Back in 1994, a local retailer was offering a package deal on new ZZ3s with optional Twisted Wedge heads (only optional heads they offered & the ad claimed an additional 75 hp - not that I believed it ). The price was right, so I bought it and installed it in my '80 along with headers, hi-flow cat and Stage II Q-jet. I've never been terribly thrilled with this engine's performance, and I've had two different Vette shops ask me why I decided on those heads (they weren't trying to sell me another brand, just seemed puzzled).
So, I see where Edelbrock is offering a new D-port head for small blocks, and I know a lot of you like AFR's stuff. Would I see enough difference if I changed?
Even if not, what would you say the best head for this engine is? Is the AFR 180 too "small"?

 

In my humble opinion, there's probably nothing wrong with the AFRs that you already have, the 180s are pretty good heads and unless you are going to go with a much bigger cam, and a single plane intake, you probably aren't going to get much better performance out of other heads.
If I was looking to add some performance to a stock ZZ4 or ZZ3 I'd look at adding a little bigger roller cam and/or 1.6 rockers.
If I was going to go with a set of heads right now, I'd go with Edelbrock Etec 200's and they are probably are a little big for my street driven ZZ4 and would be better on a 383 stroker, 400 or one of the stroked 400's. I heard and read that the larger runners decrease velocity of the air charge and will cost some power on a 350 at low and mid range, where most of my driving is done.

 

An engine is only powerful as the cylinder heads. According to Hot Rod, AFR has a formula to estimate an engine’s horsepower based on the flow (cfm) of the cylinder heads. Here is the chart for an 8-cylinder:

HP = 0.25714 x cfm x # of cylinders

Flow (cfm) / Power (HP)
100 / 205.7
150 / 308.6
200 / 411.4
250 / 514.3
300 / 617.1
350 / 720.0

For a street engine, the secret is to have the cylinder head flow as much cfm through the smallest intake port. I have started a chart for this, here are the top five:

Average CFM/CC from 0.300”-0.500” Lift
1. AFR 180 (1.28)
2. Edelbrock Performer 74 cc (1.26)
3. Edelbrock Centerbolt (1.26)
4. Edelbrock E-Tec 170 (1.25)
5. Edelbrock Performer 64 cc (1.25)

All very close, but AFR 180 flows more cfm per cc of volume. I believe the flow per volume is a good indication of torque because it related to port velocity.

Using the top five from above, lets look at the actual flow of the heads.

Average CFM between 0.300”-0.500” Lift
1. AFR 180 (230 cfm)
2. Performer 74 cc (215 cfm)
3. E-Tec 170 (213 cfm)
4. Performer 64 cc (213 cfm)
5. Centerbolt (208 cfm)

Using AFR’s formula from above, these are est. HP numbers (just for comparison):

1. AFR 180 = 473 HP
2. Performer 74 cc = 442 HP
3. E-Tec 170 = 438 HP
4. Performer 64 cc = 438 HP
5. Centerbolt = 428 HP

Finally, you need to look at the intake cfm versus the exhaust cfm or the Intake/Exhaust ratio. You can have a great intake port and make some serious torque, but you have to get the gas out of the cylinder head also.

Average Intake/Exhaust Ratio from 0.300”-0.500” Lift
1. E-Tec 170 (77%)
2. Performer 64cc (77%)
3. AFR 180 (76%)
4. Performer 74cc (73%)
5. Centerbolt (70%)

According to Lingenfelter, between 75-85% is optimal. Note: E-Tec 200 is one of the best at 82% and the ‘Vette head from the ZZ4 is also excellent at 80%.

If you can afford the AFR 180, I would go with those, if not, I think the E-Tec 170 would be my second choice. I think they require a Vortec style intake.