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Old 11-01-2006, 09:14 PM
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Default Dual curve system

hey all,

I am wondering if there are any MSD products available that can work with a standard electronic distributor but actually dictate two separate ignition curves, depending on the flick of a switch.

what i actually want to achieve is one curve for petrol and one curve for propane. the petrol curve is for a mild engine, say initial of 10, total of 34 by 4,000rpm. for LPG, i want something that is initial of 12-14, total of 28, all in by 2000-2200 rpm (much earlier).

are there any dual curve controllers? if not, i would be equally happy with a setup that works by basically just using the normal MSD 6AL (for example) to run the petrol, then (with the flick of my fuel selection switch), enables some add-on module that over-rides the mechanical advance of the distributor (?) and enforces its own advance curve?

any help much appreciated!

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Old 11-02-2006, 08:41 AM
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I have forwarded this question to another gentleman that handles all of our 'Dual Curve' questions. Expect an answer sometime within the next 24 hours.
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Old 11-02-2006, 03:56 PM
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Our Dual Curve products can be viewed at .

Our PN8795 provides the function that you are describing. The timing curve can be viewed on page 13 of the old 8790 series instructions at:

The PN8795 requries a minimum positive signal of 3-5V 1 ms duration.

The timing curves are pretty much the same for these applications, and are conservative to avoid illuminating the MIL, yet still improve performance for alternate fuel to recuperate some of the losses in octane and fuel properties. These products all provide additional timing on top of the stock gasoline timing curve.

We also have a version for Ford Duraspark ignitions and on board computer applications with MAF or MAP sensors.

(You can see these on our website under Products and Timing Controls)

Note: PN4066 is OBSOLETE.


Ford Timing Control, Duraspark LPG, 76-83 V-8 Cars/Trucks, 78-87 V-8 Heavy Trucks

Ford Timing Control, Duraspark, CNG, 76-83 V-8 Cars/Trucks, 78-87 V-8 Heavy Trucks

GM Timing Optimizer, LPG/CNG, 87-95, Cars/Trucks, 4, 6, 8 Cyl., w/Map Sensor

Electronic Recurve, Ford w/TFI, LPG/CNG, 84-91 Cars/Trucks, GM w/Large HEI Cap, 75-90 Cars/Trucks, 4, 6, 8 Cyl. PN40622 Replaces PN4062 Instructions

Ford Timing Optimizer, TFI/DIS, LPG/CNG, 87-96 Cars/Trucks, 4, 6, 8 Cyl.

Chrysler Magnum Advance, LPG/CNG, 87-96 Cars/ Trucks, w/FI, 4, 6, 8 Cyl.

I hope you find this information helpful. Let me know if you have any other questions.

Best regards,
Johnny A. Martinez
Dual Curve-Sales & Support Manager
MSD Ignition
1490 Henry Brennan Dr.
El Paso, TX 79936
Tel. (915)-857-5200 Ext. 2275
Fax (915)-856-2109
Email: ,
Web site: ,

Last edited by msdtech22; 11-02-2006 at 04:02 PM.
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Old 11-04-2006, 07:32 AM
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thanks so much for that, it looks to be exactly what i need. I must say i dont really understand what it is getting at when it says "the DCI reduces ignition timing by 15 degrees", maybe you could explain that a bit more?

but from what i can tell, if i buy this unit, and wire it up exactly like in its instructions (for dual fuel), and have my distributor curved correctly for PETROL, then when the fuel switch is flicked, it will create/enforce the suitable propane curve?? is that right?

can i ask where i can buy this unit from? it is not available through summit racing.

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Old 11-07-2006, 11:10 AM
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Please see the information below for the operation method of our older Dual Curve ignitions; 8790 series up to 8794.


The Dual Curve Ignition will electronically delay the factory set timing signal 15 degrees. The user mechanically moves the distributor timing (ahead or advanced ) back to the original factory gasoline (petrol ) set point. The Dual Curve with it's 15 degree delay for gasoline can then provide timing advance for the higher octane CNG fuel. At idle on CNG, only13 degrees additional advance will appear on your timing device. The other 2 degrees of timing are used to compute a smooth, accurate timing for rpm changes. The fuel selector switch will select the proper timing program.

The last version of the 8795 did not require advancing the distributor. On late models vehicles with MAP or MAF based timing, our timing advance units provide additional timing by complementing the sensor signal to the computer to add timing on top of the stock curve. These applications do not require moving the distributor.

The newer version of the 8795 comes in a 6x4 inch gray housing as opposed to the old 8795 which came in a 8 x 4 inch black housing.

The Latest (Gray) 8795 does not require retarding the distributor. The logic is built in to calculate the advance and is selectable to provide an additional 8-10 degrees on top of the stock timing curve for alternate fuel (LPG/CNG) when 12V are applied to the blue wire.

Last edited by msdtech22; 11-07-2006 at 11:25 AM.
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