So I have a 91' RS with a 305 TBI with an external coil. I understand that most will say that the external coil dizzy is better and has more output, but i was wondering if an internal HEI dizzy would work in its place? The dizzy that is in the car now has quite a bit of play in the gears and such and it is pretty old. I have a brand new MSD Streetfire dizzy with the internal coil that I want to put in it. I was also thinking I could use the vaccuum port on the throttle body that was for my THERMAC, for the vaccuum advance on the new dizzy. Anyone know if this will work with just a little wiring alterations?

 

You can't put a vacuum advance distributor on a fuel-injected car.

 

even though a throttle body is a half-breed? can you explain what part wont work? just curious.

 

There's nothing half-breed about TBI.

The ECM needs signals from the distributor to measure engine speed, and needs to send signals to the distributor to control timing. Hacking it up to take timing control away from the computer is pointless.

 

One mechanic mod, is another mechanics hack. Not saying this will work, but it's notexactly pointless. All it takes is a bad shot of gas to throw your O2 sensor off a bit which that signal gets sent to the computer and then in turn can make other things, such as timing advance, work ineffectively. Maybe not for good, but for that moment at least. I wanted to do this because I have a brand new StreetFire dizzy that I wanted to use instead of buying a another unit. The StreetFire dizzy qould be advanced by the vaccuum which is going to increase with acceleration by default. No biggie, thanks for the insight Apeiron!

 

It's not solely about advance, it's also retarding - the computer does both depending on the sensor readings and such. Computer also changes fuel according to distributor changes, as well as changing timing settings according to fuel changes. It's a sybiotic relationship - I highly doubt you'll get a vac-adv dist to work inan otherwise computerized system.

If for no other reason - the fact that after 30,000+ TGO members in the last umpteen years haven't been able to pull it off, it's highly unlikely that you will. That's one great thing about the age of 3rd gens and TGO - if it was possible, it's already been done! If it's not been done, then it's not possible to do.

 

The computer controlling the timing, even with our primitive computers, works a whole lot better in the big picture than the old analog/mechanical stuff ever did.

 

Yeah trust what these guys say. Sell the distributor you have and get the correct one. I have a used one you can buy. I'll even throw a new ignition module on it. All you'll have to get is a cap and rotor. problem solved. PM me.