Ramon Duvernay

Sirs,
I have a 86 Pontiac firebird with a bad lg4 305 engine in it. I want to know If you can get away with putting a 350 engine in it with some ching pow 180 cc heads a a 222 @ .050s crane Z cam with variable duration lifters AND not having to get a new custom chip for it? It is a Quadrajet engine. Has anyone done this?

sofakingdom

iTrader: (1)

There's not much "chip" out there for 86 carbed setups.

That's a small enough cam that it should be easily within the adjustment range that the carb has. Most likely the things you'll need to change will be the idle air bleed (probably will want to go CCW about a turn) and sec air valve tension (will want to be lowered from 7/8 turn for 305 to about 5/8 turn for 350).

I'd recommend skipping those lifters. Just use regular ones.

Ramon Duvernay

The lifters that I Already have are the Crane cam high intensity ones, super quiet one. I don't think the lg4 has a knock sensor on it anyway. It should bleed down the cam to act like a 214 duration at idle

naf

iTrader: (7)

KS started in 85, easy enough to see whether your 86 has one now but it certainly should have had one at some point early in its life

the ccc system should handle that set up pretty easily

performance chips for this system mostly just changed the timing curves. the basic functionality of the fuel trim was pretty universal among packages that would accept that carb setup without complaint

Ramon Duvernay

Sofa,
will running shorty headers affect how the idle air leed and sec air valve are adjusted at all? THK for the help so far.

Vader

Assuming the headers have a provision for mounting an O² sensor the system should function reasonably well. Ultimately, the carb may require a bit of secondary adjustment if the vacuum at higher RPM is changed by the cam, but the adjustment should be no more difficult than the usual, routine adjustments performed at a complete tune-up.

sofakingdom

iTrader: (1)

Not by itself; mostly, the change in CID will dictate that. Although the headers will generally make the motor want more fuel, to go along with the more air that the headers allow it to pump through. That's what adjusting the idle air bleed does.

And I apologize, it will probably want to go CW, not CCW. CCW leans out idle and part-throttle. But, once you start tuning on it, it will become obvious what the right way is, because the engine will run better one way and worse the other, until you hit the optimum point. A dwell meter will help: ideally you'll want the carb's control range to be such that the MCS duty cycle is about 50%; which is, 30° on the dwell meter, on the 6-cyl scale. Or at least, nowhere near 0° (ECM is seeing an extreme rich condition at the O2 sensor and tries to correct it) or 60° (ECM is seeing extreme leanness and tries to correct that).

As Vader points out, this all assumes the whole feedback system is in proper working order, which includes making sure the O2 sensor is functioning correctly.

I STONGLY recommend you NOT use those lifters. Just put regular ones in it. Back when I was building motors alot, SEVERAL people paid me to take that crap OUT and put regular ones in. I remember one guy insisted over my objections that I use them when I built his motor, and then hated em so bad he came back and had me delete em. It's one of those ideas that looks great on paper and in ad copy, but out here in meatspace, not so much.

naf

iTrader: (7)

I wouldn't recommend making any changes to the IAB without using a dwell meter or scanner.

If the system was now known to be in functioning order and properly adjusted, a small change to the IAB screw might be assumed to be warranted BUT not for a motor with a system of unknown functionality AND adjustment.

Acquiring a dwell meter or scanner will not only allow precise adjustment but enable one to troubleshoot the system and ensure it is working properly in the first place. A mal-adjusted, or faulty, ccc-qjet system is, in most cases, to assumed to be the present condition in an LG4 of this age and suspect pedigree.

Adjustments to operation of the secondaries is divorced from the circuits that the ecm for the ccc-qjets control.

A mal-adjusted (or functionally deficient) ccc system may appear to idle fine, have 'tolerable' throttle tip in but will never deliver the mileage and efficiency that it should.

If you're not now averaging better than 20 mpg on the highway it's a clear sign of an issue.

The good news is that the equipment required is inexpensive and the help easy to acquire, especially here. No point in swapping other stuff out until what you have is confirmed to be right.