66 425 crankcase pressure

[Slick66]

Hi so on my compression test, each cylinder shows 150 except for #7. This one shows 30 dry,32 wet. Also when I hook up air to the cylinder top dead center, I can hear the air rushing through the exhaust manifold. The blowby is strong and visual. How can I have so much blowby if the exhaust valve isn't seating properly???

[cartercarbaficionado]

Amazon has a cheap boroscope. you might wanna look in that cylinder. lord knows my 350 did the same thing and had a hole

[Slick66]

Hi thanks for the response. I do have a borescope. There is some ultra light scuffing on the cylinder walls and the top of the piston has some notable catbon buildup. I'm deciding on finding a replacement engine or rebuilding mine. Any advice would be greatly appreciated thank you.

[cartercarbaficionado]

Hi thanks for the response. I do have a borescope. There is some ultra light scuffing on the cylinder walls and the top of the piston has some notable catbon buildup. I'm deciding on finding a replacement engine or rebuilding mine. Any advice would be greatly appreciated thank you.

rebuild is probably the easiest since the toronado uses a ultra low intake compared to a normal 455 plus it's getting hard to find 455s. it's hard enough that I'm having an easier time finding big block bucks and cheap 454s that would bolt in.
it seems like you probably just have some excessive clearance in your piston rings for some reason. how many miles are on that engine?

[Slick66]

About 92k now. I got it at 89k and back then the car could pull fairly hard to 80 I've just never had it over that. I did change over to a blue streak coil and right after that I noticed a miss so I brought it home to examine things. That's when I noticed the intake manifold gasket is leaking oil at the corners of the china walls front and rear. I put the old coil back on but the miss continued on and then rapidly got worse along with loosing all but none of its power in the course of the next two months.

[cartercarbaficionado]

About 92k now. I got it at 89k and back then the car could pull fairly hard to 80 I've just never had it over that. I did change over to a blue streak coil and right after that I noticed a miss so I brought it home to examine things. That's when I noticed the intake manifold gasket is leaking oil at the corners of the china walls front and rear. I put the old coil back on but the miss continued on and then rapidly got worse along with loosing all but none of its power in the course of the next two months.

100k is overdue for a rebuild.
remember these cars barely lasted 80k if they didn't rust out first

[Slick66]

Yeah plus I'm seeing now that the psi on compression should really be up around 185 190.

[Jelonek]

That is my problem