head swap 906 to 915

[73-charger-383]

i have a 68 383 that was originally a 2 bb car.  Now i've got a factory four barrel intake, carter 750 carb, 1 3/4 headers and stock 906's.  How much hp should i expect to gain with a switch to 915 closed chamber heads.  They are for sale locally and are pretty cheap, but if it's not going to make that big of a difference, i'll just start saving for some eddy's.  (it's still got the stock cam btw)


-what kind of horsepower would this setup produce if i put an engle k56 in?

thanks in advance
mike

[69chargerdad]

the 915 head is nearly identical to the 906 casting when it comes to flow numbers. However the 915 casting offers the closed combustion chamber which will increase your compression ratio. The gains would be very little, and depending on what kind of condition the heads are in you may spend even more money to get them into running condition. If it were me, I would save the money for aftermarket aluminum heads or port the 906's. Just my 2 cents

[dodge freak]

Those aluminum heads need 10-1 or better compression, iron heads not as much, something to do with heat. Anything that will increase compression helps to make more power, as long as it does not ping. If you are not going to change pistons I would stay away from any aluminum heads unless it has smaller combustion chambers.

[73-charger-383]

so, a set of ported 906's will outperform closed chamber heads on a low compression 383??

[Chryco Psycho]

I doubt it , the 915 should easily outperform the 906 heads just on the increased compression & yes if you use Eddys you will lose another point of compression due to heat loss to the alum so for example with 906 you have 9.5 : 1 compression , with 915s you will have 10.5:1 & with eddys on the same piston you will hjave effectively 8.5:1 

[BigBlockSam]

remember alum heads are great but on the street you run into other problems . like traffic or super hot days trying to cruise around for hours . your mixing two differant metals. that heat up and cool at differant temps. I've over heated my bigblocks over 240 degrees with no damage. try that with alum heads on a cast iron block. trouble   

[Chryco Psycho]

yes you will need a set of not so cheap cometic gaskets with any alum head too

[73-charger-383]

so, with the 915's left stock, and an engle k56.......with the setup i mentioned before......what could i expect for hp??

--and thanks guys==

[8WHEELER]

I have not run the engle K56 cam yet, so I can't help you with numbers, but it is a very good cam.

But also keep in mind, 'if you have not already checked'' there are some small valve 915 heads out there,
I have seen a few sets. So they would have the same valve size as a 516 head, the heads are the same
except for the valves.

Dan