I just picked two 455 motors to put in my 68 442 project. They both need rebiuild, but curious about the heads, and which set to use. One set is "G" cating and the other is "K". Whicg head is better. Plan on mild street build for daily driver, nothing more than a mild cam and headers.

 

Their both good heads. G,s are 71, so have harden seats. K,s are W30 replacement heads, and use on a lot of boats. K ,s may have the larger valves? If they need new valves you can put in larger valves.,in either.I would probaby use the K. But if you want to sell a set, you could go with the G,s as the K,s may be easier to sell, and bring a little more money.

 

Well, not quite. By the mid-1970s, the only heads in the Olds parts system were J and K castings. K heads superceded all the performance head applications, J heads superceded all other applications. Saying that K heads are W-30 replacement heads is like saying that J heads were replacements for C heads. They were the best available at the time, not necessarily exact replacements.

 

The Ka will have 2.07 intake valves. The G may have either the 2.00 or 2.07 intakes. But you can cut out the small valve head seats and have the larger ones installed as Harv said. Depends on what your plans are for head work. I'd be comfortable with either one, but believe the larger intake valves would breath a little better. John

 

Is there really a difference between the G & GA or K & KA heads? These are GA and KA.

 

i would go with the g heads but if you can find a set of big valve c heads you will have more power than you can handle make sure they are the big valve and not the small valve heads you wont be disappointed

 

Purchase a brand spankin new set of big valves, and have your machinist correctly install them in whatever set you think will look better on the car. They will flow almost exactly the same as the other, and be within 2% of the C heads (no porting).
Get 2.125 intakes, 1.625 exhausts for max power.
See my response on ROP concerning spring seat depths.
JMGDO
Jim

 

I am leaning towards using the KA heads, but I think I read somehwere about the exhaust crossover needs to be blocked? Can someone enlighten me on this issue. Boy, this is not like chevy where you only had to deal with round or rectangle heads. Do the GA heads have the same characteristic? If the GA heads have the big valves (which I suspect they do), would they be a better bet. This is not going to be a drag car, just good street performance driver.

 

No more so than on any other Olds head. If you are not planning on an ultimate performance race car, don't worry about the crossover.

 

MUCH easier than the BB Chevy.
You forgot to mention closed/semi/open chamber BBC heads.

Other than valve sizes, and spring seat depths, these heads are pretty much identical. Measure the valves to be sure.
Pull out the set that will be the easiest to lift (it just does not matter), and take them to the machine shop for a standard rebuild. You will be happy with the performance, because they will be going on a 455. You don't have to do anything else.

 

Just as has been said, for a daily driver any of the heads will do. The valve size will not make any difference. For a cruzier, troling the streets, long drives in the evening, after you close the hood no body can tell the difference.
Flip the coin and pick which ever.

Gene

 

Not trying to hijack the thread, but since you guys were on BB I thought I'd ask. I know a guy selling a 455 with J heads for @ $400. I did hear that these were restrictive and should be avoided. I know its a newb quest, but are engines these even worth buying?