Valve Seat Angle

[ratmaster]

Anyone ever tryed 30 degree valve seats in a SBC? My project has a 350 CFM 2 BBL with a marine intake. I am very limited in flow including the heads (200 CC). Any power gains at or near 6500 RPM? Or would there be more at a lower RPM? My project is a NASCAR dirt hobby car.

 

[MaxRaceSoftware]

What's the cam's Int/Exh max theoretical valve lift ???

and the 2-barrell will act like a resrictor-plate
...maybe not so good with 30 deg seats ...depends
on how much you into throttle and cam lift/duration/centers
specs Larry Meaux (meauxracing@mindspring.com)
Meaux Racing Heads
MaxRace Software
ET_Analyst for DragRacers

http://www.mindspring.com/~meauxracing/

 

[ratmaster]

The cam specs are as follows (.050 lifter rise):
INTAKE TIMING EXHAUST TIMING
Duration 250 Deg 250 Deg
Open 17 BTDC 53 BBDC
Close 53 ABDC 17 ATDC
Cam Lift .363 .363
Valve Lift .545 (1.5 Ratio) .545
Lobe Center 108 Deg
Overlap 62 Deg

However, I will be using 1.65 ratio on the Intake and
1.6 ratio on the Exhaust

Thanks for the response! Judging by the posts in this forum, your knowledge and expertise is valued. Your opinion will not fall on deaf ears here!

 

[MaxRaceSoftware]

with .545/.545 lift i wouldn't use 30 deg seat/valve angles
the 45 deg seat angles will make more hp/torque
with .545/.545


i probably only recommend 30 deg with .400 to .450 lift or less and along with carb not a restriction (high manifold vac)

at 6500 rpm you will almost need a 750 cfm carb to keep up
Larry Meaux (meauxracing@mindspring.com)
Meaux Racing Heads
MaxRace Software
ET_Analyst for DragRacers

http://www.mindspring.com/~meauxracing/

 

[ratmaster]

Thanks again for the response, Larry. I appreciate the help!

 

[carnage]

I hate to expose my ignorance but I really would loke to know the benefits of the various valve angles. I have heard of 45 30 and a three angle valve job. I have two motors in the works soon and while I am not looking for 4 digit horsepower (out of these anyway) I would like to know more about the advantages and disadvantages of the various valve angles for when I have the heads redone

 

[MaxRaceSoftware]

Carnage the answers to your question depends upon many factors like

1-max theoretical valve lift
2-duration @ .050"
3-centers cam ground on
4-intake centerline
5-int and exh valve diameters
6-tulip or nailhead valve head shape for int/exh valve
7-compression ratio
8-wedge,canted-valve,hemi,pentroof, 2 valve or 4 valve
9-head flow on int and exh sides
10-headers ? OEM-manifolds, OEM-mufflers or race

one of the most important factors to which seat angle will work is the max. theoretical valve lift of cam you will be using

for street engine with low-lift cams like .400" lift or less ..the 30 deg seat angles are not bad

as you go .450 and higher ..use 45 seat angles

as you go very large diameter intake and exhaust valve sizes
and large overlap period cams ..you can move towards
55 deg seat angles

------------------------------------------------------
basically a good 30 top, 45 seat , 60 bottom on intake is not too bad at all lifts

30 top, 45 seat , 53 to 55 deg bottom , 60 bottom on exhaust
---------------------------------------------------------

with a cam Lift/Diameter ratios above .25
a really good race valve job might be something like
38 top , 45 seat .040-.060 wide, 60 bottom ,70-75 bottom on intake..blend into bowl...with 30 deg backcut on valve
.050" margins to .080" margins

38 top , 45 seat .050 to .060 wide, radius bottom ..blend in to bowl area with no backcut on exhaust
could use a 30 2nd top cut on heads above the 38 top cut
.080" margins to .120" margins





Larry Meaux (meauxracing@mindspring.com)
Meaux Racing Heads
MaxRace Software
ET_Analyst for DragRacers

http://www.mindspring.com/~meauxracing/