Any time you start any project it generally will be to your advantage to mentally step back, grab a large legal pad and a pen and write out, what you intend to accomplish and what you'll want to buy in parts, the potential cost and think about how well the changes may or may not work.
if your not 100% sure of the intended results it pays to do a bit of research and usually that involves either doing some related math, or in depth research on previous builds and mods others have done and what their results were.
I would Not get overly fixated on making a purchase decision, based on the advertised cylinder head flow numbers the heads your looking at might have advertised.
I can,t tell you how many times I see guys buy cylinder heads based on the peak flow numbers and then mate them to a cam lift and duration or an intake manifold that won,t come close to allowing the heads to reach their flow potential, if your heads flow lets say 280 cfm at .700 lift and your cam only has .560 lift, or your engine is matched to an automatic transmission that shifts at 5700 rpm, your engine never gets close to the cylinder heads max flow rate thats advertised.
people building any engine need to stop and do the math and think things through.
lets take that example above
a 350 engine has about 44 cubic inches of displacement per cylinder
at 5700 rpm , thats 124688 cubic inches(theres 1728 cubic inches in a cubic foot)
that means the port must flow 73 cubic ft a minute, but remember theres a 720 degree cycle and that intake port may only be open for roughly 220 degrees, or 1/3rd of the time frame, so the required flow would be closer to 219 cfm
remember that the numbers are based on steady flow at 28" of vacuum, but the engine has a 720 cycle during which the intake valve is effectively open during significantly less degrees of rotation.
in my experience the difference in performance has a great deal more to do with cam timing and compression ratio, and drive train gearing and exhaust scavenging efficiency than and port cross sectional area differences, and yes the larger ports tend to be noticeably better in the upper rpm ranges and keep in mind the weak link in the chain idea, here.
basically , if the intake manifold air flow is restrictive and/or the cam timing , and exhaust scavenging efficiency in the upper rpm range won,t allow the port to reach maximum rated flow the heads will never reach the rated flow, but if the ports so small (cross sectional area) the port car reach a point that it cant keep up with the air flow rate intermittent pulsed demand.
or put a different way that AFR 180 cc head may give impressive torque numbers at some limited rpm ranges but
Id be betting heavily that the 195cc or even a 210cc port head, even on a fairly small 350 displacement engine, would produce better mid rpm range and peak hp numbers if the engines set up to use the extra potential air flow they can provide.
that of course assumes the intake, cam timing and exhaust scavenging will also allow the larger ports to reach their flow rate potential.
obviously if your other components can,t keep up theres no advantage to using the larger ports with their potentially higher flow rates.
look at this chart below , theres less than a 6% difference in port cross sectional area between a 180cc and a 210cc AFR cylinder head port, Id bet a good deal of cash that its not the AFR heads, (BRODIX, TRICKFLOW,DART,PROFILER, )
(or most any other 195cc-210cc heads) you selected that will be the restriction too power, but the fact that the cross fire intake ,cam selected and drive train gearing and exhaust scavenging(and related flow restriction) are more major factors in determining the power curve, If it was my car Id go with the 195cc AFR heads
and I doubt youll see any measurable lower rpm loss as a result and your marginally more likely to see some gains in the upper rpm ranges (IF you select decent matched components that potentially do allow the increased air flow.
here's a chart FROM THE BOOK,HOW TO BUILD BIG-INCH CHEVY SMALL BLOCKS with some common cross sectional port sizes
View attachment 8970
on the better 23 degree SMALL BLOCK AFTERMARKET HEADS THERE'S ABOUT 5.5 INCHES OF INTAKE PORT LENGTH ON AVERAGE FROM INTAKE GASKET TO THE BACK OF THE INTAKE VALVE AT THE FAR EDGE
USE THE CALCULATORS to match port size to intended rpm levels... but keep in mind valve lift and port flow limitations
http://www.wallaceracing.com/runnertorquecalc.php
http://www.circletrack.com/enginetech/1 ... ch_engine/
calculate horse power from intake port flow rates
http://www.wallaceracing.com/calcafhp.php
http://www.wallaceracing.com/calchpaf.php
http://www.wallaceracing.com/ca-calc.php
http://www.wallaceracing.com/max-rpm.php
http://www.wallaceracing.com/lpv.php
http://www.wallaceracing.com/chokepoint.php
http://www.wallaceracing.com/chokepoint-rpm.php
http://www.wallaceracing.com/area-under-curve.php
http://www.wallaceracing.com/piston-speed-velocity.php
http://www.wallaceracing.com/header_length.php
Volume (CCs) of Head Gasket
CCs of Head Gasket = Bore x Bore x 12.87 x Thickness of Head Gasket
COMMON SBC INTAKE PORTS
felpro # 1204=Port Size: 1.23" x 1.99"=2.448 sq inches
felpro # 1205=Port Size: 1.28" x 2.09"=2.67 sq inches
felpro # 1206=Port Size: 1.34" x 2.21"=2.96 sq inches
felpro # 1207=Port Size: 1.38" x 2.28"=3.146 sq inches
felpro # 1209=Port Size: 1.38" x 2.38"=3.28 sq inches
felpro # 1255 VORTEC=Port Size: 1.08" x 2.16"-2.33 sq inches
felpro # 1263=Port Size: 1.31" x 2.02"=2.65 sq inches
felpro # 1266=Port Size: 1.34" x 2.21"=2.96 sq inches
felpro # 1284 LT1=Port Size: 1.25 x 2.04''=2.55 sq inches
felpro # 1289 FASTBURN=Port Size: 1.30" x 2.31" 3.00 sq inches
http://users.erols.com/srweiss/calccsa.htm
Your RPM computed from your Cross Sectional Area of 1.95
(the smaller AFR HEADS)
and Bore of 4.03 and Stroke of 3.75 is 5,569.12 .
Your RPM computed from your Cross Sectional Area of 2.05
(the Larger AFR HEADS)
and Bore of 4.03 and Stroke of 3.75 is 5,854.72 .
you,ll barely notice the about 300 rpm shift in the power band on the lower part of rpm range but appreciate it much more on the upper edge of that power curve
heres a chart FROM THE BOOK,HOW TO BUILD BIG-INCH CHEVY SMALL BLOCKS with some common cross sectional port sizes
(measured at the smallest part of the ports)
USE THE CALCULATORS
http://www.rbracing-rsr.com/runnertorquecalc.html
http://www.wallaceracing.com/chokepoint.php
http://www.wallaceracing.com/header_length.php
http://www.superchevy.com/how-to/en...-0902-chevy-engine-port-variations-measuring/
http://www.hotrod.com/articles/choosing-the-right-camshaft/
http://garage.grumpysperformance.com/index.php?threads/bits-of-383-info.38/
ID suggest you select from heads from these sources
Jegs; 800/345-4545; Jegs.com
Summit Racing; 800/230-3030; SummitRacing.com
Scoggin-Dickey Parts Center; 800/456-0211; ScogginDickey.com
TRICKFLOW
http://www.trickflow.com/egnsearch.asp? ... 4294867081
http://www.trickflow.com/customerservice
1-330-630-1555 • 1-888-841-6556
BRODIX
http://www.brodix.com/heads/heads.html
479.394.1075
DART
http://www.dartheads.com/products/cylinder-heads
Dart Machinery; 248/362-1188; DartHeads.com
AIR FLOW RESEARCH
http://www.airflowresearch.com/
toll free: 877-892-8844
tel: 661-257-8124
Patriot Performance
Patriot Performance; 888/462-8276; Patriot-Performance.com
RHS
http://www.racingheadservice.com/rhs/cylinder-headshtml
Toll Free: 877-776-4323
Local: 901-259-1134
EDELBROCK
http://www.edelbrock.com/automotive_new ... main.shtml
Edelbrock; 310/781-2222; Edelbrock.com
BMP (world products)
http://www.theengineshop.com/products/cylinder-heads
Tel: 631-737-0372
Fax: 631-737-0467
BUTLER PERFORMANCE
http://www.butlerperformance.com/products/cylinder_heads/cylinder_head_labor.html
866-762-7527
BLUE PRINT ENGINES
http://www.blueprintengines.com/ind...sb-chevy-aluminum-cylinder-heads-cnc-machined
1800-483-4263
PRO-FILER
https://www.profilerperformance.com/
937‐846‐1333
RELATED threads and info you may need
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http://garage.grumpysperformance.com/index.php?threads/crossfire-sleeper.12732/page-2#post-69838
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