Low compression cylinder 7 and 8/ blowing smoke out of valvecovers
 

Ok guys I have a 540 BBC that had the 502 MPI intake on it with a vortech supercharger running 5lbs. the charger blew up so I went to a carbureted setup.(8.5:1 ratio) Since I got the carburetor on it there is a bunch of smoke coming out of the valve covers. I let it run for about an hour on the hose and a short run idling on the water for about an hour. thinking the rings needed to reseat after sitting for about 7 monthes. I did a compression check and found that most of the cylinders were between 135psi and 150psi except cylinder 7 and 8 which were both at 75psi. Im assuming that the rings are either worn out or not seated fully. Is there any adatives that I could use to try to get them to seat or should I pull it apart for a ring job. motor supposedly has 50 hours on it. there was no smoke before I took off the MPI intake.

thanks in advance

What happened to charger? Sounds like some shrapnel went into the engine and damaged those 2 cylinders.

Bore scope time, i doubt at 75 psi its just a ring issue

pull it apart,

according to the shop that took it apart, it was either over spun or lack of oil pressure at high rpm. I ran a magnet all through the oil and didn't get a single piece of anything. I understand that its likely though.

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Bore scope it and look for scapes on the cylinder walls im assuming

Depending how bad it was over spun, the impeller can make contact with the volute. The impeller can also male contact if the throttle is closed quickly at a high rpm and the blow off valve isn't big enough. It is easy to tell if the impeller made contact, just look in the air inlet around the impeller. You will see scrap marks and or damage to impeller.

I used to run my Vortechs 10,000 rpm about max rpm; but had a big blow off valve.

If I had to guess you have a couple pistons that don't look so good. Like the tops eaten away from detonation. Bore scope will tell u in a second. Plugs won't necessarily show any evidence at all. No need to pull the head just pull the engine and plan on a bad day. Likely other pistons will show signs of detonation also. I didn't catch earlier post but did you have wideband o2 sensor? I hope I'm wrong but just seen this recently. Right down to the smoke out of the valve covers and probably a rear main seal will be out also.

The cylinders are likely coated with streaks of aluminum as well as the tops of the pistons will make Freddy Krueger look like he belongs on front cover of GQ. Like I said I hope I'm wrong but... just went through this on an engine I'm working on. Oil wont show signs. It can but not always by any means.

Btw what carb/carbs set up do you have currently?