GreenieG

hi i dont much about carbs so i wondering if anyone could give me some advice. i got a 87 z28 with a t5 tranny and a 305 v8 which i might swap out for a 350, but no matter what i wanna keep it carbed so my question is should i just get a new quadrajet or say something like a holly double pumper, i want my car to have some giddy up but other than that i dont intend to race it or anything just daily drive it for school and work(which ain't to far away so no worries on gas) so yeah if anyone can give me some advice thanks.

camaronewbie

You need to keep the factory carb setup. There's no performance gains with an aftermarket carb, and you get less mileage. The factory computer controlled carb setup is really the best available option for performance and mileage both. If you suspect you have carb issues for some reason, have it rebuilt, but keep the factory setup.

If you go against this, you'll need to replace the distributor as well with a vacuum-advanced distributor, as your computer will not be functioning at all anymore without the factory carb and therefore you'll get no advance/retard of timing from the computer.

PeteZ28

For a stock engine certainly keep the original carb. For a modified engine, try the ccc qjet. It may work OK but I don't think they do in all cases. Mine seems lean (slight stumble) at small throttle openings. Manifold vacuum on modified engines (it cam change) is changed and affects ignition timing also. Your are just not sure what you have using the original computer controlled system with a modified engine. What might work well to add power for a daily driver is a 350 or 383 with stock-type cam and healthy compression with the original qjet and distributor.


If you go against this, you'll need to replace the distributor as well with a vacuum-advanced distributor, as your computer will not be functioning at all anymore without the factory carb and therefore you'll get no advance/retard of timing from the computer.[/QUOTE]

This is not really true. Removing the stock carb does not shut off the rest of the system. Put correct resistor across the MC sol and a dummy TPS sensor plugged in and the distributor will have advance.

I tested this at 600, 1000, 1500, 2000, 2500 rpm. Advance was as follows:

With working TPS: 26,24,30,33, and 42 degrees
With non-actuated TPS: 23,24,34,34, and 35 degrees

This was with the ccc-qjet installed. Yes there was probably some measurement error also, but obviously there is advance. Even though the service manual says the TPS does not control ignition timing, it appears that if the computer does not see the throttle opening it may have some programming in it to limit advance to 35 degrees. Adding a brackets and links to actuate the TPS with an aftermarket carb would keep the advance close to if the original qjet was installed. Again if a non-stock cam is used it alters carburetor signal and timing also. For skeptics: Page 6E-132 1984 Helms Camaro service manual. The ECM uses information from the MAP (or vacuum) and coolant sensors in addition to rpm to calculate spark advance as follows:

Also from the SM: To properly control ignition/combustion timing the ECM needs to know:

Crank position
Rpm
Load (MAP or vacuum)
Atmospheric pressure
Engine temperature

So going to an aftermarket carb doesn't mean automatically the distributor has to be replaced also. I do agree that if it does run well with the ccc-qjet on a modded engine than keep it, but in some cases it will not unless modded also (more than just secondary metering rods).