Chris Here is some info to look over as you plan for future racing As you increase the amount of nitrous you want to use, usually to hit better ET goals, the nitrous control system needs additional considerations. I've had the fun of designing and installing nitrous control systems from 400 hp single stage to 3 stage 750 hp systems. A 50 to 125 shot is somewhat forgiving. Nitrous adds Horsepower meaning as the engine rpm decreases the engine torque increases and sometimes to the point of destruction. A 200 shot adds 200 hp and 200 ft.lbs of torque at 5200 rpm. At 2600 rpm that equates to 400 ft.lbs of Additional torque. I've watched cars launch and stall and lose an engine. As a precaution an RPM Window switch is added to the system. It is set so the Nitrous can't come on before a certain rpm (Usually 3500 rpm) and the nitrous is shut off at least 200 rpm before the upper rev limiter setting. This next one is mainly for big nitrous loads but I will add it just as an FYI. Lets say you're at half track and you back off the throttle just enough to shut off the nitrous. It takes a moment for the nitrous to clear the intake manifold but the timing goes back to full advance instantly. Some racers simply run the total advance a few degrees retarded as a safe guard and some ignition systems allow you to set a timing return ramp rate. Here is a diagram showing a MSD 7AL-3 I eventually switched over to the MSD Programmable Digital-7 (PN 7530T). Got rid of all the rpm and retard modules and gained a bunch of features. The top "Launch control relay" coil attaches to the launch rev limiter input so the nitrous is disengaged for WOT launch. The bottom power relay supplies power to the solenoids and connects to the "RET #1" input to retard the timing when the nitrous is on. It is also controlled by the Carb WOT switch and the fuel low pressure switch. The return side of the relay coil connects to the RAS output which is configured as the RPM window switch to control the nitrous rpm on and off points. Paul
Paul we have missed you around here the past 6 months!! Please visit often!!! BTW the MSD parts I took pics of are for sale...
Thanks Sean. I appreciate your response. I will visit more! Life seems to have gotten crazier, not just for me but for everyone else also. Paul
Paul, First let me say thanks for taking a moment to look through this and provide some great Information. I have used nitrous to some extent but this was almost exclusively on EFI setups. I am very familiar with the rpm switches as well as the fuel pressure safety switches. I understand their values. I have not though ever worked with the 7 series msd stuff or anything more than say your standard 6AL with timing control. This would be a bit of overkill on this particular project, but definitely Information worth learning. The diagram you provided is great and really makes it easy to help understand the system. Chris ---------- Post added at 05:56 AM ---------- Previous post was at 05:50 AM ---------- Can you shoot me a pm with what your asking for those parts?
Chris It looks like you can use the MSD ignition with your present HEI distributor. If the distributor has the 4 pin module, the module is discarded and the reluctor/pickup triggers the MSD unit directly and the MSD output fires the HEI coil. If there is a 7 pin module, it has an output to trigger the MSD unit and once again the MSD unit fires the coil. If you use the MSD 6A or 6AL, the distributor mechanical advance is kept and you will need a retard box as you are already familiar with. If you step up to the 6AL-2 programmable PN 6530, you lock out the mechanical advance and program your own advance curve. It also has a nitrous step retard so there is no need for any additional retard box. This is the unit I install for the street/strip users. Then I add the MSD PN 8969 Digital RPM window switch to complete the system. Will you be bracket racing against a dial in time or heads-up? Paul
Can do either but I want to start with some heads up racing. I like the idea of the 6AL-2 and the window switch but was thinking going to a pro billet distributor and msd coil.
If you use the 6AL-2 and the crank trigger then you only need the distributor to distribute spark and you wouldn't need the expensive billet dist. This will also allow you to phase the distributor rotor. Paul
I see what you mean. ..except for the part about phasing the rotor. I'm not familiar with this. What is that exactly?
It is important to have the rotor directly in line with the contact in the distributor cap when cylinder pressure is the highest. You want to minimize the chance for spark crossover and maximize spark energy to the plugs. So let's say you are pulling the total timing back to 28 degrees for a 150 shot. You would set the crank at 28* BTDC (For #1 compression stroke) and turn the distributor till the rotor is dead on the cap contact for cylinder #1. The easy way is to mark the #1 location for the cap on the side of the distributor then remove the cap and use the mark to align the rotor. On our big nitrous engines we would drill a small hole in the top of the cap so we could see the rotor alignment with the cap on then cover the hole with electrical tape. It's attention to all these little details that can make or break a program. I love the crank trigger arrangement in that the timing is spot on and stable. It becomes a thing of beauty to watch the timing mark with the light. Ok maybe that's too much. Some of us are easily entertained. Paul
This applies to me too, haha I can't learn enough. They say the devil is in the details, and I want this ride evil as hell!
