Jaxian

Ok, I understand the theory behind how this works, it’s the actual application of it that has me a bit thrown off. Let me recap the theory of the Crank Reference Angle setup on the FAST XFI. They want you to move the motor to 50 degrees BTDC for a magnetic pickup distributor and line up the reluctor with the pickup for number 1 cylinder. This happens on my distributor to put the rotor tip exactly under the number one post.

Now the reason for this took me a few minutes to understand but here’s the deal. The XFI gets the trigger signal at 50 degrees before it has to fire the plug. What it does is look at the number you entered in the software under Crank Reference Angle, that being 50 degrees since that was what they said to turn the motor to. Then it looks up the ignition table and looks to see what you want the advance to be at that RPM, say 30 degrees, then, it subtracts that setting from the CRA and comes up with 20 degrees. Meaning it waits for 20 degrees after getting that trigger signal to fire and it should hit right on 30 degrees.

They do tell you to put a timing light on it to make sure the ECU and the actual timing tab agree and you can adjust the CRA in the program if it’s off a few degrees so they are both saying the same thing. The reason they pick 50 degrees is apparently the ECU needs a 10 degree buffer to do the fuel and ignition computations and they figure in normal circumstances you won’t run more than 40 degrees advance so it should always be able to do the math in time and fire the coil when its supposed to. So that’s the first part of the setup and the theory behind it. Pretty straightforward.

The second part is to kind of compensate for what is actually happening. They say with the distributor tightened down roll the motor to where you will make the most power. Say 30 degrees again. Now of course the rotor that was right under number one post at 50 degrees has moved. Since the distributor moves at half speed that 20 degrees of crank movement moves the rotor 10 degrees out from under the number one distributor cap post. The idea then is that you use your phaseable rotor and move the tip back under the number one post. My problem is when I went looking for distributors the one MSD recommended was the 2345. It was the only one that would fit the application and had a cam position sensor and all. Problem is, it doesn’t have a phaseable rotor. They say at the end of January beginning of February they will release the 23451 that will have a phaseable rotor but as that was three months off at the time that didn’t really help much.

So my problem is this. To pass smog my car has to have an idle timing setting of 6 degrees. That is 44 degrees off of the 50 degree CRA they use. Even at half speed that the distributor runs that means the rotor tip has moved out from under the number one post 22 degrees when it goes to fire the coil. Since each distributor post only has 22.5 degrees of space on either side of it before the tip of the rotor is closer to another post that is means its going to fire at idle at the absolute last possible moment before its closer to the next cylinder. I have the feeling this isn’t going to run so hot.

My guess is FASTs response to this will be, ‘too bad, you should have bought a distributor with a phaseable rotor’. I already know MSD’s response because I called them with the issue. They said, “You can’t phase the rotor, you can’t move the reluctor, just don’t worry it will probably be fine”.

Since I know a lot of you have done this before I was wondering what you did to deal with it. I know there is an Accel distributor that is marked in their literature “for use with Gen VII ONLY”, that has all the features of the new MSD 23451 but obviously I didn’t want to get it since I don’t have a Gen VII and MSD said the 2345 would work fine. I am not rich and don’t want to have to wait two months and buy a $500 distributor and throw this brand new one away, so I am sure there must be some way to make it work well. I looked at the 8420 Cap A dapt distributor cap kit with phaseable rotor that is supposed to work with all Pro Billet distributors but the FE Ford ones but the MSD tech said it wouldn’t work. I asked that second MSD tech how to get around the problem and he just said he didn’t know. Any ideas? I would like to start the car this weekend. I must just not be understanding something basic here I guess.

Blown Vette

http://www.fuelairspark.com/Catalogs/NP2006/Page2.gif

Jaxian

That distributor looks like an exact match of the MSD 2345 down to the small details. I wonder if they just had MSD make some for them and moved the rotor phasing to compensate for the CRA angle. I have tried calling them a few times to see but haven't gotten through. Still, it ends up like the 23451 in that I would have to buy another distributor if they won't change mine for me. Will try to call FAST and MSD and see if either can answer. Still it's a brand new product and people have been running these for years so I am still wondering how they used to do it. Thanks for the link.

EDIT: Got through to MSD, the tech said because of the gear reduction at the distributor the rotor moves 90 degrees between posts, not 45 degrees. I had just diveded 360 by 8 and gotten 45, I had never heard of the rotor as he said "cramming 90 degrees between the posts". So, very interesting, will have to physically check. He also said the FAST was just an MSD distributor rebadged.

TONYDEE64

I went through exactly the same thought process as you did when I went with the FAST box and a MSD 2345 Dist. (you and I apparently think too much!) Don't worry, you will be just fine. The reason they want you to use a phasable rotor is so you can align the rotor with the post where you make the most HP, theoretically providing an easier path for the spark, thus a more accurate spark event. Don't worry, you will be fine as the spark can easily make the jump. I think this exact problem is precisely why crank fired distributorless ignitions are the hot ticket. If you think about it, any computer controlled car with a distributor does the exact same thing as your FAST ECU.

Jaxian

Thanks Tony, that is a huge load off my mind. I kept trying to tell myself to just put it in it will be fine, but to hear it from someone who actually has done it counts for a lot more. Again, thanks a ton man.

SloRvette

Your car isn't going to be very happy idling with 6 degrees of timing. That 6 degrees is for when the computer isn't controlling timing on a stock ecm car. EST is disconnected. Think of that 6 degrees on a stock car the same as the 50 degrees on a FAST equipped car. That's just where the computer expects to see a signal sent from the distributor and bases timing calculations off of that. Stock cars ususally idle around 19 to 25 degrees TDC with the computer controlling timing.

I wish you'd listened to me about the Accel distributor. It really makes this easier.

You can also go up to 65 degrees TDC for a crank reference angle if that gets you better rotor phase. You need to allow 10 degrees diference between your max timing in your timing table and your crank reference angle.

Rusted40

dunno if your distributor is made like my #85501 MSD
but I pressed the reluctor off it, discarded the key
and put set screws in it to make it "phasable"

no problems YET

Jaxian

Turns out there was an easy solution. If you use the 8441 Cap A Dapt big cap kit and the 8421 rotor you get everything you need. I have pictures of it in this thread if you want to see what it looks like and how it fits a Super Ram motor.

http://forums.corvetteforum.com/show...1232745&page=2

Hopefully that can save someone else grief since it took some doing to get the right part numbers out of MSD.