there is a pretty significant difference between what my tach says, and where the rev limiter of my 6AL kicks in.

i would think that the MSD box is more accurate, because it is directly controling the ignition system. and, the factory gauges aren't known for being the most accurate.

what do you guys think?

-brian

 

The MSD is more accurate. Factory tachs can be off by a couple 100 RPMs.

 

how much is it off?

 

tachs aren't off a certain amount of rpm usually, they are usually a percentage off of the whole. If you can understand that

MSD is more accurate, my factory tach is usually off about 1000rpms or so when i had my 6BTM. put the chip in for 3,000 and the rev-limiting wouldn't kick in until i saw 4,000 on my factory tach

 

hmmm makes me wonder. I want to get a new tach and a MSD box soon. If the factory dash is showing 1k more at say 5500rpm youd be wasting good power.

 

no, you have it reversed. in *my situation* if the tach in the dash is showing 5500rpms, then in reality it is only @ 4500rpms. Not the other way around.

What i did to alleviate this situation and to know where/when to shift is i bought a proform shiftlite with an adjustable dial on the rear (no chips needed) for $50.

I'm going to use that along with my FAST ecm to accuratly figure out shift points. The shift lite will also be accurate because the wire it uses to sense rpm is either via a MSD tach output or the negative side of the coil.

cheaper than getting a whole tach which i had done previously, just set it about 200rpm prior to where you want to shift. That way you see the lite and by the time you react you are shifting where you want to