Quote:
Originally Posted by BruceWilkie
Sounds like you want the look. Low rise intake, exhaust manifolds? If that sorta stuff including low speed performance are concerns, this head and other high flowing heads are probably the wrong choice. You cant have a head intended to make big power at high rpm on smaller motors or big power on big cube engines and expect great low end too.
Always choose the head thats best suited for your application.
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I did not intend this to mean RA5 wont work at lower rpm. A head optimized for lower rpm range will work better at low rpm. A head intended for higher rpm power is better suited to do just that. If it happens to work acceptably at low speed thats fine. Some larger ports work acceptably that you would think otherwise.
To back what TomS is saying... One only needs to look at Fords 351c 2v head. The ports appear large but performance is zippy its generally a bigger port than a Pontiac d port for sure. The 4v versions were notably down in power at low speed. Same for std and CJ big block 429/460 fords factory iron(large and larger respectively) Part of the low speed loss was greatly attributable to cam specs! (and a choked factory ex port)
I agree cam profile can make a huge difference in how things behave.
FWIW I can drop a Pontiac 2.11 valve in the intake port of My Kaase heads with room to spare. It will still be driveable though. 413 cfm head flow, near .750 net lift cam with modest duration(288/298 adv 264/272 .050" .430 cam lift 1.83 effective rocker ratio) and modest overlap.(not a big cam duration for 528 cubes) My 528 is not yet complete but there are lower compression 521-557 ci versions with similar duration but shorter lift cams(Comp xr292 typical street grind) out there making 750 hp on the street and very driveable even with a victor and dominator and pump gas.(some on these boards would argue its not driveable) Pk power near 6500 expected. Im utilizing a tunnel ram and a pair of 750's and race gas or E85 due to my 13:1 compression. It will still be driveable and should still exceed 800 hp. Kaase says I'll have a fatter tq curve with the tunnel ram over the victor but smaller 750 carbs I'm using wont give significantly more hp over single domi victor combo. I could have opted for Edelbrock heads or Ford Racing SCJ with similar sized port slightly smaller bowls and valves. Id lose around 100 hp up top and gain very little above idle with the same cam.
The straighter the shot from the carb where the fuel is atomized to the center of the cylinder the less impact of supposedly lower velocity ports causing problems. There is more to velocity than meets the eye on a flowbench vs what is going on in the engine itself. Atmospheric pressure vs cylinder pressure, abrupt flow stops/starts from valve motion, reflected waves from those shocks, sonic wave reflections, carburetor air/fuel atomization, laminar vs turbulent flow, strength of exhust "slug" creating negative pressures behind it enhancing pressure differential as the intake opens at overlap, chamber purge of residual ex amount when the exhust closes at end of overlap. I hate to talk Ford on a Pontiac board but Kaase will tell you the flow number is merely the result of finding the best shape to meet the parameters. Much the same as my telling you folks you design a cam around an application not the LSA or .050 numbers.
The pics below are a Kasse p51 cylinder head 2.25/1.74 valve size. Top of the line in factory size/port location/bolt pattern Ford heads. (wimpy compared to pro stock pro mod heads available for the big ford.) These heads are intended for 429 thru @ 600 cid applications.
Valve im using for comparison is a 2.11" Pontiac.
I dont think Lynns revised RA5 head is too big unless your doing a Jim hand style tractor motor.