Distributor springs

[Roostr84]

I am replacing the distributor in a car of mine, its an HEI and I noticed that the springs under the rotor are much tighter in the new one as opposed to the old. I assume this just brings the full advance in quicker. As this is not a stock engine i am wondering what i should do to decide what tension of springs to use. What is a good way to determine this. Thanks.


Chris =)

I think the exhaust fumes have finally gotten to me!!

 

[BluThndr71JMMY]

Get the Moroso (I think) springs kit from your local hot rod shop. It has 3 sets in different colors - soft, med, hard -- experiment with them until you find a setup you like. It's a painstaking process, but there it is. I may have done it the hard way. Best thing is to find a friend who is expert at these things. Good Luck.

 

[Steve_Chin]

Soft springs bring the advance in quicker than stiff ones. Depending on your camming, gearing, compression ratio, vehicle weight, you might want a slower, longer advance curve or a quicker curve. Most moderately cammed Chevies seem to like ~36 total degrees of advance in by 2600 RPM. If you have high compression, big tires, or wierd gears, you may want to slow the curve. The curve in an HEI is governed by the weights (there are literally a couple of hundred different profiles), the advance cam (aka center plate, of which there are about 50 different profiles), and the spring rate. Changing any of these will alter the curve. The weights and cam work together to form the shape of the curve and the total amount of mechanical advance provided. The weights and springs work together to form the rate of advance.

 

[Roostr84]

Ok Steve i was hoping you would chime in on this one. Here is my combo. A 383 with around 9.8:1 compression, edelbrock performer rpm heads, a comp cams extreme 268 cam, with an air gap manifold and 795 cfm q-jet. The vehicle is my 87 Monte carlo SS. Probably around 3600-3700 lbs. It has a 4.11 rear and 235/60r15's on it...any guess on the advance?

Chris =)

I think the exhaust fumes have finally gotten to me!!

 

[Steve_Chin]

Sounde like a really similar build to my buddy's 383 in his Blazer (he's got a slightly hotter hydraulic roller in it). He's running 36 degrees total advance in by 2600 RPM. I'm trying to con him into a little more advance to see if it runs better because I've gotten reports from a number of guys (including my own personal experience) running Edelbrock heads on another make that running more advance than was normal with the factory heads seems to give 'em a bit more performance.

 

[Roostr84]

Thanks Steve..I'll give it a shot and let you know how it works out.

Chris =)

I think the exhaust fumes have finally gotten to me!!

 

[Roostr84]

Ok get this one steve, I bought one of Summits "performance" blueprinted distributors, and this is the specs on it. Their settings are 14 degrees of mechanical advance at 2200 RPM and 10 degrees of advance @ 11 inches. For a grand total of 24 degrees at 2200 RPM. I thought that their would be more advance dialed in than this. Does this sound correct to you.

Chris =)

I think the exhaust fumes have finally gotten to me!!

 

[Steve_Chin]

Wow... Short advance on both the mechanical and vacuum fronts unless they're talking about distributor advance degrees (double to get crankshaft degrees and RPM). I would want to get something on the order of 25 crankshaft degrees of centrifugal advance at about 2400 crankshaft RPM. For the vacuum, a lot of guys like 10 or so degrees out of the can, but I like to run more to try to get better gas mileage.

 

[Roostr84]

So Steve do you think i should install the lighter weight springs that came with the distributor. They came with a lighter and a heavier set than the ones already installed. I guess the vacuum is set up fine at 10 degrees. Will the springs add enough though considering it is at 14 degrees of mechanical advance now.

Chris =)

I think the exhaust fumes have finally gotten to me!!

 

[Triaged]

The springs only change how fast the advance comes in. You would need to change the spacers (or something like that?).

'71 Blazer CST w/ a 400sbc, 4" lift, 36" Supper Swampers, and alot of rust
<a target="_blank" href=http://community.webshots.com/user/triaged>See it Here </a>

 

[Steve_Chin]

Triaged is more or less right. Reference my earlier post about the shape of the center advance cam and weights playing a role in how much centrifugal advance the distributor will provide. I usually rob weights and cams out of junked cars and distributors and mix 'n' match until I get the curve I am looking for. You'll nbeed a good dial-back timing light or a harmonic damper that is fully degreed (and indexed to your timing indicator and your crank's TDC) and a good portable tachometer in order to set the curve yourself (or you'll need a distributor machine...).