Power gained from valves with slimmed stems??
Power gained from valves with slimmed stems??
(OP)
Hey guys..
I am having valves made for my engine with stems slimmed from 7mm to 6mm, and the heads .5mm oversized.
Is there much power to be gained from this? Any charts or articles about it?
Here is the thread with the info on the valves I am having made. They are for a VW 2.0 16v.
Thanks- Josh
http://forums.vwvortex.com/zerothread?id=998263
I am having valves made for my engine with stems slimmed from 7mm to 6mm, and the heads .5mm oversized.
Is there much power to be gained from this? Any charts or articles about it?
Here is the thread with the info on the valves I am having made. They are for a VW 2.0 16v.
Thanks- Josh
http://forums.vwvortex.com/zerothread?id=998263





RE: Power gained from valves with slimmed stems??
In my limited experience, there appears to be no power gain that is directly associated with slimming of the valve stem. The main benefit comes from weight reduction which can allow for higher RPMs. This comes at the price of valve durability and a reduction in the valve's ability to conduct heat.
Regards,
Bryan Carter
RE: Power gained from valves with slimmed stems??
The valve stem will in fact be strengthened re breaking strength if the stem dia is turned down to match the root dia of the retainer groves, however the valve will bend easier, and stretch easier. It will also as Bryan indicates, loose some of it's ability to conduct heat from the head, down the stem to the guides.
Some engines give more power with slim valve stems, it all depends on where the restrictions are in the port and streamlineing of the guides etc. All in all, it is easier to get air to flow around a thin stem than a thick stem.
Increasing valve head size is also maybee, maybee not, depending on the original size and bore size and chamber shape. Generally bigger is better, but the bigger the valve, the more critical it becomes to have a chamber design that does not shroud the opened valve. eg if a valve almost touches the cylinder bore, not much gas can flow around that side of the valve.
Regards
pat
RE: Power gained from valves with slimmed stems??
Seriously, let me make myself a little clearer. The theory behind turning valve stems down is that it will help with airflow around the stem. Obviously a thinner stem will present less of an obstruction to airflow than a thick one.
Different engines with varying valve include angles and port configurations will see varying degrees of improvement after performing this modification. I know many people speak highly of this trick, but I have only experienced with it briefly. On the particular applications that I tried it with (little motors, bug turbos, high boost) I saw little return (in terms of HP) on my investment, and picked up a severe exhaust valve cooling problem for my trouble.
So, for me, it's one of those mods I can take or leave. By the way, the sodium that's inside of sodium-filled exhaust valves... burns like the devil if you get it on your hands. Don't even ask me how I know this.
Good Luck,
Bryan Carter
RE: Power gained from valves with slimmed stems??
I guess it's not a good idea to cut opened a sodium filled valve, as sodium plus water equals caustic soda plus heat.
Skin contains water
Ouch s**t d*m f**k, how do I wash this off, ouch.
Regards
pat
RE: Power gained from valves with slimmed stems??
Of course V8 race engines are using smaller diameter valves for weight reduction. I believe they are around 7mm (Ø.276)
RE: Power gained from valves with slimmed stems??
RE: Power gained from valves with slimmed stems??
My supplier/manufacturer said there will be no problems whatsoever with this. They have applications for Honda engines with smaller 5mm stems and much higher RPMS with no problems.
RE: Power gained from valves with slimmed stems??
Happy flowing.
Shaun TiedeULTRADYNE Arl,TX(stiede@ev1.net)
RE: Power gained from valves with slimmed stems??