I'm in the process of rebuilding a pontiac 69 400 for my 69 bird, block code xh head code 62. I was going to replace all the rockers and have received a fantastic price on a new 1.65 to 1 roller rocker set. Anyone know if these will work with this engine. Or should I just go with a stock rocker. Any input on a cam I thought about the original grind for this engine or a stock ram air cam , any other suggestions on a good cam for this engine . Pistons will be bored 10 over to get rid of some scratching .I've also been told to have the new pistons milled down a bit to lower the compression to around 9:1.Is this necessary, Kind of backwards form what I use to do. Help and advice are always appreciated.

Yes.
Not necessarilly.
068 cam or equal.
Don't.



Q

Wow... Q nailed it right on the head... with so few words! Lol... **** engineers... Lol..

Brett - 67 Drop Top 455!

I probably should expand on the rockers, though.

The majority of modern cam grinds that are "copies" of the 068 already have lift numbers that reflect 1.65 rockers when using 1.5 ratio rockers. If you choose to use one of these aftermarket cams AND 1.65 rockers, it is in your best interest to have the heads set up for the additional lift and have the push-rod holes enlarged. In addition, you will have to convert your screw-in studs to 7/16" and get adjusting nuts (Poly-Locks) to maintian proper valve train geometry. Also, I advise going to larger diameter pushrods, sized for the cam / valves / rocker set up.

Q

Hey Q, How much do you have to grind from the close side of the pushrod hole? Say on a cam with around a .500 lift.

Robert

Robert, it won't take all that much to enlarge the push rod hole. Basically all your doing is making the round hole oval, about an 1/8" or so.

Brett - 67 Drop Top 455!

Hey Brett, Can you think of any downside to grinding that 1/8" or so out of there?

Robert

The only down side would be if you grind too far.

Q

PS: Sorry I missed the question. I was away from my computer for a couple days ...

No, other than taking it too far like Q said... just a little at a time, that's what I did with mine and checked as I went, all is good.

Good luck, and take your time!

Brett - 67 Drop Top 455!

Cool, That's what I wanted to hear. I just picked up a porting kit yesterday. The rolls should work fine for that.

Robert

Measure first - they are 1/2" from the factory, but double check that they haven't been done once already - and grind away on the rocker side until they are about 5/8". That will leave plenty of clearance on one side, and material on the other.

Q

Yea Q, Hard numbers. That's what I wanted to hear. So how much does it generally lower the CR when you unshrowd(sp?) the valves. Last I heard was about an 1/8" around the outer edge and then polish the rest of the chamber around the seat area. Shouldn't be much I wouldn't think.

Robert

That's definitely a Banshee question. It toally depends on the motor and the heads you start with. Obviously, a larger chamber head will gain more cc's in that operaiton than would a small chamber head. And, the effect of those gained cc's is dependent on the motor. There's no rule of thumb that U can quote you, but Tom can.

Q

I was just guessing about the same amout of material as an additional eyebrow in the top of the piston. I think , if I remember right, they say those are about 7cc for all four. 1 3/4cc per valve can't be too far off the mark. What do ya think?

Robert

Thanks for the input on this. I was out of town and couldn't reply to this post. Back to the engine I'm going with the 68 cam as suggested. The roller rockers were a wash turned out to be a poor product. I am curious though how you can tell the difference between the Stock 1.65 rockers from the 1.5, any physical difference.