Captain Z

Do "valve jobs" result in more power to the motor? Can someone explain what occurs here and whether or not it's a good idea for the beloved Z. Thanks.

teking

i've been told it's similar to a "rim job" .. which I assume deals with the wheels??? ....

Larry T

...now that's funny...

mercruiser

A three angle valve job is a process where the valve seat is ground at 3 different angles with 3 different stones. This improves air flow in and out of the combustion chamber. I'm sure it would help any high revving engine that does not have this process completed for the valve seats.

Fast06Z06

They have gone to all new extremes such as 5 angle jobs and using different seating angles like 12 degrees versus 15 which supposedly seals better. Any good machine shop give you exact specs on what you can do. Most important is to the change the valves all together to stainless for strength.

Red C6 Z06

I always thought it was mostly for sealing: sealing the valves against their seats (all those angles you guys were talking aobut), and sealing the stems in the guides. There must be lots of side benefits though like replacing valves, cleaning up the heads/combustion chambers, opportunity to change springs and/or rockers. If you are going to all the trouble to do the valve work you might as well get all these other goodies.

Captain Z

Would this result in any quantifiable extra power to the rear wheels?

Red C6 Z06

If you have leaky chambers (gas flowing past either the exhaust or intake), it would help a bit. Of course if it was leaking past the intake valve you would be igniting the intake gas in the manifold!!! but honestly I can't imagine a major power increase on a C6 Z06 unless it's been beaten to death.

Fast06Z06

Basically the more angles you have the rounder the valve seat will be, forcing a smoother, and quicker flow of air:fuel into or out of the combustion chamber. Moves air faster and more efficiently.

It also creates a tighter seal and allows other improvements that require high cylinder pressures which produce more power. The valve seat job itself will help some in scavenging gases and creating a better flow but a really measurable horsepower gain. It is more like part of the big picture and package when getting your heads done

0Randy@DRM

Well, most of the gains in working with seats come in the lower lift numbers up to about .400 or so. After that the valve is "wide" open and that is where the port work comes more into play. Remember the valve goes like this.
Closed
.100 lift
.200
.300
.400
.500
.600
.650
.600
.500
.400
.300
.200
.100
Closed

The seating angle normally stays the same. The throat cut shows the most gain on the flow bench from my experience. Most modern valve seat cutting is done on a "big mill", stones are kinda a thing of the past, but they do work well if the right guy is running them. The stones make it pretty hard to get the install height the same across the whole head. I ended up making my own tool for cutting 2.055 valves in the older heads. It has two angles with some curved parts of it. She looks good, and very little hand blending needed after.
Like said before it's part of the package. The stock LS7's are pretty damn good right out of the box. Doing this alone just for performance would be kinda a waste of time and money. Now on a engine with some miles, getting the seating part of the seat "freshen" is always a good thing.

Randy

tjwong

Randy one other issue which I am sure you are aware of is the issue with refacing the Ti intake valves. From what I have heard once someone grinds or refaces a Ti valve, it removes the nitride coating which gives the valve a very hard wear area. If that coating is removed from either lapping or grinding then the valve will wear prematurely. Have you heard of this or is someone blowing smoke up my back side?

IQ AUTO VETTE

Fast06Z06

I've heard the exact same thing, hence why I recommended changing to stainless valves at the same time.

0Randy@DRM

Some valves don't like to be worked on. LS7 intake and LT5 exhaust are two that I wouldn't go grinding on.

Randy

tjwong

That is what I figured as well. How are things going down your way? I have been swamped up here, we finally got some nice weather and now I am bitchin about the heat

But then you got a HUGE valve that is pretty heavy.

wstaab

Ti engine valves are hard coated to prevent wear of the valve seat face and stem. If you remove the coating by lapping it will wear out the seat face of a Ti valve during normal operation. Titanium is very light and reasonably hard but does not wear well in applications that have metal to metal contact. I use one new Ti valve as the sacrificial valve to hand lap all the seats in both heads after a five angle valve job. Then install your new Ti valves and all is like new again.

OnPoint

If done well can improve flow and improve sealing.

If done poorly can result in no improvement of either, decrease in valve life, and be a cashectomy.

tjwong

That is exactly what my machine shop has been doing. We found a set of Ti valves that were in a set of LS7 heads. These were aftermarket Manley valves that were spec'd out without the coating, we found excessive valve face wear after <1800 miles. The seats were hand lapped in and the valves were replaced with a set of GM Ti valves and the owner has been happy ever since.

glass slipper

Just curious, what is it about the LT5 exhaust valve that makes you say that?