Inliners International Forums General Discussion Hi Performance recurve HEI distributor

I have been told that a lot of idle and or drivability problems can be corrected by recurving the distributor. Can anyone tell me what recurving does, and when it should be done? Will just advancing the base timing for the idle problem move the same problem to a driveabilithy problem because to the total timing will be incorect.

If your running a after market Cam Meaning More then stock. It is good to have the dist. recurved to match The cams Power band. Come paired to the stock cam. Hope this helps.}[oooooo]

Re-curving the dist advance usally is done to allow more centrifugal advance and the rate of timing increase in relation to the engine RPM, is changed and controlled by the strength of the advance weight springs. The weights can be reshaped slightly help control this also. Someone recently wrote a detailed post on how they went about this--- does any one else remember the Post? Paul

Hi Paul, Larry . . .

I am not sure that I am following this discussion.

In Bill Fisher's book he talks about 'chopping' the weights in the distributor by clamping them together and grinding off an equal amount of metal. He recommends doing this in relationship to the amount of increase in compression ratio over stock. This seems to make sense because the effect is to 'reduce' the rate of the mechanical advance as RPM climbs. Which means less spark lead in the lower RPM range. In my mind lighter weights or stronger springs would have the same effect on advance rate.

When you guys are talking about recurve (because of a longer duration cam) do you the mean the rate at which advance takes place - or the total number of degrees the mechanical advance mechanism can introduce? Or Both?

Since a longer duration cam will move the power band up the RPM scale - wouldn't we want to reduce that rate of the mechanical advance?

regards,
Keith

I have modified an HEI for my GMC 6. The process is complex because the weights, springs and center plate shape work together and against each other to affect the advance curve. Two excellent sources I used are available on the internet free: (1) "Changing the Advance Curve on HEI Distributors" by Jim Hand and (2) "Ignition Timing for Modified Engines" by Dave Andrews.

I got my HEI to match the curve recommended by Dave Andrews and it made a great imorovement in performance and driveability. If you decide to follow Jim Hand's recommendations, go easy when you file the weights. A few (2-3)file strokes will retard the advance starting point point and widen the range by 1 degree.

The sites listed above sound like excellent sources for the information to tailor your own advance curve. Speaking on the change of the springs and weight of the advance weights, yes these could have the same or equalizing effect if not done properly. lightening the weights with the addtion of a weaker spring could put you back in the same spot. The shape of the weight were it touches the advance cam will change how much the Dist can advance. Also the size of the pin on the bottom of the advance cam and the slot it fits into will control the amount of advance it can reach when the advance weights sling out.Both the rate and the amount of advance must be considered when tailoring a "Curve".This should be done off the car in a distributor machine for best result so a person can monitor the changes in relation to the distributor RPM.Distbibutor RPM is half the RPM of the motor, so 1 degree added to the centrifugal advance is actually 2 degrees when operating in the motor.Paul

Is it true that the after-market [Moroso] V8 HEI recurve kit springs will also work on a GM L6 HEI?

For Orange Sunshine -

except for the main shafts, reluctors, and pole pieces every internal part of the V8 HEI will interchange with the Inline model. This includes the module, coil, rotor, and the advance weights springs and bushings. The vacuum advance units are also completely interchangeable BUT they come in a bunch of different advance curves and diaphragm spring tensions so you can spend a lot of time learning about which one will do what or the easier way is to buy an aftermarket performance vacuum advance unit that is adjustable. I'm pretty sure Crane and Edelbrock both offer the adjustable vac units and they're around $20 - $23.

Just some advice before you dive into one is work with one thing at a time. Don't make all sorts of weight and spring changes and toss a vac unit into the mix at the same time or you'll find it very frustrating and confusing unless you have it on a distributer machine and have time to sort it out.

Mike

f. hainey- I have been trying to find the two articles you mentioned. I have had no luck. What was the website these articles were at? Thanks.

Hud I,

Sorry, I should have been more specific. The two websites for the articles are:

http://members.aol.com/dvandrews/timing.htm

http://www.boyleworks.com/ta400/psp/distcurve.html

Thanks fh. I am gathering info. on recurving a hei unit. That is going to be one of my winter jobs.