How Long Does A Flow Cytometry Test Take

| How-To - Engine and Drivetrain

Aftermarket Heads - Head to Head

Dyno Testing to Make up one's mind What Aftermarket Heads are Actually Worth

An old hot rodding aphorism is "airflow is everything." Well, if y'all consider that in its simplest terms--an engine is cypher more an air pump--and so airflow is everything.

For years, gearheads have been porting cylinder heads and installing oversized valves in the name of increased flow, only simply how much horsepower is realized by way of better-flowing ports? Moreover, is port shape more important than port volume? For that we did dorsum-to-dorsum dyno testing to determine exactly where myth meets reality. All tests were done on the aforementioned small-cake, on the same day, using the same dynamometer. Going head-to-head are early-'80s GM Bow Necktie bandage-iron heads versus country-of-the-art Air Flow Research (AFR) 180 CNC-ported aluminum heads to determine if, in fact, airflow is everything.

The Test Mule
The mule motor for this comparo is a moderately healthy 327 that was originally built in the mid-'80s using old-school speed secrets. TRW popular-upward pistons swing from stock GM v.7-inch rods that are moved via a GM three.25-inch-stroke steel crank. The rotating assembly is balanced, but is of only decent forcefulness, with the exception of the Milodon heavy-duty rod and primary bolts. Up pinnacle, GM Phase I Bow Tie fe cylinder heads. In '86 the heads were sent to Engine Paradigm Development (EPD) for a competition valve job, pocket porting, gasket matching, and the installation of necked-downward stainless steel 2.055-inch intake/i.60-inch exhaust valves. COMP Cams one.52:ane roller rockers were actuated past a GM Duntov 30-thirty mechanical lifter camshaft. Later, an Edelbrock Performer RPM intake teamed with a Barry Grant Mighty Demon 650-cfm four-barrel funneled the fuel/air mix. An MSD billet benefactor, 8mm wires, and 6AL ignition replaced the stock wares. Recently the Duntov had been replaced with an aggressive mechanical roller cam/lifter/timing-chain kit from Contest Cams. Power was practiced simply certainly not stunning, and in that location was one primal chemical element of former school that needed to go--namely the heavy, old-tech Bow Tie castings.

The Large Question
Everybody talks a big game virtually how aftermarket heads make big power, but what are we really talking nearly here--25, 50, 100 horsepower? We've seen too many tests where aftermarket heads make big ability over smog-o-rama boat-anchors, but that'southward a no-brainer. Especially, we wanted to know how well aftermarket heads stack up against decently designed, mildly ported heads. To go along the playing field level, the AFR 180s were decked to generate 70cc com-bustion chambers to lucifer the 70cc chambers on the Bow Tie heads. While the AFRs come up standard with 74cc or 68cc chambers, y'all can custom-club them with a specific deck height, and consequently a specific combustion sleeping accommodation size. Without a doubtfulness, if the combustion chambers were smaller, compression would have been college and the engine would accept accomplished more. However, the focus of this dyno test was to keep variables to a minimum in order to maximize consistency and testing accuracy.

Menstruation Testing
If airflow is everything, then it would make sense to run the largest, highest-flowing intake ports possible, right? Well, not exactly. As flowbench testing has proven, port shape is merely equally important as port size in determining overall flow. Carefully shaping an intake port not but provides meliorate peak period, just information technology more than evenly delivers the air/fuel mixture over the valve head, resulting in improve cylinder filling and improved power. Interestingly, our ported Bow Tie heads actually had larger (cc) intake runners and larger valves, only they flowed less than the smaller-runner, smaller-valve AFRs. Some other thing to call up is that smaller runners evangelize improve velocity (resulting in quicker throttle response and ameliorate low-rpm ability), so for the street it is always appropriate to employ the smallest runner possible while yet fulfilling your cfm needs.

AFR generates its outstanding menstruum numbers for a variety of reasons. First, it has spent hundreds of hours in R&D and dyno testing to create port shapes that perform. Moreover, all AFR heads feature CNC-ported intake and frazzle runners. The CNC-porting maximizes the runner shape and volume and is absolutely consequent from port to port and caput to head. All as well ofttimes, hand-porting delivers a fabulous first port with increasingly worse results as the homo with the grinder tires throughout the day. Many aftermarket heads can be had with optional CNC-porting, only AFR offers 5-axis CNC porting for more than fine-tuned work.

In the following chart, compare the intake and exhaust port flow between the ported Bow Necktie caput and the AFR casting. Although the AFR 180s flow more summit cfm, of equal importance is that they also flow better in the lower elevator areas, which translates to ameliorate depression-rpm power and crisper throttle response.

Superflow Flowbench Head Flow Test
The same operator evaluated both sets of heads on a Superflow SF600 catamenia bench. All data was measured using the (manufacture standard) 28-inches water low baseline. Also, frazzle period was measured with a one 3/4-inch-diameter primary piping in place for both heads.

Exam
For the baseline exam, nosotros had the 327 wearing the GM Phase I cast-iron heads (see caput flow sidebar). All testing was done on pump gas at normal operating temperatures, with Hedman street headers expelling through dual exhaust and mufflers. Numerous dyno pulls dialed in the Mighty Demon'southward jetting, air bleeds, and idle mixture. Distributor timing was incrementally increased until power roughshod off. One time trimmed in, a final dyno pull yielded a respectable 401.9 hp and 359.v lb-ft of torque. Interestingly, the Bow Tie heads flowed improve than expected on the menses bench, but dyno numbers immediately puffed a longtime myth well-nigh the 327--although information technology freely pulled past vii,000 rpm, power speedily dropped off after 6,500 rpm. Average ability (321 hp) was decent, but certainly not much to brag nearly.

Off came the atomic number 26 heads and the Fel-Pro Perma-Torque head gaskets. The deck was wiped make clean before a fresh set up of 0.040-inch-thick (see head gasket sidebar) Perma-Torque multi-layer gaskets were installed. We immediately noticed the AFR's drastically lighter weight (see sidebar). Note that the AFR 180s are a direct bolt-on and incorporate internal EGR passages for l-state smog compliance along with external accessory bolt holes. The ARP caput bolts were reused and incrementally torqued in sequence. Before reinstalling the intake and carb, we fit new Fel-Pro intake (PN 1205) gaskets that incorporate larger-than-stock openings to properly mate with the CNC'd intake ports. After the induction was in identify, the MSD distributor was reinstalled, the engine was fired up, and the heads were immune most x minutes of burglary running.A few dyno pulls revealed that the AFR heads warranted carburetor jetting changes. In one case that was optimized, ignition timing was advanced until power savage off. With the AFRs, the 327 liked about three degrees more total ignition advance over the iron Bow Tie heads--likely due to the aluminum head'southward nature to reflect less heat into the combustion chamber. In general, more heat generates more power, merely at the chance of detonation.

The dyno numbers showed that the AFR heads delivered 41 more summit horsepower and that boilerplate horsepower was upwards, too. Moreover, the AFR heads kept flowing strong by 7,000 rpm, while also delivering quicker, crisper throttle response. Interestingly, virtually high-flow aftermarket heads are known for increasing power, yet torque unremarkably doesn't change much. With the AFRs, we were pleasantly surprised to see peak torque increment by a solid 14.5 lb-ft, a welcome addition with torque shy, small-cube 5-8s such as our 327.

Conclusion
Hard numbers from the dynamometer show that aftermarket heads practice brand a notable difference; for this exam nosotros went with AFR'south Competition Parcel heads that are regarded by many every bit the all-time-flowing 180cc heads on the market place. Consequently, if yous go with a less radical, smaller port, and/or non-CNC-ported aftermarket head, before-versus-after power may be less. Regardless, this test shows that although aftermarket heads tin can be expensive (AFR 180s listing for $ane,324-ane,999 per pair, depending on options), the byproduct is a solid increase in power.Truth told, our motor combination wasn't optimized for the AFR heads, which ultimately injure ability. A more than aggressive and/or open up-plenum intake manifold would take been a much wiser choice for the high-flowing heads, but hood clearance issues eliminated that pick. Because our 327 will shortly receive a Vortech centrifugal supercharger, the previous 0.015-inch-thick head gaskets were replaced with much thicker 0.040-inch versions that knocked down compression by well-nigh 0.65 of a point. (Notation: Going from our electric current x.03:1 to the previous 10.68:1 would likely increase power by about 3 percent--about 11 hp in our example.) Moreover, the COMP Cams roller cam installed was ground with the upcoming supercharger in mind. Rather than running a 108- or 110-degree lobe separation angle, nosotros went with a blower-friendly 112-degree LSA that ultimately hurt naturally aspirated ability but should prove beneficial with forced consecration. Regardless, our high-winding, 442.8hp 327 should testify plenty potent when it takes residence in the engine bay of a '66 Nova Super Sport. Likewise the 41hp increase over the previous setup, the AFR'southward alloy construction shaves almost 33 pounds off the nose of the Nova, which should make the car experience even more energetic.

Check out the intricate CNC-porting on the AFR 180's intake runners. The porting is stunning and the process ensures exactly the same dimensions from port to port and caput to head.

Ported GM Bow Tie AFR 180 CNC
Elevator (Inches)	Intake Flow (cfm)	Frazzle Menstruation (cfm)	Intake Flow (cfm)	Exhaust Flow (cfm)
0.{{{200}}}	116	107	140	112
0.{{{300}}}	169	143	201	152
0.400	212	166	244	190
0.500	239	169	260	208
0.550	225	172	262	214
0.{{{600}}}	228	174	263	219

Caput Gasket Thickness vs. Pinch Ratio
Although bore size affects pinch ratio, Fel-Pro reports that a general formula for computing how head gasket thickness affects compression ratio is every bit follows. For every 0.005-inch thickness increase/decrease, gasket volume changes by about 1 cc, which translates to slightly less than 1/8 (0.125) of a bespeak of compression ratio. We did the verbal math on our 327 V-8 and came up with these figures:

Gasket Thickness	Compression	Notes
(inches)	Ratio
0.015	10.68:ane	Steel shim previously on 327
0.020	10.61:i
0.030	10.31:1
0.040	10.03:i	Fel-Pro gasket used on this exam
0.050	9.76:1

<{{{H3}}}>Dyno Test

	Bow Tie		AFR 180 CNC
RPM	HP	Torque	HP	Torque
3,000	194.5	340.iv	194.6	329.5
3,{{{100}}}	198.8	336.nine	194.9	329.8
3,200	205.3	336.9	201.0	329.9
3,300	214.1	340.eight	209.7	333.7
3,400	223.1	344.six	217.7	336.three
3,500	230.v	345.nine	225.0	337.6
3,600	236.3	344.7	230.6	336.4
3,700	242.0	343.5	237.0	336.5
3,800	246.viii	341.1	244.4	337.8
3,{{{900}}}	252.v	340.0	251.eight	339.2
iv,000	260.9	342.6	260.3	341.viii
4,100	270.iv	346.4	270.8	346.9
4,200	280.0	350.1	282.5	353.2
4,300	288.eight	352.7	293.four	358.three
4,400	296.half dozen	354.1	303.4	362.ii
4,500	304.5	355.4	312.5	364.8
four,600	312.5	356.7	321.7	367.ii
4,700	320.4	358.one	331.0	369.8
iv,800	328.v	359.4	340.v	372.half-dozen
4,900	335.4	359.five	348.8	373.9
5,000	341.one	358.3	356.0	374.0
5,100	345.6	355.9	363.2	374.i
five,200	350.0	353.5	369.1	372.8
5,300	355.6	352.three	375.0	371.six
5,400	361.1	351.2	382.two	371.7
5,500	367.viii	351.iii	389.3	371.8
5,600	373.3	350.1	396.5	371.9
5,700	377.3	347.vii	402.3	370.7
five,800	381.3	345.iii	406.7	368.3
5,900	383.eight	341.6	412.4	367.i
six,000	387.5	339.2	416.seven	364.7
six,100	392.half-dozen	338.0	420.viii	362.3
6,200	397.6	336.8	424.9	359.nine
6,300	399.8	333.3	430.three	358.8
6,400	401.7	329.half-dozen	435.8	357.6
half-dozen,500	401.ix	324.8	439.six	355.2
6,600	400.three	318.five	442.0	351.7
half-dozen,700	394.2	313.6	442.five	346.8
6,800	385.half-dozen	308.ane	442.8	342.0
vi,900	380.8	304.four	439.6	334.vi
seven,000	374.iv	300.1	438.9	333.3