I recently finished porting some 706 heads. I just got them back from the machine shop today. They milled them about .005". The combustion chambers came out to 61cc. Lastly, they flow tested them. The exhaust was tested with and without a short pipe attached to simulate the header. The results are below. I didn't have them tested before porting, so I don't know if I made much of an improvement. So, how did I do on the porting?

 

https://ls1tech.com/forums/generatio...potential.html

 

Looks like you made some gains.

 

the small valve and bowl are always going to be 90% of your restriction.

 

Yeah. From what I'm finding, I made more at .500 lift and up. Below that, my heads flow like stock or worse. I'm not sure why it's not higher in the low lift ranges. I left the intake swirl ramp alone. Would that have made more cfm in the lower lift ranges? My heads were flowed on a 3.8" bore, so maybe that's why they are lower....?

 

Cylinder head guys spend decades trying to find secrets, just like your looking for. If this is your 10th set of heads you’ve done, pat yourself on the back. If it’s your first, I applaud you sir. Any cylinder head guy would be amazed that you made ANY gains if it’s your first try. There’s so much science involved. Ask Corona. He’s our resident head expert. I ruined my first set. And the second set.

 

This was my first attempt at porting heads. I did watch hours of YouTube videos first, so I had a slight advantage. I'm just confused at how I made such good gains past .500", but nothing below that. I didn't touch the valve job, so maybe there's more there. I thought about buying the tools to do the valve job, but I was getting tired of working on them buy then. lol.

 

Those are good numbers for intake and exhaust. I ported 243 heads that are on my LS1 Camaro and it runs strong as hell. I'm sure your 706s will do well on your build.

 

I was really hoping to beat the stock flow numbers of a 243 or 317 head. Maybe that goal was too ambitious. I am glad that I made some gains though.

I attached my 317 heads flow chart below. The porter (professional) flowed them before and after. The "post" numbers are after porting. I was trying to beat the other numbers. I fell short on the intake side, but my exhaust flow at .400 and on was better. I'm pretty proud of my exhaust ports.

 

Utinator-any pics of your work? I ask because I enjoy pocket porting these heads and just cleaning them up. I never attempt to "port" them.. Just clean up casting flash and try and make the ports, and bowls, as uniform as possible. The only other thing I do is smooth out the short side radius where it transitions into the valve seat area. Some people say to leave the short side radius alone... Others say to work it. Just wondering what your thoughts are, and if you have pics. Oh, and I do open up the "top" of the exhaust port at the exhaust gasket mating surface to give it a "D" shape. I leave the bottom of the exhaust port flat, and just round out the top of the port to match the gasket.

This stuff interests me greatly but I just don't have the time to send the heads out before and after for testing. If I could find someone close to me here in Houston who has the equipment I would literally work a port a little-then test, then work the same port a little more-then test, and keep going on that single port until I figured out what works, and what doesn't and then attack the rest of the ports after figuring out what works and I have a plan in place. I like that some people make little bucks that they fit down into the port. By using a small buck in each port checking as you go they get them more uniform.

There is a guy that goes by Head Flow Inc on youtube that has decent videos. The port throat work where you are only supposed to open up the throat to a certain percentage of the valve seat/head area was good info for me. I'm sure I destroyed some heads in the past by opening up the throat area just under the valve seat too large as I just did not know what I was doing, and thus destroyed the venturi effect. Funny thing-I was watching the power nation videos with Pat Topolinski and he literally wiped out the throat just under the valve seat completely making it like a straight wall from the valve seat down into the bowl and then flow tested those heads and they flowed really well. That was on a 4.3 V6 head they were working on... It's funny how his heads responded really well to removing the throat area, and yet everyone else says you have to have that throat area in there for the heads to flow right... Again, I LOVE the theory behind this stuff.. but only know enough to be dangerous at this point. Eric Weingarten is another REALLY knowledgeable person on Youtube. It's a shame many of them don't get right into the meat of the matter. You have to sift through hours of videos to get those little nuggets.

 

This is a time vs results situation. If you have time to mess with heads play around with it. But if time is limited, it's better to bite the bullet and get some cnc stock castings from TSP , Katech or AI. This isn't a reinvent the wheel situation.

 

Yeah, I basically did the same thing. I watched those YouTube videos that you mentioned. I'm not real sure about the "throat" area. I didn't make a tool to measure or check if it was perfectly round, or what size it was. I just tried to smooth out the transition from the steel valve seat to the aluminum. I guess that's the throat area. I just went by feel. I ground down the valve guide boss. I left the swirl ramp alone. I didn't widen the intake ports. I just did a little blending on the casting lines. On the exhaust, I ground down the valve guide boss. I raised the roof about 1/10in. I could have gone 1/4in, but I wanted to make sure it wasn't bigger than the stock manifolds. The gasket is bigger than the manifold, so I used the manifolds for a template. I did some grinding on the side walls next to the valve guide. That made the port a little wider, and transitioned into the raised roof area. I also did some work in the combustion chambers. In the "valve shrouding" area, I made the stock cutouts longer, and slightly deeper. I think I ended up with a max diameter around 3.81in. The head gasket is 3.83in, so it should be fine.

There must be someone in Houston that can flow test LS heads. We have a few places here in San Antonio.

 

Here's some recent pics.

 

 

but of course we got someone to flow heads in Houston... Also your question of does a smaller Bore flow less? Yes it does..
if you had a bigger than 3.8 bore here's a idea just 4 you.

Btw I love cylinder heads and I can say this: your a Better guy than me. I ported the plenum of my own SV 4500. Something I'll Never do again and the thought of porting 8 runners. Just get the gun and shoot my hands.

Thought about what you've did and said to self, What would be another gain with this head 🤔

https://ls1tech.com/forums/generatio...00-valves.html

 

Most of the ported heads remove the swirl ramp on the intake. I think that hurts low flow mixture but does help flow more at higher velocity. Someone can correct me if I'm wrong on that.

 

Looks like you did good work on the intake and exhaust. I have a set of 862 heads that I ported in a similar way to my 243 heads including going with a 2 inch intake valve. I polished the exhaust port; that's something many do on ported heads.

 

On the throat percentages I think they are stating you want the bowl just under the throat to be WIDER than the actual throat, and then the valve seat area where the sealing angles are cut is also WIDER than the throat. This supposedly produces a venturi effect. Think hour-glass shape with the bowl being under the pinch point in the middle, and the valve seat area being above the pinch point area. The pinch point (throat) supposedly speeds up the flow of the air/gas mixture as it gets constricted into a smaller space the velocity increases. That's the theory. Supposedly just having the bowl the same size as the throat is a no-no. Also, I believe the hardened metal valve seat just under where the sealing angles are cut is the throat area that is supposed be touched only to make it perfectly round, or reduce the ID of the throat area to 87-90% of the actual valve size. Again... without having the equipment to literally test after making minor changes it just seems like a guessing game. I believe that buying CNC ported heads may be the easiest way to move forward. They take all the guess work out of it, and you know they have the equipment to test this stuff and they know for sure what works... and what doesn't. Maybe studying a CNC ported set of heads would shed some light on what they do to improve the flow.

 

The local machine shop told me not to take the swirl ramp off. Maybe it's just not recommended for the smaller bores, like the 5.3L. Maybe with a bigger bore, you have enough velocity to use the extra port area. I'm not sure what the reason is, but I decided to listen to the more experienced machinist on this one.

 

I thought the smaller bore would flow less, but I wanted more realistic numbers for the 5.3L bore. Maybe my ported 706 heads would have beat some of the stock 243/317 flow numbers with a bigger bore. It definitely would have been closer with a bigger valve. Maybe next time I port and flow a 706 head, I'll have it done with a 4" bore. That would be interesting.

I have an extra set of 706 heads in the tool shed. I have been thinking about finishing them, and putting them on my Camaro. Everyone says the 317 heads are the worst for my LS1, but they do flow good. They were also milled, so the compression is still stock. I could steal the valves from the 317s, and drop them in the 706s. My ported 706 exhaust ports flow about the same as the ported 317 exhaust. The intake flow numbers are way off though. Maybe the bigger valve and a bore would get them closer...? I need to finish putting the 5.3L together before I start another project.