Engine turns over after shutoff
09-11-2016, 11:37 AM
#1
Racer
Thread Starter
Engine turns over after shutoff
New 468cui, stock heads, Straub cam, CR 10,5, static compression 196psi.
Ignition at 12 initial, mechanic 18 at 3500rpm, manifold vac to distributor
10 deg (MSD Pro billet and MSD 6AL), rebuilt Qjet, using 95 oct gas.
Why does it turnover after shutoff?
Ignition at 12 initial, mechanic 18 at 3500rpm, manifold vac to distributor
10 deg (MSD Pro billet and MSD 6AL), rebuilt Qjet, using 95 oct gas.
Why does it turnover after shutoff?
09-11-2016, 03:38 PM
#4
Pro
In my experience, the typical cause for dieseling is usually too high idle speed. Sometimes idle can be set too high to compensate for low initial timing. If the initial is set correctly you may want to try a lower idle speed.
In your case, you mention a Straub cam. I ran one a while back, and it liked a ton of initial timing.
I had dieseling with that engine until I bumped initial up (around 20 or so if I recall correctly - but you will need to figure out the right setting for your combination). I then dropped idle speed and eliminated the dieseling.
I personally would see if it likes more initial so you can drop your idle speed settings and close your throttle blades more than they are now - restricting air flow into your engine at idle and when you shut it off.
Occasionally, this wont help and you may just need to add a solenoid to keep your throttle blades open enough for idle. Once the car shuts off, the solenoid then allows the blades to snap shut.
In your case, you mention a Straub cam. I ran one a while back, and it liked a ton of initial timing.
I had dieseling with that engine until I bumped initial up (around 20 or so if I recall correctly - but you will need to figure out the right setting for your combination). I then dropped idle speed and eliminated the dieseling.
I personally would see if it likes more initial so you can drop your idle speed settings and close your throttle blades more than they are now - restricting air flow into your engine at idle and when you shut it off.
Occasionally, this wont help and you may just need to add a solenoid to keep your throttle blades open enough for idle. Once the car shuts off, the solenoid then allows the blades to snap shut.
Last edited by cooper9811; 09-11-2016 at 03:39 PM.
09-11-2016, 04:49 PM
#5
Racer
Thread Starter
In my experience, the typical cause for dieseling is usually too high idle speed. Sometimes idle can be set too high to compensate for low initial timing. If the initial is set correctly you may want to try a lower idle speed.
In your case, you mention a Straub cam. I ran one a while back, and it liked a ton of initial timing.
I had dieseling with that engine until I bumped initial up (around 20 or so if I recall correctly - but you will need to figure out the right setting for your combination). I then dropped idle speed and eliminated the dieseling.
I personally would see if it likes more initial so you can drop your idle speed settings and close your throttle blades more than they are now - restricting air flow into your engine at idle and when you shut it off.
Occasionally, this wont help and you may just need to add a solenoid to keep your throttle blades open enough for idle. Once the car shuts off, the solenoid then allows the blades to snap shut.
In your case, you mention a Straub cam. I ran one a while back, and it liked a ton of initial timing.
I had dieseling with that engine until I bumped initial up (around 20 or so if I recall correctly - but you will need to figure out the right setting for your combination). I then dropped idle speed and eliminated the dieseling.
I personally would see if it likes more initial so you can drop your idle speed settings and close your throttle blades more than they are now - restricting air flow into your engine at idle and when you shut it off.
Occasionally, this wont help and you may just need to add a solenoid to keep your throttle blades open enough for idle. Once the car shuts off, the solenoid then allows the blades to snap shut.
Tried 16, but it pinged way out...
09-12-2016, 09:19 PM
#8
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While it's idling can you rotate the distributor to advance the timing a little bit to see if the idle speed increases? If it does, that indicates that the low RPM timing is too retarded, and could be the cause of the dieseling issue (due to the throttle blades being opened further than necessary).
09-12-2016, 09:30 PM
#9
Pro
Do you know that 12* (plus the vacuum advance addition) is the correct idle timing for your particular engine combination?
While it's idling can you rotate the distributor to advance the timing a little bit to see if the idle speed increases? If it does, that indicates that the low RPM timing is too retarded, and could be the cause of the dieseling issue (due to the throttle blades being opened further than necessary).
While it's idling can you rotate the distributor to advance the timing a little bit to see if the idle speed increases? If it does, that indicates that the low RPM timing is too retarded, and could be the cause of the dieseling issue (due to the throttle blades being opened further than necessary).
This is pretty much the same place I was headed. If it pings at higher RPM, maybe you really need more initial, but should limit the total mechanical to control ping. I would bet you can lower idle speed this way and decrease (if not eliminate) the likelihood of dieseling.
09-12-2016, 10:38 PM
#10
Burning Brakes
When you say "Stock Heads" do you mean Cast Iron? Let us know how you end up solving it.
I'm thinking about using a Straub Cam on a BB 427 also 10.5 comp. I'm trying for a combo (Cam, Heads) that will allow running 91 Oct. without Dieseling or Detonation. Straub pointed me towards aluminum Heads.
I'm thinking about using a Straub Cam on a BB 427 also 10.5 comp. I'm trying for a combo (Cam, Heads) that will allow running 91 Oct. without Dieseling or Detonation. Straub pointed me towards aluminum Heads.
09-12-2016, 10:46 PM
#11
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This is pretty much the same place I was headed. If it pings at higher RPM, maybe you really need more initial, but should limit the total mechanical to control ping. I would bet you can lower idle speed this way and decrease (if not eliminate) the likelihood of dieseling.