Valve's --(Woz)

old forum · hod rodder Joined: 04 Oct 2001 Posts: 15499

I was chattin to this dude about the early model large-valve heads and he said that the porting was also larger too. So, does that mean i could go and grab a late-model head, put bigger valves in it, port the fuck out of it and end up with a head thats as good or even better than an early model one? What are good replacements for the 40/42mm inlet vales? [and what size are they?] When you put in bigger valves it obviously means that you can make the opening behind the valve bigger too, yes? What is the physical limits of the valve size? Is it due to how close the piston gets, how close the exhaust valve gets, or how close it gets to the cylender edge?
And also - while im still thinkin'... would there be a point in enlarging the exhaust one as well? which is more important?

Finished now!

Woz

old forum · hod rodder Joined: 04 Oct 2001 Posts: 15499

Port size is more limited by valve size than available metal because with decent lift the valves hit each other and the pistons before the reach the optimum level of flow for a head ported to within a poofteenth of a millifart of the water galleries.

A ported late model head with larger valves will definitely be better than a stock early model head...

old forum · hod rodder Joined: 04 Oct 2001 Posts: 15499

Early model heads have better ports and smaller combustion chambers, as well as the bigger valves.

If you improve the ports of a late model head, and install the inlet valves from an early model head, then you still have a bigger combustion chamber which means a lower comp ratio. This will have to be over come in the pistons, or shaving the head.

With any head, you can get the seats ground to suit the early big valves, I did this a couple of years ago, I think machine work was $60. The exhaust valves are where I believe an improvement should be made, as they are realtively small.

As far as I can remeber, valve size is limited to the proximity of each valve to the other, and the diameter of the piston.

old forum · hod rodder Joined: 04 Oct 2001 Posts: 15499

I have to disagree with AG on this one. I have a late model head ported as far as it can go (safely) to the water galleries. And it is still only as large as a standard early model heads. They are surprisingly different in design, the earlier heads having straighter inlet ports and provision to widen enormously. Also the combustion chamber is more rounded with no little lump around the spark plugs. For whatever reason they changed the chamber design, Im sure it has something to do with fuel economy, but as for flow and portability, the TX heads are the best. As for finding one in good nick.....

old forum · hod rodder Joined: 04 Oct 2001 Posts: 15499

Sorry, I didn't mean to say that a ported late model head was as good as a ported early model head... just saying not to spend the $130 I was asked to pay (I laughed and walked off) for a ok condition TX head... when I can get late model heads for as little as $20 each.

As for the lump (behind the plug) in the combustion chamber... that is the first thing I hit with the die grinder...