Distributor curve

[CamaroAdam73]

So i ran into some bumps in the road with my 403 and i'm just trying to narrow things down and make sure i didn't make any mistakes here. I set the curve in the distributor using this kit..

http://www.summitracing.com/parts/mor-72300/overview/make/oldsmobile

I went with the medium set of springs to start.


The engine is an olds 403

http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=1463&sb=0

Lift : 491 / 476
Duration: 278 / 296
Range 2000-5800
She idles at 1000-1100

Rear gears are 3.42's, originally i thought they where 3.73's but no.

My question is, using this kit do i want a faster rate of spark advance or slower based on my setup?

 

[Fox80]

It doesn't tell everything by what "curve kit" you put in it. I explained all this in another thread, "Timing problems" in the engine swap section

 

[CamaroAdam73]

Good write up fox. Based on the cam specs i listed, what set of springs for the centrifugal advance would you start with?

 

[Fox80]

If I were to do it I always put the heavy set in first, because I want to verify the total mechanical advance that is in the plate. Put the heavy springs in, start it with the vacuum line unhooked and plugged bring the car up to 3,000-3,600rpms and set the dist. to 36 degrees. Let the motor return to an idle (if it will) and read the timing, it should read between 8 and 10 degrees. Or I have even wired the advance in the rest position to make sure the springs are not allowing movement at an idle. If it does try the next softer ones until it wont return to the number it did before. You now just set the mechanical advance for your motor. Now if your dist returns to far then the advance plate has to much advance in it, and needs fixed to limit it to TO NO MORE than 30 degrees total, or it will never work right with the vacuum line connected. You also need to verify the TDC on the balancer. The kit in the top photo is a MSD advance kit WAY better quality than the china curve kit sold by many companies in the bottom photo. The bushings they use last a lot longer, and the weights are more precise. But a curve kit doesn't change the total mechanical advance that is set by the plate that it all sits on, with a performance type cam you need to verify the idle vacuum, less than 15 you will need to change the vacuum cylinder like the article says. Remember no matter the motor a vacuum advance dist. is not a drop in item it must be tuned to the motor. Do the work, get it right and you will be rewarded with way better fuel economy, a car that can sit in traffic all day and not get hot, exhaust valves that last longer, less cylinder blow by. Don't want to do the work, put a mechanical advance only dist. in it will run ok

 

[Fox80]

I found a good picture of a positive mechanical advance dist., it takes a spintron type machine to set this up like that but it will give you a dead on advance limit. The mechanical stop screw is used to set the initial timing, the limit screw sets the total mechanical advance

 

[pontiacgp]

If you get an MSD distributor you can get different bushing to set your advance and springs that come with a chart to let you know how fast you get to your max advance. I have an E-curve distributor as a back up where I set the curve and max advance digitally. I don't like the HEI distributors with the heavy coil sitting on top of the cap which can move the cap under heavy breaking and cornering

 

[Fox80]

It's impossible for the cap to spin on the dist. housing that's what that square locator peg is for if the housing spins buy a good hold down clamp. I ran locked out HEI on big power circle track cars for 15 years with the coil in the cap never had that happen, so I doubt a stock type street car will ever exert enough force to rotate the dist.

 

[pontiacgp]

I never said the cap will spin but it will move

 

[jetsetw31]

I never said the cap will spin but it will move

Yes It can. If the 4 lock down clip springs are worn enough to allow it, the cap will bounce, rock from side to side, etc. Even with new caps you can literally lift the cap up by hand. (Of course with much resistance, but it is possible.) Only the CCC distributors eliminated that issue. The ones with their screw down caps.

 

[olds307 and 403]

The HEI is a great distributor. That being said, you need the mechanical advance curve to come in quickly. Hopefully the Moroso weights allow this before 3000 rpm, the stock weights do not. You do need a stop screw as shown to limit the mechanical advance, grind as necessary to achieve your maximum advance. They all add extra timing in higher rpms. Just be careful when tapping the hole to keep the shavings out of the magnetic pick up. I went with the Mallory breakerless. I can set my base anywhere, they have keys to set the amount of mechanical advance. With the lightest springs, all in just over 1500 rpm! I would try the lightest springs and see where your advance comes in with your dial back light. Give it a quick high rev, you will probably see an extra 3-5 degrees.