Okay, I recently swapped a "recently rebuilt" 305 into my previously dying (okay, dead) 83 Firebird 2.8L. It has the 350 Turbo tranny that was attached to the engine in the 85 Camaro it came out of (which was wrecked). Anyway, to get to the point, the car is still only marginally powerful, barely breaking traction even though it has 14" wheels and the originally low gear ratio (3.08 maybe). It's also averaging 8-12mpg gas mileage, usually 8, which someone told me in another board section is rather bad.
So anyway, my question is, what things should I look at when trying to diagnose whatever is draining power/gas, and what types of mods are cheap/efficient that deliver reasonable power? The carb is a Q-Jet, but the guy who did the swap is going to find another one because mine doesn't have a working choke (won't start easily).

 

What are the details of the engine? What was the engine code? Has anything been done to it like a cam swap or a new intake? Was it left completely stock when it was rebuilt? It's probably an LG4 and if it's stock I wouldn't expect too much power out of it anyway. Running perfectly those things only had about 150-155 hp at the crank.

 

Yeah... my suspicion is that it's a completely stock LG4, but I've been trying (failing) to find out exactly what engine code. I'll try to find the casting number or whatever. (I'm kinda new at the car stuff!)
I guess I just meant to ask about general diagnosis ideas for mileage stuff.

 

What carb and distributor is on it, and is the right computer properly installed and operating?

If this is all the computer-controlled stuff without the computer, then there are several things that are going on, all of which will make it suck gas like no tomorrow and still run real lazy.

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"So many Mustangs, so little time..."
ICON Motorsports

 

They didn't use the TH350 in 1985.

Maybe you have a 75, that would explain the little power.

 

Cheap way out is to try and fix the qjet.
I have an 85 camero with 350 and turbo 350
and it got 14/15mpg with a edldebrock 200$
fix. but i highly recomend a holley "510-0-80457s" its about 220$ chrome 600 cfm electirc choke carb that can be purchased at autozone. it's not a cheap fix but its a 18/22 mpg fix well worth the money. and that 18/22 is with a 350 with a lt4 cam. so you have to get the same or better mpg with a 305.

 

Thanks for all the discussion.

I just got off of the phone with the guy who did the transplant and he decided that I need a new Q-Jet. Apparently used ones are hard to find in this area. If no luck I'll buy new.
But this

RB83L69: Yes, it does not have the computer
system which originally controlled the car operating. What types of things do you mean, in general? The guy hasn't done much 6->8 swapping, despite lots of same motor swapping.

MacGyver: I'm guessing now that despite the camaro being an 85, nothing in it is from that year. The originally injected engine has been carbed before I bought it.

And thanks SUPER-SPORT-CHEVY for your recommendation. That may be what I end up doing.

"Third-Gen-4-Life!"

 

Wanna see it? I think it's awesome. It's the, uh, red one out front, not the van in the garage!

 

Well, if the parts you have on the engine are the computer-controlled onees but the computer is missing, then 2 things will happen right off the bat.

• The mixture control solenoid in the carb will go to the full rich position and just sit there. So, you will get the power enrichment mixture 100% of the time; idling, cruising, etc.
• The distributor has no mechanical advance (advances timing as RPMs increase) and no vacuum advance (advances it some more when it's under light load, like cruising). The computer is entirely in control of the ignition timing. Without it, your timing will be as much as 30° retarded from where the factory designed it to be, let alone optimum.

Make sure you have a non-computerized carb and dist on there before you go any farther. The engine has no hope whatsoever of decent gas mileage or performance if it has the stock stuff installed but no computer controlling it.

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"So many Mustangs, so little time..."
ICON Motorsports