[Goatracer1]

My wife's car has a rebuilt 389 4 bbl. I know nothing about the rebuild since it was done before I bought it. I am going to change the heads to reduce compression. I already own the ones that I am going to use. 2 questions. How can I tell if they used 389 pistons or 400 pistons when they rebuilt it? Also how can I tell 1.5 rockers from 1.65 ones?

[Joe's Garage]

You should be able to find a part number and possibly an oversize stamped on the head of each piston. GOOGLE those numbers and it should tell you which pistons they are.

Not only were the bore sizes 389 or 400-specific, the valve angle on the heads differed, requiring different valve reliefs for each displacement.

1st pic is a 389-style with the narrower valve reliefs for 389 heads.

2nd pic is a 400-style with the larger valve reliefs (bigger and further apart).

3rd pic is the dreaded 8-valve-relief style that goes both ways.

4th pic shows the difference in stock 1.5 vs 1.65 rocker arms with the 1.5 on the left and the 1.65 on the right. Notice that the indentation for the pushrod is closer to the fulcrum on the 1.65 rocker arm. That's what changes the ratio.

5th pic is the top of the same two rocker arms, with 1.65 on the right.

Aftermarket roller-tip rocker arms should be marked with a part number or ratio. Again, Google is your friend.

Hope this helps.

[steve25]

You did not mention what era heads your switching over to, but note that your current push rods ( 326, 389 and 421 types ) are shorter then what you will need for the mid 1967 and later heads.

Also note that as you drop down below a 9.5 compression that the timing curve you run ( including vacuum advance) is key to maintaining good throttle response and somewhat decent fuel mileage.

If this was not maximized with your old heads then be sure to take the time to do it now.

Also if it turns out that your motor has pistons with only one type of valve notch, and that notch is for early heads then you can get away with running the later valve angle heads as long as the valve lift of your Cam is not over .430” and the Cams duration is not too much ,

[tom s]

Pre 67 heads use diff style rocker arms than 67 and up.Determine the heads will help tell you what the engine started at.Tom

[77 TRASHCAN]

Sooo, what year is car? Could still have different 389, from origin.

Have you thought ugh that about changing my cam, instead?

[turbo69bird]

Good info .hadn’t realized the piston differences as I always did later stuff, and ordered what I needed .

Anyone got a way to tell the springs apart? I have original RAIV RAV and regular springs kicking around in coffee cans need to be able to ID the differences .

[steve25]

Neither type spring will work in a D port head with out either cutting the spring pads a ton, or run longer then stock valves.

The RAV springs are just one spring with a flat wire damper.
Must you run used springs ?

[tom s]

I think Vs have a taller installed height also and were made and setup for solid lifters.I think I still have a stock setup with the spring cups.Tom

[turbo69bird]

Originally Posted by steve25

Neither type spring will work in a D port head with out either cutting the spring pads a ton, or run longer then stock valves.

The RAV springs are just one spring with a flat wire damper.
Must you run used springs ?

No I just have them some are used some are NOS I just have a lot of parts all jumbled together after I moved and I want to separate them so figured I’d ask how to ID them .haven’t even looked at them in 25 years just have a bunch of cans of RA parts from back in the day. A lot of things were changed but I always saved the old parts .

[Goatracer1]

The engine is a 1962 and it is original to the car and a California engine. Yes I did know that the push rods and rockers are different. The heads are 1968 #62's that came off one of my race cars 25 years ago. The chambers were opened up and the heads have been kept warm and dry and saved for just such a project. I asked about the pistons because I assumed the engine was bored when rebuilt and I hoped they used 400 pistons.

[Goatracer1]

Before anyone says anything about the intake I do know they (and the valve covers) are different also. I will check the cam lift also but I plan on running a Stock .405-.409 lift cam.