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Wings 07-12-2004 10:07 PM

30 degrees at idle & 38 at 2000+ OK?
My 383 seems to like 36-38 total advance (I only have mechanical advance) but at idle it only drops to ~30 degrees. Is this OK? Idles great. How much total advance should Mechanical advance give you? I have tried different weights and springs but only get a total of 6-8 degrees above idle. Adding vaccume to this setup causes several problems and performance issues I would rather stay away from.

coldknock 07-12-2004 10:36 PM

It should be much lower than that at idle. Make sure the weights aren't sticking. The springs may be too weak and allow the weight to swing out too soon.


k-star 07-13-2004 05:27 AM

more info
What distributor are you running??

Is this a street, strip, stree/strip car???

What cam, intake,carb, gears trans???


Wings 07-13-2004 06:54 AM

Cold knock,
I'll try the heaviest springs and lightest weights I have. I can always lighten the weights if I need to. How many total degrees should I be getting from mechanical advance? How does this affect performance/engine life etc.

68 GMC short bed (4100 lbs with driver)
The distributor is a HEI-Accell (have tried 3 different sets of springs & weights)
Heads Dart Iron Eagles - bowls blended/ports reworked
Forged pistons 10.7:1 actually CC'd at 10.25:1
XE-268 CAM
1.6 rockers
RPM intake
2500 stall
TH-400 with transgo kit
410 posi rear

k-star 07-13-2004 08:05 AM

If you don't have any problems with hot starting it i would let it just as it is. It's not going to hurt anything.


coldknock 07-13-2004 10:22 AM

An iron headed 383, 10.25-1 comp, small cam, tight converter and 4100lbs to boot. Even with 4.10 gears it'll ping like a tin can full of ball bearings with 30 degrees of initial timing.

10-12 initial and no more than 36 total would be a good starting point and that's a little on the high side.


k-star 07-13-2004 11:14 AM

With the 4:10 gears the motor will spend very little time ever running under the 2000 rpm's where all his advance is in by.....

Is the motor showing any signs of detonation???

what fuel are you running???? what rpm does it idle at????

Is this street driven car???? I was assuming it was a race car but i don't know why i thought that???

If you are having problems,you will need to remove the distributor and check the advance slot under the mechanical advance and see why the distributor only has that small amount of advance in it.


TurboS10 07-13-2004 12:05 PM

Sometimes with a nasty cam and low compression you may need that much idle, but that is a strange case or a poor combination when it is needed. I think that 20 initial should be plenty if you can get it down there. If it is not hard to crank, it is likely not going to hurt anything to leave it.


Wings 07-13-2004 03:50 PM

No sign of detonation with 93 + boost. Even on a hot day lugging up a hill. The mufflers (flowmaster 40's) are pretty loud though & I may not be able to tell if it's faint pinging. Idle at about 850. It does have a geared starter because a standard starter would barely turn it over at any timing setting. It seems awfully powerful to me the way it is, but I'm not sure what a 400+ hp engine should feel like.

Anyone know how many degrees of mechanical advance I should be getting? 8-9 degrees does not seem right to me.

tresi 07-13-2004 06:37 PM

The weight and springs do not set the amount of advance. They control how fast the advance curve is. If you look under the plate that the weights ride on you'll see two pins riding in their own oval shaped slot. The pins are attached to the piece in the center of the weights that the springs hook to. When these pins bottom out in the slot the advance has reached its' limit. The size of the slot varies by original application.
If this distributor is used or has set around awhile the fist thing to do is to remove the distributor and completely disassemble it for cleaning. The shaft and bushings are well know for becoming carboned up to the point that it can limit the advance or cause it to stick mid range of the advance curve. You get it apart by driving the pin out of the drive gear.
If everything is clean and you happen to have a distributor that was made with very little mech. advance you can file of grind the slots for more travel. Some times the little plastic bushings will break and get jambed in the works.

Rhansen 07-13-2004 07:01 PM


Originally posted by Wings
Anyone know how many degrees of mechanical advance I should be getting? 8-9 degrees does not seem right to me.
My stock HEI has 20 deg. of mech. advance

k-star 07-13-2004 07:57 PM

my bad...
I am going to have to agree with coldknock on this one. When i orginally answered i thought it was a race car, not sure why i thought that because you never said it in your post..... At any rate if you are street driving it i would try to get the timing set at around 18/20 inital with your 36 total in by 2000.....

All the HEI's i have ever worked on have had way to much mechanical advance and i have had to weld the slot shut to limit it.

It sounds like you need to dig into the distributor and find what is going on with it.
the problem with a motor like yor running is you are never going to "HEAR" the detonation. It's just going to destroy something first. At the very least you need to pull the plugs and look for signs of detonation.....

Good call coldknock,,, i just missed it was a street car?????


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