[IROC_385z]

As of now I have got the "cam" from the summit curve kit, stock weights and the blue springs from the Crane adj vacuum kit. Does the cam control how much total mech advance is added or just the rate? I kinda have to use this summit one because the other ones that I have don't seem to work right, the would allow instant advance at idle because the don't seem to sit up agains the weights until the weights are extended some.

I am getting a noise at about 2500 WOT that sounds like 2 metal tranny lines rattling against each other, am I hearing detonation? Both my brother and myself heard it and did not think it sounded like "rocks" or "steel BBs" in a can....or rabid monkeys banging a back of hammers on my pistons, LOL.

Here is my timing curve:

Base 13
1000=13
1200=15
1400=18
1600=20
1800=24
2000=27
2200=30
2400=33
2600=37
2800=43
...
3500=50
4000=47
4500=45

I know it looks odd, the timing backs down again at higher RPM, but that is what the light showed!

So since my timing, at about 2500, is over 34 then I am assuming that IS infact detonation I hear...but I don't KNOW what is sounds like!! What can I do go cap this timing off?

Thanks guys, I know you all will be able to help.

[edge]

Did you check it with the vacuum advance disconnected and the port plugged at the distributor?

Are you certain that the timing tab and balancer are correct?

Are you using an adjustable timing light?

[IROC_385z]

The vacuum advanced was disconnected and all ports on the carb are plugged. the port on the vac-advance itself is not plugged...does THAT matter?

The tab is right.

The gun is an adjustable light.

[edge]

I'm sorry, I meant to say plugged at the "carb". I just wanted to be sure that vacuum advance was not kicking in and skewing your results. As long as the port is plugged at the carb, your okay.

Can you verify your timing light with another? I have heard that they can sometimes be off, especially if it is an off-brand.

Ed

[IROC_385z]

I can probly find another one, sure. It has always been accurate in the past but I think some guy down the road has one I can borrow.

[johnsongrass1]

I know it looks odd, the timing backs down again at higher RPM, but that is what the light showed!

The cam is moving forward against the resistance of the oil pump shaft and retarding timing. You can run a thicker timing cover and cam button or tighten up the timing chain. For right now, I wouldn't worry to much. It's only a few degree's. It's not really enough to affect power a great deal.

Your hearing detonation allright. Lighten up the springs so you can get all your timing in by 2800-3000rpm. If you still hear detonation at cruise, but it goes way with a slight throttle increase, back off the vacuum advance till it's gone. Then add a degree or two as compensation for the occasional bad trank of gas.

[454C10]

Yes, 50 degrees of timing is too much. 38 to 40 degrees of total mechanical advance should be all you would ever need.

Sounds like you need heavier springs to reduce the timing at 2500.

And you should reduce the slot length in the advance mechanism to reduce the total timing to 40. Can you disassemble the distributor and weld some of the advance slot up to reduce travel of the pin?

[IROC_385z]

Originally Posted by johnsongrass1

The cam is moving forward against the resistance of the oil pump shaft and retarding timing. You can run a thicker timing cover and cam button or tighten up the timing chain. For right now, I wouldn't worry to much. It's only a few degree's. It's not really enough to affect power a great deal.

Your hearing detonation allright. Lighten up the springs so you can get all your timing in by 2800-3000rpm. If you still hear detonation at cruise, but it goes way with a slight throttle increase, back off the vacuum advance till it's gone. Then add a degree or two as compensation for the occasional bad trank of gas.

IT is a factory Hydraulic Roller and has the stop-plate that bolts to the front of the block...i don't think it can walk. Why would I lighten the springs? I am getting too much total advance and it seems that it comes in too quickly! And my vacuum advance is not hooked up yet, that is a whole-nother can or worms.

Now 454, what is this you speak of with welding the "slots" shut? I do have a welder and can do this, but where do I do it and how much?

Also, I thought that stock HEI weights only allowed 20* mechanical advance?

[454C10]

Well, there are different hei's out there. The extra smogger hei's had more advance due to extra low timing at idle.

It looks like you are getting 35 to 37 degrees of timing from the mechanical advance. I have one on my truck that does 25.

Yes, just tear down the distributor a bit and look for the mechanical advance slots. They are easy to see once you take it apart. I have welded up my slots even with an old arc welder. You will need to pull the pin at the gear to seperate the housing from the shaft to get to the slots. A little weld in one of the slots then clean it up with a grinder. It is good to set up a total of 20 degrees advance then set the initial timing at 20 then adjust the spring strenght to control the advance rate.

How much is a good question. Measure the slot and subtract the pin thickness. The distance you measured is equal to 35 degrees (in your case). If you only want 20 degree then weld up 0.429 of that distance so than 0.571 remains. (20/35 = 0.571).

One advanvce slot my be shorter than the other one. Weld on the shorter one.

[bracketeer]

There is 360 degrees in a circle. The crank spins in a circle. There are 8 pistons on the crank. 360 deg divided by 8 cylinders equals 45 deg. The furthest you can advance the engine is 45 deg or you are firing on the next cylinder. You say you had 50 deg of advance at 3500 rpm. That is impossible. You would be 5 deg into the next cylinder. The motor would bog out until the advance dropped back far enough to get hitting on the right cylinder. This is way the timing is dropping back at 4500 rpm. You've got a bad timing tab. Try backing you static down to 8 degrees and see what happens. Then keep setting the static back until you hit 40 deg total.

[NXS]

bracketeer, are you SURE?

[IROC_385z]

Good point, but for every 360 degrees at the crank you have 720 at the distributor, which gives you 90 degrees to advance, no? The balancer shows markings for up to 50 or 60 degrees, im sure you can go more.

I know the mark is set fine. When I built the motor I lined up TDC and the balancer matched the 0 on my tab...I then put a line of red paint on each so I could read it easier. I know the balancer is not walking because at Idle is always read's the base timing.

[bracketeer]

I learned the 360 degree part in school! I am postive on the 8 cylinders. If my division is ok then the 45 deg part is right. The rest sounds feasible. I still say the timing tab is wrong. I have found one of mine out 4 deg. I actually have one on my new 400 that's dead on.

[IROC_385z]

Wow, we posted at the same time, LOL

[bracketeer]

Good point, but for every 360 degrees at the crank you have 720 at the distributor, which gives you 90 degrees to advance, no?

The crank spins 720 deg to every 360 deg of distributor. You have it backwards. My first posting should have said 360 deg of dist not crank. My mistake. So 46 deg of dist is putting you on the next cylinder.