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Re-curving an HEI Ignition

385 Views 7 Replies 3 Participants Last post by  PSIG
I recently purchased an DUI HEI from Summit. I expected to provide information concerning my engine/drive train and get a re-curved distributor out of the box. Seems DUI has stopped doing that and sells through Summit verses direct to customers.
I have used HEI distributors for years without any significant issues so with an eye towards buying American and having a really reliable product I decided to upgrade to the DUI HEI. And now it seems I will have to re-curve my new distributor myself. I cannot purchase a new Crane 99600-1 re-curve kit (out of stock). I have the remains of a Crane #99600-1 that I used on a previous application and those parts seem to be in a usable condition. I plan on moving those slightly used pieces over to my new DUI. I used the cam lock out set at max restriction/limiting vacuum canister travel and adjusted the canister @ nine turns out (ported vacuum). The mechanical advance springs are supposed to go to full advance at 2500 rpm. I did not use the supplied centrifugal weights provided in the kit. This setup ran well in a previous cheap HEI distributor. Any advice/comments concerning my plan to move some parts and re-curve my new distributor myself would be appreciated.
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Zero suggestions with zero info. Keep the goals of tuning the ignition at the front of your brain (why you are doing what you are doing), and tune what you have to your engine, fuel, and performance goals in each area of operation. Good luck!
Examined my new DUI from Summit. Paper work indicates "calibrated to: 24% at 3000 rpm" I believe this indicates 24% degrees of centrifugal advance all in @ 3000 rpm? The vacuum advance has a very short slot and the number 482 15. I assume this means this vacuum advance has 15% of advance, so no limiter needed? I will use it as is with 12% mechanical advance (with vacuum disconnected and plugged). I will try manifold vacuum initially and ported vacuum later to see which is best. I will look for weaker springs to bring centrifugal advance "all in @2500 rpm". This is an iron head D3's with dished pistons and runns well on 85 octane. This is in a 1/2 ton pickup with stock C6 325 rear gear. Camshaft is a "extreme 4x4 RV type" Anyone with experience with DUI and tuning them would be helpful.
This is kinda like having a conversation with myself. NBD. I think some of the issues I have experienced with my two previous HEI ignitions, related to the lack of a clean consistent 12v power supply. On one of these ignitions the module failed prematurely and I believe that early failure was related to the aforementioned lack of a clean 12v power supply. The second failure was traced to a defective tachometer that intermittently grounded out the HEI distributor. During diagnostics and repair of this failure I cut the tac wire to resolve the grounding issue and as I was examining the power wire for the HEI, I discovered a frayed connection in that circuit that could have been arcing to the engine. I have been using 16 gauge wire to power the HEI, my bad. I really like installing Bosch relays in these 56yo Ford circuits. I have them in the headlights and in both the auxiliary fuse block and primary fuse block for all the original circuits. This is what I will do for my new DUI HEI. I will install a 12 gauge wire from the pigtail on the distributor, connect that through a Delco two point plug using high temperature silicone 12 gauge stranded wire. The 12 gauge wire connects to my 40 amp Bosch relay which is powered by a 12 gauge wire from the positive battery post. The Bosch relay is triggered by an 18 gauge wire from the ignition hot post on the ignition switch. I will not put a fuse in this circuit for now. One of the tricks I have done over the years is to install a "power post" by running an 8 gauge wire from the battery positive post into the cab (this is fused @ 50 amps). The power post circuit provides a ready source of clean battery voltage in the cab, cleans up the positive post at the battery and powers both the main fuse block and the auxiliary fuse block. Comments, questions?
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Sounds good to get going. The distributor power wiring is rather overkill, but will work fine for the 7-8 amps those things draw. I would test the distributor on the engine to determine the total the advance plate and canister will provide (you don't have to run the engine, but that's OK too). If it tests at 24° mechanical, then your base timing will be 10°. But with unknown or untested parts, I would set by all-in total of 34° and let base fall wherever it will. Go from there to read your current curve, test drive, experiment where it's weak, tune vac timing, have fun.
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I use the Moroso HEI recurve kits myself. Have never had an issue with them They're readily available on ebay, summit, jegs, etc.

It seems that DUI has lost some of it's quality control. I inspected my DUI and noticed that the advance weights were loose and flopping around, closer examination revealed that the E-clips that retain the weights were missing. I retrieved a set from an old distributor and installed them. Holding the distributor and turning the gear reveals a notchy sticky condition likely caused by a misaligned busing. DUI claims they have an extra busing on the shaft for stability so hopefully this is not an important issue. The DUI instructions talk about Ford oil pump drive shafts that may be to long and cause binding. I measured the depth of the shaft drive (Female) and compared it to an old functioning distributor. The old distributor had a stop about an inch in. The DUI had no such stop and in fact the only thing stopping the oil pump shaft would be the spring pin that retains the drive gear. I have installed my Crane adjustable vacuum advance and will use the limiter cam all in to restrict the vacuum advance to about 7% total. So, 24% centrifugal, 7% vacuum and 12% mechanical advance and I should be good for the initial drive-ability test. I am at 3000 feet elevation and run this truck on 85 octane. Average daytime temprature in the summer is around 90% with 20 % humidity. An suggestions/comments.
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It's a place to start. Try it, and you may find at altitude it will need more timing. The engine doesn't care if it's throttled or at altitude, it's still a lower-density charge with lower effective compression, and will typically need more advance for optimal timing. Find it by testing. (y)
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