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Old 04-03-2013, 05:08 AM
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Help with Heads

i have a sbc 406 with eagle forged crank,eagle forged rod 5.7,kb pistons,xr288-10 cam..236 intake,242 exhaust,110 lobe @.05,edelbrock performer intake,holley 750 mech secondaries......i currently have the jegs aluminium heads 180cc intake,72cc combustion chamber, 2.02 intake,1.6 exhaust.......this motor is just not making anykind of power like i think it should.....should i change the heads and if so what should i get? i just think i need to be making more power. how does this setup look or what should i change to make power. any input will be appriciated.

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Old 04-03-2013, 07:44 AM
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what are the tune up specs you are currently using?How many CFM do the jeg heads flow?
what makes you think its not performing correctly?
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Old 04-03-2013, 07:48 AM
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Timing!!
What's your initial timing?
You need lots of initial with that setup.
18-20 initial. 14 in the dizzy and another 10 from the vac advance all in by 3400.
Also. What car? What trans? Rearend? Convertor?
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Old 04-03-2013, 07:58 AM
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71 chevelle.turbo 350.10 bolt w/3.73.....2800 convertor
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Old 04-03-2013, 08:19 AM
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nvyblue03
would you post tune up specs and clearances please,and CR
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Old 04-03-2013, 09:11 AM
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Quote:
Originally Posted by nvyblue03 View Post
i have a sbc 406 with eagle forged crank,eagle forged rod 5.7,kb pistons,xr288-10 cam..236 intake,242 exhaust,110 lobe @.05,edelbrock performer intake,holley 750 mech secondaries......i currently have the jegs aluminium heads 180cc intake,72cc combustion chamber, 2.02 intake,1.6 exhaust.......this motor is just not making anykind of power like i think it should.....should i change the heads and if so what should i get? i just think i need to be making more power. how does this setup look or what should i change to make power. any input will be appriciated.
There can be a lot of tuning problems but let's start on the heads, these are great heads for a 350, they just can't feed a 406. The ports on these heads can't feed the valves, larger valves would be of no help. This engine, as cammed, needs a 210 cc head. 1.6 rockers would be minimally helpful against 1.5s as they will kick the valve open further, faster on the ramp which will let the port feed the valve sooner and stretch out the time the port spends at maxed flow thus will feed the cylinder a little better as it will act like the duration of the cam was extended a bit. Over the top of the lobe the additional lift would not be helpful as the port just can't feed the valve anymore than it is. A longer duration cam would be helpful but then you get into how do you get the compression up to counter the later than you already have closing intake valve. So if you mess with the cam you're going to also mess with the heads and maybe the pistons to get a crown shape that dials the compression in. This can get complicated and expensive pretty quickly.

In the end the only real solution is a large port head while keeping a careful eye on Dynamic Compression Ratio (DCR) while your there.

Bogie
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Old 04-03-2013, 10:18 AM
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agree with fb,nvyblue03 needs to participate here
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Old 04-03-2013, 10:36 AM
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Without knowing the piston crown configuration, nobody here can tell you anything. If the pistons you have in the motor now are flat-tops, the static compression ratio could be 10.5:1, if they're 30cc dished pistons, the static compression ratio could be 8.5:1. Until we know the skinny on the pistons, we're flying blind.
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Old 04-03-2013, 11:27 AM
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i am running 10.5:1 ratio....i have 1.6 rockers as well. f-bird...what kind of cam should i be running....also would it be worth the money to get my heads or ported or go with something different. i feel decent power down low but not much in the mid range.....i am going to check my timing this afternoon.. what would be accurate timing do yall think?thanks
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Old 04-03-2013, 11:38 AM
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read post # 6 and the others
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