By porting the heads, you're making the exhaust and intake ports larger, correct? What is pocket porting, race porting (I guess that's what it's called). I'm guessing you can port the heads in different sizes or stages. Why would you go thru all the work of pulling the heads and only mildy porting them, why not go all out? Can someone please explain this to me. I'm hoping by next summer I can have this done.

 

Mark,

Man, you do know how to pick the good questions...

The theory behind porting heads is to improve flow in and out of them. This generally involves removing material to make the net size of the ports larger, but not always. Some truck- and tractor-pulling engines don't do well with large port volumes, so the trick can be trying to massage more flow without enlarging too much. In some cases, ports are even welded closed to some extent so that the ports can be reshaped without enlarging them excessively. They want to maximize flow velocity for greater cylinder charging at lower RPMs. You may want some of that same effect on the street, which is why some people opt not to go "all-out" in porting their heads. It's all in how you intend to use the engine.

But for our purposes, the general idea is that larger port volumes are desireable, since most of us want better flow in the higher RPM ranges, not in the truck-pulling end of the band. And it isn't just enlarging the ports that makes the difference, but improving the design so that the flow in and out of the chambers encounters the least restriction. This means straightening port runners, making the port size more regular along its entire length, and smoothing the transition from the intake flange to the valve bowl, and into the chamber. The same has to be done on the exhaust side. Changing the intake and exhaust port locations is not even out of the question.

"Pocket" or "Bowl" porting is generally the term used to enlarge the area in the valve bowl areas (above the valves) to reduce flow restrictions in those areas. This should usually include cleaning up the valve guide boss that protrudes into the bowl to smooth flow around it as well.

"Port matching" generally refers to shallow reshaping of the intake and exhaust ports near the manifold flanges to smooth the transition between the manifolds and the heads.

"Short-side Radius Blending" is the process of reducing the sharp transition from the side of the valve bowl nearest the port flange to eliminate the customary "hump" of material so kindly left there by the factory.

As for "race porting" I'm not familiar with that term. To me, it's a lot like the terms I've heard floating around in ***** circles, like the references to "half-race" and "full-race" camshafts. What the hell is half a race? If I'm racing, I'm not going just halfway. Those terms say absolutely nothing about a particular piece of hardware, but a whole lot about the person spewing them out...

Any complete head porting should involve all of those, as well as straightening the overall port shape and eliminating "bottlenecks" or restrictions in the port runners. The radius in the valve bowl area, for example, can generally be improved to allow better flow at the near-side of the valve. And a complete job should include a high polish on the finished exhaust ports to prevent carbon buildup and reflect heat from the head surfaces.

The best advice I can give in doing any port work is to think like an air molecule. I was given an analogy by a person with more experience than most of us put together. He advised to imagine the air molecules as tiny bicycle racers on a closed course. They all want to get there as easily and quickly as possible, but there isn't enough room for all of them. There will be a lot of pile-ups at those sharp corners, some riders are going to crash at those bottlenecks and screw up the race for everyone, and everyone goes faster if they can see the finish line. Your job is to design the course to accomodate the most riders at the highest speed.

Make the path as straight an uneventful for the incoming air and exhausting gasses, and you will have improved flow. Sometimes this can mean intentionally breaking through a port wall and welding extra material in to close the runners. Sometimes you can raise the port ceilings so that the air has a straighter path to and from the valves. Study the designs of the ports and runners, and the flaws will become obvious - so will the solutions. When you see that, you can get out your grinder.

You should also be aware of the design flaws in many factory heads. There are some places that have relatively thin walls, and water passages are cast throughout the head. You need to be aware of those items before you grind or machine too thin. You can usually get a good look at both sides of the walls if you peer through the cooling passages.

It may be best to get a used pair of heads for practice, and if they turn out well, you can do the valve installation and have a good set of ported heads. If there are problems, all you're out is an old pair of heads, but you've gained a lot in experience. Start with iron heads, since they are a little more forgiving and machine well without loading up the tooling. Once you have mastered the iron castings, try aluminum if you want.

 

I did mine on my mazda's 305, I just ported out and smoothed everything up. it seemed to help quite abit, it revs pretty hard for a 305. the "race" you were talking about I assume is when you have each intake runner and exhaust runner flowed so that they match EXACTLY to each other. that way you won't have 1% more flow on one and not the other. around where I live it costs like $175 to have the "race" ported or flowmatched is how I've heard of it. I hope I helped a little

 

Yes, good question, and as always, a good answer from Mr. Vader.

Mark, you asked almost the same question as I did several months ago. Check out this thread https://www.thirdgen.org/techbb2/sho...threadid=30744 to see what I mean. Vader didn't respond to that one, but the answers are almost the same.

The only things I would add to Vader's response is that the chambers should also be polished for the same reasons the exhaust ports are; and, you can improve flow quite a bit by working the valves themselves as well.

The CHP "My Generation Camaro" pocket porting work was almost a joke. Yes, they cleaned up the bowls, but didn't even touch the guides. Ugly.

I like the "half race" and "full race" stuff, too. I get a chuckle every time an old timer (older than me, anyway) comes up to the '57 and starts talking to me about how they used to have one "and it even had a 3/4 racing cam in that 265 - I could pull the front wheels six inches off the ground!" Of course, most of them can no longer keep seperated in their minds what they actually had from what they wished they'd had... ("Of all the things I've lost, I miss my mind the most.")

 

I'm actually Getting ready to port my 305 heads next weekend ..I've got everything apart right now

So I'm trying to gather up all the good information I can (this topic did help too)

But do you guys know if theres a good article out there that will help me out more ???

I have taken a look at "Daniel Burks" Article on our site here .... but I was looking for something a little more involved

really, any good articles or more information at all would be a great Help ..
Thanks

 

If you have the Standard Abrasives' Deluxe Porting Kit, you have the best instructions for the do-it-yourselfer out there. Also available to download here http://www.sa-motorsports.com/diyguide.shtm .

If you're looking for more than that, you'll need flow and volume testing equipment. And, you're getting into the "tricks of the trade" area, and probably well beyond the DIY realm.

 

Thanks for all the great answers. I'll be sure to book mark this page.
Oh, and one more thing. The hemi, the ports on their heads are a hemisphere shape right? What made that so good?

 

Not to get into the heavy "mutual admiration" bit, but 5-7 offers some great advice.

I would agree that a flow bench is a requirement for final testing on "fully race ported" or "race-prepared" heads, but short of a trip to the flow bench for $75.00 per hour of testing, you may be able to get your hands on some of the proprietary templates that are copied from "race-prepared" heads. Contouring your ports to match these templates should have results very close to the "race-prepped" heads, and will certainly be better than most stock and aftermarket raw castings.

I would provide a link to these places if I had one. It's very easy to make your own from card stock. Once you have a satisfactory intake and exhaust port finished, just cut the templates to fit in several places in the runners and bowls, and make all the same.

 

Anyone have any ideas how much HP or 1/4 time I could knock off by porting my heads. Right now I have 8.5:1 compression with 1.94/1.5 int/exh port sizes. The compression could be raised by getting a thicker gasket right? Should I go with higher compression, with the intake and cam I'm having added. Also before I do head work, I want to get a higher stall TC.

 

Mark, depending on what set of head you have and the quality of the work, you may see anywhere from no gain to 30-40hp.

Other thing is a thicker gasket will lower the compression ratio, and thinner gasket will raise the compression ratio.

 

David Vizard gives a fairly detailed description of porting various small block chevy heads in his book on: How to build Max Performance Small Block Chevys. You should be careful when porting as you can do more harm than good if you go beyond proven methods. Yes, a thinner gasket will rise compression slightly and try to get one with the smallest bore diameter that will fit your engine,no sense in having one that's way over size.

 

If anyone has said this shoot me... I didn't have time to read the posts.

Porting will always increase the size of the heads in terms of size (cc) and this can be good and bad. A heads main powerplay is mixture velocity, because at low lift or rpm, the higher speed the air rams into the port the more air gets in, and that means more power. Incrasing the size of the port reduces the velocity because it is expanded and less concentrated. This oversize can inhibit an engine when vacuum is low, so you make the power in the upper rpms.

This means that Cfm is a good indicator of top horsepower, but the Cfm/cc ratio is a good indicator of torque. This ratio is why bigger isn't always better with heads, as the cc climb the ratio falls, and so does torque!

 

<h1>BANG!</h1>

 

Ooooooy!!! I'm hit! The humanity!!! Good bye cruel board!

 

Yes. Get that book. It can be bought through (if they don't have it on stock) Barnes and Noble.

I just bought it ~2 wks ago. It pretty much states a lot of what Vader and five7kid said, but Mr. Vizard has a lot more time and room to explain it. And he does a very good job of using terms that even I can understand.

It's explained so well, that you almost say "Why didn't I think about that?". He makes it sound so simple, you feel like you've overlooked the obvious the entire time you're reading it. And you can say "OK. That makes sense."

Again, not saying that Vader and five7kid didn't say anything valuable. They did, and always do, but both time and size limits what they can teach here.

AJ

 

Is this the book?

 

Yes.

 

1st answer to the question is a question, have you ever seen chevy heads in as cast state before they are put on the engine? i have a set of new vette heads that wont be going on my motor before a clean up at least. as the casts get more and more used over time they start to vary where the shouldnt. i have ports that dont match the rest of the ports as they should, the D ports on the exhaust side are not all the same size and 1 almost isnt a D anymore. i have a camera and can take pics of what i mean, anyone know a good spot to host some pics for free?

in the combustion chamber where the spark plug holes have been tapped there is aluminum spikes from the tap that will also need to be removed before install or i will have a det. problem in a few cylinder compared to the rest. the heads are still good but a clean up will allow more compression and more timing with less det. and carbon build up in the chamber and ports. i dont plan to hog these heads out, light porting and clean up but nothing radical, i'm shooting for 165-170cc intake runners.

 

http://www.gmtips.com/3rd-degree/dox...-port/port.htm

This link has some good tips.