302 heads on a 289

[65springtime]

I was checking my push rods, rockers and springs on my number matching 289and by one of the rockers and spring there is a 302 on the head. So looks like I have 302 heads on my 289. Is there an advantage to this? There is also this on the heads-B-A and 3K4.
Thanks, John

 

[Realmongo]

Based on the info you gave, I am thinking these are October 4, 1973 D2OE-6090-BA heads with 58.2cc chambers whch are larger than the 54.5cc 289 heads. So this arrangement should drop your compression from about 9:1 down to about 8.5:1.

 

[65springtime]

Is that a good thing? I am just not up on the compression. What does the lower compression mean for me? By the way, thanks for the reply. John

 

[mustangmutt]

Lower compression means lower performance, but it also means lower octane requirements. If you are just cruising your car they are fine.

 

[65springtime]

That will be fine. That is all I am planning on doing is cruising. No hot rodding. Been there done that. I wonder if I will still need to add a lead aditive to the fuel with these heads being 73 heads? Are the push rods the same? I had one bent push rod (the reason for checking the heads).

 

[mustangmutt]

I believe the Pushrods are the same. If one is bent you might have a stuck lifter. The heads on my 72' have studs with nuts that hold the rockers on. The nuts get tight 1/2 to 1 turn after there is no play in the pushrod between the lifter and the rocker. As far as the heads being compatible with unleaded gas, I couldn't say for sure. I'd run the additive just to be on the safe side.

 

[65springtime]

I pulled the lifter under the bent rod and it came out very easy so it was not stuck. Someone told me that the PO might have over reved it. I know I did not. I respect the old girl. These Mustangs are really fun to drive. Mine is a three speed manual on the floor. I am a big guy (I do not mean fat) 6' and 220# and it is a little hard getting in and out of the car. Looks like I could wax the whole top of the car from one side. I bought the car last Febuary. Thanks for the help.

 

[gregski]

Based on the info you gave, I am thinking these are October 4, 1973 D2OE-6090-BA heads

Not sure how you are getting that part number off the information provided, or I should say lack of information. Unfortunately the actual part number prefix is stamped under the heads, and I'm not sure it's worth taking one off just to confirm the part number. But that would give you the definite year of those 302 heads.

 

[gregski]

I pulled the lifter under the bent rod and it came out very easy so it was not stuck.

I don't think that's what's considered a stuck or collapsed lifter. A stuck lifter means the hydraulic components inside the lifter are stuck. So in other words the lifter itself will slide in and out of it's hole just fine, but the part inside the lifter itself does not move up and down. What is supposed to happen is the inside of that little lifter moves up and down a bit with oil seeping in, ie hydraulically. Maybe pull out another healthy one and do a stare and compare on them, but don't mix them up they should go back in to their respected holes.

 

[Realmongo]

The factory 289 heads used pushrods that were 6.825" long. The 1974 model year (3K4 = 1973 October 4) 302 heads you have with positive stop rockers are listed as 6.905" long.

 

[robbz28]

If the PO rebuilt the engine then its a good chance the pistons could be higher compression than the originals, so I wouldnt bank on that car having 8.5:1 compression...but it is possible, if he went back with factory spec pistons. If you are running under 10:1 (which you more than likely are) and have hardend valves in your heads then lead additive shouldn't be needed. If you romp on it and hear the valves clattering then some additive might be required.

 

[gregski]

The 1974 model year (3K4 = 1973 October 4) 302 heads...

So which number do you go by in case of a conflict, for example my 289 heads have these numbers:

7H9 (1967 August 9) yet they are stamped C80E (1968) in this case this makes a big difference the 64-67 heads had smaller combustion chambers therefor yielded higher compression and were more desirable than the larger chambered 68 heads, so which ones do people like me have?

Unfortunately I think mine are the less desirable 68 heads, they were simply made ahead of time in late '67 as parts usually are, please tell me I am wrong.

 

[Realmongo]

So which number do you go by in case of a conflict, for example my 289 heads have these numbers:

7H9 (1967 August 9) yet they are stamped C80E (1968) in this case this makes a big difference the 64-67 heads had smaller combustion chambers therefor yielded higher compression and were more desirable than the larger chambered 68 heads, so which ones do people like me have?

Unfortunately I think mine are the less desirable 68 heads, they were simply made ahead of time in late '67 as parts usually are, please tell me I am wrong.

You have early 1968 Model Year heads. You need to look at the last letter to determine which head you have. If it is C8OE-6090-F, you have the small chamber (53.5cc) 4V heads. The C8OE-6090-J, K, L, or M are 2V heads that have 63cc chambers.

 

[67rcks]

If you zero-deck the block you will get to 9.3:1 compression even with d2oe heads. IMO zero-deck should be done to any rebuild engine. 9+:1 is the minimum compression for any performance-oriented car with mild cam.

It is difficult and expensive to reach higher compression in 302 due to its shallow cylinders. You would need aftermarket alluminium head and very few (if any) are below 58cc. Then you would need dome pistons.

You have to have hardened valve SEATS to run unleaded gas. All valves are hardened. No 70's stock head has hardened seats.

 

[2+2GT]

You have to have hardened valve SEATS to run unleaded gas. All valves are hardened. No 70's stock head has hardened seats.

On a daily driver, I'd recommend the hardened seats. Plain iron seats prob'ly only last about 100,000 miles on unleaded. If it's a cruise night/car show only vehicle, you'll never put enough miles on it for this to be a problem. Amoco has been selling unleaded gas from 1889 'til today, and they never had customer complaints about valve failure.

 

[67rcks]

engine with iron seats can also run on unleaded gas if you add to it lead additive when filling the tank. it does not make much sense to take good working engine apart just to replace valve seats.

 

[gregski]

You have to have hardened valve SEATS to run unleaded gas.

I thought so myself but then I found this interesting discussion.

Do I really need to have hardened seats...