RE: Three Angle Valve Jobs

[Anonymous]

I'm glad someone adressed this. You are right...for the most part. The seat is cut with either a 3 angle cutter if it is done on a guide and seat machine, or with stones if ground (both are only as good as the machinist). The reason though for this is not performance, but for proper seat width! A stock(original) head is usually machined with only two angle: Seat angle (most are 45 some are 30 degrees), and the top angle (15 degrees less than seat angle to 0 degrees ).
If any machine shop charges exra for this, I would turn around and walk out! And don't fall for that Car Craft, Hot Rod b.s. about 5 angle, 7 angle, 9 angle, 9851 angle hi-po valve jobs.Find a reputable machine shop in your area, NOT nessesarily the guy who builds the $50,000 blown big blocks, and Definately not the guy who sells $895.99 350 chevy's. IF ANYONE HAS A LEGIT MACHINING QUESTION, i WILL TRY TO ANSWER BEST I CAN.

 

[goinbroke2]

Are you saying any more than 3 angles does nothing for flow?
How about seat angle and it's effect on flow?

 

[Twinscrew]

More than 3 angles does in fact increase flow. 5 angles flow more than 3 and 7 angles flow more than 5. The more angles, the smoother the radius becomes, increasing laminar flow at the boundary layer. However, a 3 angle valve job is completely adequate for all but the hottest street applications, in fact, some condsider it overkill. I believe that if you've invested in porting( blending the bowls and improving the short side radius) that the 3 angle job completes the job. If the ports have not been improved, no performance will be gained from just a 3 angle valve job.

 

[LaGrasta]

This is what I've gathered as of late… a three angle is really not going to make a difference in most of our engines. I'm never going to "drag" my bird so I guess paying for the three angle is just wasted money.

 

[addo]

I would disagree with that. Anything that is simple and adds a little efficiency is worth doing; it's also environmentally responsible.

 

[Stubby]

What he said is a three angle is a must.
Think about it, your seat is ground at a 45 degree angle. After several years of running the seat becomes wider because of the pounding it has taken. When you grind the seat it becomes even wider. To establish the proper width seat you must grind the top with another angle (most use 30 degrees for a 45 degree seat) then grind the bottom of the seat with a another angle (most use a 60 degree bottom angle for a 45 degree seat)

By grinding the top and bottom you narrow up the seat and place it where you want it on the valve.

The shop should do this on every head it works on or they are a second rate shop. I have seen shops who would just grind a 45 and maybe knock the top down a little just to keep the seat on the valve. It will make the engine run but thats about all I can say for this type of valve job. You wind up with a real wide seat that collects carbon, affects heat transfer from the valves and usualy will not last as long.

What we used to do was tell the customer all of our valve jobs are three angles. We also had a high performance valve job that included a little extra charge for setting all of the valves the same depth,back cutting the valves, and setting up the springs for the cam. The customer was also informed that there could be extra charges for these proceedures if we ran into something off the wall. (Mismatched springs, retainers, valves, ect)

 

[LaGrasta]

In theory, I totally agree. I'm not even sure how much more money we're talking. In the total job of a rebuild, it's minor I'm sure.

 

[jamyers]

I think it's worth it, even if you don't do any bowl porting. And it's actually very easy to do your own basic porting, time is the main ingredient.

Two relatively cheap and easy things you can do that will really wake up an engine. Even if it's only a small percentage on a street engine (which is where I live and drive), all those small percentages can really start adding up in terms of not only power, but economy and engine life.

 

[Lazy JW]

...The shop should do this on every head it works on or they are a second rate shop...

Yup. Just ask the machine shop how much extra they charge for a three-angle valve job, and if they reply that it is standard to do three angles, go for for it. Otherwise, take your business elsewhere. If you want a five-angle, nine-angle, or sixty-eleven angle valve job be prepared to pay more. If you just want to make the engine run and don't care about performance or longevity then do the old farmer trick of lapping them in by hand and forget about the angles.
Joe