906 heads on a 413

[413Polara]

Have a line on a set of 906 heads for my 413. Wondering if anyone here has had a set on a 413 themselves and what kind of difference they made. My motor has been bored .030” over and had a slightly hotter cam put in it, unfortunately that’s all the info I have on that. I’d read that the 906 heads with the bigger exhaust valves would cause a loss of compression and possibly hurt performance. Any info would be appreciated, thanks guys!

 

[496 polara]

Larger exhaust valves than your stock heads and also a larger combustion chamber which will lower compression. 906 heads likely flow better as well.

If you are running the stock 413 valve covers they may not fit. Early valve covers were 4 bolt IIRC. The rocker arms and pushrods were different than later setups as well.

 

[DanielSlocum]

Doubtfull the better flowing ports of the 906 will make much difference on a very mild build. Loss of compression will seriously hurt torque.
Milling about .040 will get the compression back. mildly porting and install of 1.74 ex valve in your 413 heads might be a good option.
Thicker .040 head gasket will also hurt compression vs stock type steel shim gasket at .020.

 

[R413]

Do you know what year your 413 is? How does it run now? Do you like it?
Do you know what heads are on it now? Do you have a photo of the end of the head?
It has newer pistons so could be it's lower compression already, not many choices on 413 pistons.

Loss of compression is real from closed chamber to open chamber is real, and not good.

I'd stay with closed chamber heads.

 

[413Polara]

Do you know what year your 413 is? How does it run now? Do you like it?
Do you know what heads are on it now? Do you have a photo of the end of the head?
It has newer pistons so could be it's lower compression already, not many choices on 413 pistons.

Loss of compression is real from closed chamber to open chamber is real, and not good.

I'd stay with closed chamber heads.

The 413 is a 1965, it runs well currently. I do like it, just wanting more power out of it and floating some ideas around. The heads I’m not sure, I’m hoping to get the casting number off them this week as the valve cover gaskets need to be changed anyways. I can try and get a photo of the end of the head. As far as I know they’re the heads that came on the motor originally.

Sounding like a pass in the 906 heads though. Maybe just an intake swap would give it something more. There’s hopefully a set of 4.10 gears going into it in the spring that should make it more interesting.

 

[R413]

What carb is on there? Are the secondaries opening? Does it go full throttle?
What parts are bolted to this engine?
How high of RPM will it make power?

Gears are #1 to improve performance. camshaft, carb, intake

 

[Dave6T4]

1965 413 would have 6-bolt valve covers. A change to steeper gears will give you the best "seat-of-the -pants" performance improvement feel. Maybe upgrade to Edelbrock intake and 750 cfm. carb. Hard to guess what your current compression ratio actually is, but a change to "906" or other open chamber head will drop it a full point. I have open chamber "452" heads on the 440 in my '64 Polara. They are similar to a "906", but have the bonus of hardened exhaust seats. I feel the lower compression with a good open chamber head makes it easier to deal with today's crappy fuel, without pre-detonation. With high compression and poor fuel, you are forced to retard ignition timing to avoid "pinging". There could be a bigger power loss here, than with open chamber heads with better porting and larger valves.