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Discussion Starter · #1 ·
I pulled my motor cuz it wasn't firing on all 8. Figured maybe head gasket if I was lucky and replace all gaskets while I was at it. What I found was two burnt exhaust valves due to pitting at the seats. I'm runnig a 400 B block (73) with 516 heads. My question is by switching heads (915's ?) how much horsepower could I expect to gain? Or should I just pay to get the 516's rebuilt? ::)
 

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If somebody already put hardened seats in those old 516's, stick with the 516's. 915's are pretty pricey these days and need hardened seats too $$$.
 

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Im gonna say the reason for your valve problem is they are not hardened seats and you should expect the same problem with the 915's
 

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Could he use 452's from a later moder? I'm curious as I may run 400 in my 79 2wd and I don't know yet what heads it has, but I run across 452's alot for a couple hundered
 

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The 452's have the correct seats or actually they have a hardeneing process done to them
 

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67MIke said:
Could he use 452's from a later moder? I'm curious as I may run 400 in my 79 2wd and I don't know yet what heads it has, but I run across 452's alot for a couple hundered
Check them for cracks, they are lean burn heads.
 

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I am in almost the same spot as you. I am going tomorrow to look at a pair of 915's that have been mildly ported and shaved .050 They are (apparently) $200 cdn so its a good buy. Ran in the 11's in a BB dart. But I also have a pair of 516's and if these 915's dont work out (or I may sell em.. who knows..ebay dont ya know) I will be doing a the 516's with hard seats and probably stepping into 1.74 exhaust while I am at it. With the larger valve and a cut back on it it should flow a little better and be a real good head. Unless your switching to a pop up forget the 452's but with a good piston the are a great choice too. But the 915 with hard seats is the best of the bunch, but you wont gain much over the 516's. A little better flow but not much difference in HP rattings between 66, 67, 68 440's so the head can't be worth that much.
 

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that and with the 915s closed chamber you hafta watch the deck height / the 67 motors had a negitive deck height where some other years had a positive deck height / that means the piston might hit the head
 

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Discussion Starter · #9 ·
I found a good deal on a pair of rebuilt 452's for about $180 ea, which is cheaper than having the seats and everything done to my 516's. Bummo, what means swithing to a pop up? Pistons?
 

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Ya, pop up or domed pistons. There is a nice pair of 452's already done with a 3 angle etc on ebay right now for cheap. The only thing to watch on the 452 is that while it is a true induction hardend seat it is not a thick process, so maybe 2 valve jobs or 1 heavy handed valve job and the hard process is wiped off the head.
 

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The push rods between the heads discussed here will all be the same, unless you have changed rocker arms from hyd to adj, or flat to roller cam
 

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Another thing to watch for in the 452's is spark plug diameter. A set of 452's from any Series 3 (later model) could have the extra cooling holes and use the smaller spark plug. I'm not sure what your options are for HP plugs on these types of heads. The extra cooling holes may not be a problem either, they just wouldn't be used - closed off by the block and gasket.

There is also a formula for shaving the intake manifold mating surfaces when the heads are shaved. You will know it the first time you set the intake down on the heads and the bolt holes don't line up. I think it's about .018" on the intake when you shave .050" off the heads. But check to make sure.
 
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