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Valve Stem Angles, Do they Matter? Truth or Fiction?

24K views 35 replies 13 participants last post by  barnym17 
#1 · (Edited)
A while back a person made this comment:

"We have built Pontiacs, Fords, Chevies, Olds, Buicks, Hondas, Mopars and others over the years. Most all have been on the dyno and the heads always on the flow bench. 14 degree valve angles have no bearing in this conversation and are meaningless. In fact, stock 14 degree Pontiac big block heads are TERRIBLE flowing heads and to claim that's something special makes their actual flow even more laughable. Even Stock Edelbrock heads are NOTHING to right home about. Almost any decent aftermarket 23 degree Chevy head is either going to equal a stock Pontiac head with the better CNC variations blowing away even the Edelbrock head, all 14 degrees of them. NOW, step up to a RR 23 or 21 degree or 13-18 degree Chevy small block head and your in a different ballpark compared to the typical Pontiac aftermarket head. Only the very best Pontiac big block aftermarket heads are going to be in the same range as what these upper level types of heads offer."

Now my question is which is it? In one sentence this person says 14 degree valve angles are meaningless and in another sentence s/he says step up to a 21 degree or 13-18 degree chevy small block head and you’re in a different ball park. Now I take different ball park to mean superior, untouchable, to create a gainful advantage.

Now we all know that the stock gen 1 sbchevy has a stock 23 degree valve stem angle but nearly all top dog aftermarket heads tilt the valve stems closer 10 and 4 degrees. For example Dart race series heads claim “Dart 15’, 16’ and 18’ aluminum small-block cylinder heads offer a dramatic performance improvement over conventional 23’ designs.” When moving up the ladder to a pro stock style Little Chief head (notice the Indian’ish name given to this head, kind of remind you of a brand P engine) the valve stems are further pushed to 11 degrees where they claim “The huge flow resulting from the 11 degree angle”. They say that if you want to build the “ultimate bad-nasty small block race motor, you want the Little Chief.” Does valve stem tip angles matter?

A flow test @28 of water showed that a sbchevy head casting # 462, 156cc, peaked at 218/142 cfm @ .600 lift, a 23 degree head. Going to a 13 degree valve stem angle TFS 200cc was able to squeeze out 265/211 cfm @ .600 lift. To keep it even, a WP Sportsman II 201cc, same valve size and port size flowed at 243/156 cfm @ .600 lift. That is a 22 cfm difference in intake flow comparing to approximately 45HP difference on a 8 cylinder engine.

Another flow test of mid to late 1970’s model Pontiac head 6X-8 with 153cc intake ports came in at 214/158 cfm @ .550 lift, 28 inches of water. A #16 head ported flows 250cfm @ .550 lift on the 160cc intake.

Before and after tests of Edelbrock 2.11/1.65 Pontiac heads flowed 290/208 cfm @.600 lift, 215cc and 299/217 cfm ported.

For comparison Edelbrock 2.02/1.60 Performer RPM sbchevy heads flowed 227/176 cfm @ .600 lift, 170cc and 248/192 cfm ported.

Now if remember, the above professional engine builder claims that “In fact, stock 14 degree Pontiac big block heads are TERRIBLE flowing heads and to claim that's something special makes their actual flow even more laughable. Even Stock Edelbrock heads are NOTHING to right home about. Almost any decent aftermarket 23 degree Chevy head is either going to equal a stock Pontiac head with the better CNC variations blowing away even the Edelbrock head, all 14 degrees of them”.

VICTOR 23° HIGH-PORT HEADS - APPROVED FOR NASCAR TOURING CLASSES
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PERFORMER RPM WITH ANGLED PLUGS
Chamber Size Intake Port Size Valve Sizes (in/ex) Bare (single) Complete (single)
70cc 170cc 2.02"/1.60" #60619* #60719*
64cc 170cc 2.02"/1.60" #60949* #60999*
PERFORMER RPM WITH STRAIGHT PLUGS
70cc 170cc 2.02"/1.60" #60639* #60739*
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.100 .600
#60719, #60739 73/61 140/108 200/144 238/163 244/175 244/183

PERFORMER RPM PONTIAC
Chamber Size Intake Port Size Valve Sizes (in/ex) Bare (single) Complete (single)
72cc 215cc 2.11"/1.66" #60589* #60599*
72cc (semi-machined) 215cc 2.11"/1.66"(B) #60509* N/A

.100 .600
#60599 71/69 143/120 208/151 253/173 272/191 286/199

By the way, a Edelbrock/Chapman 6104 head w/236cc intake will flow 314/250cfm @ 28”. These are 18 degree high dollar heads. What happens when we tilt these valves another 3 degrees with the Edelbrock 15 degree 283cc intake head? 363/254cfm @.600 lift.

I guess valve stem angle don’t matter?

This thread will only deal with Gen 1 Chevy small block 23 degree valve stem angle head vs. all other non 23 degree valve stem angle wedge/compound wedge Gen 1 Chevy small block head. This is going to be done to keep from stepping on other's toes or breaking someone's heart.
 
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#2 ·
They can both be correct. When talking about valve angles, it depends on the head around them. You can't compare valve angles on a chevy to valve angles on a mopar any more than you can compare port volume between the two.

Just like port volume, valve angles are meant to be compared within similar heads. A 23* chevy head might not flow as well as an 18* chevy head, but trying to compare a pontiac's 14* head has no bearing on the subject.

Like with port volumes. I hear people talking all the time about how this SBC head flows more with 200cc than this BBC head with 300cc. That means nothing, since the distance from the port opening to the valve on the BBC head is so much longer. A 300cc BBC port might have a smaller cross-sectional area than a 200cc SBC.

In general, each head has a "sweet angle" that is a compromise between shallow valve angles and short turn radius in the port. As a vague generalization, less valve angle makes better flow, but only up until the point that the sharp bend in the port starts choking it off. That might be 20* on a chevy head and 4* on an Olds head, but comparing the two is pointless. One way that folks get around that sharp turn is by raising the intake port. That maintains the same radius in the port, but provides a favorable, straighter shot at the cylinder. Higher ports have been used on factory engines, like the vortec and the LT4 with great success, even at the factory 23*. One of the downsides is packaging. The Vortec carb intake is a full 1.5" taller than the GM-issued non-vortec intake to accomodate the higher ports.

But I digress. Suffice it to say, when dealing with valve angles, comparing them ONLY works within the same engine family and its only a relative comparison at best. Way too many things factor into net flow to say that one head will definitely flow better than another with simply an angle change.
 
#3 ·
Going to a 13 degree valve stem angle TFS 200cc was able to squeeze out 265/211 cfm @ .600 lift. To keep it even, a WP Sportsman II 201cc, same valve size and port size flowed at 243/156 cfm @ .600 lift. That is a 22 cfm difference in intake flow comparing to approximately 45HP difference on a 8 cylinder engine.

Same engine family, same valve size, same cc ports. This is the closest similarity in heads to compare different valve stem angles and its a chevy vs chevy in this comparison.


WP
vs.
TFS http://64.233.161.104/search?q=cach...s+twisted+wedge+head&hl=en&gl=us&ct=clnk&cd=7
Oh yea, check out "A Death in the Family" at the bottom of the article.

Again, my consensus and others is that valve stem angles do not contribute to horsepower or flow gains. What do you think?
 

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#5 ·
Comparing the valve angles of SBC heads to the valve angles of another engine is useless; too many differences exist like port geometry determined by pushrod location, head bolt locations and such.

There’s no question that with all things equal the reduction of valve angle can provide benefit. I consider the potential benefits to fit into four groups.

With a reduced valve angle:

1. The port approach to the valve can be changed.

2.The flow cone inside of the cylinder has a superior location with less obstruction with the cylinder bore.

3.The combustion chamber shape and size (determined by valve layout and angle) can be altered taking on a smaller shorter geometry.

4.Valve relief in the pistons can be reduced.
 
#6 · (Edited)
automotive breath said:
Comparing the valve angles of SBC heads to the valve angles of another engine is useless; too many differences exist like port geometry determined by pushrod location, head bolt locations and such.
.
Ok, lets move this discussion off of the "Comparing the valve angles of SBC heads to the valve angles of another engine is useless" over to a sbchevy vs sbchevy. I used that portion to set up a historical relationship of what was being used back in the 60's and 70's and where it was coming from. It seems that comparing a sbchevy part to another brand xyz engine part that it touches a nerve especially when the brand xyz part performs better, even if its just perceived that way.

For the rest of this discussion we'll keep it all chevy and examples like this:

Going to a Chevy sb 13 degree valve stem angle TFS 200cc was able to squeeze out 265/211 cfm @ .600 lift. To keep it even, a Chevy sb WP Sportsman II 201cc, same valve size and port size flowed at 243/156 cfm @ .600 lift. That is a 22 cfm difference in intake flow comparing to approximately 45HP difference on a 8 cylinder engine.

Same engine family, same valve size, same cc ports. This is the closest similarity in heads to compare different valve stem angles and its a chevy vs chevy in this comparison.

WP
vs.
TFS http://www.hotrod.com/techarticles/trick_flow_twisted_wedge_head_dyno_test/ Oh yea, check out "A Death in the Family" at the bottom of the article.
 
#7 · (Edited)
Quench, you're comparing apples to oranges again. Just like in the original thread that this discussion came up in.

The Pontiac Performer RPM head has 215cc intake ports and the SB Chevy has 170cc ports, a 45cc difference.

How about comparing a SBC head with a similar port size to the Pontiac RPM heads? A 210cc AFR SB Chev head will flow 289/220 int/exh at .600 lift. Compare that with the 290/208 on the Pontiac heads. At least these heads have similar port sizes...

Price?
Pontiac RPMs: ~$1700 through Summit
SBC AFR: ~$1500 through Jegs

The AFRs also have 2.08/1.60 valves instead of the 2.11/1.65s on the RPMs.

The 205cc AFR LS1 head has a 15 degree valve angle... AFR says they'll flow 298/230 at .600" lift. Their 225cc heads are rated at 320/250 at .600.

Your link brings me to a Google search page and it shows nothing about TFS heads. TFS does have a 13.5 degree head for LS1 (Gen III) engines, these are totally different than Gen I/II engines.
 
#8 ·
Blazin72 said:
Quench,

How about comparing a SBC head with a similar port size
.
The link is fixed.

I already addressed how this discussion is going to move in post #6 so the only thing that is relevant in your post is what is left of your post in the above quote.

This thread will only deal with Gen 1 Chevy small block 23 degree valve stem angle head vs. all other non 23 degree valve stem angle wedge/compound wedge Gen 1 Chevy small block head. This is going to be done to keep from stepping on other's toes or breaking someone's heart.

Question, was the switch or demise of the 23 degree valve stem angle head to the other less than 23 degree valve stem angle heads destined in order to remain competitive in top endurance speed events SUCH AS NASCAR?
 
#9 · (Edited)
Top level NASCAR engines don't use 23 degree heads either. They use SB2.2 heads, or at least they used to. They may have something else now, I don't know. The SB2.2 valve angles are 11 deg intake and 8 deg exhaust. BUT, heads like these also use raised runners which alleviate the sharp turn in the port you'd get if you kept the "standard" port location. Again, I believe somebody explained this in the thread you originally brought this up in.

When was that Hot Rod article written? A while back I asked about the Twisted Wedge heads and was told that those were becoming a thing of the past...

Also, I can't think of too many people on this board, or anywhere else for that matter, that actually have a small block built to take advantage of the MASSIVE size of those Victor 15 and 18 degree heads you listed in your original post. Those heads have a 250+ cc intake port, they are far beyond anything you, myself, or just about anybody else would have a need for.

I don't think the Gen III engine is being used in NASCAR either...
 
#11 ·
Blazin72 said:
Top level NASCAR engines don't use 23 degree heads either. They use SB2.2 heads, or at least they used to. They may have something else now, I don't know. The SB2.2 valve angles are 11 deg intake and 8 deg exhaust. BUT, heads like these also use raised runners which alleviate the sharp turn in the port you'd get if you kept the "standard" port location. Again, I believe somebody explained this in the thread you originally brought this up in.

When was that Hot Rod article written? A while back I asked about the Twisted Wedge heads and was told that those were becoming a thing of the past...

Also, I can't think of too many people on this board, or anywhere else for that matter, that actually have a small block built to take advantage of the MASSIVE size of those Victor 15 and 18 degree heads you listed in your original post. Those heads have a 250+ cc intake port, they are far beyond anything you, myself, or just about anybody else would have a need for.

I don't think the Gen III engine is being used in NASCAR either...
No where in my post did I say that NASCAR is currently using 23 degree heads.

There are raised port 23 degree heads as well, so whats you point? This is a discussion about "valve stem angles". If you cant stick to the topic then you should either start your own thread or move on.

"Again, I believe somebody explained this in the thread you originally brought this up in." (Blazin72, 2006). Again, you are trying to jump topic and bring something up you are trying to turn into a win/lose competition instead of a discussion about "valve stem angles". If you cant stick to the topic then go else where.

"When was that Hot Rod article written? A while back I asked about the Twisted Wedge heads and was told that those were becoming a thing of the past..." (Blazin72, 2006). Again, you are trying to jump topic and bring something up you are trying to turn into a win/lose competition instead of a discussion about "valve stem angles". If you cant stick to the topic then go else where. Your point is illogical since the Gen 1 was designed back in the mid 50's and still popular with hotrodders.

"Also, I can't think of too many people on this board, or anywhere else for that matter, that actually have a small block built to take advantage of the MASSIVE size of those Victor 15 and 18 degree heads" (Blazin72, 2006). Again, you are trying to jump topic and bring something up you are trying to turn into a win/lose competition instead of a discussion about "valve stem angles". If you cant stick to the topic then go else where.

Again, this is only dealing with GEN 1 SMALL BLOCK CHEVY, NOT GEN 3.

Blazin72, if you are trying to turn this discussion around into something else then start your own thread on how to kill a discussion thread. If you have something that pertains to valve stem angles then do so. I am trying to figure something out or learn something here one step at a time.
 
#12 ·
Take a look at the picture below. The head on the left is a camel hump head while the one on the right is a Vortec. Both are 23* heads, whereas Pontiac uses about 14* and Olds uses about 6*.



First lets look at the three major angles that come into play: The angle of the valve compared to the stroke, the angle of the valve compared to the port, and the angle of the port to the intake runner.

First of all, Automotive Breath is right. In most situations, the straighter the valve is in relation to the bore, the more efficiently it will be able to deliver charge to the cylinder. Its also usually true that a smaller angle from the port to the valve delivers more air. All things being equal, decreasing the valve angle in relation to the stroke (like going from 23* stock angle to 15* aftermarket) INCREASES the angle between the port and the valve. The secret is finding a valve angle that maximizes one while not crippling the other. Too little valve angle will make too much of a turn in the port. Too much valve angle makes a nice straight shot at the valve, but then it has to turn more in the bore and it cripples flow. That's why many aftermarket performance race heads have raised ports. It softens the angle between the valve and the port.

Now, let's use the photo as an example. Those are both 23* heads. In the case of the Vortec, they have raised the ports. This doesn't improve the valve-to-cylinder angle, but it does improve the port-to-valve angle. So, even in the same manufacturer we see that saying one valve angle is the best or worst is pointless. The vortec head has more "room" to play with port location compared to the early camel hump.

The third angle comes into play as well, however not nearly as importantly. Unless you're using a tunnel ram intake, the intake has to make two turns; one from the vertical flow of the carb, and then another as it enters the head. Raising the port often increases the angle that the flow has to take as it enters the head. Its pretty mild, and manufacturers sacrifice hood clearance with taller intakes to combat it nicely.

But, back to valve angles. As you can see, heads that are low and compact typically have low port roofs. Combining small valve angles with heads like this can create a really sharp short turn in the port and create flow problems. The olds heads are a prime example of this and, to a lesser extent, the caddy and pontiac heads as well. Whereas stock Chevy heads could be described as having too much valve angle, I would describe the Olds heads as having too little. If someone made alternate-angle perfromance heads for Olds, they would probably INCREASE the valve angle to ease up the turn in the port and improve flow.
 
#13 · (Edited)
curtis73 said:
Take a look at the picture below. The head on the left is a camel hump head while the one on the right is a Vortec. Both are 23* heads, whereas Pontiac uses about 14* and Olds uses about 6*.
.
That was really good Curtis and the kind of discussion I am trying to establish in this thread. However, lets at least use brand A, B, C, D, E, F, etc in the posts so as not to turn this back into a brand war if you know what I mean. Maybe you could edit the brand names in your post.

This is along the lines of what Curtis is talking about: http://64.233.161.104/search?q=cach...VORTEC+HEAD+CUT+AWAY&hl=en&gl=us&ct=clnk&cd=5
 

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#14 ·
Interesting stuff. I allways wondered how the different valve angles effected the heads.

Check this out. I was reading some NSCA rules about Pro comp and all motor class.


In the rules for weights

BASE WEIGHTS
• 2,800 lbs - Small Block, Inline Valve, 13-21 degree valve angle, 7.8 lbs/ci to 360ci, 4.0 lbs/ci over 360
• 2,800 lbs - Small Block, Inline Valve, <13 degree valve angle, 8.1 lbs/ci to 360ci, 4.0 lbs/ci over 360
• 2,800 lbs - Small Block, Inline Valve, >21 degree valve angle, 7.1 lbs/ci to 360ci, 4.0 lbs/ci over 360

Looks like they show >21 degree heads having a disadvantage in an all out 8 second race motor. I wonder if the same is true with say a 450hp small block.
 
#15 ·
I think it's been more or less stated already -- valve angle alone is meaningless. So is port volume/size. The entire head design is a compromise, and all parts relate to the other. For example, I'll use what I know best and hasn't been mentioned: AMC/Jeep six cylinder heads! Nothing I say about them should offend anyone!! :D

Early AMC/Rambler heads (the basic design used for the 4.0L came out in 1964) use very large ports with only slightly tilted valves. I don't know the angle, but they are nearly straight up. The ports have to make a near 90 degree turn down to the valves. These flow great at idle, but don't flow well at high speeds because of the sharp turn.

Now lets jump way up to 1987 and the first 4.0L. Well, actually, to 1984 and the first AMC four, which was derived from the six cylinder block. The "new" engine received a new head (as stated -- block is basically a six with the two center cylinders cut out -- some other changes were made, but that's irrelevant to the discussion). The new head design featured smaller, raised intake ports (compared to earlier six cylinder ports, which did get smaller and slightly better in the 70s) with a little more valve angle and new combustion chambers to match. When the 4.0L was designed, it got a stretched four cylinder head along with EFI. The difference was a jump from 110 hp in 1986 with a carb to 177 hp in 1987 with the new head and EFI. The power jump can't be attributed all to the head, of course, but the head definitely made a big difference.

Now go to 1991 and the 4.0L H.O. There was a 13 hp increase in power due to the intake ports being raised another 1/8" (approximate!) over the 87-90 design. Valve angle remained the same. The only other change was some minor reprogramming of the computer and advancing the stock cam by 2 degrees (IIRC). Advancing the cam moved the power peak up a little higher, and along with the reprogramming allowed Jeep to eliminate the EGR valve (the main purpose for the advance and tuning changes). Most of the power increase, especially at lower rpm, can be attributed to the port change. I arrive at this conclusion due to reports from Jeepers who run the H.O. head with carburetors on earlier 258 block. They report gains of 20-40 hp from the head swap alone. There is a little compression gain in most cases, but the wide power change is due to variations in engine builds.

Valve angle alone is meaningless. If you could change the angle in a head designed with a specific angle in mind, I doubt there would be much (if any) change in performance at all. The whole package -- angle, port, and combustion chamber -- has to be taken together.
 
#16 ·
farna said:
I think it's been more or less stated already -- valve angle alone is meaningless. So is port volume/size.

Valve angle alone is meaningless. If you could change the angle in a head designed with a specific angle in mind, I doubt there would be much (if any) change in performance at all. The whole package -- angle, port, and combustion chamber -- has to be taken together.
I disagree, attached is as excerpt from a catalog comparing a low port 18 degree to a bow tie 23 head. Although its the V6 its still a Gen 1 design. I will have more to come.

The remainder of your post only reintroduced other variables and is leading to confusion. Not that I cant understand it but lets try to stick to the guidelines so we can keep this discussion very narrow and then explore the other variables later on either in here or I will create a new thread. Possibly after a while I will combine the threads and present some recommendations for the first time engine builder so he or she can get the best bang for the dollar.
 

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#18 ·
Correct. If you drew a line up through the center of the bore, and a line up throught the center of the valve stem, the angle between the two would be 23*.

Farna speaks wisely. He knows what he's talking about.

I did you one better. Instead of discussing brands, I made a generic picture. Its attached below. The blue line represents stroke or bore centerline. The red line represents valve angle, and the green line represents the port direction. As you rotate the valve toward a smaller angle (closer to parallel with the bore CL) you increase the angle that the port has to turn. The way that is typically combatted is to raise the port.

Angle milling is an excellent example of this. You mill 1-2* into the surface of the head so that the valve angles are more straight, and since the ports rotate with it, its a win-win, but simply casting a new head with a different angle is where the comparison gets hazy.

We've seen from past experience that Chevy heads perform better in a stock port location at closer to 18*. Most of the full-on race 15* heads have completely different port layouts requiring special headers and intake manifolds so they're out of an apples to apples comparison.

If you could have a head made out of putty or simulated on a computer that you could live-test flow at valve angles with everything else remaining the same, you would see that it peaks flow at a certain angle. Lets say we tested the head from 25* to 0* and the top of the bell curve was at 18*. What that means is, the increase in flow you got from straightening up the valves met with the decrease in flow you created by sharpening the curve in the port. After that 18* point, any increase you would have gained at the valve, you choked by increasing the turn in the port.

Think of it like cleaning your sidewalk with a garden hose. The strongest cleaning comes from hitting the sidewalk straight down with the water, but if you have to kink the hose to get that angle, its not going to be as effective. The cleanest sidewalk would come from finding the angle where the decreasing water flow meets with the closest-to-straight angle. Now, in this case, you have the option of raising the rest of the hose so that it DOESN'T kink, which is equivalent to raising the port in the head. Some heads (like the one I drew) have space to do that. Others don't. I think specifically of my Caddy heads. There is just no room to play around with port position, so unless there is enough aftermarket support to cast new heads, intakes, and valvetrain components, its not going to happen.

That's also what keeps most people in the stock valve angle for their build; price. If I can make my 400-hp goals using a stock valve angle for $1000 or 420 hp with an altered valve angle and potentially $2000 more in special valvetrain parts, headers, and intake, I think I'll stick with the cheap :) But... if I were a race team, the sponsors pay for it, and that 20 hp could mean $100,000 more prize money,
 

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#19 ·
Here we have it right from the horses mouth, a cylinder head manufacture:
"If there is one constant in this big, crazy, spinning-wildly-out-of-control world, it's this: horsepower wins races. Oh sure, racers will tell you stuff like suspension settings, driver skill, and plain old dumb luck are important. But deep down in the furthest corner of their souls, they know it's raw, screaming horsepower that takes the checkered flag.

The cylinder head crowd at Trick Flow Specialties understands this Primary Law of the Universe -- their famous Twisted Wedge and R-Series aluminum heads are ample proof of that. Now they've gone to an even greater degree in the search for more power. Actually, make that 18 degrees, as in their new 18 degree aluminum heads for small block Chevy. And do those heads make power -- we have the dyno tests to prove it.

Why 18 is Better

Before we get to the dyno results, let's get into the theory behind 18 degree heads. The number refers to the angle of the intake and exhaust valves in relation to the head's deck surface. By contrast, conventional small block Chevy heads have a valve angle of 23 degrees.

So what's the big deal about 18 degrees? The shallower valve angle allows the cylinder head designer to use a smaller volume combustion chamber to help boost the engine's compression ratio without going to large-dome pistons. The combustion chamber on the Trick Flow 18 degree head is 56cc versus the 64cc chamber on most high performance 23 degree heads.

The Trick Flow heads, like all 18 degree heads, require shaft mounted, offset roller rockers. Trick Flow used these Jesel 1.6/1.5 ratio shaft rockers for the dyno tests.

Another big advantage of the 18 degree valve angle is valve location. The valves in a conventional 23 degree head are .275 in. from the cylinder bore centerline. When the valves are close to maximum lift, they become shrouded by the combustion chamber and the cylinder walls. That hurts the engine's ability to breathe--and that hurts horsepower.

In 18 degree heads, the valves are right on the cylinder bore centerline. The valves are also relocated to position the intake valve closer to the bore center, and the exhaust valve closer to the cylinder wall. This unshrouds the intake valve at maximum lift and allows the use of bigger valves.

The Trick Flow 18 degree heads are machined for 2.150 in./1.625 in. valves, and can accept intake valves up to 2.180 in."

Valve stem angles alone are meaningless? They certainly allow a whole host of side benefits that otherwise could not be done without a change in valve stem angles.
 
#20 · (Edited)
Yes, valve stem angles alone are meaningless. Just because their heads make more power because of the 18 degree valve angle, doesn't mean that on a different brand head with a different port that 18 degrees will make a difference on them.

That's all we're saying. 18* is not a magic number. It IS on those heads that have undergone millions of dollars of R&D with different port types, but to just randomly say that all heads perform better with a different valve angle is not true.

I would also agree that for MOST chevy ports, 23* is probably not optimum. Maybe 18* is, but on Dart's 18* head, they might pick up some flow by going to 18.347*, and on Trick Flow's heads, maybe they'll pick up some by going to 16.884*. You can't do that, since you have to make a standard so everyone can buy parts. You shoot for the average and do your best with what you have.

I think we posted at about the same time, but look over my last post. I talked about the garden hose analogy and how a straighter angle is most effective, but if it kinks the hose its not as good. Think of every different head as a different hose. One hose is rubber, another vinyl, and anotherone is a cheap plastic. They all have different angles at which they would kink and start reducing flow, so they all have different angles at which they clean the sidewalk best. Plastic kinks easier than rubber, but the smooth vinyl flows more water... yadda yadda. The point is, its not black and white. Its more like cam selection; this range of cams works with this range of compression and RPM range. Its not a one-angle fits all thing.

There are literally millions of port profiles out there, all of which have unique characteristics. All we're saying is, if you change the port, you are no longer talking apples to apples. I don't care if you go from Vortecs to LT1 heads which have very similar ports, they might have different optimum angles.

Trick flow is only saying that they increased power potential by designing an 18* head. They aren't saying that 18* is best for every head and every brand. And, although I fully beleive that 18* makes power on those heads, they also outline about 6 other factors that they used, like moving the valves closer to center, increasing compression, an altered combustion chamber that unshrouds the valves. Although you and I know that 18* makes power on chevys, if i didn't know that, I might argue that the trick flow heads made more power because of the 6 other factors in their design, not the valve angle.
 
#21 ·
curtis73 said:
Yes, valve stem angles alone are meaningless.

I think we posted at about the same time, .
Yes we did post near the same time.

Good discussion and analogies. Now, to take theory to track, since most people/builders follow or buys what wins on Sunday, would a team have to abort and think beyond the 23 degree head and switch over to the 18*, 15*, and so on heads in order to remain competitive?
 
#22 ·
Well, the win on sunday, buy on monday is a thing of the past in my opinion. Back in 1969, you could check an RPO box and order a race car for the street. The technologies were remarkably similar. Today, if people watch the race on sunday and buy a Chevy on monday, its strictly because of brand name recognition. 99% of the public doesn't even know what a valve is or does let alone how different angles affect power, they just saw their favorite driver win in a Ford built with an identical tube chassis to the Toyota racing beside it, so they go buy a V6 mustang with a wing on it.

The valve angle difference conundrum is pretty tough. You have to have a pretty hairy engine before you really need 18* heads, especially since the manufacturers don't make any "street" heads in 18*. Most of them are big-port, big-valve, high-rpm and high-dollar. I think the majority of people would rather keep it simple and cheap. Like I said before, the extra 20 hp from changing valve angles can come at an extreme cost, and if you bend a rocker arm in the middle of the desert, you can't just drive to Auto Zone and buy a replacement.
 
#23 ·
I found this pretty interesting:

SHAWN MENDENHALL FROM COAST HIGH PERFORMANCE

CHP: It there anything to be said for going old school?
SM: The only advantage for the 23-degree setup is the bore. With a larger bore size, it's easier for the heads to breathe, and you can start with a factory block, which you can still get at a swap meet. It costs more to do a 4.125-inch bore in the newer motors, because you need cylinder sleeves and custom pistons.
CHP: What does the future hold for the traditional small-block configuration?
SM: Until there's no more gas, people will have fun with them. As long as there's a desire for 23-degree parts and people still have stuff stashed in their garages, they're never gonna go away. Aftermarket blocks are more within the average guy's reach.
CHP: You mentioned 18-degree heads. What are your thoughts on the subject?
SM: The 18-degree stuff is old-school racing technology. Make it user-friendly, which is already starting to happen, and it's gonna really change the market. You can make good power with 18-degree heads--they're gonna be able to make a ton of horsepower on the street.
 
#24 ·
According to these late model rules there seems to be weight factor when running different valve stem angle heads. Now I wonder if they check the valve stem angle, head part # and or if the head was angle milled like Curtis pointed out (good point)?

V. Aluminum Head Engines - Engines utilizing aluminum heads with cylinder head valve angle within plus or minus 2 degrees of standard original equipment cylinder head must weigh a minimum of 2375 pounds and must utilize a 390 C.F.M. carburetor.

VI. Engines utilizing aluminum or steel heads with cylinder head valve angle that is not within 2 degrees of standard original equipment cylinder head must weigh a minimum of 2425 pounds and must utilize a 390 C.F.M. carburetor.

http://209.85.165.104/search?q=cach...8+degree+mopar+heads&hl=en&gl=us&ct=clnk&cd=5
 
#25 ·
Most of those rules are pretty loose. They probably check part number because angle milling can only make a 1 or 2* difference. They make those rules and check them based on the spirit of the sport. They know that they might be ported or use shaved valve stems, or other inner magic, but that's the way the game is played.
 
#26 ·
All else being equal, the 18 degree set-up, including intake manifold, pistons, and other parts specific to the 18 degree head will out-horse a similar 23 degree set-up. The rub is that this is most noticeable in high-horsepwer, racing type engines. For most street/strip or street engines, the horsepower gained with the 18 degree set-up is far overshadowed by the added cost and loss of drivability as compared to a 23 degree set-up. If the 18 degree set-up becomes more popular and developed for street type engines, it would still be hard to supplant the ubiquitous 23 degree set-up.

tom

Did I say set-up enough?
 
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