So I was the guy who destroyed a 4.3L a few months back. Now I have a new 4.3L in the car, but about 5 months ago and 2k miles ago it started a slight knocking. Now its getting to a full-fledged knocking above 3k rpm. My question is how much longer do you guys think this engine has? I was finally gonna throw in some oil stabilizer and see if I get any extra oil pressure. I run about 40/50psi cold idle/moving and 15/20psi hot idle/moving. I am starting to dislike the 4.3L but to its credit, I don't know many engines that could survive 2k miles on a rod knock. I should add I don't have the low oil pressure light at idle like my last engine did a year out from its death.

 

It's hard to say how long the engine will last, could be years, could be tomorrow.

 

They go downhill fast once they start hammering. Stop driving now and either fix it or junk it. It's not a reliable vehicle that will last the Winter. Tomorrow may be its last time. I think that is the answer to the question you are really asking.

Been there, done that! It's simply the price that you pay for the way you are driving. Either get a vehicle that will take it, buy a lot of vehicles, change your driving habits, or be prepared to walk a lot! I have done all four over the years and speak from experience.

After many years I found the best combo was to have a primary vehicle that I drive very nicely on the street, and a built racer that I drive very hard on the track. Kills my desire to drive fast on the street as I know I could absolutely and definitively smoke posers who are being impatient with me. I just chuckle to myself and slow them down even a little bit more when traffic is oncoming, before traffic clears and they go past me in a big huff!

 

When you say you put on a new motor, was it newly rebuilt or a swap from another Blazer?

 

It was a used engine.

 

Well, I guess I will drive it till it dies. I hold out hope it will last even if it probably won't. I have no other choice really. Then I will go and buy a Midget or Saab to drive in New York winters. The sad part is I never really pushed this engine. Honestly though, I think the transmission will go first oddly enough.

Also, the second engine was from an 01 Bravada with a blown trans with 120k miles that had the top end rebuilt and put into my Jimmy.

 

The 4.3 IMHO is a solid platform for builds. It is just not used widespread for tuning because it is so easy to get a V8. Replacement engines mostly die because of neglect in servicing. 120 k miles is a lot, if you hardly ever change your engine oil. Running without air filter or damaged air filter elements. Running it over longer periods with faulty ignition or injection which can cause carbon buildup, etc. etc.
It causes ever more slush and deposits within the engine and especially oil passages. Revving the engine when it starts-up right away pounds on bearings. Add the restrictions by deposits, the worn bearings. Then you rebuild the top which is all on a sudden performing better again and changes the load on the bearings...
...and there goes the rod bearings.

The connecting rods are the most solicited bearings in an engine anyway. And contrary to what you would think, turning the piston around at the top dead center is where sometimes the highest bearing loads occur.

The issue with your engine is in my opinion the auto-cross thing. You bounce a car and you ride it in oval shapes a lot with high side forces. I would guess that one of the rods at #'s 1 or 2 gave in. That's the furthest away from the oil pump, where oil pressure is the lowest.

If you drop in a used engine into a toy I would always suggest to take the whole engine apart and give it a thorough examination. Taking it apart means, cylinder heads come off get cleaned and valvetrain checked. Maybe the valves need cleaning and lapping.

At the bottom end I would always check all the rod and crank bearings, clean out all oil passages and make sure that bearing dimensions and crush are what they should be. Then put it back together. Now you know that it is either solid or flawed.

For racing a 4.3 V6 you will IMHO definitively want a remote oil cooler for the engine and a transmission oil cooler for sure. Spinning a bearing on these engines is as probable as it is with an SBC V8.

In autocross you will have to think about your oil supply under pressure. Big no-no is running it with low oil level as this may uncover your oil-pump pick-up. Even if just for half a second it drops oil pressure dramatically on the bearings (especially the front ones) which overheats them, scuffs them and eventually when they give they will spin causing the feared con-rod knock.
I would always modify the oil pan depending on the application. For autocross the leas that comes to my mind is properly set baffles, even flappers to keep the oil around the pickup even when braking hard. Splashing forward of the content in the low aft section would be my concern.

Take it apart, make yourself familiar with the engine you race, look at the broken part. Show it to some engine builders, they will likely tell you what the reason was.

My 94 Blazer is properly maintained, I regularly service it, but also regularly (couple times per month, when really warmed up) I revv it to the limiter at 4'300 rpm. The engine I'm building for it has oil and transmission heat exchanger. Still I'm thinking about a dry sump modification which would allow more flexibility with future tuning. But here we are talking serious money. The build so far has over 3'000 $ in parts in it not counting on the machine work.

 

Not running proper baffles in your pan is an engine killer when drag racing or doing the auto cross thing. The cost of a custom pan is high as stated. Pickups fall out also, that's why they're brazed into place on a race engine. If these things aren't incorporated into a build the engine will suffer for it. Your ignition system can kill an engine also as well as the fuel system. If either isn't up to snuff you get detonation and that will be all she wrote for the engine. Cooling systems are also important for racing. You might want to think about some of these items when you do your racing thing. Racing is a very expensive proposition when all is said and done. There isn't a system on your vehicle that won't need addressed sooner or later and if these items aren't addressed you can look forward to more failures in your future. The most important items I can think off off hand are the fuel, oil and ignition systems. Any of these can kill an engine very quickly.