Tach accuracy

[72 LS5]

I put a second hand MSD6AL box in ol Blue a few months ago and it had a 6000 pill in it. A few times the tires broke loose and the tach swung past 6 grand and I didn't feel the limiter kick in. I've been real careful not to over-rev it and figured the MSD may not be working 100%.

 

So this weekend I bought the set of 5000 rpm pills and stuck a 5600 in there, again the needle went past 6k. Finally, with the 5200 pill, the limiter kicks in just shy of 6000. Dang - my tach must be waaaaaaaay off. Like almost 600 rpms off. It's a VDO that I've had in the car for probably over 20 years.

 

My question is this: Can I be confident that the MSD box is giving me the correct rpm for the limiter?

[Sam (Bones)]

hook your tach to the negative side of the coil and try it again

[Mike 57]

I have a Auto Meter play back tach. When I down load my run I see the exact rpm that I choose for my launch on my MSD. I also have hit the the high limit chip a few times and it has never gone over 7000.

I still have the factory tach and it is slow to respond and then swings past the RPMs that the Auto Meter shows.

[72 LS5]

Mike - so your MSD is spot-on from your download, that's good. I'm going to have a factory style tach when I install the gauge package in the future, so I won't be putting too much stock in the accuracy. As long as I trust the 6AL box, I'm good.

 

Sam - with the HEI gutted and MSD hooked up, I wasn't sure you could still use the negative side of the coil. I have the tach hooked to the port on the box.