Ported heads or Larger Valves??

[je50769]

My friend and I are in a heated discussion on which is better, ported heads or buying new heads with larger valves. In truth they are about even but which would grant a larger power increase??

[bjdm151]

Porting the heads and increasing the valve size can have nominal effects on power production, however, these mods are not really necesarry unless you have done some other serious mods first. If you have a newer car (especially a naturally aspirated) the port design and valve sizing are probably perfectly matched and more will be lost than gained concerning power. But if you are increasing or adding boost or moving the rpm range higher, some gains can be made.
Overall though I would have to say that buying new heads with larger valves would be better. If your buying them from somebody like edlebrock or world, they will probably have larger port volume (ported) and have the larger valves. If you talk to the manufacturer they can probably tell you what product would serve your needs best.

[383PhoenixAm]

Actually, it depends more on the type of engine. If it is an import car then no, neither will do you much good without modifications. As for larger items like V heads, both are great mods but the outcome can't be decided since there are too many factors. For instance, some stock heads have poor attributes and combustion chambers to begin with, and there is not much room for improvement. If you have good casting heads, though, porting them will give great potential, and bigger valves don't make much of a difference unless you're upping the displacement. As for buying new heads, it would depend on budget. For example, 081 castings on chevrolet engines can be ported to have attributes similar or better than an aftermarket Vortec head in an untouched form, but a more expensive head like AFRs will blow all else out of the water, even if other heads are ported. It all depends on budget, but if it wasn't a factor, I'd say go aftermarket with the larger valves.

[civickiller]

imo, i think porting is better because more people port there head then getting larger valves. if larger valves was more valuable in gettign hp i think it would be said that it does creat more hp and people would get larger valves

[sierrap615]

i don't think larger valves would do as much without enlarging the restrictive stock port sizes.

[MagicRat]

I would agree with all the above posts except for civickiller.
To answer your question, aftermarket performance heads are ALREADY ported, that is the ports are usually shaped to be better than stock right at the point of manufacturing, and are much better than porting your own.
The companies that make them have sustantial R&D budgets and usually can get better results than what you can get done on the stock heads.
However, as the other replies say, the aftermarket heads will get the best results if combined with other mods, such as a better exhaust, camshaft, intake etc.

[civickiller]

why dont you agree with what i said ?

[SaabJohan]

In many cases the ports are large enough from standard, the problem is their shape. Valves are usually large enough get a quite large increase in power.

Note that "the larger the better" isn't the case with ports, flow velocity can be too low, decreasing the ram-effect.

So typically the shape of the port must be modified, and then the valve must be lifted higher, typically a valve must be lifted .4 times the inner seat diameter until it's the inner seat diameter which limits the flow.

In some cases one port can be better than the other, so for example an exhaust port might need more job done on it than the intake port (or the other way around).

There was a guy that had a small firm that ported heads, he succeeded to get more power out of an engine (Yamaha I believe it was) than the factory itself did. But on the other hand he also did some work for some manufacturers.

In extreme cases the ports are completely redesigned, valve position and angles may be altered as well as combustion chamber design. There is also a difference between valves and valves.

[sracing]

In most all cases larger valves will provide more HP. They typically do this by moving the peak torque up in RPM range. Porting can do the same, but without a $10,000+ flowbench, you will simply be guessing at any improvements. Porting can just as often hurt flow as to improve it. And in many cases, the manufactures porting is fine for the application.
Simple flange matching can improve flow as much as 5 - 10 % over the manufacture's stuff, and there is little risk of hurting the flow.

Jim
SR Racing

[quaddriver]

who is doing the work? you or a shop? and are the heads iron or AL?

A shop might have the equipment to grade the effort, you likely wont. If you insist on doing the work yourself, it limit it to a gasket match port. If you are decent and have a dremel, try cleaning the bowls. if you are really good, polish the combustion chamber.

the other caveat is with AL it is too easy to go too far. with iron, its often just best to clean off the sand occlusions.

what motor? that also changes the answer. if you said 'chevy small block gen 1' Id say 'go buy a set of L31s and be done with it'...