i have a 73 455 block with stock internals. will the 1965 425 A heads work properly on this motor or should i try to find a set off 455 heads? aftermarket heads are way out of my budget and all the 455 heads i find are 73-76 low comp smog heads. i ve been told the 1965 425 A heads are virtually identical to some performance 455 heads and they are rated at 390 horse which is right around where i want the car to be. any help will be greatly appreciated.

 

Yes the A heads will bolt up just fine. They have a different style of rocker arms than the newer heads, but the 1965 442 ran with that setup.

I don't think they're significantly better or worse than the other common castings from the 60's and early 70's.

John

 

However, you will need to drill out the push rod holes in the A-heads to compensate for difference in cam bank angles. Check with Olds engine builders for the exact amount. Not much.
425 #A coded block (65 only, 45 degree and had .841" lifters)
455 #F coded block (68-76 ALL 39 degree and had .841" lifters)

 

Just did a motor 1966 400 with 39 cba and used starfire B heads that came on a 425 which was a 45 cba motor and using stock pushrods (5/16) there was no clearance issues when I mocked everything up. Motor has 500 miles on it and no issues what so ever. I did not drill out the pushrod holes any larger, I believe you will get in trouble if you use 3/8 pushrods.

 

1965 A heads used the old style rocker setup, might be hard to find. valve seats aren't going to be hardened either. supposedly, A heads flow a little better than most of the rest of the olds alphabet, on the exhaust side due to the lack of an A.I.R. bump.


bill

 

Thanks for the help guys! Im also curious as to the hp rating. Heads are 390 horse so will my 455 have anywhere near that with stock internals? I know the pistons have a deeper dish so im wondering if i should upgrade to a beefier stock set. Any suggestions?

 

In all honesty, those pistons are your biggest hurdle to clear.
In my opinion they are pretty useless. If you used those pistons with ANY stock chambered Olds head A-J and a .040" aftermarket gasket you would be at 8.2:1 compression.

If you had a decent set of slugs in there for some compression, 390 horse could be achieved relatively easily.

If you left those pistons in, you can pretty much bet on it only being around 2-300 horse and sucking down just as much gasoline as a 400 hp mill.

 

the heads aren't 390 horse-the whole package they were a part of was rated at 390 horse, which is debatable.


bill

 

please elaborate bill. im trying to get as much streetable power out of this thing so please tell me what issues are i may run into. i would like to keep the budget as low as possible of course but im willing to do what ever i have to to kill every rice burner in town! this is my first olds so im counting on veterans like you guys to point my in the right direction. thanks.

 

More or less in order of importance for power in a given cubic inch configuration:
camshaft
heads/intake flow/carburetion
headers/exhaust
compression ratio

 

so camshaft choice should be first prioroty? im running a performer intake with holley 750 double pumper and the A heads so what cam would be reccomended for optimal performance if i go with a 9.5-10:1 piston? i already had the heads rebuilt so id like a cam that doesnt require aftermarket springs, or would a W-30 camshaft be better? im coming over from pontiacs and they are night and day appearantly.

 

I feel the heads (flow) are the most important. JMO

 

Head flow is very important if the camshaft is in the ballpark. Most people compromise the cam selection for convenience in valve springs, hydraulic, etc. and the HP output is correspondingly limited. You need to decide what your goals are, and whether you are willing to pay attention to the details needed for use of a "big" camshaft to get the power. Different people also have different definitions of streetability. I drive on the street with 4.57 gears, and a bigger cam than most use on the street. Others feel the 328 deg. W30 cam, or modern replacements in the same size range, are "too big" especially if they want to run 3.23 gears. I rated the cam first because I don't care how good the heads and intake are, if you run a mileage-master cam, you won't have much power. Even if stuck with J heads and a flat iron intake, you can make decent power with the right cam. Sam Murray's 67 W30 D/Stocker has run 10.82/122 with unported C heads, 400 engine, flat iron intake. Of course, he scienced out the whole car to do that.

 

That is a great bit of insight! Im gunna talk with a local speed shop and see if we can come up with a good balance of power and drivability! Thanks for the help!

 

Sam Murray's 67 W30 D/Stocker has run 10.82/122 with unported C heads, 400 engine, flat iron intake. Of course, he scienced out the whole car to do that. Yes the car is dialed, but it did take 500 HP to do that, Q-Jet, flat stock intake, stock heads?, stock type pistons. Point is, details are everything.

 

x2

 

On the Olds 425 A heads there are a couple of minor things to note:

1. The oil drain back holes are significantly smaller than the later holes.
2. 4 of the rocker arm studs on each head go through into the intake port. Not really a big deal but a small amount of sealer should be used.
3. And as mentioned above the stock rocker arm setup uses a unique 3/8" stud versus the later 5/16" bolt.

 

Given that this thread is a decade old, I hope this has been resolved by now.

 

Im surprised there’s so much stuff that pops up that’s this old. On another forum I’m on, if a threads three years old without a reply, it goes into an archive discussion thread. It can be revived, but at least it’s not in the current set of threads and aren’t always being resurrected accidentally.

 

Usually it's because a new user has done a search, the old thread pops up, and the user responds without looking at the date. The thread then shows up with a new post and people respond, again without looking at the date. Worse, people will respond to the original question and not the latest post, which frequently happens when someone resurrects a dead post and then asks a completely unrelated question.