big block cylinder head question

[496coronet]

Good evening! About 20 years ago I bought a 1972 Chrysler Newport with the plan that some day I'm going to rebuild the heavy-duty 230 casting 400. Some day is now here. It's got the 346 heads and I'm ok with that. KB 240 pistons hung on the factory rods on a steel 383 crank, all nicely balanced. Putting in the old-school P4452993 .474 cam. Yes, there are a bazillion other cam choices, but I love the idle of this one. Engine is going into my '67 R/T while the 440 is on the stand. Factory AFB 3426S carb. Headers. Manifold undecided; maybe stock iron 383 (so I can use the factory big block unsilenced) or Performer RPM. Time to do some bashing of the 18-spline and dana 60.
So before I buy all the engine parts I'll need without doing any research, I've got a couple of questions for you guys that know a thing or two about big block cylinder heads.
1. What is the valve guide boss diameter? The Lunati dual springs I spec's for the job have an inside diameter of 0.697" and I'd hate to have to cut off that guide boss.
2. Is it a good idea to use spring locators on the bottom? Not a "big" cam by any means but the locators (assuming they'll fit around the guide boss) just seem like a good idea.
2. What are the chances those original 346 heads have hardened exhaust seats?
It is a pleasure being on this forum!! Thank you for any and all help, comments, etc.
Kevin Pacholka

 

[pnora]

Good evening! About 20 years ago I bought a 1972 Chrysler Newport with the plan that some day I'm going to rebuild the heavy-duty 230 casting 400. Some day is now here. It's got the 346 heads and I'm ok with that. KB 240 pistons hung on the factory rods on a steel 383 crank, all nicely balanced. Putting in the old-school P4452993 .474 cam. Yes, there are a bazillion other cam choices, but I love the idle of this one. Engine is going into my '67 R/T while the 440 is on the stand. Factory AFB 3426S carb. Headers. Manifold undecided; maybe stock iron 383 (so I can use the factory big block unsilenced) or Performer RPM. Time to do some bashing of the 18-spline and dana 60.
So before I buy all the engine parts I'll need without doing any research, I've got a couple of questions for you guys that know a thing or two about big block cylinder heads.
1. What is the valve guide boss diameter? The Lunati dual springs I spec's for the job have an inside diameter of 0.697" and I'd hate to have to cut off that guide boss.
2. Is it a good idea to use spring locators on the bottom? Not a "big" cam by any means but the locators (assuming they'll fit around the guide boss) just seem like a good idea.
2. What are the chances those original 346 heads have hardened exhaust seats?
It is a pleasure being on this forum!! Thank you for any and all help, comments, etc.
Kevin Pacholka

I doubt you will need locators. Springs can be a problem. Inners can rub the guide. Back then we used to get the guides cut for proper seal fitment and the smaller seal would not get raked off the guide by the inner spring.

 

[496 polara]

That cam should not require double springs. Love that old school cam btw. One of my favorite mp cams.

 

[69Bee]

Guide diameter is large, 0.625" or larger. If you want Dual valve springs, cut them for positive seals for 0.562" OD guides. Should not need spring locators like pnora said, the head has good spring pockets. Depending on the OD of the spring, you might have to cut larger spring pockets. Now, as far as hardened valve seats, yes, they are "Flame Hardened" or "Induction Hardened. Problem is, after how many valve jobs do they reach a point where the hardness is affected. Put hardened exhaust seats in now, instead of the second time you go back in.