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On my quest for a budget 400 horse 306 ci small block, I have a couple of low cost options for heads. A decent set of aftermarket heads can run $950-$1300. A pair of custom ported stockers can run $700+ while using STOCK valves! With some garage talk with Tom and Brenda from T&B racing engine and machine I was on my way to a DIY port job. And I have to admit that the end results are WAY more satisfying than I expected.
What I started off with is the F3ZE-AA casting cylinder heads-the GT40 iron heads. Stock they come with a 1.78" intake valve and 1.54" exhaust valve. The intake port is said to flow around 185-190 cfm stock and the exhaust is somewhere around 125-130.... I know, what a performance head!
Some of the qualities of this casting (in which I will use to good measure) is the basic shape of intake and exhaust ports. In the picture below, you can see how the valve guide is placed closer to the long turn radius, as opposed to some heads that place the guide farther down protruding into the port. The port is also shaped so that the flow of air "swirls" into the chamber (use a long thread and some compressed air and its clearly visible). The short turn radius is also fairly smooth from the factory. Note, the picture below has already been cut for a 1.94" valve.
View attachment 3210
The exhaust port is okay, at best. You can see the thermactor hump in the photo below. There, you can also see where the machined surface (from the 1.6" valve throat cutter) meets the cast surface of the exhaust port. As much as I would have liked to work this exhaust port more at the valve guide, water lurks under it.
View attachment 3211
To get started, I cut up some scrap stainless steel and Tig'd up a head stand. You don't need this, but it makes things a lot easier when you spend upwards of 50 hours with it.
View attachment 3212
Some other tools I used was a flexible neck flashlight, a die grinder with an assortment of carbide burrs, sanding rolls, and cross buffs. You'll need eye and protection and a dust mask. You'll need the intake and exhaust gaskets and an assortment of measuring devices.... oh, and a calibrated eye ball and finely tuned finger.
The intake port:
With the 1.94" intake valve throat cutter, it was obvious the machined surface needed to be blended into the bowl. You can see the ridge in the first picture. I widened the bowl on the short turn wall (the right side of the port in the picture) and blended that about half way down the runner. Care must be taken to create a smooth streamline surface. Use your finger and light shadows to find waves or lumps in the wall. Next, skinny down the valve guide sweeping it into the intake roof. Finish with an 80 grit finish. This is how mine turned out.
View attachment 3213
The runner recieved only a flattening/smoothing of the pushrod bump and some work to the roof behind the valve guide. Gasket matching-although doesn't add a lot to your flow-doesn't hurt either. An 80 grit surface will keep your fuel suspended in the air... but this is a little extreme.
View attachment 3214
The short turn radius was blended and worked so that it decreased in radius, blending it into the intake runner floor. A finished runner should resemble this.
View attachment 3216
Note, the picture is upside down.
View attachment 3215
The exhaust port:
Like the intake port, I needed to blend the throat of the larger valve into the bowl. The exhaust port's valve guide was laid back to the emissions intrusion and from there, the exhaust port roof was raised .125". The floor was untouched and the short turn radius was worked in the same way the intake port was. A minor widening of the port was needed for the larger valve.
Some pictures of my exhaust port finished with a medium polish.
View attachment 3217
View attachment 3218
View attachment 3219
The Combustion Chamber:
While removing metal from the combustion chamber will lower my compression, the engine I'm running has a 2.6cc domed piston and with 63cc combustion chambers, this puts the engine at 10.3:1 compression. The stock chamber is about 61 (I didn't measure the before). Saying that, I unshrouded the intake valve about 1/16" and laid back the hump where the spark plug threads into. Then the chamber was polished. Some dimples where left because it would cost me too much material to finish them out.
Before
View attachment 3220
After
View attachment 3221
Like I said earlier, I have 25-30 hours in EACH head. But the difference WILL be felt. At 28", the intake flowed 245 cfm and the exhaust flowed 201 cfm! Whats more exciting is the fact that the ported intake flowed more air at .300" lift than the stocker did at max cfm. The ported exhaust bettered its stocker's best at only .200 lift.
Also, the valves I used are REV race series with an undercut stem and were swirl polished. T&B then cut the valves and seats for a performance 5 angle valve job.
Here's a finished head (and I'll load up more later).
View attachment 3222
What I started off with is the F3ZE-AA casting cylinder heads-the GT40 iron heads. Stock they come with a 1.78" intake valve and 1.54" exhaust valve. The intake port is said to flow around 185-190 cfm stock and the exhaust is somewhere around 125-130.... I know, what a performance head!
Some of the qualities of this casting (in which I will use to good measure) is the basic shape of intake and exhaust ports. In the picture below, you can see how the valve guide is placed closer to the long turn radius, as opposed to some heads that place the guide farther down protruding into the port. The port is also shaped so that the flow of air "swirls" into the chamber (use a long thread and some compressed air and its clearly visible). The short turn radius is also fairly smooth from the factory. Note, the picture below has already been cut for a 1.94" valve.
View attachment 3210
The exhaust port is okay, at best. You can see the thermactor hump in the photo below. There, you can also see where the machined surface (from the 1.6" valve throat cutter) meets the cast surface of the exhaust port. As much as I would have liked to work this exhaust port more at the valve guide, water lurks under it.
View attachment 3211
To get started, I cut up some scrap stainless steel and Tig'd up a head stand. You don't need this, but it makes things a lot easier when you spend upwards of 50 hours with it.
View attachment 3212
Some other tools I used was a flexible neck flashlight, a die grinder with an assortment of carbide burrs, sanding rolls, and cross buffs. You'll need eye and protection and a dust mask. You'll need the intake and exhaust gaskets and an assortment of measuring devices.... oh, and a calibrated eye ball and finely tuned finger.
The intake port:
With the 1.94" intake valve throat cutter, it was obvious the machined surface needed to be blended into the bowl. You can see the ridge in the first picture. I widened the bowl on the short turn wall (the right side of the port in the picture) and blended that about half way down the runner. Care must be taken to create a smooth streamline surface. Use your finger and light shadows to find waves or lumps in the wall. Next, skinny down the valve guide sweeping it into the intake roof. Finish with an 80 grit finish. This is how mine turned out.
View attachment 3213
The runner recieved only a flattening/smoothing of the pushrod bump and some work to the roof behind the valve guide. Gasket matching-although doesn't add a lot to your flow-doesn't hurt either. An 80 grit surface will keep your fuel suspended in the air... but this is a little extreme.
View attachment 3214
The short turn radius was blended and worked so that it decreased in radius, blending it into the intake runner floor. A finished runner should resemble this.
View attachment 3216
Note, the picture is upside down.
View attachment 3215
The exhaust port:
Like the intake port, I needed to blend the throat of the larger valve into the bowl. The exhaust port's valve guide was laid back to the emissions intrusion and from there, the exhaust port roof was raised .125". The floor was untouched and the short turn radius was worked in the same way the intake port was. A minor widening of the port was needed for the larger valve.
Some pictures of my exhaust port finished with a medium polish.
View attachment 3217
View attachment 3218
View attachment 3219
The Combustion Chamber:
While removing metal from the combustion chamber will lower my compression, the engine I'm running has a 2.6cc domed piston and with 63cc combustion chambers, this puts the engine at 10.3:1 compression. The stock chamber is about 61 (I didn't measure the before). Saying that, I unshrouded the intake valve about 1/16" and laid back the hump where the spark plug threads into. Then the chamber was polished. Some dimples where left because it would cost me too much material to finish them out.
Before
View attachment 3220
After
View attachment 3221
Like I said earlier, I have 25-30 hours in EACH head. But the difference WILL be felt. At 28", the intake flowed 245 cfm and the exhaust flowed 201 cfm! Whats more exciting is the fact that the ported intake flowed more air at .300" lift than the stocker did at max cfm. The ported exhaust bettered its stocker's best at only .200 lift.
Also, the valves I used are REV race series with an undercut stem and were swirl polished. T&B then cut the valves and seats for a performance 5 angle valve job.
Here's a finished head (and I'll load up more later).
View attachment 3222
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