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.

Attached Files

port same.doc (145.0 KB, 11 views)

Let me get this right, the 23 degree sbchevy head valves do not open on the bore centerline when viewed from the side?

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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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.

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.

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?

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.

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.

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...us&ct=clnk&cd=5

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.

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?

__________________
Ya cain't fix stoopid, but ya kin TAX it!

set up. There, you had missed one.

Tom, have you dug into the L92 casting released by GM Performance yet. It's an LS2 style casting. As cast cylinder head technology is about to put what we though were decent castings of the past,,,,,on the trailer.

Based on the observational logic gleaned from other threads on this engine website...

and applying that logic to this thread......

The 18* heads can NOT be any good at all or GM-OEM would have used them on all their products years ago. That proves they are no good.

(just in that mood today. )

LOL, and I didn't even get into the Dart 15* or GMPP 12*X4*/8* heads yet.