BBC 454 with 820 heads question - Team Camaro Tech
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post #1 of 5 (permalink) Old Mar 30th, 18, 05:11 PM Thread Starter
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Tom Anderson
 
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BBC 454 with 820 heads question

Hi guys I have a chance to pick up a rebuild 454 that's said to have a performance cam with a Edelbrock high rise aluminum intake , It has a set of 820 heads on it , how well do the 820 heads perform ? I read they came on LS5s and were rated at 390 hp with 500 ft of tq . I think that would be a nice engine for my 68 and be a decent tire fryer . What do you think guys ? I was going to change the heads but from what I read those heads don't sound to bad if fact they sound pretty good . Thanx in advance for everyone's input ..
I want to hear from you Big Dave because I know you will have some good input.
Tom
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post #2 of 5 (permalink) Old Mar 30th, 18, 08:52 PM
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Dave
 
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Re: BBC 454 with 820 heads question

Stock Chevy casting number 3993820
Oval Port Intake with volume of 253 cc: Exhaust 114 cc
Chamber Volume 113 cc
Flow rate at 28 inches of water, 4.125" fixture
2.06 Flat steel Intake, 1.72" exhaust (also flat steel)
at 0.100" of valve lift flows 71/52 cfm
at 0.200" of valve lift flows 145/105 cfm
at 0.300" of valve lift flows 227/144 cfm
at 0.400" of valve lift flows 260/176 cfm
at 0.500" of valve lift flows 279/190 cfm
Test by Stan Weiss World Wide Enterprises

Same Chevy casting with bigger 2.30" Manley swirl polished tuliped face stainless steel intake, and 1.90 " Inconel exhaust valve on a 4.31 inch fixture at 28 inches after being pocket ported by Weingartner Racing, Brez flow rate increased to:
at 0.200" of valve lift flows 156/- cfm
at 0.300" of valve lift flows 220/- cfm
at 0.400" of valve lift flows 273/- cfm
at 0.500" of valve lift flows 295/- cfm
at 0.600" of valve lift flows 315/- cfm
at 0.700" of valve lift flows 337/- cfm
at 0.800" of valve lift flows 350/- cfm

This illustrates two things. Bigger valves make a big improvement in head flow, and fixtures size can bias the readings (you are no longer comparing apples to oranges but and orange to a tangerine). Now note the difference in flow rate between stone stock and the modified (and almost as expensive as an AFR aluminum head). Is that 26 cfm difference worth the expense? No it isn't unless you want to win at any cost and class rules say you are stuck with this head. That price of that 50 horse difference would be better spent on better heads (with a raised exhaust port; which is what is holding this head back). In a stock BBC head the exhaust port is the cork in the bottle.

Your question and the answer to why I typed all of this in response is a generality (rule) in engine building. You take your peak flow rate at the highest valve lift your cam produces (I doubt if your cam can pick the valves up into the 0.800" range), and double it. That is an estimate of the peak horsepower potential of the head. In this case about 560 horsepower max assuming everything else works in your combination (that isn't going to happen either statistically: the odds just are not in your favor).

Big Dave
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post #3 of 5 (permalink) Old Mar 30th, 18, 09:37 PM Thread Starter
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Tom Anderson
 
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Re: BBC 454 with 820 heads question

Big Dave
I knew you would have a good answer but your way over the top for me can you break it down to a basic yes or no if the 840 heads are decent . This is just a street car and it will not be going to the track . I am just looking for something that will pull decent and not be over the top with 650 hp . A 390 horse that has 500 tq would be more then enough for me and I thought for my reading this motor should do it . This motor is a little above a stock LS5 since it has a cam and intake and even is it were a small lift cam it's still better then stock . I was going to pull the heads and go aluminum but I don't wanna throw good money out the door
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post #4 of 5 (permalink) Old Mar 31st, 18, 05:54 AM
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mike
 
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Re: BBC 454 with 820 heads question

I think Dave gave you the facts and left the yes or no up to you. If 390 hp is ok with you don't spend the money. If you are trying to eak out every last pony out of your engine then get better heads.
Sounds to me getting the aluminum heads would be throwing money out the door in your case. If you want to get a jolt to your hp then maybe a small wet nitrous system when you want an extra 100 or so hp(cheaper then heads).
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post #5 of 5 (permalink) Old Mar 31st, 18, 09:03 AM
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Dave
 
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Re: BBC 454 with 820 heads question

Or change the rear gear to a higher number. Acceleration is all about torque. Gears multiply torque. Won't change your gas mileage as a BBC delivers dismal mileage no mater what you do.

Big Dave
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