Hey guys, new here, and thought you could give me some insight. Kind of long, I just hope you can bear with me here.

I recently swapped to this carb setup on my Iroc from TPI:

-350sb
-Holley 750vs
-Edelbrock performer rpm intake
-Brodix 200cc heads
-Comp Cam Xtreme Energy 218/224 duration .495/.502 lift @.050. 110LSA
-700r4 trans

When the smoke cleared and it was finished, I was happy with the result, great power increase, and increased rpm range over the TPI setup.

Well, after about two weeks of having the car run, I had a little scare today. I was driving lightly and realized that my oil seemed abnormally low, at around 10-15psi (usually operates in the 30-50psi range). So I tried to throttle up, and it jumped to 30psi, but climbed dangerously low again. I also thought I could hear a slight tapping. I put it in 1st gear to try to get the rpms slightly higher to see if the sound increases with rpm, and at around 2000-3000, I could hear the dreaded knocking, but oil is still at 30psi. If you have ever driven a car with a bad wheel bearing, picture that noise. But it seems like if I wind it out, the knocking goes away...it's really only in that 2000-3000 range, and it's not 100% consistent with the engine rpm. Like the knock doesn't follow the speed of the engine, verbatim. I am not down on power at all it seems, and I am not getting any stalling. I pulled the dipstick, and oil is where it should be (I put in an extra quart to be safe, I know I lost a bit because of a slow drip at the timing chain, which I have yet to address.) The oil doesn't appear to be black, or metallic or anything like that.


It just baffles me that I am not down on power and I am not stalling here. Other rod knock cases I have heard of had these symptoms. I have ruled out an exhaust leak, and rocker tick. Timing is set accurately. It seems like its coming from the passenger side head/block area. Are these symptoms consistent with a spun bearing? Should I plan on pulling the motor in the coming weeks and dropping in a new crank kit?

This confuses me...
I recently swapped to this carb setup on my Iroc from TPI:

-350sb
-Holley 750vs
-Edelbrock performer rpm intake
-Brodix 200cc heads
-Comp Cam Xtreme Energy 218/224 duration .495/.502 lift @.050. 110LSA
-700r4 trans???Whats the 700r4 got to do with the carb you installed?
If you didn't just install the 700r4 (or even if you did), based on what you are explaining, check the flexplate for cracks or any loose bolts... as a rod knock doesn't go away, but putting a load on a broken flexplate or increased RPM quiets it down. They usually crack around the crank bolts, or the converter bolts loosen up letting the bolts slap around in their holes... pull the cover off and take a good lookie see, it should be obvious. Good luck!

In "the beginning" a bad rod bearing will knock when it is "unloaded."
You might hear it at cruise and possibly at idle.
When you blip the throttle, you'll hear it just as the rpm's start to fall.
vrooom...knock knock knock... putt putt putt

Of course that is in the beginning. they get worse.

What happens is that a spinning bearing is no longer in the place or shape it was intended to be.... and doesn't stay in one place.... and clearance is not consistent... so the symptoms are not consistent either. You won't have a power related problem until it siezes or breaks the rod, unless other problems are concurrent. And then like Jim is saying about the "unloaded" aspect, a piston is pushing down on that bearing with varying amounts of force, and under those varying conditions you won't see the same symptom.

Did you put an electric or mech fuel pump? Mech fuel pump rods can Knock. You say you're knockin right by the fuel pump amigo, but that wouldn't affect oil pressure. I imagine you put an electric anyway.

You won't see an oil problem on the stick. Pull your filter and pour some of it across the palm of your hand.

Did you change oil after changing intake? Antifreeze gets in the engine sometimes when you pull intakes.

Also you say your rpm range increased from tpi, for 2 weeks, now knocks:D . Yup sounds like you spun 1 to me:D
Probly was gonna anyway, at least you had fun and aren't afraid to work and I like that... let us know what you find/do. Good luck

usually with a spun bearing on a fuel injected motor, the power loss is due to the knock sensor pulling timing because it" hears" the rod or main knock...i dont know if this is your experience or not...just some exteranious info...can you hear the knock at idle???fi so, you can do a cancel test...(seems like i`m saying that alot lately...lol...)pull the wires loose from the plugs so that they are in contact with the plug, but not locked onto the plug...then start the motor, and pull the wires 1 at a time...you`ll know which cyl is the culprit when you stop hearing the knock, as the piston will just be along for the ride so to speak...the sound on the bad cyl will at the least change, as the dynamic of the cyl pressure will change...what kind of oil filter are you using???could be that you plugged the filter from the swaps, and need to change the oil...thats where i`d start...the flexplate thing is also a great thing to look at...

This confuses me...
Whats the 700r4 got to do with the carb you installed?
If you didn't just install the 700r4 (or even if you did), based on what you are explaining, check the flexplate for cracks or any loose bolts... as a rod knock doesn't go away, but putting a load on a broken flexplate or increased RPM quiets it down. They usually crack around the crank bolts, or the converter bolts loosen up letting the bolts slap around in their holes... pull the cover off and take a good lookie see, it should be obvious. Good luck!


Sorry for not clearing that up. The 700r4 has been in there all along, I just figured it would be pertinent to put that information in, as I have heard of these issues with torque converter bolts in the past. I'll give that a check though too.



Did you put an electric or mech fuel pump? Mech fuel pump rods can Knock. You say you're knockin right by the fuel pump amigo, but that wouldn't affect oil pressure. I imagine you put an electric anyway.

You won't see an oil problem on the stick. Pull your filter and pour some of it across the palm of your hand.

Did you change oil after changing intake? Antifreeze gets in the engine sometimes when you pull intakes.

Also you say your rpm range increased from tpi, for 2 weeks, now knocks:D . Yup sounds like you spun 1 to me:D
Probly was gonna anyway, at least you had fun and aren't afraid to work and I like that... let us know what you find/do. Good luck


It's the stock in tank pump with a mallory regulator. Probably the easiest thing to do for me at this point right now, but once the time comes to do a new rear, the intake electric will come out and I'll put an inline electric one in.

I didn't change the oil after the intake swap, because originally I was going to keep the TPI system and tune that, but it got pretty hairy. I changed the oil after the can and head swap, ran it for about 3 days, and changed the oil again. The carb swap came about 2 months later. But when I did that, I was certain that none got into the motor, the only bit that did was a few droplets inside the valley but I soaked those up with a rag right away.

Haha, yeah the TPI is notorious for falling on it's face at 4500rpm. I definitely took it up to 6000rpm on more than one occasion. Hey, but I always figured, if I'm gonna break it, I'm gonna do it right. :thumbsup: You're right though, I am not afraid to get my hands dirty in the least. The only issue I have is a time issue being a college student, but other than that, if I need a rebuild, you can trust it will be done, haha.

usually with a spun bearing on a fuel injected motor, the power loss is due to the knock sensor pulling timing because it" hears" the rod or main knock...i dont know if this is your experience or not...just some exteranious info...can you hear the knock at idle???fi so, you can do a cancel test...(seems like i`m saying that alot lately...lol...)pull the wires loose from the plugs so that they are in contact with the plug, but not locked onto the plug...then start the motor, and pull the wires 1 at a time...you`ll know which cyl is the culprit when you stop hearing the knock, as the piston will just be along for the ride so to speak...the sound on the bad cyl will at the least change, as the dynamic of the cyl pressure will change...what kind of oil filter are you using???could be that you plugged the filter from the swaps, and need to change the oil...thats where i`d start...the flexplate thing is also a great thing to look at...

I'll try the cancellation test. You can barely hear a tapping at idle, what some may confuse for an exhaust leak, but I just resealed everything, and I know that the fel pro gaskets I put in aren't leaking. The noise of an exhaust leak is slightly different than this. The collector gaskets are dead soft aluminum too, so I can't see (or even hear) any problems from those.


Thanks guys for your help. Hopefully next weekend I'll be able to turn up some more answers, but you answered my initial question about not being down on power but still having a knock. The whole situation sucks, but dealing with it is something that needs to be done. I refuse to let this car sit on my lawn and be forgotten about.