DUI Issues

P

Patrick C

New member
Hello, I purchased a dui from IH north after providing them with vehicle information. It took about 2 weeks to arrive from performance and I took it to the shop yesterday for the install. I have never fooled with distributors at all, so I needed some help. I have a 79 Scout ll with a 345 4bbl. The guys replaced the provided water neck and stabbed the dui off #8 at 0 degrees tdc. They also replaced the plugs with autolite 85's (I have always ran these with no problems) gapped at .05. And new live wires. She lost a lot of power and stalled on me several times after a test drive. Monday they will try to fix her again.

Is there a recommended initial timing setting for the dui? Performance instructions says refer to the manual which recommends 0 degrees tdc. Also, what plugs should I have used and will there be a difference if I open the gap to .055 instead of .05. I think their gap tool only went to .05!

Thanks
 
No conventional tip spark plug should ever be gapped higher than 0.045". To do so will greatly enhance the possibility that one or more side (ground) electrodes will break off when in operation. That type spark plug was never meant to be used in engines which required "high gap", electronic distributors. A "dui" is a simple, inductive discharge unit and requires nothing special in the way of plug, same for any of the aftermarket capacitive discharge boxes.

If davis recommends that kind of gap, then will they also pay for engine repair when the time comes?

I'd totally disregard whatever the oem base ignition timing is. The advance curve and potential in that dui distributor is somewhat more "pronounced" than any oem distributor. Set the base timing to whatever specification allows the engine to perform as it should.

The oem base timing was determined to work (barely) in accordance with all emissions components in operation on the engine and functioning properly. That is not what you have now. If you insist on setting the base timing using a light, then I'd run it at 6*btdc initially and see what happens. That is probably the "low" end of the scale for use with "regular" grade fuel. I'd also think that your final base timing setting will be closer to 10*btdc.

In actuality, I use this system on all the stuff I work on for setting the base timing:

http://www.forums.IHPartsAmerica.com/ignition-tech/2122-ignition-power-timing.html
 
Patrick:

I am doing the same install in about a week. Let me know what you end up setting the timing too. I have heard that 12 btdc is the sweet spot for our engines.

Performance's FAQ talks about spark-plug recommendations and timing settings:

link to FAQ's here
 
That 12 degree initial figure stated in the dui FAQ's is merely an example. A number of factors will influence where the optimum timing is for a given engine. This is not really a one size fits all deal. Results May vary. That's why it is necessary to perform the power timing procedure as outlined by michael on an individual basis.
 
I moved it from 0 to 10 degrees btdc and wow what a difference. It ran like a champ, but valves rattled a bit on upgrades. I knocked it back to about 8 btdc, and I am am very happy. I really notice a change in the mid range area, but very smooth acceleration 1 through 3. Love it
 
I'm back again...we've been without power and cell phone since Sunday afternoon except for very short periods of time.

The information that davis supplies regarding their product is very generic. And no doubt they have rarely ever run any ihc-produced engine for any period of time to develop a full array of information for ignition systems! They build one adapted distributor for the ihc product and that's it, they have developed no other info. I'm sure the data they have for chryfordolet is far more advanced since that is the market for their product.

We know what timing specs are used with the ihc-produced product for best performance (and that includes best fuel economy), these numbers are no secret at all! We know where to start and what is going to be the outcome based on running "regular" grade fuel and we know what will happen regarding additional engine modifications or use with the highest octane pump gas currently available.

This factor alone is why we must always know the entire engine scenario when folks ask for help like this. We must know the entire engine situation and whether or not the vehicle itself is for "offroad use only".

The "clatter" or noise you hear under load which you attributed to valve noise has nothing to do with the valves! It is a byproduct of detonation (rattle or ping), meaning that the fuel octane rating being used at that time is insufficient for the base timing you have applied. Simply retarding the base timing just a touch from that point will eliminate the noise and you will retain the same engine power output. This is exactly what the information posted regarding the power timing situation describes!
 
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