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Discussion Starter · #1 · (Edited)
Spoke to a tech rep at MSD, who suggested the 8361 distributor for a 496/turbo 400/3.73 with Vortech V7 application. Its in a '70 chevelle and used mostly for bracket racing, but is driven on the street to the track and may soon have an 80 mile round trip to the track if a contemplated move finally happens. I add 112 octane race fuel to 93 pump gas when I arrive at the track and average about 100-102 octane then.

The heads are aluminum edelbrocks and the static compression is 8.5:1. Cam is Comp Cams blower cam with .540 lift, 240 duration, 114 LSA.

The 8361 is supposed to be identical to the popular 85551 but also has vacuum advance, which I believe remains helpful for street use. The rep also recommended the 8207 SS coil over the Blaster 2. I use the MSD 6BTM with a tired HEI unit currently.

Before dropping the coin, is there any other feedback on this? There is also the digiatal 7 series but apparently isn't so necessary if compression is under 13:1. The 6520 ignition box is supposed to be a "tweener" between the 6AL and Digital 7 series.

This forum has saved my skin before and little feels worse than making a purchase just to learn you bought the wrong stuff again. My cam is iron, but I also see some people going to the melonized GM gear, which has to be honed out at a machine shope. Does my bacon need saving yet again?
 

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I would keep the 6ALBTM and run the 8361 dist and a procomp or simular coil like the accel or blaster2. I know several guys running this setup and prefer it over the digitail boxes. I personally save cash anytime I can but I wouldnt recomend trying to save a buck at the expense of my engine. That said the digitail boxes seam like a pretty big expens for not much gained. just my 2 cents
 

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Discussion Starter · #3 ·
Good to learn there isn't much to gain with the additional expense of the digital boxes. The cost is about 50% more. The appeal had also been in changing the timing curve without disassembling the distributer, but I'm sure the timing curve with spring choices in the 8361 vacuum advance distributers are based on much R&D.

Still wondering if the cam gear on an iron cam is the same big issue as with a billet cam, if there any experiences on this out there. The instructions on the 8361 distributer say it has a .500 shaft so the GM melonized gear may not need honing - I don't know the Inside Diameter of the GM gear or if its necessary. I'm sure MSD would want to prevent gear failures in customers engines as they are so costly and hard on a companies' reputation. I didn't ask the MSD tech about the gear but know this was a large issue on the billet roller cams.
 

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I'm going to switch to the 7531 box from my 6al and btm. The 7531 is alot more money but it is the last box you will need. Peak horsepower you will see virtually no difference between the two but when it comes to managing power to get the car down the track there is a world of difference. Being able to retard timing through the first few seconds is very helpful if your car is traction limited. Virtually every high powered blower and turbo cars run this box because of its features and reliability. Which leads to the next reason I'm switching, reliability. The btm's are known for having the internal diaphram burst which means no retard. The 7531 uses a map sensor that is 1000X more durable. I've also had issuse getting my btm to do what the knob says it will do. A friend and I both have btms and neither one did what it said out of the box. Put a regulated air supply to the btm and double check what its doing and when, you'll see what I mean.

The 7531 will also handle the vac advance for you and the amount is totally programable. And its one box, not the wiring nightmare under my dash right now.

The bottom line is I should have bought the 7531 the first time. Now I have a bunch of stuff that kinda works that will sit on the shelf.
 

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Discussion Starter · #5 ·
Thanks for feedback on blown application - I'll be sure to check my BTM boost pressures against what's really happing to timing. I'd mistakenly assumed it was doing what its supposed to.

I don't currently have traction problems - run ET streets on '70 chevelle at 11.1/122 MPH with 4150 LB race weight in Denver with 7000-9000 Density Altitude with 7 lbs boost, footbraking at 2K. I think there's more in it, but want to sort out the timing first. I've got some things to look at on the BTM, and hadn't considered a burst diaphragm, but maybe less likely at my lower boost level. I see the sticker shock on the digital unit, but there's a large investment in the motor to protect. Probably cheaper than a State Farm policy.
 
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