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Old 05-26-2012, 09:59 PM
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double hump heads questions

currently i have a 79 z28 with a cam intake and a carb... currently a 13.8 1/4 mile.... i have a 670 cfm street avenger on it and i think whats killing the power is the heads... im looking to go to some double hump heads due to the fact they are everywhere and are rather cheap. My plan was to get some 461 or 462 heads and spend some spare time porting and polishing them. The pistons i have are 4 valve flat top and with the 76 cc combustion chamber on the heads i have now.. the main question is going to a double hump head with a 64 cc chamber should bring me in the neighborhood of 9.5:1 compresstion, but how much more hp would i actually gain from going 8.6:1- 9.5:1 with the performer rpm intake and 670 cfm carb. the exhaust is a full header with flowmaster 40's.

would it be worth it to go to ported and polished double humps approx 400-450 invested or should i just save my money for new heads like the dart shp for 900 ??

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Old 05-26-2012, 10:12 PM
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1.21 giga-watts???!!!!
 
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That bump in compression is worth only 4%-5% more power. If you are making 300 HP, you get a whole 12 more horses.

Save your money, buy the Darts, and put a cam in it that will take advantage of the better flow numbers of the new modern heads. Don't forget, it's not just the ports that are better on the new heads, the new heart or kidney shaped chambers are head and shoulders superior to the old bathtub style chambers of double hump heads.
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Old 05-26-2012, 10:20 PM
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really??!?!

only 12??? the cam is a comp cams magnum 480 lift and 280 duration... so the cam is good due to the fact im running 3.73 with a Detroit and s street fighter turbo 350..... the rpm intake being 1500-6500 and going to the 670 cfm as opposed to the 600 that's on there now.... i thought between the intake the carb and going to 2.02's and a 64 cc would gain around 50 hp or so.....
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Old 05-26-2012, 10:26 PM
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1.21 giga-watts???!!!!
 
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You asked how much more power you would get with the compression increase. 4-5% is the answer. Sure, add after market heads and you'll gain more, like around 40. But just swapping double humps in place of the smog heads? You have the answer.
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Old 05-26-2012, 10:27 PM
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fair enough.... shp it is... thank you sir
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Old 05-26-2012, 10:29 PM
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1.21 giga-watts???!!!!
 
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Good luck.
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Old 05-26-2012, 10:29 PM
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apparently ill need it...lol
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Old 05-27-2012, 02:42 AM
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Quote:
Originally Posted by 79z28dude
apparently ill need it...lol
13.8 ain't too bad for smog heads and that old Magnum grind. Stepping up to even Vortec heads will open your eyes.
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Old 05-27-2012, 08:07 AM
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would the vortech build more than the double humps?
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Old 05-27-2012, 09:25 AM
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Yes. Vortec heads are better for street engines. It's not popular, but the fact is, "double hump" heads were obsolete in '69 when 041 "arrived". They also lack the accessory mounting holes needed for anything after '67. Not an insurmountable obstacle, just an unnecessary one.

A more modern cam grind would help, too. The Magnum series were good "in their day", but that was 20 years ago. We far prefer the Xtreme Engergy grinds today. The Lunati "VooDoo" grinds are also very good for a modern build. If running "pump gas", these are much better.

FWIW

Jim
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Old 05-27-2012, 09:56 AM
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1.21 giga-watts???!!!!
 
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79,
Any modern head with a heart or kidney shape chamber is the way to go. Edelbrock, Dart, AFR, Brodix, RHS, etc. all make excellent heads that would give comparable performance on the street. Scoggin Dickey modified Vortecs would be a good head as Cobalt suggested, the 180 cc port Bowtie Vortec would be even better. Buy whatever head you can get the best deal on. Remember, it's better to buy a bare head and build them up with quality parts.

I have the 041 heads that P-body refers to. I will be replacing next year with heads with modern chambers and port designs.

Many people are turned off by the aggresive ramp profiles of the Extreme Energy Cams. I run a EX-262 which is mild and have had no problems. Something to take into account.
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Old 05-27-2012, 10:04 AM
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im just trying to run something better than a high 13 1/4 mile.... everything else is good to go... like i said before tci street fighter turbo 350 12 bolt with locker and 3.73... when i put the heads on ill be putting on a performer rpm and a 670 street master...im just trying to get around 400 hp that should get me mid to low 13's.... i was figuring about another 50 hp minimum with the new heads , intake and carb... maybe im being foolish with my time goals idk
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Old 05-27-2012, 10:18 AM
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An engine is an air pump, more air in, more power out.

Quality heads will help you the most, with the proper support parts = cam , intake , exhaust.

I ran double hump heads on my first 'hot motor' I built when I was 16 yrs old. I am now north of 55 yrs old.

Buy the modern heads is my suggestion
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Old 05-27-2012, 03:52 PM
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Vortecs are very good. Very affordable too.
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Old 05-27-2012, 04:19 PM
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Using modified double hump heads. They can actually be made to work quite well if you know how to do them.



331 CI, pump-friendly 9.5:1 CR
K&N 14"x4" air filter, Corvette drop base and lid
Holley 600 dp, choke horn milled and blended, Primary - 69, Secondary 74, Squirters - 21
1/2" Aluminum open spacer port matched to manifold, exterior polished
Edelbrock Performer RPM, port matched, exterior polished with all extraneous castings and lettering removed
Homemade lifter valley splash shield to keep hot oil off manifold bottom
Camel hump 1.94/1.50 heads hogged out to 2.02/1.60, pocket ported, port matched, pump-friendly hardened seats, 3-angle valve job
Cylinder bores clearanced to unshroud the valves
Comp Cams 1.52:1 roller-tip rockers
Crane Cam Vintage Muscle 327/350 hp cam, 222 degrees @ 0.05, 0.447" lift (with 1.50 rockers)
Doug Thorley headers, dechromed and ceramic-coated
2.5" mandral-bent exhaust (including tips), 2" cross-over just before rear axle
DynoMax stainless Ultra Flow mufflers
Millerspeed 1-1/2 Gilmer under drive belt drive system (added after dyno run and found by Car Craft to add 10 hp @ 5,500 RPM)
Mallory Hyfire IV CD ignition box triggered off Accel points
Mallory high voltage chrome coil
Mallory spiral-wound coil wire
Mallory solid copper plug wires, ends soldered to wires
Champion plugs
37 degrees total ignition advance
Carter high volume fuel pump
Melling high volume oil pump
Open breathers
Polished aluminum high flow water pump
160-degree thermostat
Flex fan with polished aluminum spacer
Polished aluminum one-wire 100 amp alternator
Header Power Bracket
Keisler TKO600 5-Speed
Hurst shifter
3.70:1 positraction
225/60/15 Firestone Firehawk SZ50s on 7-wide Western 30-spoke Turbine Wheels
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