Big valve head

[Diesel]

Wondering if there are any write-up's out there showing bigger valves ground into a stock 12v head? Looking at pictures it seems like our valves are tiny compared to the space in the combustion chamber.

[skilletky]

have not seen any write ups, but my old boss said that he had a valve job done on his and had bigger valves put in. dont know if he really did or not. he liked to stretch the truth on alot of things.

[Tacoclaw]

I can't imagine the valves being worth much until you're in the upper echelon of performance. Depending in how much they cost, I would think a decent twin set to bump pressures up some would be a better choice.

[PToombs]

Some flow porting would go way farther than bigger valves. Numbers 1 and 6 are very restricted and bigger valves would be a waste without opening them up.

[Diesel]

I will look into some porting on the head then.

[PToombs]

A decent cam like a Hamilton is good too. Several guys on here have them and the difference is noticeable making no other changes. You might want to try that 1st, the $700 for the cam is probably the same or less than a porting job.

[m880cummins]

I can't remember off the top of my head why in most cases better to keep a smaller exhaust valve (look it up online) but I think you would get way more results from some basic porting. I did 2 heads at home and really just cleaned up the bowls and exhaust ports of roughness and I noticed a difference.

My next cylinder head venture will be milling the plenum off, major port work and decking the head 0.040-0.080 or whatever it takes until the valves are unshrouded. Running this with some heavily fly cut marine pistons and lots of timing would be a helluva setup.

Charlie

[Tacoclaw]

You enlarge the inlet because it's always easier to push pressure than to draw a vacuum. Not horribly applicable in our cases when there's 40psi blasting through the intake valve, but getting clean air in is priority over getting exhaust out. With boost, the piston recompressing it, and all the extra combustion heat, that exhaust will get out one way or another.

I've read a few places over on CompD that completely unshrouding the valves isn't the best thing. Can't remember why, but they seemed to lean towards matching the valve pockets to the valve angle somewhat. Maybe opening it up to a complete new angle, but getting rid of it seemed to not be the best way.

[PToombs]

I read that someplace too. It causes turbulence and you get less air in because of it.