Hot Rod Forum : Hotrodders Bulletin Board - View Single Post - First time porting heads
View Single Post
  #29 (permalink)  
Old 01-05-2013, 08:22 AM
ap72 ap72 is offline
Last photo:
Join Date: Jun 2005
Location: St. Louis, MO
Age: 31
Posts: 9,544
Wiki Edits: 0

Thanks: 20
Thanked 404 Times in 377 Posts
Originally Posted by hcompton View Post
This is 100 percent true. Most factory heads work well because the intake side is under a lot pess pressure to pull the charge in than the exhuast side. The exhuast is going to come out. Because the piston is going to force it out. Most factory heads are very unbalaced because of this fact.

But with heads designed for efi you got to assume it is also built to run with little to no over lap. Now with a poor flowing exhuast port a larger cam with good overlap will not scavange like it is designed to so the exhuast ports always need attention first when starting with an efi head.

Most ford guys are amazed to see the exhuast bump in the 80s and 90s 5.0 engines. It blocks most of the port and by itself its worth 20 hp and will make sure any bolt on you install only works so well. This is also the reason some cars will respond to bolt ons and make 500hp and other will never pass the 300 mark.

On the intake side in this case i would think there isnt much power to be gained past the removing of the ruff casting surface to a smoother sanded surface.

Some none efi heads have the opposite problems. Balance is the key and getting the ports to flow enough to support the rpm the cam is requesting from the engine.

Just some general info to spur discussion.

it's actually 100% wrong... a 5cfm gain on the intake is worth more than a 5cfm gain on the exhaust, even though the % difference is smaller.

Also, the Vortec intake tract is better than previous sbc heads, but the exhaust is NOT worse, its actaully a hair better too, just not as much as the intake. People get caught up in the intake/exhaust ratio and fail to see what they're really looking at on the exhaust side. Also, there's NO crossover, which is a pretty big deal compared to most other stock sbc heads.
Reply With Quote
The Following User Says Thank You to ap72 For This Useful Post:
Camaro_Nut2001 (01-05-2013)