Porting Question
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Porting Question
Rookie question... porting a set of heads for the first time, should I grind down the bump in the exhaust port? I've read mixed results in the archives about this. If so, do I basically grind it down to the back wall/roof? These are 302 heads. THX.
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From: Calhoun GA
I ported the "bump" down on a set of 302/5.0 heads....IMO it is just a restriction. The GT-40 heads flow better than the stockers, and they don't have this bump like the other small block heads have...if that will give ya something to go on.
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From: Calgary
I am also thinking of porting my 302 heads; on the exhaust should I match the outlet to my headers...then carry this dimension all the way along the port? Or would that be taking too must material away.
How exactly do I match the port to the header or the intake manifold...something to do with the gaskets right?
How exactly do I match the port to the header or the intake manifold...something to do with the gaskets right?
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From: Fleming Ga
No. You want the header ports to be a little larger than the head ports t o stop exhaust paracytics from blowing back into the exhaust ports. Just square up the D shape, remove the bump, tear drop shape the valve guide bosses, remove the casting lines and blend everything toward the bowl. In the bowl itself, grind it round and blend. If you look into the bowl from the chamber side you will see that's its rectangular shape. Polish the whole exhaust port.
On the intake side, don't do a lot of grinding unless you are going with a larger cam. It's not the intake side of stock heads that are restrictive and if you grind too much then you slow the velocity down and kill your low end torque
On the intake side, don't do a lot of grinding unless you are going with a larger cam. It's not the intake side of stock heads that are restrictive and if you grind too much then you slow the velocity down and kill your low end torque
Posting Guru
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From: Northern California
fordxxx, on the exhaust, first you need the gasket that you intend to use with your headers. Take some dye (Dykem) or even a sharpie and mark around the exhause ports with the dye. Bolt your exhaust gasket into place with the exhaust header bolts so that it is in the right position. Scribe the outline around each port along the edge of the gasket. Remove the gasket, you should be able to now port to within 1/16 of a inch of the exact gasket shape without having anything getting in the way of the flow. The area just under the valve, referred to as the short turn radius is an area that you want to pay close attention to. This is an area that you can loose a considerable amount of restriction by tapering, rounding and smoothing the short turn radius (dont take too much metal, as there is a water jacket under this area, and if you go through, the head is a throw away). The rest of the port work is as mentioned for the valve guiide, blending, reshaping and full polishing.
Posting Guru
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From: Destin/Ft. Walton Beach,
94F150 gave you the general idea of the correct method. Be aware though, that if ported improperly, you can end up with LESS power instead of more. Trust me. I thought I knew what I was doing, until I gained access to a flow bench. Some of my early attempts at porting looked great, but flowed like crap. At least they all flowed less evenly. 
Posting Guru
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From: Northern California
That really is a good point Steve. Its really easy to make a port look nice, but hurt the flow. In the shop I worked in, we would just do a small amount in one area if we hadent worked on that particuilar head much before, and then flow test to see where we were at. It really took longer for the first head, but you could see where you were making your gains and then try to get that particular area to flow the best possible before moving on to the next area. Everything was logged in a book then, and we had quite a reference manual of techniques and gains expected for each different head. Even with several years of porting in a racing shop, I have tried to push the envelope too far more than once and hit the water jacket.
There are a couple of previous porting threads on this site that have links to sites that visually illustrate the basic porting techniques that you would use for these truck applications. You'll have to do a search to find them unless JW or someone can post these links. Following these instructions should keep you on the "gain" side of the porting!
There are a couple of previous porting threads on this site that have links to sites that visually illustrate the basic porting techniques that you would use for these truck applications. You'll have to do a search to find them unless JW or someone can post these links. Following these instructions should keep you on the "gain" side of the porting!
