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Hoping to get some good advice from those a lot smarter than me...
I picked up a ZZ502 short block that I plan to build for my '69 coupe. Have no plans to race - just a solid street performer with good low-mid range torque and power. Not looking for something that'll rev higher than 6500 rpm.
The GMPP cylinder heads that come with a ZZ502 long block are 290 cc/110 cc oval port heads with 2.25"/1.88" valves (PN 12363390). From my research, it seems that, although the intake port size is on the low end, they would probably do well for a street motor.
Other research tells me that I should think about stepping up to a larger intake port (305-315 cc) and to consider square port heads instead of oval. The price difference is a few hundred a head.
What do you guys think?
Also, there are several similar size heads with smaller (2.19") intake valves available. Should I stay focused on the larger valve size or does it make a difference for my use.
I would go with AFR 290 oval ports (roval ports really). Big flow up top and great port velocity down low... Make big power and give up nothing down low. Be aware of the raised exhaust ports and header fitment. Another option is the Brodix Race Rite 270cc. They have stock exhaust port locations. No reason to go bigger then 290cc on a 6000rpm 502.
If your looking for an oval port head with port sizes that will line up with a performer rpm for hood clearance, good flow numbers and bottom end to midrange performance I would look at these. http://www.airflowresearch.com/index.php?cPath=68_121
There will be others that say you need a bigger rectangular port head but these have a 112 CC chamber and can be flat milled to 102 CC. They will also support 750 HP. Most of the bigger heads have the larger chambers that limit the amount you can reduce cylinder size for a little more compression. You will also want to use a thin head gsasket. This will get you up around 10 to 1 compression and combined with a better cam you should be able to get 600-650 very streetable HP.
Have no plans to race - just a solid street performer with good low-mid range torque and power. Not looking for something that'll rev higher than 6500 rpm.
For what you want to do with the car, there are plenty of ways to go that would probably satisfy you.
The AFR 290cc heads mentioned above are excellent, but do have a .375" raised exhaust port and a fairly steep price.
The Edelbrock/GM heads that you mentioned are good heads at a good price with a stock exhaust location. They wont make the power the AFRs will, but you may not notice on the street.
The Brodix Race Rites are another good choice, and also have a stock exhaust location.
Trick Flow ovals are a good head and are priced better than most, but they have a .300" raised exhaust which may or may not be an issue.
Even a set of bowl ported factory ovals would be good for your application, but would lack the aluminum bling you might be looking for.
If you feel the need to go rectangle, just keep them small and you will be OK.
The Race Rites come in a 294 cc rectangle version & the AFR 305s should be fine too.
Someone has a program they were hyping for those heads (GM 290 ovals), their were some really good numbers and port size. Maybe someone remembers who it was and you could talk to them. Maybe look at the AirWolf heads or something from Spier Racing. Just some other options than brand "x".
The AFR's mentioned are a good head. But for $3000; they better be. IMHO, there's better ways to spend your money unless 0.2 seconds faster at the drag strip makes a difference to you. The raised ports would have been a problem in my car, but that can be remedied. Keep in mind, in stock form, you will only have about 9.7:1 compression with the GM heads and less with the others unless you mill them down.
The GM/Edelbrock heads will support somewhere north of 600 hp. I have one brand new for sale in the parts section - shameless plug - if you go that route. And the brodix race-rites are perhaps a bit better. Unless you are making other changes to the 502, you won't see a whole lot of difference between any of these heads. As a minimum, I would get the cam reground to something bigger. I've built several 502's and they really respoond well to a bit bigger cam.
Here is a good reference for comparison purposes. Higher flow with the same port size will always make better power across the entire RPM range with all other factors the same. There is a reason AFR heads cost more. Your choice or availability of intakes that will fit under your hood will make a difference on head intake port size.
Bigger is not always better (The highest flow numbers and/or largest port volume). — Flow Velocity or the speed of the air through the port is just as important. We want the best flow numbers with the smallest port volume and the highest velocity (up to a point). Remember to compare all flow numbers. — Low lift flow does help performance.
Just looking at flow numbers near or above maximum Valve lift for your camshaft is meaningless. Look for the best average flow from mid-lift to just before maximum lift of your camshaft.
For street engines airflow at 0.400-inch lift is a good place to evaluate flow.
02-15-2012, 10:49 AM
ZZ502 Cylinder Head Recommendations
