Bubba times his car
Thread Starter
Burning Brakes
Joined: May 2014
Posts: 884
Likes: 128
From: Rhine Georgia
Bubba times his car
first off, I'm the Bubba. I've been working with latest Lars papers and my new shiny timing light. 383 with 234/244 cam HEI. Installed AR12 vac (pulls 15). Limited my mech advance to 15. Engine seems to like lots of initial advance. I have it set to 21 atm.
21 initial + 15 Mech = 36...connect vac and it adds 15 more so I'm at 51.
BUT I'm having a hard start issue with motor is hot. Nothing too bad just enough to bug me. should I drive it as is or drop my initial down?
21 initial + 15 Mech = 36...connect vac and it adds 15 more so I'm at 51.
BUT I'm having a hard start issue with motor is hot. Nothing too bad just enough to bug me. should I drive it as is or drop my initial down?
Le Mans Master
Joined: Jul 2006
Posts: 8,117
Likes: 104
From: charlotte north carolina
Your numbers look good. Unless you're getting pinging, leave it as be. As a test, retard the initial 5 degrees and see if that helps the hard start. If it does help, consider modifying the distributor to increase the mechanical to compensate. And if you're not getting any "trailer hitching" while at medium speed cruise, the numbers with vacuum look good also.
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
Your numbers look good. Unless you're getting pinging, leave it as be. As a test, retard the initial 5 degrees and see if that helps the hard start. If it does help, consider modifying the distributor to increase the mechanical to compensate. And if you're not getting any "trailer hitching" while at medium speed cruise, the numbers with vacuum look good also.
Two things:
Did you check and make sure TDC is "0" 100%
What kind of distributor do you run?
Jebby
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
The Mr. Gasket curve kit for HEI adds some "pull" to the advance.
MSD units have bushing for this. A stock or motor with mild cam will want to "pull" a lot. A radical motor will want to pull very little if any.
15 initial +21 to get 36 total is a great spec really...and a terrific baseline.
That is the biggest issue I have with HEI distributors is from experience they just do not pull a lot of advance for a mild street motor.
Try this: It is cheap and easy to install.
http://shop.mr-gasket.com/hei-advance-curve-kit.html
Jebby
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
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Melting Slicks
Joined: Apr 2009
Posts: 2,632
Likes: 112
From: Great Plains Iowa
A 21 degree initial advance is an awful lot of advance for any starter to overcome and it would certainly crank over very hard. OEM HEI's typically have a 20 degree mechanical advance but many of the aftermarket HEI's have around 24 to 25 degrees. If you haven't actually measured the amount of advance your HEI has I suggest you do so and then you'd know for sure.
To find out how much advance your HEI actually has set your initial timing to zero (with the vacuum advance disconnected) then see how far your timing advances on your damper.
To find out how much advance your HEI actually has set your initial timing to zero (with the vacuum advance disconnected) then see how far your timing advances on your damper.
Thread Starter
Burning Brakes
Joined: May 2014
Posts: 884
Likes: 128
From: Rhine Georgia
I only used the blue and silver spring.
I've used a roll pin to limit the weight travel on my HEI and by my math, 51 Total - 21 initial - 15 vac I'm left with 15 mech. I was getting little over 20 before I modded it.
I've used a roll pin to limit the weight travel on my HEI and by my math, 51 Total - 21 initial - 15 vac I'm left with 15 mech. I was getting little over 20 before I modded it.
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
Forget the vacuum advance, it is not relative. Keep it...but not for the sake of this conversation.
You need more Mech., like 20-21. Set initial at 15-16 with that setup.
This will help your hot start. and run the same upstairs.
Jebby
Thread Starter
Burning Brakes
Joined: May 2014
Posts: 884
Likes: 128
From: Rhine Georgia
Try not limiting it.
Forget the vacuum advance, it is not relative. Keep it...but not for the sake of this conversation.
You need more Mech., like 20-21. Set initial at 15-16 with that setup.
This will help your hot start. and run the same upstairs.
Forget the vacuum advance, it is not relative. Keep it...but not for the sake of this conversation.
You need more Mech., like 20-21. Set initial at 15-16 with that setup.
This will help your hot start. and run the same upstairs.
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
Thread Starter
Burning Brakes
Joined: May 2014
Posts: 884
Likes: 128
From: Rhine Georgia
Big Update:
I went to pick my 7th grader up and car acted like it vapor locked. I had to idle in line for a few minutes waiting to pick him up. Engine temp was only 200ish at the max. After little over 1 hour car started and ran fine.
With my old timing setup I picked him up 2 days ago and waited in line 3 times as long and temp went to 220 and no problems.
So I'm thinking its gonna be my new timing and that I need to drop it back to more a factory setup and leave well enough alone.
Just some FYI I dont have a fuel return line or a carb spacer to help with vapor lock. I plan on getting both.
Am I on track or could it be something other than too much advance causing my stalling?
I went to pick my 7th grader up and car acted like it vapor locked. I had to idle in line for a few minutes waiting to pick him up. Engine temp was only 200ish at the max. After little over 1 hour car started and ran fine.
With my old timing setup I picked him up 2 days ago and waited in line 3 times as long and temp went to 220 and no problems.
So I'm thinking its gonna be my new timing and that I need to drop it back to more a factory setup and leave well enough alone.
Just some FYI I dont have a fuel return line or a carb spacer to help with vapor lock. I plan on getting both.
Am I on track or could it be something other than too much advance causing my stalling?
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
Your cam has a pretty good duration. Also likely a late intake closing point. Maybe lots of overlap as well. these things combine to make low cylinder pressure at idle with plenty of contamination from the previous exhaust cycle.
This means it takes a lot of time to burn the intake charge (relatively speaking) so igniting the mix early is needed to get a reasonable burn. This requires lots of ignition lead at idle. 21* of initial is probably not out of line for that engine. With vacuum your are getting 36* at idle.
My engine has a 219@.050 roller cam on a 108 lsa. It wants lots of ignition lead as well. I'm at 19* initial and 17* of vacuum giving me 36* at idle. Idles very well there.
My guess is your stalling issue is not related to your timing.
This means it takes a lot of time to burn the intake charge (relatively speaking) so igniting the mix early is needed to get a reasonable burn. This requires lots of ignition lead at idle. 21* of initial is probably not out of line for that engine. With vacuum your are getting 36* at idle.
My engine has a 219@.050 roller cam on a 108 lsa. It wants lots of ignition lead as well. I'm at 19* initial and 17* of vacuum giving me 36* at idle. Idles very well there.
My guess is your stalling issue is not related to your timing.
Thread Starter
Burning Brakes
Joined: May 2014
Posts: 884
Likes: 128
From: Rhine Georgia
My guess is your stalling issue is not related to your timing.
I'm gonna try and duplicate the problem in my driveway tomorrow. Idle in gear holding brake after car warms up. If it stalls I'll drop timing and test again.
Last edited by Bloodzone; Aug 22, 2015 at 04:48 AM.
Melting Slicks
Joined: Apr 2009
Posts: 2,632
Likes: 112
From: Great Plains Iowa
Forget the 15 degrees for the moment; its the 21 degrees of initial advance that bothers me as any engine would be hard to crank with that much advance. 21 degrees is 3-1/2 times as much as the recommended 6 degrees.....................