289 heads on a stock '72 302?

[lil red]

I am planning a rebuild of my 302. I have come across a set of rebuilt 289 heads (casting C6OE). WIll these work with my motor? The build will consist of the following:
Comp Cam K31-216-3 (cam, lifters, timing gears)
Weiand dual plane intake
Holley Truck Avenger 4 barrel carb 670 cfm
I already have headers and dual exhaust with flowmasters. Thanks for any input.

 

[bax]

They will work. They have a small combustion chamber and will bring your compression ratio up. Perhaps more than you may want.

 

[lil red]

Thanks, bax! Any idea (guess) where my compression would end up. Its not a daily driver, so I dont mind running super unleaded. If that is all it would take.

 

[bax]

It could bump you up to the mid 10's + and yes put you in the 93 octane crowd. Also you will lose the positive stop rockers. You will have adjustable rockers with the 289

 

[ol gray mare]

I have 289 heads on my '70 302. I can run regular without any pinging during daily driving, but have to go with premium when towing or running hard, dunes etc.

 

[broncnaz]

not all 289 heads are the same just as not all 302 heads are the same. The C6OE heads should have a 54 cc chamber and may or may not have adjustable rockers. A lot of 289 heads have 58 cc chambers which supposeldy a lot of bronco 302 heads also have.
Unless the 289 heads are the adjustable rocker type theres really no benifit especailly if they have smaller chambers if the bronco heads are 58 cc then goiong to 54 cc heads should only bump you up 1 point as Bax said loooking at high 9's for compression. While not a big deal as I dont believe the 72 heads had hardened exhuast seat I know for a fact the stock 289 heads dont have them with todays gas it would be better to have the hardened exhuast seats. they wont wear as quick.
Also if they are the adjustable type you will need hardend pushrods and non rail rocker arms. Another quick and easy way to tell is if the pushrod holes are more like slots then they are adjustable and need hardened pushrods. If the Pushrod holes in the head are round then they were not the adjustable type and more than likely had rail type rocker arms.

 

[John Marinan]

If the heads are M code they will be 63cc. If they're C code they will 52-55 cc with thermo provision. If you can use 63s it would be easier to bolt on a set of E7s. This would give you hardened seats, positive stops, and much better flow, these heads are cheap and plentifull, make sure to get rockers, bolts and fulcrum guides They're about $50.00 each used, a typical valve job, without springs is about $140.Check the spring height with a new cam.

 

[Scott C.]

If your rocker arm studs are straight then they are adjustable. If they have a shoulder then they are fixed. The fixed are necked down to a 5/16" thread and the straight are 3/8" thread. I have never seen a factory 289 head with out adjustable rockers. You will also want to use the cast rockers with the guides that hang down to align the rocker on the vavle stem. The stamped ones will tend to wonder off the valve stem.

 

[broncnaz]

in 66 289's started using non adjustable rail rockers.

 

[John Marinan]

in 66 289's started using non adjustable rail rockers.

Rail rockers will wear out the valve tip. This is a bad design, if you use these heads install non rail rockers with guide plates.

 

[broncnaz]

Theres no real wear issue/differance all rocker arms of that era wear the same the big issue is that rail rockers shouldnt be installed on heads that didnt have them in the first place as the valve tips are not long enough and the rail rocker could push the valve spring retainer down and cause the locks to come out.
Still If I had the choice I wouldnt run rail rocker arms but usually theres not much of a choice. Also rail rocker arms can have clearance issues with high lift cams due to the slot in the rocker not being long enough.
I've yet to see any heads that have rail rockers and valve tips that were more worn than non rail rocker type. I just looked at 6 sets of used rail rocker heads no abnormal wear on any of them

 

[lil red]

Theres no real wear issue/differance all rocker arms of that era wear the same the big issue is that rail rockers shouldnt be installed on heads that didnt have them in the first place as the valve tips are not long enough and the rail rocker could push the valve spring retainer down and cause the locks to come out.
Still If I had the choice I wouldnt run rail rocker arms but usually theres not much of a choice. Also rail rocker arms can have clearance issues with high lift cams due to the slot in the rocker not being long enough.
I've yet to see any heads that have rail rockers and valve tips that were more worn than non rail rocker type. I just looked at 6 sets of used rail rocker heads no abnormal wear on any of them

broncaz ... So, I am thinking of getting a valve job done on my stock heads. I am curious, you said a high lift cam could cause issues with rail rockers. How much is too much?

 

[broncnaz]

I've run cams with .512 lift with no problems but you always need to check to make sure there is clearance at full lift. both in the rocker arm slot and the rail tips and valve retainer especailly after any machine work has been done. Most of the cams we tend to use in broncos wont cause a issue.
While I personnaly rather have screw in rocker studs and adjustability in most cases our broncos dont see the RPM's or have big enough cams to justify the conversion of stock heads.
You could run the non rail type rockers but the heads need to be converted for guide plates and screw in studs. By the time you spend the $$ to do that you could just about buy aftermarket heads already setup and way better than any stock heads.