I am replacing the 305 heads on my 327. I need to replace the push rods some are bent. Which push rods do I use for that setup? 305 to match the heads or 327 to match the block/cam? Is there a difference between them?

 

305 cylinder heads are the same as 350 heads, they just have slightly smaller combustion chambers than 350 heads of the same era. The question is which 305 heads do you have. They bolt up fine, it's a matter of compression ratios that will determine whether or not it's a good idea.

A 327 block is the same as a 350 block by the way.

Also, pushrod length is determined by which length pushrod gives the correct rocker arm geometry. This varies among different motors. Several different factors affect that. There's no easy answer for the correct length pushrod, since factors around the cam lifters, and block affect it just as much as factors involving the heads, rocker studs, rocker arms, and valves/valve springs do.

 

I knew the heads and motor/ block were the same as the 305/350 just bore size and port size makes the cubic inches, my problem is I have 3 bent push rods that didn't just bend on their own there is a reason. Because of the bent rods the gains through the heads became rounded out. The new heads I bought are out of a 1989 caprice 305.
Auto parts store tells me there is a difference between the 1987 iroc 350 and the 66-67 327 push rods.
How do I go about getting the proper rods? I don't want to go through all this work and create another problem down the road.
The heads are almost identical with the old ones wobble arms bolt pattern only difference I can see is the new heads will have a center bolt to hold the valve covers down...

 

The '87 IROC 350 has nothing to do with your build. It uses roller lifters, your 327 does not.
The '89 Caprice 305 also had roller lifters, but again, that doesn't matter.
If you're using stock replacement pushrods, any pre-'87 will be the same. But if you're using a performance cam, then you may be putting the valves into the pistons, which could bend pushrods, or you could be putting the retainers into the guides, which would bend pushrods.
Those Caprice heads are the dreaded swirl-ports, they're not helping you make any power, but they're good for off-idle torque.

 

I'd recommend you buy an adjustable length pushrod to find the correct length. Since you're using a flat tappet cam (right?), then use the adjustable length pushrod that spans that length (I honestly can't remember, 7.5-8" or something??). You may need "checking" springs, that are weaker than standard so you don't bend the checking pushrod (or just hold the valve up with your hand if you want). You want to mark the valve tip, and rotate the engine over and check the "witness mark". You want the most narrow witness mark, closest to the center of the valve. Narrowest is most important.
My setup took pushrods that were pretty close to stock, but slightly off (~.050?"). I think I ended up with a Ford length of something, since they were cheaper than custom made ones.
That'll get you the right length, which *might* solve your bent pushrod issue (it did for me). Check your gaps when re-assembling, it valve coil gap, retainer-boss gap, etc.

 

OK all good info guys, One thing that i have been thinking about since i don't know anything about how or when this mis-matched motor was put together if they used old rods that may have been bent to begin with or for some reason got hot. I can't imagine anyone doing that but i think its something i have to consider.
The CAM is not stock, i have not gone as far as seeing what type is in it. Even if i used the stock 327 heads if the cam is not original i am back to square one arent i? I can use the 66-67 stock push rods but if its off as much as .05 thats huge.
Anyone have any suggestions as to what i should do with this? I just dont know which direction to go. I am hosed either way with this unless i start from the CAM up and keep things original. This engine for now has to get me by until i can find the 350 engine that belongs in the car, on the other hand i do not want to just throw it together and hope for the best, that 327 is worth something to someone.

 

Okay, many 327s were built with flat-top pistons, and most replacements were also flat top. Combine that with your current heads, and you may have enough compression that a stock cam could cause low-rpm detonation.
The cheap and easy way to start is to get one of those cheap plastic Pushrod Length Checker tools. Do that with a stock pre-'87 pushrod, and see what result you get. Check both intake and exhaust, especially the cylinders that had the bent ones. But also check some others.
Those are like $10?, and are foolproof to use.
If your results with that are okay, then you need to check your retainer-to-guide clearance, especially for the valves that bent the pushrods.

 

What year did the bellhousing bolt pattern change on the v-8? Thanks, grego.

 

Never. But this should be your own thread.