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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, 08:20 AM
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Timing should be 24-26deg at idle 34-36deg @ max advance (a 10deg advance bushing)

Jetting 70 to 74 pri 80 to 84sec 4.5" power valve .031 shooters.

What is the 1/4 mile ET and MPH?

What is the car lacking? low rpm torque, top end power?, RPM????

What is your power goal.... ET/MPH goal from that combo?

Both the cam and the 180cc heads are small for big serious horsepower.
But it should be no slouch on the street.

Exhaust system is critical too. It has to flow to make power. Test with open exhaust and collector extensions.

The MPH from a 1/4 or 1/8 mile drag test tells the tale of how much HP it is making. (with known car weight w driver)

While I really like the Jegs/Profiler aluminum heads (If that is the head you have), I would not have used the 180cc head on this 406 motor.
(It can be improved a lot with porting)

Last edited by F-BIRD'88; 04-03-2013 at 08:30 AM.
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Old 04-03-2013, 08:35 AM
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If this motor has a dished piston or a flat top piston and (72cc heads) and the Deck clearance was not dialed in
("0 deck") then the cr will be modest.
What piston? what installed TDC piston deck clearance?

If you want 500hp you can get it but you will have to change things.
The cam is not serious enough. The converter and gears are not serious enough if you are going drag racing.

But you need a performance baseline to verify your hunch on this cars performance.
(a day at the drags to get some time slips..."test and tune" on sticky tires)
I see a 110-112 MPH (1/4 mile) car here.
Assuming correct tune up/setup.

When ever dealing with a combo that is not performing to expectation:
Always start with doing a basic engine cranking compression test first to verify general engine health. FIRST
real simple.

DId I mention EXHAUST SYSTEM and fuel system

Last edited by F-BIRD'88; 04-03-2013 at 08:50 AM.
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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, 09:58 AM
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You are jumping the gun in assuming the heads are the cork in this combo.
(the 180cc heads would not have been my choice for this motor but they can be tweeked easily.)
The cam is lame.
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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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Old 04-03-2013, 02:15 PM
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Get it tuned up/set up correctly and get a performance baseline (Some time slips) with sticky tires
before making any assumptions.

A out of the box distributor curve will not be right.
The basics are in my posts.
This is a good time of year for track testing. The ET slip never lies. Get some sticky tires.
You need to clairify exactly which Jegs heads you have.
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