When oil is introduced in the combustion chamber would it promote or inhibit detonation?

Reason Im asking is my buddy finally ripped appart his built 355 and we found evidence of detonation based on the copper showing on the bottom main and rod bearings. But before we discovered that, we noticed A LOT of oil was being sucked into the engine from inside the lifter valley. One of several reasons the motor was being ripped appart was because of severe oil consumption so it looks like we figured out where it was coming from. I also know the tune is on his motor was pretty conservative. Timing isnt anything crazy compared to tunes you might see from PCMforless. But the old school drag racing engine builders who looked at the bearings said the motor was running lean and/or has too much spark advance which has me wondering... could oil in the combustion chamber mimic the problems associated with running lean or having too much spark advance?

 

Detonation will show on the brgs as a pin size spect or discoloration.Ya can not feel it in the brg but in the sunlight ya can see it(sunlight for this old fart) They will very in size as to how severe the detonation is/was and the amount of spots.
If ya see copper then the oil was lacking-many miles-or not enough clearance or poor quality(not H series or equivalent). I can tear down one of my sprint car engines after a season and not see copper with "H" series brgs.
If his DCR was marginal the oil in the cyl's would up the compression and may cause detonation.

 

Some metal went through the motor(reason #2 it came out for inspection) but none of the bearings were spun and it had about 30-40k miles on it. I dont know what his DCR was but its a Bret Bauer cam in a ~10.5:1 compression motor.

 

Sounds like poor quality or not clearenced right.(guess- as I can't see the brgs) How much copper is showing?

 

Brad has it backwards the top side of the bearings had a polished look to them which i was told is detonation. The reason the bearings are showing copper is the cam gear came loose after i was messing around in the motor and didn't get the cam gear tight enough and it worked loose and the gear rubbed the timing cover and the old cam rubbed the back freeze plug and caused a lot of metal to go through the motor.

 

If it don't have the speck's it ain't detionation. The spects are hard to see and the brg has to be in the light just right.
Don't know what to tell ya about the "shiny" top brg. I would have to see it to know. There are thing's going on that are very hard to describe and only a good eyeball on the piece can know.
Was the top half smooth(like new) but shiny or was copper showing in places that were not due to metal?

 

Yeah youre right it was the top side.

 

Theres no doubt a lot of the wear was due to metal shavings in the oil... some bearings had deep grooves to prove it. But Id think if metal shavings were the only cause then youd find bearings being worn all the way around which we never did see. We might be able to get some pics of the bearings if they havent been tossed yet but all you need to do is imagine taking a scotch pad to the center of the upper bearing and then polishing it smooth.

The only places showing copper were the top sides of the rod and main bearings. None of the others showed any significant wear.

 

Might suspect the clearences or oil volume/pressure. The quality of brg has a lot to do with that in a high load situation(RPM's,Hose,Blower). I never put anything less than "H" series brgs in anything that has a cam. Not saying other quality levels won't work but the "H" series has never caused a failure and I tend to stick with what works for me. When I can run a 360CID all season,many laps and high RPM's on dirt and the bearings look like they could be used again,I tend to say that is good enough. These are wet sump engines too with a conventional oil pump (special but conventional).

 

Yeah I doubt it based on the motors his builder cranks out.

All I was really wanting to know is how oil effects combustion(such as octane rating) and if it can lead to detonation... bare in mind it was burning a considerable amount of oil, something in the range of a quart every 500 miles.

 

If ya got oil in the top it will cause detionation if the DCR is/was on the raged edge. It don't compress and takes up space in the CC volume so in effect it is making the chamber smaller.

 

To answer your original question, oil contamination reduces the octane rating of the fuel and increases the chances of detonation.