I just purchased some REV 0.5MM oversized H22 valves. I am going to place them into a head to replace the bent valves but I want know what's makes them good, compared to stock valves!

 

yeah iv wondered this question my self. dosent the vavle still open "X" high and air come threw?

im sure some one knows?

 

Well, your intake valves let air and fuel into the combustion chamber, and exhaust valves let the burned fuel and air out of the combustion chamber. Some air/fuel always stays in the chamber. You just can't get all of it out in one cycle. Bigger valves means that you can get more air/fuel into the chamber and more of the burned air/fuel out of the chamber. Bigger opening for the air to flow through means more air flows through.

 

That's a lot. Very specific!

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by slamdlude &raquo;</TD></TR><TR><TD CLASS="quote">Well, your intake valves let air and fuel into the combustion chamber, and exhaust valves let the burned fuel and air out of the combustion chamber. Some air/fuel always stays in the chamber. You just can't get all of it out in one cycle. Bigger valves means that you can get more air/fuel into the chamber and more of the burned air/fuel out of the chamber. Bigger opening for the air to flow through means more air flows through.</TD></TR></TABLE>

Not always true. I've read multiple times now that OEM size valves are the way to go, on an N/A motor(for the H22). Bigger isn't always better; volume vs velocity.

 

it has no sense to install bigger valves on stock unmodified head. All you get is bigger restriction to air flow.
Bigger valves has to play with bigger valve seats and ports -&gt; modified cylinder head

 

The only time OS (oversized) pistons, valves, and US (undersized) rod bearings, main bearings, etc. are used IS WHEN YOU ARE DOING A REBUILD AND THE HEADS, BLOCK AND CRANK HAVE BEEN re-MACHINED, which will require you to use the OS and US parts. There is no reason to use these parts otherwise - in fact they won't fit!

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by TheJGB3 &raquo;</TD></TR><TR><TD CLASS="quote">The only time OS (oversized) pistons, valves, and US (undersized) rod bearings, main bearings, etc. are used IS WHEN YOU ARE DOING A REBUILD AND THE HEADS, BLOCK AND CRANK HAVE BEEN re-MACHINED, which will require you to use the OS and US parts. There is no reason to use these parts otherwise - in fact they won't fit!</TD></TR></TABLE>

That's what I wanted to here!

 

OS valves will impede flow in stock size bores as the valves will be more shrouded.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by vinuneuro &raquo;</TD></TR><TR><TD CLASS="quote">OS valves will impede flow in stock size bores as the valves will be more shrouded.</TD></TR></TABLE>

So what should I do to the head that I plan on installing them in?

 

Ask your head porter, he'll know. If you're not going to a larger cyl bore, working the head to accommodate the larger valves might hurt you. Once again, you head porter should know.

It's a good idea to questions <U>before</U> buying parts.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by vinuneuro &raquo;</TD></TR><TR><TD CLASS="quote"> It's a good idea to questions <U>before</U> buying parts.</TD></TR></TABLE>

They were pretty cheap! $50.00

 

What good is cheap if they are the WRONG PARTS?

 

someone told me oversized valves, being bigger?, change the compression ratio. is there any truth to this or should i not listen when he jabbers anymore?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Storm_Rider &raquo;</TD></TR><TR><TD CLASS="quote">someone told me oversized valves, being bigger?, change the compression ratio. is there any truth to this or should i not listen when he jabbers anymore?</TD></TR></TABLE>

He might be referring to flat faced valves.