Oval or Square Port on my 496 BBC? - Hot Rod Forum : Hotrodders Bulletin Board
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View Poll Results: Oval ports or Square on my particular 496 build?
Oval ports all the way, torque baby! 4 80.00%
Square ports, let that baby breathe! 1 20.00%
Voters: 5. You may not vote on this poll

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Old 06-02-2010, 07:33 PM
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496 BBC, TH400 12 bolt w/ 3.73
 
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Oval or Square Port on my 496 BBC and more...

Hey guys, I know there are a ton of threads relating to this question, however I am right on the border for cubes to choose between the two so would really appreciate some advice. Please dont flame me too bad lol!

So...

I am upgrading from a pair of oval port gm 781 heads to a set of aluminum oval or square ports. I am considering going with a set of the bare procomps and building them with the Lunati kit designed for my cam along with stainless Manley valves. I will be installing a 496 stroker kit (Eagle) in my 454 and am wondering if a good set of ovals will flow enough to get me to the 550-575 (would looove to crack 600) crank hp range. I am using an Eagle cast crank so will for sure be keeping my rpm below 6500, plus my valve springs are 142/402 so wont take any more rpm than that. Also my intake and cam all all designed for sub 6500 operation. Here are the parts I am using on this build:

496 Eagle cast crank stroker kit
18cc Mahle Forged Dome pisons (10.2 to 1 w/ 118cc chambers)
781 GM oval port heads
Lunati Hyd Roller Cam (241/249 @.050 w/ .625 lift exh/int)
Lunat Street Series Retro Lifters
PRW 1.72 Aluminum Roller Rockers
Edelbrock Air Gap RPM oval port intake
Holley 850 double pumper w/ annulars
1 7/8 Headers, 2 1/2" dual exhaust
TH400 w/ B&M Nitrous Holeshot converter (3000)
12 Bolt posi w/ 3.73 gears

This is a street build w/ the occassional strip use (twice a year or so). I am more concerned with torque and throttle response than peak power at 6000+ so thats why I was leaning towards the oval ports.

Also I was wondering if my mechanical fuel pump that flows 110 gph will be enough for my 496 needs?

What kind of power differences should I expect using oval vs square?

Thanks for all the help guys! Mike
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Last edited by ChevelleSS; 06-02-2010 at 07:51 PM.
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Old 06-02-2010, 08:12 PM
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BOBCRMAN@aol.com likes to start with bare ProComp heads. He should be along in a little to line it all out for you.

As far as fuel delivery, I use an old formula that figures the need, then doubles it to account for pushing against inertia through relatively small lines. For instance, a motor will normally use about 0.5 lbs per hp hour. So, at 600 hp, the motor will use 300 lbs per hour. Gasoline weighs about 6 lbs per gallon, so 300 divided by 6 equals 50 gallons per hour. Doubling that calls for a pump that will deliver 100 gallons per hour.
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Old 06-02-2010, 08:26 PM
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Quote:
Originally Posted by techinspector1
BOBCRMAN@aol.com likes to start with bare ProComp heads. He should be along in a little to line it all out for you.

As far as fuel delivery, I use an old formula that figures the need, then doubles it to account for pushing against inertia through relatively small lines. For instance, a motor will normally use about 0.5 lbs per hp hour. So, at 600 hp, the motor will use 300 lbs per hour. Gasoline weighs about 6 lbs per gallon, so 300 divided by 6 equals 50 gallons per hour. Doubling that calls for a pump that will deliver 100 gallons per hour.

Thanks for the advice, much appreciated. I am new here and hope others will chime in on my head dilema along with some power expectations. Here is a pic of my 69 guys, thanks for the hand! Mike
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Old 06-03-2010, 01:59 AM
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Old 06-03-2010, 05:06 AM
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With that cam and street use I'd go oval.
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Old 06-03-2010, 05:43 AM
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Quote:
Originally Posted by BBCMudbogger
With that cam and street use I'd go oval.
Can you enlighten me to your reasons please? Thanks! Mike
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Old 06-03-2010, 05:51 AM
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I agree. Oval ports will work great. If you were running a bit more radical cam. Aftermkt heads would be the way to go. I try to use the .660-.680 lift cams. As big blocks like lots of lift..

I did a re fresh on a big chevy for a customer recently. He runs it in a 55 chevy old time gasser. He's getting older ( late sixties) and wanted to "tame down" the old rat. Removed a .700+ cam. Went to a .680 roller cam. Changed from old ported Rect port iron heads to oval aluminum aftermkt. heads (Pro Comp). Dropped compression back a bit.

Just for grins he took the fresh car to the track. It went faster than when it was a serious drag car. He now has brought his big block Jeep to the shop for a "de-tune"....
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Old 06-03-2010, 06:27 AM
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Sounds like you're after some serious power. Regardless of heads, you might consider a solid roller cam/lifters.

The BBC has a heavy valvetrain, and decent lift requires a lot of spring pressure to control things.
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Old 06-03-2010, 06:51 AM
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Rect ports need rpm to breath you gonna turn 7k on the street?...LOL the BBC does have a heavy valvetrain but maybe using 11/32" valve stems instead of 3/8" and titanium retainers lighten it some.What is the rpm range of the cam you speced?
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Old 06-03-2010, 07:10 AM
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Quote:
Originally Posted by BBCMudbogger
Rect ports need rpm to breath you gonna turn 7k on the street?...LOL the BBC does have a heavy valvetrain but maybe using 11/32" valve stems instead of 3/8" and titanium retainers lighten it some.What is the rpm range of the cam you speced?
Its the Lunati Voodo 60213 Hyd Roller Cam. Here is what the website says:

"Hydraulic roller, rough idle. Serious street/strip camshaft. Needs 10.5:1 compression ratio, 3000-3500 RPM stall speed converter and 3.73 or better rear gears. Works well with plate style nitrous systems or smaller superchargers with up to 12 PSI boost.

•Advertised Duration (Int/Exh): 292/300
•Duration @ .050 (Int/Exh): 241/249
•Gross Valve Lift (Int/Exh): .625/.625
•LSA/ICL: 110/106
•Valve Lash (Int/Exh): Hyd/Hyd
•RPM Range: 2600-6200"

I called Lunati direct before my initial setup decisions and they said this cam would be good to 6200. Is this true with my setup? 142/402# valve springs, oval ports, 496 cubes?

Anybody see any mismatches in my setup?

What kind of hp peak and curve would one expect w/ ovals?

Thanks again for the help everybody!

Last edited by ChevelleSS; 06-03-2010 at 07:22 AM.
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Old 06-03-2010, 08:59 PM
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Quote:
Originally Posted by ChevelleSS
I called Lunati direct before my initial setup decisions and they said this cam would be good to 6200. Is this true with my setup? 142/402# valve springs, oval ports, 496 cubes?
Would be true with ANY hydraulic roller profile. The heavy lifter tends to leave the lobe profile at speeds in excess of 6200. It's just a rule of thumb with hydraulic rollers. You want revs, install a solid roller with rev kit springs in the cam valley.
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Old 06-04-2010, 05:16 AM
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I assume you have someone to check the balance on the assembly right?
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Old 06-04-2010, 11:33 AM
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Quote:
Originally Posted by BBCMudbogger
I assume you have someone to check the balance on the assembly right?
Oh ya, my local machine shop is doing the bore/hone/deck/balance fresh for the 496... Thanks for caring man! LOL!
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Old 06-06-2010, 07:04 AM
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Any guesses to my expected hp/quarter times with this setup?
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