Just wondering if you should expect any HP gains from a 3 angle valve job on stock heads. What exactyl is a 3 angle valve job..one of my friends keeps on telling me its how they clean the head Lets hear it

Marcin

 

Look at it this way: imagine looking at your head where you're looking at the ports from the side. Draw a line across the middle of the port opening (from the parts of the seat closest to the chamber) and then intersect it with another line that runs down the center of the valve. You should now see an inverted "T" that resembles something like the axis on graphing paper. When a valve angle job is done (i.e. a 3- or 5- angle), your intention is to have certain parts of the seat at different angles in relation to these axis. Like a 30* angle on the outer part, a 45* on the middle part, and a 90* angle (perpendicular to the seat face, parallel to the valve centerline) on the inner part, or mouth, to blend it in with the bowl area. You need special dies that are designed to keep you parallel to the valve centerline in order to cut it straight, or else you may skew the plane and your valve will not sit flat on the seat. I doubt you'll see much of a gain with near-stock ports and stock valves though.

Lloyd or Phil will be able to better explain it as to how it increases flow (cross-sectional area, turbulance, discharge coefficients, etc). If we're lucky, Chuck will stop by too (but he hasn't been on in a while).

 

If I'm not mistaken, a 3-5 angle valve job will help with low lift flow characteristics.

 

I am not sure how much HP there is but there is definitly some CFM there. Not sure how much difference there would be with a valve job only and no porting when dynoing but on the flow bench, you would see a cfm gain.

The valve jobs "job" is to seal the valve, help cool the valve and to allow the A/F to enter/exit the cylinder. The flow has to go AROUND the valve and by changing the angles and widths (and # of angle) you can make the flow go around the valve better. Depending on the width and angles of the seats and backcut angle on back of valve, you can gain CFM at various lift points and lose cfm at other lift points. You just have to find a compromise with what lift you want flow and how much you can increase flow there. All in all a good valve job will pick up flow at all valve lift points but if you get picky and want more flow in a certain area, you are usually able to get it (at the expense of a few CFM at other lift points) with minor changes in backcut angles.

Here are some flow #'s from an LS1 head and the ONLY change was the back cut angles. . . .

lift...back cut angle
..........30....33....36
.200...131/139/138
.300...199/205/203
.400...249/254/248
.500...286/287/283
.550...295/296/290
.600...299/292/296

This is the same port, portwork, valve job and the ONLY change was the back cut.

NightTrain66

 

Well said Lloyd. I would guess that a swirl polish on the back side of the valve would also affect the CFM. I don't have access to a flow bench so I can't verify the guess - Disclaimer...

 

Another question related to this:
I just pulled the heads off my car while I'm doing a cam and headers and a bunch of other stuff and decided that I would send my heads to a shop for a valve job and have them replace the seals and springs. I'm debating weather I should have them port and polish them too. How much could I see in horsepower gains from this? Should I also have the intake done? What about a bigger throttlebody? It's natuarally aspirated with a 224/236 cam kit from Combination Motorsports, headers, and cat-back.

Thanks,

Andy

 

Andy,

It's near impossible to make a guess as to how much power you'll gain from a port job. It depends on how optimal the port is for the combination.
AND, it's not all about flow numbers. I've seen plenty of lesser flowing heads make more average hp and torque compared to higher flowing heads. The size of the port in relation to how well it flows is important too.
Just to throw numbers out there..... I'd say you could see gains of anywhere from 15-40 hp with no other changes but the heads. And yes, I would have the intake ported also. It's an extension of the cylinder head as is the rest of the induction system.

-Mindgame