I just got done talking with my engine builder and he said that since I will be using stainless steel valves in my new motor, that I should go with a 4 angle valve job over a 3 angle valve job. The car is 60% street and 40% strip. Any thoughts? Should these be back cut? Thanks Mike
If you want to be real trick, find someone who does a NASCAR-type valve job. It is an infinite-angle deal. There is only one true discrete angle, at the actual seat. The rest is a curve, a constantly changing smooth blend from entry to exit. Requires a special cutter.
A Radius valve job (radius above and below valve seat) is great for the exhaust, but I would stick with a standard (Multi-angle) valve job for the intake. Backcutting of the intake valve can show improvement in many instances.
Greg, Would you mind elaborating on this and sharing more of your knowledge. On one hand it would seem best in both instances, intake and exhaust, to have the smoothest curve possible. I imagine that a multi-angle job would create some shear to improve mixture atomization?
A radius valve job on the intake side will generally show an increase of air flow thru the port, but flow numbers are not everything. The sharp multiple angles of the valve job on the intake side will make more power. A flow bench is a great tool, but CFM is not everything. Port cross sectional area and localized velocity and fuel management are a big part of the HP Equation.
Greg, I have heard of some head porters using a wet flow bench to see how the port acts. Have you ever used or see any value in a wet flow bench? I have heard the sharp multiple angles will help keep the fuel in suspension. Is this true?
The port walls and valve seat angles are all part of the "boundry layer" in fluid flow. A textured boundry layer doesn't help keep the fuel in suspension per say it helps vaporize the droplets of fuel that cling to the port wall by creating turbulance at the boundry layer. One of the advantages of CNC porting is it creates a perfect texture for vaporing the fuel. The big players in CNC porting all deliver their heads as is without polishing. Polishing the CNC texture will add a few cfm on the flow bench but also loses a few hp on the dyno. A mirror finish of the port does not provide the increase that intuition suggests. In fact, within intake systems, the surface is usually deliberately textured to a degree of uniform roughness to encourage fuel deposited on the port walls to evaporate quickly. A rough surface on selected areas of the port may also alter flow by energizing the boundary layer, which can alter the flow path noticeably, possibly increasing flow. This is similar to what the dimples on a golf ball do. Flow bench testing shows that the difference between a mirror finished intake port and a rough textured port is typically less than 1%. The difference between a smooth to the touch port and an optically mirrored surface is not measurable by ordinary means. Exhaust ports may be smooth finished because of the dry gas flow and in the interest of minimizing exhaust by-product build-up. A 300 - 400 Grit finish followed by a light buff is generally accepted to be representative of a near optimal finish for exhaust gas ports. The reason that polished ports are not advantageous from a flow standpoint is that at the interface between the metal wall and the air, the air speed is ZERO (see boundary layer and laminar flow). This is due to the wetting action of the air and indeed all fluids. The first layer of molecules adheres to the wall and does not move significantly. The rest of the flow field must shear past, which develops a velocity profile (or gradient) across the duct. For surface roughness to impact flow appreciably, the high spots must be high enough to protrude into the faster moving air toward the center. Only a very rough surface does this.
Great advice - I just had a set of small port T/A Stage1 Street Eliminator heads done by one of the guru's in the Nascar arena - Al Dickson at HRD. The heads are spec for the new 455 Buick IHRA crate motor class. Rules state that no cylinder head or intake porting allowed. We followed the rules to the letter. The valve job is the infinite angle type as you describe. Also, as far as valve shape, back-cutting etc. go, the best approach is to order custom valves shaped to optimize the flow over the given rpm range at which the valve will be spending the most of its time open. This is critical - if you have .550 lift at the intake valve for instance - big flow at .650 -.700 lift are useless. No matter who you have doing your heads, they need to understand this point. The guys doing this for a living understand that 60-70% of the potential in a cylinder head is in the valve seat itself. realizing the rest of the potential in the cylinder head comes from porting, combustion chamber valve relieving and decking. Another key point in cylinder head technology is getting the deck height correct relative to the valve seat and valve during the period over which the valve spends most of its time open. Put another way on my unported TA stage 1 street eliminator heads, we picked up 50 cfm on the intake side after decking. These are a few key points the experts take into consideration when building a set of cylinder heads. Another key consideration in the building a killer set of cylinder heads is intake manifold type and design. Again the experts know how much plenum volume is required as well as port shape to maximize flow over the valve lift range. Here is quick run down of my project: Unported -TA small port Stage 1 Street Eliminator heads with custom valves set-up for max lift at valve = .550" ( Decided to leave my Stock eliminator cam shaft in place which is only .500 lift) Intake Lift Flow .200 - 150 cfm .300 - 219 cfm .400 - 263 cfm .500 - 298 cfm .550 - 311 cfm .600 - 299 cfm .650 - 295 scm Exhaust Lift Flow .200 - 121 cfm .300 - 160 cfm .400 - 185 cfm .500 - 201 cfm .550 - 203 cfm .600 - 204 cfm .650 - 204 scm (Exhaust flow numbers taken without a pipe - with pipe max exhaust flow was 219 cfm @ .550) All flow numbers are conservative as the the bore size cup used on the flow bench was 4.25". Actual engine bore is 4.385". The flow numbers are mildly interesting but here is the cool part - Second decent shakedown run time slip data shutting down at 800'-1000': Car Weight w / driver: 3600 lbs 9-18-2010 4:35 pm Spokane, Wa DA - 4220 ft (temp - 76.1, RH - 46.7%, BP-27.46inHg) 60' - 1.429 330'- 4.238 660'-6.641 mph - 101.68 1000 - 8.744 1320 - 10.726 (both feet on the brake pedal hard in an elimination trying to get another pass - broke out on 10.90 dial) 1320 mph - 103.03 May not seem that impressive at first glance but considering unported Stage 1 heads, an unported SPX intake, holley 850 and a true .500 lift in a 3600lb car - I was happy with the initial couple of runs. Cost: $1450 for raw castings T/A Performance (480) 922-6807 begin_of_the_skype_highlighting**************(480) 922-6807******end_of_the_skype_highlighting (note: let the cylinder head shop start with bare castings - easier than fixing another shops mistakes.) $1741 to build the heads including an $800 set of custom Ferrara valves and milling the intake to port match the heads Horsepower Research Development (HRD) : (208) 762-9600. Total head cost: $3,191 SPX Intake Manifold: $400 Used Holley 850: $400 (still need to pay Tom Rix - lol) Total Bill: $3991. Please feel free to email me with any questions: m900rider@gmail.com (Jody Plummer)
Hi Greg Not to change subjects, but I am looking at running the Edelbrock Bee hive springs, on my iron Stg1 heads. I was wondering if there was anything I need to do, or watch out for? What should the valve height be set at? Thanks
Sounds like it can't be done with your Buick 3/8" diameter valve stems and valve guides. Converting to 11/32" diameter stems & guides is required. The Edelbrock aluminum heads already come with 11/32" parts. http://www.v8buick.com/showthread.php?t=208153 Additional pros/cons with beehive springs: http://www.v8buick.com/showthread.php?p=1725700 Devon
