I just got my first car , a 1989 pontiac Firebird with a 305 tbi and a 700r4 trans . Now the car's got 317 000 kms on it and it's the original engine . I done a lil' tune up (air filter,breather,oil change n filter) and the engines runs great at idle . The exhaust system seems to have leaks somewhere cause it doesnt sound normal in the car and it backfires when the rpms drops also the valves seals are probably worned since it burns some oil too . So i got 2 questions : Does it backfires because of the seals and the exhaust or because of the timing ? Should i rebuild this motor or put a new one in it (thinking about a LT1 , a LS1 or an older 350 4 bolt main with a 4 barrel carb.)?





Thank you

 

golden,

That's about 197,000 miles..... If that engine is completely original (never rebuilt) it is IMPO about due.

You've should do a bit of research and determine what fits your billfold best. You can get a complete long block engine (block & heads) for about $1500. That's a NEW engine NOT REMANUFACTURED. It would be a relatively easy swap if you do not have to comply with any emission requirements and you go to a carb. You'll probably end up spending $2500 on that option before you are driving down the road again.

If you decide to rebuild your 305 that will cost you atleast $1000 after parts and machine shop services (boring, honing, cleaning, inspection, etc.) that assumes there is no major damage inside there. Since the car sounds like it still runs pretty good, you'll probably get away with $1000. Most guys around here will recommend not rebuilding a 305. Unfortunatley, they are not the ones writing the checks for your vehicle so you have to decide based upon all the factors what you need & or want, versus the depth of your pockets. Generally, I tend to agree that replacing a 305 with a 350 is the better choice for most people. My son and I did the same but ONLY because we were able to get a used 350 block for $50. An advantage to rebuilding your 305 is that you can retain your TBI and do nothing to the Computer or wiring harness.

I know almost nothing about LT1 and LS1 swaps there is a forum/stickie dedicated to this and it's a better source of information than I am. Gonna cost a whole lot more for one of those.

As far as the back firing is concerned it could be caused by a number of things and anything I say will probably be wrong. It could be Timing, Valve SEATS, or the Fuel Delivery System.....

Since the engine has nearly 200,000 miles on it, it's burning oil and backfires..... I think it sounds like your on the right path looking into replacing or rebuilding the engine.

Sincerely,
Kurt

 

My inital LT1 swap with 6-speed cost me just a tad over $3000, and that was me doing all of the work. When it spun a rod bearing it only cost me around $900 to rebuild, that was all of the machine work, bearings, gaskets, and rings.

Now granted, I had a brand new Perma-dry oil pan gasket new seals in the timing chain cover so I didn't have to buy a complete kit so it was cheaper to rebuild it.

What it really comes down to is how comfortable are you with doing a rebuild.

 

Does a pontiac 400 or 403 engine would fit right in? And if i plan to add some power should I chang the 700R4 for a turbo hydramatic one?

 

The Pontiac engine part is detailed in the "Important/Useful Information" sticky at the top of this forum.

TH700s can be made to handle the power. Whether you do that depends upon how much you want/need overdrive. A TH200-4R is a pretty good choice if going with a Pontiac engine, as it is easy to make capable of the power, and most have the BOP bellhousing pattern.

 

Once you start replacing the bottom end of the 305 you should just build a 350 more bang for your buck. Blocks are easy to find and for the same money you have a much better engine. If you build a mild 350 the fuel economy is about the same.