I have the heads off already for a headgasket/piston repair, and i am wondering if i should do a little porting whil ei have everythign off. The heads just got back from the machine shop, also i have already gasket matched the TB to intake, intake to heads, and heads to headers.
If i do some porting what areas would be most benificail, and what things whould i look out for?

 

If you have the tools, it's not that bad, and it helps. Every cfm extra is worth 2hp!!
Check out this site.
http://www.sa-motorsports.com/diyport.aspx

 

Don't do it, you'll only destroy yourself!!!


The truth is if you're good with your hands you can make a nice improvement for cheap. You just need to research it well before you touch the heads with a grinder. Grinding away in the dark and indiscriminately hogging the port out is ill advised. By far the best tool for educating yourself is being shown in person what to do by someone who knows what they're doing.

Here's a link to some flow bench numbers and description of the porting when I did a DIY port job on my LT1 heads. Careful, it gets ugly.

http://web.camaross.com/forums/showthread.php?t=468320


It's pretty easy to go in and bulk up the midrange (.300 to .500" lift) flow numbers by 10 to 15% in a reasonable amount of time. If you haven't ported a set before plan on spending at least an hour per port. Not a whole lot of grinding is required to get to this level but you need to take your time and only grind in the right places. A peak flow of 235cfm is pretty realistic if you do a little research first and are good with your hands. That sounds pathetic compared to the wonder 280cfm pro port jobs but you can do that at a much smaller port volume than the pro heads that go 195cc's or more. An improvement in this range would certainly be noticeable over the stock 205cfm. It would probably net around a 20 HP improvement if you're running a mild cam.

If you want much more than this it's a lot more difficult and time consuming. I eventually hit 265cfm but had to do about 2 or 3 times as much grinding and a higher level of skill and artistry is required. The port volume on the intake side was at somewhere between 190 and 195cc's of volume but it was a LOT more involved in terms of time and grinding. I didn't know it at the time but the larger volume SBC port jobs raise the intake roof enough to break into the rocker stud hole by most of 1/8". I never broke through into the rocker stud holes so there was probably some flow left on the table there.

If/when I do a more advanced porting job again here's what I'd do: Start off by raising the port roof as much as is conservatively possible (on the LT1 heads you're not even close until you break through into the rocker stud holes), slim and streamline the valve guides and guide bosses, deepen and widen the bowl area on either side of the guide (especially on the side of the bowl next to the wall that seperates the paired intake ports), open up the valve seats to 85% to 90% of the valve diameter, make the port as wide as possible in the pushrod area of the port (a home made yankee caliper makes it easy to know how much meat is left), and widen the port over the hump area of the floor. Don't touch the port floor other than to blend the valve job into it and smooth out the casting flash, screwing with the port floor is the quickest way to screw things up and it's actually pretty good stock.

This long list isn't needed to hit 230 or 235 cfm, if done right this long list should put stock ported heads easily above 250cfm and maybe 270 or 280 if done exactly right. Problem is that a lot more skill, talent and time is required to have any consistency between the ports when you enlarge them by close to 20%.

To get a nice and easy 20HP in a lot less time just do the bowl work mentioned above, streamline the guides, open up the throat below the valve to about 85% of the valve diameter and open up the pushrod constriction by raising the roof a little and widening.

Later, Michael

 

Since they have already been to the machine shop why mess up the work they already did?

 

Definitely read that thread and others by grammerman on the topic. Pay particular attention to what the experienced engine builders say in those threads.

 

there is a lot more to head porting than cfm gain at peak. That is the absolute wrong way to look at head porting. You may gain 30 cfm at .500 but kill low lift where flow is really important. Have a pro do it. flow at 28" is not very indicative of how well you ported them either.

 

Yes, killing the mid-lift flow to pick up the peak flow is not the way to go. That is only likely to happen when you screw around with the port floor or go hog wild grinding and screw up the basic shape of the port. No way it's going to happen on a mild pocket port job.

Streamline the guide and boss, widen the bowl on either side of the guide, and open up the valve seat I.D. a little and blend it into the pocket. My heads picked up 15% over 20% in flow across the entire lift range from this sort of treatment and came up the most in the low and mid lift flow. A mild pocket port is not rocket science regardless of what people who have never done it with a flow bench say. I have done it with a flow bench

And by all means go read the other threads Steve9899 mentioned. You'll find virtually no useful information there from any of the critics. The same "experts" that dogged me out for daring to port my heads and post the results had lots of great "experienced engine builder" wisdom to impart. Stuff like running a .400" lift cam or saying that my pocket ported set of stock heads which picked up 10% to 20% across the entire lift range would make less power than the stock heads. Some engine builders there. It was actually a hatchet job by people with an axe to grind. Imagine that.

Steve, if you spent a little time educating yourself in front of a flow bench or on a dyno you might be better at sniffing out B.S. rather than repeating it in ignorance. I tuned with a chassis dyno at a former job and have seen exactly what pocket ported heads are worth, have you?

I guess the numerous real worlds "experts" with tons of dyno and flowbench porting data are barking up the wrong tree when they say pocket porting is a win/win scenario. That David Vizard is a dumb ***. The web is full of wannabe experts who don't have jack experience porting heads that say so anyway. Head porting is not an all out race job vs. stock head choice. There is a lot of room in between for a significant improvement without a large cash outlay. Why so many people who haven't a clue try to turn smoothing out a rough port into rocket science is a mystery to me. A man's got to know his limitations though, maybe it's best that they view a simple process in awe. Certainly better for people selling porting services.

Cheers, Michael