1973 "346" 440 Cylinder Heads vs. "906/452" Heads

[Charger Fan]

From research on this forum, I've learned the difference between 906 and 452 heads is hardened valve seats and I believe there was 2 cc's less volume on the 906 heads. I believe they flowed about the same. Can someone confirm? So my question is, how do both stack up against the 346 heads on my '73 440 relative to flow? I think the 346 heads have the same volume as the 452 heads (81.5 cc's) but the 906 heads are smaller at 79.5 cc's?

 

[496 polara]

The 346 was the introduction of semi hardened seats for the unleaded gas IIRC. Stock for stock I don't think there is much difference in flow.Still an open chambered head with cc's between 85-90cc in un modified form. The cc's you posted may be nhra blueprint spec/may not be but any open chambered unmodified head I have seen comes in higher.
Ya'll correct me if I'm wrong.

 

[Geoff 2]

MM magazine did an extensive flow & porting feature on these heads about 25 yrs back. They are all very close in flow, not enough difference to worry about.

 

[493 Mike]

I have 346 heads on my spare 440. .030" over, 509 cam, replacement Speedpro pistons, Isky rocker arms. Pretty simple combo but, ran a 12.68 in my 66 wagon at T&T years ago. I did use the Direct Connection porting templates on the heads, and they still have 2 cracked exhaust seats. Found them while grinding the seats and just put it together anyway!
Mike

 

[Curiousyellow71]

From research on this forum, I've learned the difference between 906 and 452 heads is hardened valve seats and I believe there was 2 cc's less volume on the 906 heads. I believe they flowed about the same. Can someone confirm? So my question is, how do both stack up against the 346 heads on my '73 440 relative to flow? I think the 346 heads have the same volume as the 452 heads (81.5 cc's) but the 906 heads are smaller at 79.5 cc's?

From what I remember: 452 88-90cc, most 346s run around 88cc. 906s run 86-87cc. They can vary a bit.. and I think 906 @79.5 is a blueprinted number for NHRA stock racing. When I have flowed them I did not see much difference. I think a 906 usually performs a little better on the flow bench. The lower radius of the Intake port is different for the 906 then a 346/452. I think the 906s intake ported is capable of a few cfm more then a 346 ported. The 452 and 346 respond well to most any port work. The exhaust port is pretty much identical 346,452, and 906.
The 346s were also on 71 and 72 cars. I know they didn't do induction hardening on the early heads. I don't think the method of hardening was real good until the 452 heads.

 

[PRHeads]

My advice would be to use whichever set needs the least amount of work done to them to make them usable.

With similar work, they’ll all make similar power.

 

[5wndwcpe]

Which ones are more prone to cracking under the exhaust ports ? I thought it was the 452's but I'm second guessing myself.

 

[Charger Fan]

Even though I’ve toyed with the idea of spending lots of money on the engine to maximize the horsepower potential for a 440 that I’ll only be driving on the street during weekends, I can’t justify it since the rest of the car also requires lots of attention $. Since from the responses, the stock heads are pretty decent heads. What else would you do to get a ‘73 440 equivalent to a ‘71 440? Is it just up the compression or match the cam? Also I know in ‘72 they changed the way they advertised horse power ratings. How close is a stock ‘73 440 HP to a ‘70 or ‘71 440 HP in horsepower if they were rated the same way?

 

[Curiousyellow71]

Even though I’ve toyed with the idea of spending lots of money on the engine to maximize the horsepower potential for a 440 that I’ll only be driving on the street during weekends, I can’t justify it since the rest of the car also requires lots of attention $. Since from the responses, the stock heads are pretty decent heads. What else would you do to get a ‘73 440 equivalent to a ‘71 440? Is it just up the compression or match the cam? Also I know in ‘72 they changed the way they advertised horse power ratings. How close is a stock ‘73 440 HP to a ‘70 or ‘71 440 HP in horsepower if they were rated the same way?

Compression mainly... and possibly some emission equipment was added in 73 to further decrease the sae net hp? Like EGR and possibly a smog pump?
Mopars advertised compression were less then actual. You can use one of wallace racing calculators to figure hp for a "ballpark" compression change. It's not linear there is less hp jump at the lower compressions. If a 73 is 1.5 points less then a 70..that is less then a 10hp loss.

 

[PRHeads]

If you’re looking for a HP increase, just apply the tried and true hot rod techniques used for decades.
Headers, intake, cam, etc.

Not much of it is all that cheap nowadays though.