427 SO Timing/cooling fans

[For Paw]

I have a 1966 SO with a lumpy cam (not extreme). I am running Dual Quads Holley 1850's. I started with Dual 390's but the carbs were defective from my engine builder so he replaced them with these. I have an MSD 6AL with Blaster Coil and and Ford Electronic Distributor, and a MSD 105 AMP one wire Alternator. I have disconnected the alternator while running and I am getting full current. All these things seem to be in working order.

Ever since I first started this newly rebuilt engine, I have had a lot of trouble getting it to idle when the cooling fans kick in. They are on a proper relay circuit, and all my grounds are new and in good shape. I have had to advance the timing to 18 initial just to compensate for the fans. I have done a fair bit of tuning to the carbs. It does idle pretty Ok now, but with this much advance it's getting hard to start when hot. The engine maybe has a total of 3 hrs-so it is not really broken in yet. Any ideas out there or has anyone experienced this "drag". For other reasons, I am thinking of switching to Weber stacks and wondered if this might help the idling or timing issues?

Thanks to one and all.

ForPaw

[496fe]

Does the idle get better when the fans turn back off? In other words, is there an exact relationship between the fans turning on and off and the idle getting better and worse?

This is a wierd one. Also can you give us your cam valve timing and lobe center degrees.

[For Paw]

Yes, the idle improves once the fans shut off. I am pretty sure this is a Alt or Pulley issue. The MSD that I have only gets excited at 3000 and above. It does not put our enough at Idle to keep up the draw of the fans. Lobe seperation is 110. Not sure where on the cam card is the valve timing info. Now thinking of a different 1-wire Alt that puts out the amps I need at idle.

Thanks.

[496fe]

The electronics should be powered by the battery, not the alternator. The alternator merely charges the battery, so I'm not sure that a one-wire alt will make much difference. Methinks you are going to need to solve this problem the old fashioned way - eliminate one potential problem at a time. 1) connect a multimeter in series in the MSD hot lead and watch the voltage when the fan goes on and off, 2) same thing on the coil hot lead.

Good luck,

Brian

[PANAVIA]

I think you need to measure voltage drop at idle (700-800) when the fans turn on. --

and again at 1000,1500,2000 RPM. There should be a initial V drop then the alt should kick in to prevent discharge of the battery.

The alternator sizing or index speed sounds like it is off and is not able to prevent discharge at idle.

--Steve

[wtm442]

Is your battery OK? Maybe getting weak and ready to die?

[Cobra #3170]

The cause might be related to the torque required to drive the alternator when the fans kick on, the alternator can put a significant load on the engine even if it isn't keeping with load demand at that RPM. I would not change initial advance to solve the problem because you should not alter the curve assuming it's right in the first place. In the 70's they used to use a "throttle kicker" on engines to help offset A/c loads IE speed up the idle when the a/c was turned on. If power was cut to the a/c the engine would drop back to normal idle speed. These devices could be adjusted for idle speed in both on and off conditions and mounted to the carb at the idle stop. Perhaps you could use one from a salvage yard. I have a similar problem to yours but it is related to low voltage when the fan comes on. My problem is the voltage drops to a point where the fuel injectors don't function properly at 11.5 volts and the engine won't idle. My alternator is only a 50 amp Kubuto tractor unit that can't match the load at 2000 rpm.. Since you have carbs I would bet it is alternator drive load causing the problem.

[Cobra #3170]

I think your problem is alternator torque load on the engine. An alternator can put a significant drive load on the engine at high load conditions and actually cause it to slow the engine enough to cause a "rough idle". There was a device used by Ford and others in the pre fuel injection days called a "throttle kicker" that mounted to the carb and would speed up the idle when the a/c was turned on. It was a small solenoid that functioned as an idle stop that was higher set at a higher rpm when on and went back to normal idle when off. This can be done automatically on fuel injected engines with computer stepper motor idle control but not on a conventional carbed engines. Your ignition might potentially be a problem but even an MSD will function at lower primary voltages.

[For Paw]

Thanks guys. I am almost certain it is an Alternator issue. Battery, etc working properly under load. I am going to try a different ALt, maybe a tough choice and see. The MSD don't charge till 3000 or so and idle on my engine is 1000. The initial V drop when the fans kick in kills the MSD box and I have to blip the throttle to keep it going. It has been a nasty gremlin to chase down but I am not going to let this one win.

Thanks for all your input. I will try and keep you posted.

[Jerry Clayton]

I have seen a few cars that had the power for the fans wired thru the ignition switch--when the fans came on they and everything else suffered from low current. My method of solving these issues

NO reduced or underdrive pulleys----
Wire directly from alternator to relay for fans, use temp sender to ground the relay for operation, only run current to switch the relay thru ign. switch--this eliminates extra wire length amps the ign sw must carry and supplys the power for the fans direct when engine is running

A COMMON source of electric problems in vehicles and boats---bad grounds, remote battery locations, underdrive pulleys

[undy]

There's another potential cause, a very weak idle too. A very lean idle mixture could be easily "upset" by the increased alternator load trying to keep the battery up to snuff.

Dave

[RICK LAKE]

For Paw Let's start in the beginning. Do you know the Alt output?? Yes, No, maybe? You need an Alt that can keep all the electrical loads running and keep a min of 12.5 volts going to the battery at 1000 rpms. THE ALTENATOR is what powers all the loads once the motor is started. The battery is for staring the car and backup if the car idles for a long time with everything on,lights, cooling fans, blower motor, Msd module, Msd coil, electric fuel pump, etc. The batttery also absorbs the charging spikes from the ALT. What pulleys are you running? If they are not about 6" in diameter for the waterpump and crank pulley, they are TOO SMALL. The March system is underdriven and is good for racing and high rpm motors but not street driven low rpm cruiser. Here is some facts, MSD module draws about 16-20 amps, the coil draws about 6-10 amps, coolant fans, depending on how many from 10-30+ amps, electric fump pump 8-15 amps, Head lights and tail lights about 8-14 amps depending on what type, heater blower motor depending on speed, about 12-17 amps. With just the 6 thing a have here you are over most alt outputs at idle. An MSD system will not work below 10.4 volts. This is the steady drain on the system. Turning things on and off you are looking at spike loads of double to triple the running loads. This is why your car starts running rough. Not enough juice. A 100 amp min is the standard thing with normal pulleys. Most new car that are loaded are running 200 amp alts. Your playing with the timing is not helping. What is the CCA, cold cranking amps of the battery?? You should have something in the 800-1000 if possible. If you are going to idle the car for more than a minute or 2. Shut the motor off and just run the coolant fans. Lets a solid lifter motor run at idle is not good for the valve train IMO. Get the right pulleys for the car to start, make sure you have a large CCA battery, and replace the Alt with a min of 100 amp. A 140 would be better and cost about the same. Make sure the MSD system is hooked up directly to the battery for the red and black wires. This should help fix your problems. If you have any questions call me 732-254-3536 in the evening est time Rick Lake. Ps MAD Alt and PA Alt have real easy alts to swap into your car for plenty of charging. You may have to swap your amp gauge to a volt gauge with the power increase. There kits are 1 or 2 wire. Something to look into. Rick

[Hans-Olof Blom]

The current draw for a MSD 6AL unit is 1 Amp/1000rpm. At idle this means a current draw of about 1 Amp.

A standard alternator is enough for most Cobras.

[RICK LAKE]

Hans-Olof Blom Hans if you go to the MSD site and check out Q&A you need 5 amps and 10.2 volt min. This doesn't include the coil. Do you know how big the compasitors need to be to put out on an HVC that makes 80-100,000 volts with 1 amp. About the size of a paint can. I have been running an MSD system for 10+ years on the cobra and another 15 years on my Trans-am. Number have posted above are very close to the real world numbers. Rick L. Ps I think you are saying that with the addition of 1,000 rpms the amps need to run the system increase 1 amp. It's more like 2-3 per 1,000 Also a 60 amp Atl can't power a ERA cobra with all the power on at idle with an MSD system. Alt putout is about 35-38 amps at idle. Msd, lights, blower motor, and 3 cooling fans, are over the max. I know from racing the car. Rick L.

[CHANMADD]

Guy's, I think that that kind of draw is normal.These motors are running pretty decent cams and as such don't make much torque at idle. The fans that everyone seems to run today also draw a lot....wow..earthquake right now.. . The best would be to increase your idle speed ..to compensate for the cam..not the fan. or the alternator. My motor drops 200 rpm when the fans turn on,and it has never worried me.You could probably find one of those devices from the 70...called an "idle-up" control which just opens a solenoid that lets a little air into the intake to increase idle..very simple..one wire