Valve seat angles. - what are people using?

[Shawn]

Max,
thanks for the tip on the speed controllers. I decided to try my hand at building one,and it seems to work pretty well. I posted some pics of it in the DIY stuff along with some headstands that I had built.
thanks,
Shawn

[Kyrasis6]

Max,

I'm somewhat new here to the forum. The information you post is great. I'm currently about to graduate from NASCAR Technical Institute and a lot of the info you post they covered in class, of course we could only touch on everything because both engine classes are only 3 weeks long each and are geared to bring people with little knowledge up to a decent "advanced" understanding which sucks for someone who is already more advanced.

Anyways, I was curious to know since a turbo relies on exhaust gas volume and speed to spin up is it more critical to be more conservative on the exhaust ports to keep velocity up or does the ratio between in/ex ports stay about the same with the amount of work you do to the intake?

P.S. Just think guys I basically payed about $1200 to learn what Max has mentioned in this post.

[maxracesoftware]

[SWB]

Larry,

When you examine exhaust to inlet ratio, where in the lift curve do you look? Do you choose the average of all lift points?

Sean

[maxracesoftware]

i use PipeMax to determine Piston CFM demand
at various Crank degrees...the following
is an example of 1 column of Data :

A ProStock 500 cid at 9000 RPM will require
a minimum of 548.3 CFM @ 28" test pressure

Crank Head
Angle CFM @
Degree 28 in.
0.0 0.0
0.5 6.0
1.0 11.9
1.5 17.9
2.0 23.8
2.5 29.8
3.0 35.7
3.5 41.7
4.0 47.6
4.5 53.6


30.0 331.1
30.5 335.8
31.0 340.4
31.5 344.9
32.0 349.5
32.5 353.9
33.0 358.4
33.5 362.8
34.0 367.1
34.5 371.4
35.0 375.7
35.5 379.9
36.0 384.1


Crank Head
Angle CFM @
Degree 28 in.
72.6 547.9
72.7 548.0
72.8 548.0
72.9 548.1
73.0 548.1
73.1 548.2
73.2 548.2
73.3 548.2
73.4 548.3
73.5 548.3

Crank Head
Angle CFM @
Degree 28 in.
80.5 545.8
81.0 545.2
81.5 544.7
82.0 544.0
82.5 543.3
83.0 542.6
83.5 541.8
84.0 541.0
84.5 540.1
85.0 539.2

130.0 327.8
130.5 324.6
131.0 321.4
131.5 318.2
132.0 315.0
132.5 311.7
133.0 308.5
133.5 305.3
134.0 302.0
134.5 298.8
135.0 295.5
135.5 292.3
136.0 289.0

if you could see the entire calculations, you would
see the Piston's wanting 548 CFM for a good many degrees,
if the Engine doesn't get 548 CFM , pumping losses
increase and Torque/HP suffer, and intake ram effect
occurs too late after Int Valve closing point.
if you try to close the Intake valve later to take
advantage, you loose Power Curve width and the engine
won't accelerate down the DragStrip or recover sharply
on gear changes.

>>Larry,
When you examine exhaust to inlet ratio,
where in the lift curve do you look?
Do you choose the average of all lift points?
--Sean <<

i look at all the Lift points and Flow numbers at each point
and the Total Average. Also look at low-lift CFM numbers
and valve layout in the Chamber as indication of possible
overscavenging during OverLap period. sometimes you don't
want a lot of low-lift flow on the exhaust.

if an application i'm working on has .800" Lift Cam,
i usually just multiply .87 % PerCent times .800 = .696,
and just round-off to .700" Lift, this accounts for
Lash and Valvetrain deflection losses, and accounts some for
the fact the Intake Valve doesn't stay at max Lift more than
a few degrees. also i make sure whatever Porting mods i do,
that Flow is not hurt in a .300 " Lift band, for example,
.800" Lift Cam =.700 Lift(.87), then you want great flow
at .700, .600, .500 ...this will correlate to Piston velocity.
You still need the Head to flow great at all the other Lifts,
but you must make sure the Cyl Head Flow can keep up with
Piston CFM demand adequately.

if the Cyl Head has a CSA Choke problem, it will respond to
low to mid-lift flow numbers more, and if you try to
use more Cam lift or higher rocker arm ratio, you usually
will see HP/TQ Loss as all you are doing is making the
Choke worse around max lift.

Low Lift Flow =>
i can make a 23 deg Head flow as much or more than
a 15 or 18 deg Comp Elim Head, but that 23 deg Head
might make 600+ HP, while that 15/18 deg Head will
make 700-800+ HP...so Low-Lift Flow is not the final word !

likewise, i can make an Edelbrock Victor Race Head out Flow
a ProStock Head at low lift Flow, but that Edelbrock head
might make 900+ HP, and the ProStock head will make
1350+ HP..so again Low-lift Flow is not the final word !

if you look at Piston CFM demand, you better make the
Cylinder Head keep up as close as possible with great
mid to high lift Flow CFM numbers !!
Mid-Lift to High-Lift Flow Numbers are needed at around the
time of greatest Piston velocity and at greatest "leverage",
to reduce pumping losses. increasing leverage works both ways,
either to help you or hurt you if Flow doesn't keep up
at the desired RPM range. if Flow doesn't keep up, the
pumping losses are amplified thru leverage .
(same principle on Exhaust side)

at Low-Lift, there is reduced leverage effects that pumping
losses can work thru.
Low-Lift flow is needed to take max adavantage of Wave/Inertia/Ram
effect at Intake Closing Point, and also Low-Lift Flow is needed
at Int open point to take advantage of Wave-tuning, but the
real HP/TQ numbers are in Mid -to- High Lift Flow

you could also look at current Trends in Comp and ProStock,
spreading Centers, and using 55/58/60 degree seat angles,
both which will reduce/hurt Low-Lift Flow, so again,
Low-lift flow is not where the real large HP/TQ gains are at.

[SWB]

Larry,

That makes a lot of sense!

One of these days I'm going to get with you about obtaining your software, that's a really cool bit of info it calculates for you. I'm not sure how you figure the numbers to 28" of depression, but more power to you.

Sean