Senior Member
 
Blues Power's Avatar
 
Join Date: Mar 2010
Location: LI NY
Posts: 4,734
Garage
Quote:
Originally Posted by Blues Power View Post
too many variables to tell if its good or bad

my bone stock 351C 2V with 110K on the clock. my timing at 9 BTDC
vacuum is 20 in park and 17 in drive

when RPM increased the vacuum should go down

my dizzy vac can is connect to the ported carb port not direct manifold and I have that vacuum tree thingy on the water pump disconnected.
revised

1970 Mach 1 San Jose built Dec 23 1969. Marti 1 of 7. Purchased in 1987. Original family owner of the power train
351C 2v FMX.


1993 GT 13,000 miles, Built 2-12-93 Bought 8/3/93 Auto, 3:27 Axle, cloth, sunroof, AC. Unmolested all original car. Purchased new 8-3-93. still has the factory windshield fluid.
Blues Power is offline  
post #9 of 10 (permalink) Old 05-24-2019, 01:45 PM
Senior Member
 
Hemikiller's Avatar
 
Join Date: Jun 2002
Location: Killingworth, CT
Posts: 8,625
Garage
Quote:
Originally Posted by josephqatarcarguy View Post
I will have a friend follow me and try that mate , just a question how come the car runs brilliantly..pulls hard ... starts right up .... no issues except the oil consumption?

How an engine runs is not always an indicator of overall engine health. I had a C-30 Chevy dually that ate a quart of oil every 500 miles - still started right up, ran strong and pulled well, but it was tired and ready for a rebuild. Engines that are cared for can just wear out gradually and you may not notice the difference until you actually have a metric to judge against - quarter mile times, dyno runs etc. Not saying your engine is definitely ready for a rebuild, but have you ever done a compression and leakdown test?

Nothing worthwhile is ever quick, cheap or easy, those that can't do, complain

71 Mach 1

HOLLEY TECH PAGES
FORD OE TACH HOOKUP FORD OE TACH HOOKUP w/MSD (pg 7)
Hemikiller is offline  
post #10 of 10 (permalink) Old 05-24-2019, 02:34 PM Thread Starter
Senior Member
 
josephqatarcarguy's Avatar
 
Join Date: Feb 2017
Location: Qatar
Posts: 334
I had a garage here do a compression test and it was fine ...
The oil consumption only started after the cam change ... any pointers??
Quote:
Originally Posted by Hemikiller View Post
Quote:
Originally Posted by josephqatarcarguy View Post
I will have a friend follow me and try that mate , just a question how come the car runs brilliantly..pulls hard ... starts right up .... no issues except the oil consumption?

How an engine runs is not always an indicator of overall engine health. I had a C-30 Chevy dually that ate a quart of oil every 500 miles - still started right up, ran strong and pulled well, but it was tired and ready for a rebuild. Engines that are cared for can just wear out gradually and you may not notice the difference until you actually have a metric to judge against - quarter mile times, dyno runs etc. Not saying your engine is definitely ready for a rebuild, but have you ever done a compression and leakdown test?
josephqatarcarguy is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Vintage Mustang Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in













Similar Threads
Thread Thread Starter Forum Replies Last Post
Anyone using manifold vacuum advance? PonyandTrap Vintage Mustang Forum 15 05-05-2019 07:18 AM
67 Tilt column & AC Vacuum lines - different sizes - how to run both systems? ddaytona1 Vintage Mustang Forum 5 08-12-2018 01:32 AM
Low Vacuum Reading RestoMike66 Vintage Mustang Forum 9 08-03-2018 07:11 AM
What Would Be a Good Vacuum Reading 1968Cally Vintage Mustang Forum 11 04-29-2018 09:17 AM
Holley Vacuum Secondaries Not Opening On Dual Quad Setup LeeFred Vintage Mustang Forum 9 03-25-2018 03:54 AM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are Off

 
For the best viewing experience please update your browser to Google Chrome