while the block is cracked in my 3rd gen and at the machine shop getting a new block, ive been playing with my other car. i have a 84 mazda rx7 with a carb'd sbc in it. 10.5:1 cr, aluminum heads, short sp intake, headers, msd, etc... when i pull it off the trailer at the track the oil pressure is about50-60 lbs. after it warms up to about 170 drops to 20-25 idleing. after 3 or 4 12 second passes it drops to 10-12 lbs idleing. was just running 30wt but it didnt solve the problem. switched to 10-40 semi-synthetic, didnt fix it either. anyone have any suggestions?

 

Is this on a gauge that can be trusted? (Unlike stock 3rd gen ones for example....)

If it is, time for main bearings. If they look like clean, shiny copper with grooves in them, it's debris. Which is what it sounds like you'll probably find. Might want to run a rifle brush through all the oil passages and the grooves behind the cam bearings before putting the cam bearings and plugs back in, you might save the next set of bearings from suffering the same fate (debris lodged inside the block) that way.

 

reliable gauge, pro comp mechanical. i thought it might be bearings but was interested in possible explanations. thanks sofa.

 

GM says all you need is I believe 7-11lbs of oil pressure per 1000rpm. Does it go up under acceleration?

 

Yeah, the "racer's rule of thumb" is 10psi per 1000 RPM....

But, it's not always a question just of "need"; even if the pressure itself might appear to be "enough" by the "rule of thumb", if it doesn't act right, then .... something's not right. Especially if it's been OK in the past, and begins steadily dropping over a period of time. The change or trend tells more than just the raw number does. Bummer.