289 Vacuum Gauge Reading
03-19-2017, 11:18 PM
#1
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Thread Starter
Join Date: Jan 2017
Location: Houston, Texas
Posts: 82
289 Vacuum Gauge Reading
I was checking the tuning on my 67 289 with a vacuum gauge and noted aside of it being on the low side of the normal range (i.e. 18-20in mg) that under acceleration the vacuum increases sharply. In my experience this isnt normal. Shouldn't it be decreasing under acceleration?
I also have the problem that I can only turn the dizzy so far clockwise before the vacuum advance nipple hits the coolant hose. Any ideas the fix this issue as well?
https://www.dropbox.com/s/mru1kp6qy8...%20PM.mov?dl=0
I also have the problem that I can only turn the dizzy so far clockwise before the vacuum advance nipple hits the coolant hose. Any ideas the fix this issue as well?
https://www.dropbox.com/s/mru1kp6qy8...%20PM.mov?dl=0
03-21-2017, 12:58 AM
#2
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Join Date: Dec 2005
Location: Hills of California
Posts: 5,208
Thats close to normal. (totally depends on cam) sounds like it running well so there is not likely a vac leak
at 850 rpm I get 14" (this is idle) hot engine (cold engine makes way less vac)
under light acceleration vac will drop BUT on say level ground in 2nd gear higher rpm will give higher vac readings. So vac will drop as you accelerate to 30mph then as you back off to maintain 30mph vac may read 18ingh for example in the same conditions vac may read 21inhg at 40mph in 2nd gear.
In the video you can see vac drop as the engine accelerates and then come up quickly as it holds rpm then revs down.
No load quick rpm changes will give large vac spikes like you saw.
under load at WOT in any gear vac will be zero
The more you lug the engine the quicker vac will drop off. half throttle accel in 5th gear at 40mph is going to cause vac to drop into the 2-3" range
half throttle accel in 1st at 10mph could up around 12"+
at 850 rpm I get 14" (this is idle) hot engine (cold engine makes way less vac)
under light acceleration vac will drop BUT on say level ground in 2nd gear higher rpm will give higher vac readings. So vac will drop as you accelerate to 30mph then as you back off to maintain 30mph vac may read 18ingh for example in the same conditions vac may read 21inhg at 40mph in 2nd gear.
In the video you can see vac drop as the engine accelerates and then come up quickly as it holds rpm then revs down.
No load quick rpm changes will give large vac spikes like you saw.
under load at WOT in any gear vac will be zero
The more you lug the engine the quicker vac will drop off. half throttle accel in 5th gear at 40mph is going to cause vac to drop into the 2-3" range
half throttle accel in 1st at 10mph could up around 12"+
Last edited by Gun Jam; 03-21-2017 at 01:00 AM.
03-21-2017, 06:08 AM
#3
Check Your Timing !!
I was checking the tuning on my 67 289 with a vacuum gauge and noted aside of it being on the low side of the normal range (i.e. 18-20in mg) that under acceleration the vacuum increases sharply. In my experience this isnt normal. Shouldn't it be decreasing under acceleration?
I also have the problem that I can only turn the dizzy so far clockwise before the vacuum advance nipple hits the coolant hose. Any ideas the fix this issue as well?
https://www.dropbox.com/s/mru1kp6qy8...%20PM.mov?dl=0
I also have the problem that I can only turn the dizzy so far clockwise before the vacuum advance nipple hits the coolant hose. Any ideas the fix this issue as well?
https://www.dropbox.com/s/mru1kp6qy8...%20PM.mov?dl=0
The conditions you describe (low vacuum; vacuum pot interference) indicate a distributor that is a tooth off.
If you are still running a "points" distributor, ditch it for an electronic type -- in the long run, they'll give more power, increase fuel mileage, and hold a tune better and longer.
At your altitude (Houston), your stock cam should give a steady 19-20 inches at 800 rpms.
Bosch Double-Iridium plugs gapped at .040 for a long-life tuneup.
Good Luck !!
03-21-2017, 12:29 PM
#4
1st Gear Member
Thread Starter
Join Date: Jan 2017
Location: Houston, Texas
Posts: 82
Check your ignition timing with a good (strobe) timing light -- with vacuum hose to the distributor disconnected and plugged.
The conditions you describe (low vacuum; vacuum pot interference) indicate a distributor that is a tooth off.
If you are still running a "points" distributor, ditch it for an electronic type -- in the long run, they'll give more power, increase fuel mileage, and hold a tune better and longer.
At your altitude (Houston), your stock cam should give a steady 19-20 inches at 800 rpms.
Bosch Double-Iridium plugs gapped at .040 for a long-life tuneup.
Good Luck !!
The conditions you describe (low vacuum; vacuum pot interference) indicate a distributor that is a tooth off.
If you are still running a "points" distributor, ditch it for an electronic type -- in the long run, they'll give more power, increase fuel mileage, and hold a tune better and longer.
At your altitude (Houston), your stock cam should give a steady 19-20 inches at 800 rpms.
Bosch Double-Iridium plugs gapped at .040 for a long-life tuneup.
Good Luck !!
I was thinkning about efi and electronic dizzy. There are a lot of options out there. Is MSD all the rage? Or are there other I should consider, i.e. Holley dual sync, Petronix? If I change the dizzy now can I go efi later or should I do it all at onece in a complete kit?
03-21-2017, 12:31 PM
#5
Check your ignition timing with a good (strobe) timing light -- with vacuum hose to the distributor disconnected and plugged.
The conditions you describe (low vacuum; vacuum pot interference) indicate a distributor that is a tooth off.
If you are still running a "points" distributor, ditch it for an electronic type -- in the long run, they'll give more power, increase fuel mileage, and hold a tune better and longer.
At your altitude (Houston), your stock cam should give a steady 19-20 inches at 800 rpms.
Bosch Double-Iridium plugs gapped at .040 for a long-life tuneup.
Good Luck !!
The conditions you describe (low vacuum; vacuum pot interference) indicate a distributor that is a tooth off.
If you are still running a "points" distributor, ditch it for an electronic type -- in the long run, they'll give more power, increase fuel mileage, and hold a tune better and longer.
At your altitude (Houston), your stock cam should give a steady 19-20 inches at 800 rpms.
Bosch Double-Iridium plugs gapped at .040 for a long-life tuneup.
Good Luck !!
NGK Iridium #7510 @ .040 Gap.
Center Electrode Core Material Copper Core
Center Electrode Tip Material Iridium
Gap Size 0.04 in
Ground Electrode Quantity 1
Hex Size 13/16"
Insulator Height ISO
Manufacturer Heat Range 5
Additional Info 5K Ohm
Seat Type Tapered
Reach 10.9mm
Thread Diameter 18 mm
Ground Electrode Tip Design Taper Cut
Ground Configuration Standard
Ground Electrode Core Material Nickel Core
Available at -- rockauto.com
03-21-2017, 12:34 PM
#6
1st Gear Member
Thread Starter
Join Date: Jan 2017
Location: Houston, Texas
Posts: 82
Thats close to normal. (totally depends on cam) sounds like it running well so there is not likely a vac leak
at 850 rpm I get 14" (this is idle) hot engine (cold engine makes way less vac)
under light acceleration vac will drop BUT on say level ground in 2nd gear higher rpm will give higher vac readings. So vac will drop as you accelerate to 30mph then as you back off to maintain 30mph vac may read 18ingh for example in the same conditions vac may read 21inhg at 40mph in 2nd gear.
In the video you can see vac drop as the engine accelerates and then come up quickly as it holds rpm then revs down.
No load quick rpm changes will give large vac spikes like you saw.
under load at WOT in any gear vac will be zero
The more you lug the engine the quicker vac will drop off. half throttle accel in 5th gear at 40mph is going to cause vac to drop into the 2-3" range
half throttle accel in 1st at 10mph could up around 12"+
at 850 rpm I get 14" (this is idle) hot engine (cold engine makes way less vac)
under light acceleration vac will drop BUT on say level ground in 2nd gear higher rpm will give higher vac readings. So vac will drop as you accelerate to 30mph then as you back off to maintain 30mph vac may read 18ingh for example in the same conditions vac may read 21inhg at 40mph in 2nd gear.
In the video you can see vac drop as the engine accelerates and then come up quickly as it holds rpm then revs down.
No load quick rpm changes will give large vac spikes like you saw.
under load at WOT in any gear vac will be zero
The more you lug the engine the quicker vac will drop off. half throttle accel in 5th gear at 40mph is going to cause vac to drop into the 2-3" range
half throttle accel in 1st at 10mph could up around 12"+
03-21-2017, 06:37 PM
#7
Moderator
Join Date: Dec 2005
Location: Hills of California
Posts: 5,208
6 deg initial might be a bit low but within normal range. 35 all in at 2200 is fine assuming you have the vac adv disconnected.
If you've got 6 initial + 29 adv for a total of 35 + 10 for vac at 45 over 10ingh then you are good.
if you've got 6 initial + 19 for a total of 25 all in at 2200 + 10 vac for 35 above 10ingh your timing is seriously low and will cause reduced fuel mileage, and significant power loss.
With vac disconnected your total timing should be 32 to 35. at 2200 to 3000
These engines dont run a tooth off. you might get it to back fire or stumble along if you use some throttle but they wont "run"
They dont slip teeth but once then shut down right away
However the distributor gear can slip on the shaft in rare cases and retard timing
I dont think any of that is your issue.
If you've got 6 initial + 29 adv for a total of 35 + 10 for vac at 45 over 10ingh then you are good.
if you've got 6 initial + 19 for a total of 25 all in at 2200 + 10 vac for 35 above 10ingh your timing is seriously low and will cause reduced fuel mileage, and significant power loss.
With vac disconnected your total timing should be 32 to 35. at 2200 to 3000
These engines dont run a tooth off. you might get it to back fire or stumble along if you use some throttle but they wont "run"
They dont slip teeth but once then shut down right away
However the distributor gear can slip on the shaft in rare cases and retard timing
I dont think any of that is your issue.
03-21-2017, 06:46 PM
#8
1st Gear Member
Thread Starter
Join Date: Jan 2017
Location: Houston, Texas
Posts: 82
6 deg initial might be a bit low but within normal range. 35 all in at 2200 is fine assuming you have the vac adv disconnected.
If you've got 6 initial + 29 adv for a total of 35 + 10 for vac at 45 over 10ingh then you are good.
if you've got 6 initial + 19 for a total of 25 all in at 2200 + 10 vac for 35 above 10ingh your timing is seriously low and will cause reduced fuel mileage, and significant power loss.
With vac disconnected your total timing should be 32 to 35. at 2200 to 3000
These engines dont run a tooth off. you might get it to back fire or stumble along if you use some throttle but they wont "run"
They dont slip teeth but once then shut down right away
However the distributor gear can slip on the shaft in rare cases and retard timing
I dont think any of that is your issue.
If you've got 6 initial + 29 adv for a total of 35 + 10 for vac at 45 over 10ingh then you are good.
if you've got 6 initial + 19 for a total of 25 all in at 2200 + 10 vac for 35 above 10ingh your timing is seriously low and will cause reduced fuel mileage, and significant power loss.
With vac disconnected your total timing should be 32 to 35. at 2200 to 3000
These engines dont run a tooth off. you might get it to back fire or stumble along if you use some throttle but they wont "run"
They dont slip teeth but once then shut down right away
However the distributor gear can slip on the shaft in rare cases and retard timing
I dont think any of that is your issue.
03-21-2017, 07:31 PM
#9
1st Gear Member
Thread Starter
Join Date: Jan 2017
Location: Houston, Texas
Posts: 82
I got eager and went out and checked it with the vacuum advance connected. I got this:
6 initial + total of ~42 - 45 @2200rpm. It was hard to get an exact measurement at high rpm because my scale stops at 30 btdc. I made an extra mark for 40 btdc.
6 initial + total of ~42 - 45 @2200rpm. It was hard to get an exact measurement at high rpm because my scale stops at 30 btdc. I made an extra mark for 40 btdc.