Rocker arm ratio calculator

Grinder to prevent rubbing when using rocker arms with a ratio greater than about 1.6:1. And that's a task that must be performed with the cylinder heads removed from the engine, and preferably completely disassembled.There may be instances where the pushrods do not contact the drilled opening when using high-ratio rockers. That doesn't suggest swapping rocker arms on any engine, however. It's very important to know the condition and coil-bind limit of the valvesprings being used. (That's not just limited to high-ratio rocker arms—it includes camshaft swaps, too.) It's also wise to replace the original 38-inch bottleneck studs with quality 716-inch units. Not only does it allow for infinite valve-lash adjustment, bottleneck studs can and do break when valve lift exceeds about 0.450 inch or so.[1] Rocker-arm ratio is increased by moving the pushrod cup closer to the pivot point. Comparing these two original Pontiac rocker arms, note the pushrod-cup positions on the typical 1.5-ratio unit (left) and the 1.65:1-ratio unit (right).Increasing rocker-arm ratio not only increases valve lift, it also alters the rate at which the valve opens and closes. As the lifter tracks the camshaft lobe, it transfers motion to the valve through the rocker arm. A high-ratio rocker arm increases valve lift at every point. It boosts gross valve lift by several hundredths of an inch, but it can make a camshaft seem a few degrees larger as well. And if the engine can tolerate slightly more camshaft duration and/or the cylinder heads can support additional valve lift, a performance increase usually results.[7] The new Melling rocker arms (including the rocker ball) were submerged in clean 30W before being set on the rocker stud to prevent any issues associated with dry startup.The InstallTo illustrate the effects that a high-ratio rocker-arm swap can have on a vehicle, we purchased and installed a set of 1.65:1-ratio rockers on our '74 Trans Am. Its Super-Duty 455 is arguably the most under-cammed performance engine that Pontiac ever produced. Throughout development it used a No. 041-spec camshaft with 0.470-inch valve lift, but when it reached production in mid-year 1973, the high-lift cam gave way a tamer No. 744-spec grind, which included 0.407-inch valve lift. While it improved emissions compliancy, the cam change noticeably reduced peak horsepower from 310 to 290. The 1.65:1-ratio rocker arms increases valve lift by 10 percent toward 0.450 inch, allowing our SD-455 to breath a bit deeper.Though we could have purchased aftermarket high-ratio roller-rocker arms from any Pontiac vendor or mail-order supplier, maintaining originality and ease of install was a concern. We ultimately decided upon a set of OE- replacement, 1.65:1, stamped-steel rocker arms from Melling. Our reasoning is they fit and function like the originals, will clear the stock valve covers, and operate quietly and consistently—all important factors to us. And if we aren't satisfied with the result, we can easily reinstall the original 1.5:1 rockers at any time.Installation was straightforward. We focused on one cylinder bank at a time, and addressed each pair of intake and

When trying to decide between two camshafts for an engine that will spend a majority of its life operating at low-to-moderate rpm on the street, it's better to err on the side of caution. That means opting for the one with specs that are slightly tamer."What if it compromises full throttle performance?" you might ask. Well, you'll probably be much more willing to spend an afternoon swapping rocker arms than spending a weekend installing a new camshaft just to find out!A camshaft swap is rather involved. It includes partially disassembling an otherwise good-running engine to replace the cam, and if it's a flat-tappet, there's always the risk of lobe and/or lifter failure. To simulate the effects of a slightly larger camshaft, installing a set of high-ratio rocker arms is relatively easy and sometimes enough to noticeably improve performance.Just how much of a difference is possible? We used our '74 Super-Duty Trans Am to illustrate the effects. Here's what we found.Pontiac's ApproachMost Pontiac camshafts contained a maximum lobe lift of 0.271 inch, and the Division's typical stamped-steel rocker arm featured an opening ratio of 1.5:1. Simply multiplying lobe lift by rocker-arm ratio will yield gross valve lift for a given camshaft. In the instance of many four-barrel and Tri-Powerequipped Pontiacs, it equates to roughly 0.407-inch valve lift—an amount that most Pontiac hobbyists are familiar with when speaking of stock grinds.Considering that the intake airflow of a typical cast-iron D-port cylinder head peaks around 210 cfm at 28 inches of pressure, and it does so by about 0.450-inch valve lift, the near 0.400-inch valve lift that Pontiac engineers chose was close to the head's potential. When selecting an aftermarket camshaft for an engine that uses unmodified D-port heads, it makes little sense to push valve lift much beyond 0.450 inch or so.Most modern high-performance engine rebuilds include high-flow aftermarket cast-aluminum cylinder heads or modified cast-iron originals. And many aftermarket camshafts offer a reasonable amount of valve lift to accommodate the increased airflow capacity. When Pontiac needed more valve lift to take advantage of the new round-port cylinder heads it developed for the '69-'70 R/A-IV, a stamped-steel rocker arm with a 1.65:1 ratio was employed, effectively increasing valve lift from the No. 041 to nearly 0.520 inch.Rocker-Arm RatioAccording to the late Mac McKellar, the famed engineer responsible for developing a number of Pontiac's cutting-edge cam designs—including the No. 041—increasing rocker-arm ratio is an easy and effective way to increase gross valve lift from any camshaft. It's less stressful on the block since the lifter doesn't have to travel quite as far in the lifter bore, and it reduces the side loading that occurs when running an aggressive flat-tappet grind.Rocker-arm ratio is determined by the pushrod cup's position in relation to the fulcrum (or rocker stud). Moving the cup closer to the rocker stud increases ratio, but it also changes the pushrod's path angle during normal operation. Most often, the drilled pushrod opening in a typical Pontiac cylinder head must be relieved using a

Vary quite a bit with a change of only 10° in the intake closing point.A valve open only .005” will leak when pressurized, and at cranking speed the leak is fast enough to permit the volume between BDC and IVC to escape almost completely until the valve actually touches the seat. Some engines with small valves, short cams and rapid cranking speed will be under vacuum and not pull 100% of the effective stroke (100 VE between IVC and TDC), but will also not bleed out all volume between BDC and IVC and have some light residual pressure as the valve closes.The exponent depends on too many non-quantifiable factors, especially heat loss through the jacket and normal operating temp, but between 1.2 and 1.3 is favored by most calculator authors. The calculator is best used to predict & compare changes in variables in an individual motor, not as an instrument of measurement, or comparison between different motors. The linear nature of the input data vs. the highly varied conditions in different motors will always result in misleading figures. Even if the intake valve closing point is exact, the amount of flow reversion vs. capture will still vary between different motors due to flow characterictics between valve seats, rocker arm ratios, rocker geometry, valve head shapes, &c. If you have (or plan to install) a long-duration cam, you can (and should) regain some of this lost pressure by raising the compressionratio, but the 2 effects do not always “cancel each other out” -you can’t get something for nothing. Even though a higher compression ratiowill give you back a higher pressure gauge reading, the power may stillbe lower, at least at low to moderate speeds.DCR Errors “Dynamic Compression Ratio” (DCR) is offered (elsewhere) as a method of approximating how much power will

5 out of 5 stars ( 3 ) Part Number: SUM-1202 Brand: Manufacturer's Part Number: Part Type: Product Line: Summit Racing Part Number: UPC: 190861257917 Cam Style: Hydraulic flat tappet Camshaft Use: Racing Camshaft Manufacturers Description: Summit Pro SBC 4/7 Swap Hydraulic Flat Tappet camshafts utilize ultra-modern lobe technology and are American made. The revised firing order increases power through better mixture distribution and smoother running through equalized crankshaft journal loading. The Stage 3 cam works with likes a 3.08+ gears and is the biggest that works with a stock converter. It has a steady lope with a 327 Cid. on up. Great for weekend drivers. Basic Operating RPM Range: 1,500-5,800 Intake Duration at 050 inch Lift: 218 Exhaust Duration at 050 inch Lift: 228 Duration at 050 inch Lift: 218 int./228 exh. Advertised Intake Duration: 278 Advertised Exhaust Duration: 288 Advertised Duration: 278 int./288 exh. Intake Valve Lift with Factory Rocker Arm Ratio: 0.465 in. Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.473 in. Valve Lift with Factory Rocker Arm Ratio: 0.465 int./0.473 exh. Lobe Separation (degrees): 109 Camshaft Gear Attachment: 3-bolt Remanufactured: No Computer-Controlled Compatible: No Valve Springs Required: Yes Quantity: Sold individually. Notes: Summit Pro SBC Stage 3 Hydraulic Flat-Tappet 4/7 Firing Order Swap Cam, 218/228 Dur., 109 LSA + 2 Adv, .465/.473 Lift, 1500-5800 RPM Range, SB Chevy, Spark Plugs need Rerouted Summit Racing™ Pro SBC 4-7 Swap Camshafts Summit Racing™ Pro SBC 4-7 Swap hydraulic flat tappet camshafts are American made and utilize ultra-modern lobe technology. The revised firing order increases power through better mixture distribution and smoother running through equalized crankshaft journal loading. These racing cams are available in Stage 1 through Stage 8 configurations. Order the model with specs recommended for your Chevy small block engine application. Ask a Question What type of question would you like to submit? Some parts are not legal for use in California or other states with similar laws / regulations Call To Order This is a custom order part. You can order this part by Contacting Us.

Exhaust rocker arms individually. We made sure that the lifters were on the base lobe before removing the original 1.5:1 rocker arms and 38-inch bottleneck rocker studs, and had the 716-inch ARP rocker studs and Melling 1.65:1 rockers installed in a couple of hours.During installation, we used the pushrod-drag method to set valve lash to a half-turn past zero. An alternative method is to start the engine with the valve cover off, loosen a rocker nut until the rocker begins to clack, and then slowly tighten the nut until the sound immediately goes away. Once at zero lash, the rocker nut can then be tightened to the desired amount of preload.Either method accomplishes the same goal, but some consider the latter a bit more accurate, particularly when replacing rocker arms only.The ResultsUpon initial startup, we immediately noticed that SD-455's exhaust note was choppier than before. The initial test drive proved no detectible loss of low speed street manners, and the adjustable valvetrain seemed to have a positive effect on engine operation at part-throttle cruise, as it seemed smoother. We were convinced after a full-throttle blast that the SD-455 pulled a bit harder up top. Was our seat-of-the-pants testing correct? A follow-up session on the chassis dyno would tell the tale.[10] On the Mustang chassis dyno at C&S Dyno Shop, a baseline was established at 260 hp and 331 lb-ft at the rear tires. A subsequent dyno session followed after swapping the rocker arms.ConclusionNot every hobbyist owns an SD-455 or uses a low-lift, OE-spec camshaft in their Pontiac V-8. We chose this particular vehicle to illustrate the effects of our test since it was clearly lift deficient from the factory and would show a noticeable performance increase on the dyno—and it didn't disappoint.An increase of 11 rwhp is a reasonable amount for the effort involved, and similar results are possible from many engines, but not every combination will show a performance increase. Depending upon the camshaft chosen during your rebuild and the airflow capacity of your particular cylinder heads, your engine may not show any gain with high-ratio rockers. In fact, if your Pontiac is already equipped with high-ratio rockers and its camshaft seems a bit ragged, you might consider trying a set of low-ratio rockers to tame it slightly, or even different-ratio rockers on the intake and exhaust.In the end, it's a trial and error approach to find the rocker-arm combination that best suits your engine, but it's definitely worth the effort if maximizing your Pontiac's performance is important to you.

4.75 out of 5 stars ( 12 ) Part Number: EDL-60069 Brand: Manufacturer's Part Number: Part Type: Product Line: Summit Racing Part Number: UPC: 085347600694 Combustion Chamber Volume (cc): 72 Intake Runner Volume (cc): 170cc Exhaust Runner Volume (cc): 125cc Cylinder Head Style: Assembled Cylinder Head Material: Cast aluminum Camshaft Style: Hydraulic flat tappet Intake Port Shape: Rectangular Intake Valve Diameter (in.): 2.090 in. CNC-Machined Combustion Chamber: No CNC-Machined Intake Runner: No CNC-Machined Exhaust Runner: No Combustion Chamber Style: Kidney Intake Port Location: Standard Exhaust Port Shape: Square Exhaust Port Location: Standard Intake Valves Included: Yes Exhaust Valves Included: Yes Exhaust Valve Diameter (in.): 1.660 in. Valve Springs Included: Yes Maximum Valve Lift (in.): 0.600 in. Outside Diameter of Outer Spring (in.): 1.550 in. Damper Spring Included: Yes Number of Springs Per Valve: Single Retainers Included: Yes Retainer Material: Steel Locks Included: Yes Lock Style: 7 degree Valve Stem Seals Included: Yes Valve Stem Seal Style: Positive stop Rocker Arm Studs Included: No Rocker Arms Included: No Rocker Arm Nuts Included: No Guideplates Included: No Accessory Bolt Holes Drilled: Yes Intake Valve Angle: 13 Valve Guides Included: Yes Valve Guide Material: Manganese bronze Valve Seats Machined: Yes Valve Seat Machine Style: 3-angle Valve Seat Material: Ductile iron Cylinder Head Color: Natural Steam Holes Drilled: No Oiling Style: Through head Machined for O-Ring: No Heat Crossover: No Remanufactured: No Quantity: Sold individually. Notes: Valve springs are recommended for flat tappet style camshafts. Edelbrock stud kit EDL-6009 provides better rocker shaft retention and is highly recommended for use with Edelbrock FE heads. Heads have the 16-bolt 428 Cobra Jet exhaust flange bolt pattern. Edelbrock Performer RPM Cylinder Heads Edelbrock Performer RPM aluminum cylinder heads feature threaded inserts in the rocker studs and exhaust manifold bolt holes for superior strength and durability. They also include hardened seats, bronze valve guides, and fully machined valve cover rails for a more consistent gasket seal. These heads offer improved power throughout the RPM range for greater throttle response and top-end horsepower. Countless options are available; order the model recommended for your vehicle and engine application. Ask a Question What type of question would you like to submit? Some parts are not legal for use in California or other states with similar laws / regulations Call To Order This is a custom order part. You can order this part by Contacting Us.