Optimal Engine Valve Angle

[Happily1986]

Lets have a serious discussion of what you deem is the ideal valve angle. A brief search on the net leaves no satisfying conclusive answer as to which angle is the magic number.

 

While i personally have no magic number offhand, i feel that a tighter/smaller angle is more optimised for higher flow rates with lesser turbulence. Of course if the valve angle is aggressive and the the engine manifold orientation retards air and gasoline flow, then it cancels out the effect of having an aggressive port angle.

[Nmnhnlm]

Do you actually meant the intake and exhaust port angles? If so, you can check out Toyota's 4AGE and 4AFE. The main difference is in the engine head.

 

There is no perfect angle. It all depends on what you are after. Economy/low end torque or plain high end power.

[Nmnhnlm]

http://www.billzilla.org/4agstock.htm

 

Look at the difference in the port angles.

[Nmnhnlm]

http://www.billzilla.org/4agstock.htm

 

Look at the difference in the port angles.

[Happily1986]

Hi, the valve angle is referring to the angle at which the exhaust/intake valves are orientated (angle wise) with respect to the piston chamber.

[Nmnhnlm]

OIC. You meant the valve angles. I don't think it matters much. It more limited by how much space you have for the head. Whats more important is port angle rather than valve angle.

[Happily1986]

Not really. According to what i read up, the valve angle is a major determinant in an engine's character as it acutely affects the gas flow dynamics in the piston i.e. the air-fuel mixture is to be regarded as gases. An interesting read.

 

Cam Science

Resolving the Mysteries of Lobe Center Angles

By David Vizard

 

Introduction by Scooter Brothers, R&D Director, Competition Cams:

In spite of all the material published about cams, cam design, applications and the like, our experience at Competition Cams indicates there still exists much mystique concerning cam timing and valve events. We know this because of our cam help hot line (800/999-0853), which answers as many as 2500 technical calls a day. Because we repeatedly hear the same questions-

[Happily1986]

another comment i found

 

The short answer is, narrow valve included angles make for very small efficient commbustion chambers that can handle very high compression ratios on poor quality fuel. The narrow valve angles also allow the designer to run cams with large overlaps with out the risk of the intake and exhaust valves making contact.

 

The downside is as the valves get closer to perpendicular in relationship to the bore the port has to be angled up to get it to flow properly. The obvious problem with that is finding some place to put the carb as the port gets higher and higher.

 

Older design engines like the Chrysler Hemi had wide valve included angles. The valves were tipped back so the intake port has a nice clean airflow path to the valve. Big airflow was the result, but the trade-off was combustion efficiency. These engines had a large surface to volume ratio in the combustion chamber so they needed a huge dome on the piston to get a decent compression ratio.

 

The Honda GP 4 valve engines of the early sixties were similar to the Chrysler Hemi in their layout, and had horrible combustion efficiency. Most people credit either Keith Duckworth (Cosworth) and/or Harry Weslake (Weslake) with figuring out that narrowing the valve angle was the key to making four-valve heads really work.

[Nmnhnlm]

OIC! Cool! Thats interesting stuff. Never knew it make that much of a difference. Unfortunately, I don't think there is anything we can do about it since we can't exactly change our valve angles.

 

What we can only do is valve size, lift and swirl polish tapered etc.....

[Happily1986]

yup we can't exactly change the valve angle in any case. The most people will do to improve airflow is to do porting by changing the orientation of the airflow in the engine manifold pipes so that airflow is not retarded. Alot of bread and butter cars have manifolds which retards the airflow because the porting angle is not aggressive enough. Furthermore, most car's air intake are not routed straight towards the manifold too. There is usually a air spooling reservoir because having a direct flow design might not be space friendly (i feel) so air flow is hampered especially at high vehicular speeds.

[Nmnhnlm]

  On 5/10/2010 at 6:03 AM, Happily1986 said:

yup we can't exactly change the valve angle in any case. The most people will do to improve airflow is to do porting by changing the orientation of the airflow in the engine manifold pipes so that airflow is not retarded. Alot of bread and butter cars have manifolds which retards the airflow because the porting angle is not aggressive enough. Furthermore, most car's air intake are not routed straight towards the manifold too. There is usually a air spooling reservoir because having a direct flow design might not be space friendly (i feel) so air flow is hampered especially at high vehicular speeds.

 

Btw, I think air flow is more critical for NA engines rather than Turbo. Turbo already has a big pump to shove air into the engine but not the case for NA.

[Jeleburacer]

  On 5/8/2010 at 5:28 PM, Happily1986 said:

Lets have a serious discussion of what you deem is the ideal valve angle. A brief search on the net leaves no satisfying conclusive answer as to which angle is the magic number.

 

While i personally have no magic number offhand, i feel that a tighter/smaller angle is more optimised for higher flow rates with lesser turbulence. Of course if the valve angle is aggressive and the the engine manifold orientation retards air and gasoline flow, then it cancels out the effect of having an aggressive port angle.

http://theamcpages.com/engine-design-valves-intake-ports.htm

Is this web site help. but I don`t think in Singapore any workshop capable to grind.

[Nmnhnlm]

  On 5/10/2010 at 11:45 PM, Jeleburacer said:

http://theamcpages.com/engine-design-valves-intake-ports.htm

Is this web site help. but I don`t think in Singapore any workshop capable to grind.

 

Nice article!

[Happily1986]

  On 5/10/2010 at 6:28 AM, Nmnhnlm said:

Btw, I think air flow is more critical for NA engines rather than Turbo. Turbo already has a big pump to shove air into the engine but not the case for NA.

 

I agree with you that with regards to the air flow issue, force induction engines are penalised on a lesser count than normally aspirated engine. However, i would like to point out that even with force induction, two engines side by side; if an engine has a poor air intake layout (i.e. not straight through), less than aggressive porting angle and valve angles which are excessively wide, this engine will definitely have lesser BHP gains than another force induction engine which do not have the problems as mentioned.

 

As concurred in previous postings, these factors are more or less fixed in engine designs unless one decide to grind like a bro mentioned i.e. doing engine porting. Otherwise, the engine potential is already capped from design.

[Happily1986]

  On 5/10/2010 at 11:45 PM, Jeleburacer said:

http://theamcpages.com/engine-design-valves-intake-ports.htm

Is this web site help. but I don`t think in Singapore any workshop capable to grind.

 

excellent website. any article which discusses about valve angle and such must mention about air flow characteristic be it laminar flow, pouseille flow etc. And it did. Thanks for sharing!

 

In the past, what separates the novice from the expert was relevant knowledge and experience. Now with Internet, we can close up to gap substantially by googling the knowledge that we lack, sparing the experience though.

[Chiangauto]

Valve Angle - Make More Horsepower

 

To add a 30-degree back cut to the inside diameter of the 45-degree seat angle on an intake and/or exhaust valve as a way to improve flow.

Olds Edelbrock aluminum

2.072-inch intake valve

Valve

Lift Intak

Stock Intake 35 Intake 32 Intake 30 Gain w/30-degree

0.100 68 71 70 70 2 3%

0.200 136 146 146 144 8 6%

0.300 190 196 208 206 16 8%

0.400 236 242 243 246 10 4%

0.500 232 237 237 237 5 2%

0.600 234 240 239 239 5 2%

Avg. flow 182.6 188.6 190.5 190.3 7.6 4%

 

From the results, it appears you could make a case for either 30- or 32-degree back cuts on the Oldsmobile head. The 32-degree back cut offers a slight advantage at 0.200- and 0.300-inch valve lifts.