switching 1977 302 heads onto my 1974 302

[popsbronco]

Will my 1977 heads work properly if i put them on my 1974 302 engine.
When switching over what considerations do i make.
Any tips or advice will be appreciated
Thanks in advance

 

[Hogback]

If someone would return my book i could tell you alot. You may loose some compression is one thing, so you will want to compare combustion chamber size in 77 heads vs 74.
-Is the rocker arm set-up better on the 77 heads? I know they switched to the late model design (somewhere around that year) that put less wear on the valve guides. If so, that's a positive.
-If the heads are good and free and the 74 are bad, i'd do it. I would'nt go out and buy some 77 heads, and I wouldn't spend much on them like having the guides replaced. You could easily sink $500 in them, when for a little more you could have some nice heads.
-There is a lot of misc work and costs involved. One mine anyways, if I touch one thing two things tear up in the process. Murphy's Law.

 

[popsbronco]

The 1977 heads are on my 1977 and were working fine as far as i know.The 1977 302 develop piston knock bad piston pins.So i was thinking on just switching those 77 heads on the 74 302.
What parts besisde head and manifold gaskets would i need??

If someone would return my book i could tell you alot. You may loose some compression is one thing, so you will want to compare combustion chamber size in 77 heads vs 74.
-Is the rocker arm set-up better on the 77 heads? I know they switched to the late model design (somewhere around that year) that put less wear on the valve guides. If so, that's a positive.
-If the heads are good and free and the 74 are bad, i'd do it. I would'nt go out and buy some 77 heads, and I wouldn't spend much on them like having the guides replaced. You could easily sink $500 in them, when for a little more you could have some nice heads.
-There is a lot of misc work and costs involved. One mine anyways, if I touch one thing two things tear up in the process. Murphy's Law.

 

[broncnaz]

supposedly 77 heads have 68cc combustion chambers where your 74 heads should be about 64cc so you could lose almost a full point of compression with the 77 heads on a 74 engine which would drop your comp ratio well under 8-1 also keep in mind that 73-76 blocks are .020 taller than earlier and later blocks further reducing compression.
Shouldnt really need anyother parts to swap heads just keep the 74 pushrods with the 74 engine but really I wouldnt do it because of the compression drop but you may want to verify if your 77 heads are 77 heads you may be lucky and have 76 heads which are the same as 74 heads.

 

[mr incredible]

the 77 heads will have hard seats , and lower the compression of your older motor ... wich in turn will make it run good on regular gas . and the unleaded we have nowadays . but there will be a noticeable power difference as well .

 

[DirtDonk]

According to Chilton's, the effective compression ratio for both was 8 to 1. But that could still mask a difference in combustion chamber volumes between the two, if they used different pistons in the different years.

Paul

 

[Broncobowsher]

The engines achieved different compression ratios different ways. The '74 was a taller deck, the '77 a larger chamber. Swap heads and one engine will raise compression (all the bad parts) and the other will loose it (all the working parts).

The pushrods to use for the swap become interesting.
If both heads have the same cast rocker arms, push rods stay with the block.
If the '77 has new style stamped rockers that bolt down (not a nut on a stud) then the pushrods follow the heads. Hopefully they will work or a new set of slightly longer ones may be needed if you get a lifter tick, but probably not.

It should keep you with a running engine, just maybe not as good as it should. But still better then 2 broken engines and for only a few bucks in gaskets and some time. While not ideal, it is a cheap way of keeping the horse running. I would do it if I was in that situation.

 

[garberz]

The 1977 heads are on my 1977 and were working fine as far as i know.The 1977 302 develop piston knock bad piston pins.So i was thinking on just switching those 77 heads on the 74 302.
What parts besisde head and manifold gaskets would i need??

Whats wrong with the 74'. Are those heads in need of repair?