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Porting a Head
- Thread starter Jerry
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Jerry,
I agree with Sky. Nothing is as it seems in the world of ports & gas flow. I could recommend several more books to read before attempting a "porting" job. Even then, you stand about a 90% chance of decreasing performance. Without a flow test bench & velocity measuring probes, & engine dyno to use as a learning tool, it is nearly impossible to get it right. A large part of successful porting has to do with the actual valve seat & head shape. What goes into the port has to get through the valve & into the combustion chamber smoothly.
I have ported about 10 engines ranging from motorcycles to hemi v8s. The only successful ones were under the watchful eye of a proven expert. Often selected portions of a port actually need to be filled in rather than enlarged. Just smoothing ports in the wrong places can cause loss of the turbulance which helps keep the fuel suspended in the air stream & will likely produce no gain or a loss & poor drivability.
For some selected engines there are templates available which give exact dimensions & shape at 3/8 inch intervals throught the port length. Even then, it is a whole lot of difficult work.
A "porting expert" should not be relied upon unless they have a proven record on the specific engine that you are working on.
On my recently acquired Healey engine, the previous owner had done a DIY porting job. The ports were enlarged & smoothed everywhere. The engine was a dog. I replaced the head with a Denis Welch aluminum head with "race" porting. The new head had much smaller ports & of much different shape than the ports in my old "ported" head. The increase in performance with the new head was remarkable. DW knows what they are doing.
D
I agree with Sky. Nothing is as it seems in the world of ports & gas flow. I could recommend several more books to read before attempting a "porting" job. Even then, you stand about a 90% chance of decreasing performance. Without a flow test bench & velocity measuring probes, & engine dyno to use as a learning tool, it is nearly impossible to get it right. A large part of successful porting has to do with the actual valve seat & head shape. What goes into the port has to get through the valve & into the combustion chamber smoothly.
I have ported about 10 engines ranging from motorcycles to hemi v8s. The only successful ones were under the watchful eye of a proven expert. Often selected portions of a port actually need to be filled in rather than enlarged. Just smoothing ports in the wrong places can cause loss of the turbulance which helps keep the fuel suspended in the air stream & will likely produce no gain or a loss & poor drivability.
For some selected engines there are templates available which give exact dimensions & shape at 3/8 inch intervals throught the port length. Even then, it is a whole lot of difficult work.
A "porting expert" should not be relied upon unless they have a proven record on the specific engine that you are working on.
On my recently acquired Healey engine, the previous owner had done a DIY porting job. The ports were enlarged & smoothed everywhere. The engine was a dog. I replaced the head with a Denis Welch aluminum head with "race" porting. The new head had much smaller ports & of much different shape than the ports in my old "ported" head. The increase in performance with the new head was remarkable. DW knows what they are doing.
D
Skip & Lynne
Jedi Warrior
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Jerry Please don`t do it, Larger ports are generally for high rpm big breathing engines you will make a mess. Smaller ports are generally for increasing the velocity of the incoming fuel/air charge thus filling the cylinder more rapidly and producing more botton end torque. The others are correct about smoothing out the ports you need a certain amount of roughness to keep the fuel/air charge turbulent and prevent the fuel from settling out of the mix. Just my 2 cents worth. Skip
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Jerry,
At the risk of sounding like a nut, I think that a reasonable amount of carbon on the combustion chamber & piston top actually helps power & gas mileage, as long as the buildup is not excessive.
The carbon acts as a thermal barrier to prevent combustion heat loss to the cooling system & to the oil system. This increases the engines thermal efficiency & power. Racers pay big bucks to have ceramic thermal barrier coatings applied to piston tops & combustion chambers. Carbon acts much the same as the ceramic coating. Thermal coating of piston tops on Diesel engines is done quite widely for the same reasons. While not as effective as ceramic coating, the carbon helps & costs nothing. We are only talking gains of around three percent, but still a gain.
On a freshly rebuilt & shiny race engine the power usually increases a bit until a carbon layer has developed. The metal does not stay shiny clean. The only time that carbon is a problem is if it builds up very thick. With proper fuel mixture & no oil burning the carbon will only build up to a minimal stable level & any further carbon burns off. I have pulled down high mileage engines which were still in good shape & the carbon build up was minimal.
The concept of polishing combustion chambers to a shiny finish to prevent carbon build up is largely a waste of time, as the carbon will form again in a very short time anyway.
There may be some difference of opinion on this, but it is something to think about.
D
At the risk of sounding like a nut, I think that a reasonable amount of carbon on the combustion chamber & piston top actually helps power & gas mileage, as long as the buildup is not excessive.
The carbon acts as a thermal barrier to prevent combustion heat loss to the cooling system & to the oil system. This increases the engines thermal efficiency & power. Racers pay big bucks to have ceramic thermal barrier coatings applied to piston tops & combustion chambers. Carbon acts much the same as the ceramic coating. Thermal coating of piston tops on Diesel engines is done quite widely for the same reasons. While not as effective as ceramic coating, the carbon helps & costs nothing. We are only talking gains of around three percent, but still a gain.
On a freshly rebuilt & shiny race engine the power usually increases a bit until a carbon layer has developed. The metal does not stay shiny clean. The only time that carbon is a problem is if it builds up very thick. With proper fuel mixture & no oil burning the carbon will only build up to a minimal stable level & any further carbon burns off. I have pulled down high mileage engines which were still in good shape & the carbon build up was minimal.
The concept of polishing combustion chambers to a shiny finish to prevent carbon build up is largely a waste of time, as the carbon will form again in a very short time anyway.
There may be some difference of opinion on this, but it is something to think about.
D