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-   -   428 fe with holley 850 jetting recommendations? (http://www.clubcobra.com/forums/holley-tuning/145768-428-fe-holley-850-jetting-recommendations.html)

Soundkillr 03-23-2022 04:45 PM
428 fe with holley 850 jetting recommendations?
 
I have a 428fe with a holley 850 double pumper. Im currently rebuilding it, and while its apart I would love jetting recommendations for the top end. Car runs awesome until 4500 where it just stops making power. Ive got edlebrock rpm heads and intake...but unsure of cam...
The car has two power valves. Both 6 both blown. I need new power valves and was told to try 6.5 as I have about 15 or 16 inches of vacuum. I also have 80 idle jets all the way around...and was told to try 83 in the rear bowl. Car is supposed to have 550hp.
Runs great till about 4500 and runs out of power. Any suggestions?
This is a non vacuum advance set up. Ive seen people do a power valve delete in the rear bowl...but im unsure what that would gain me

saltshaker 03-23-2022 04:50 PM
fuel pump
 
Quote:
Originally Posted by Soundkillr (Post 1504628)
I have a 428fe with a holley 850 double pumper. Im currently rebuilding it, and while its apart I would love jetting recommendations for the top end. Car runs awesome until 4500 where it just stops making power. Ive got edlebrock rpm heads and intake...but unsure of cam...
The car has two power valves. Both 6 both blown. I need new power valves and was told to try 6.5 as I have about 15 or 16 inches of vacuum. I also have 80 idle jets all the way around...and was told to try 83 in the rear bowl. Car is supposed to have 550hp.
Runs great till about 4500 and runs out of power. Any suggestions?
This is a non vacuum advance set up. Ive seen people do a power valve delete in the rear bowl...but im unsure what that would gain me
what kind of fuel pump do you have? I have a 428 with a 750dp and it stoped pulling around 5300rpm 3rd gear… add’d a carter electric pump to the fuel line and it pulled pass 6300rpm on the track .
Jon

Soundkillr 03-24-2022 06:01 AM
Currently running the holley blue pump and set at 6 psi with no fuel return.
So I suppose 80 jets squared should be enough?

S1965C 03-24-2022 03:21 PM
Normally you would square the jets if you block off the power valves. I'm thinking you are leaving power out of the car (on the secondaries) with an 80, and/or creating a high rpm lean condition.

Soundkillr 03-24-2022 05:49 PM
Quote:
Originally Posted by S1965C (Post 1504661)
Normally you would square the jets if you block off the power valves. I'm thinking you are leaving power out of the car (on the secondaries) with an 80, and/or creating a high rpm lean condition.
From what ive understood...the power valve in the back when active increases thenflow to over 80. No power valve and I should run 86 or something. So with a power valve maybe I ahould go to 83?
I could be completely wrong...but thats how I understood the power valve to operate.

MKS427 03-25-2022 03:58 AM
You may want to start here. I suspect you have too much carburetor. Engine builders use ~780 cfm carbs for similar engines at 550hp.
https://www.motortrend.com/how-to/ch...20%3D%20616.32).

mrmustang 03-25-2022 04:24 AM
Quote:
Originally Posted by MKS427 (Post 1504671)
You may want to start here. I suspect you have too much carburetor. Engine builders use ~780 cfm carbs for similar engines at 550hp.
https://www.motortrend.com/how-to/ch...20%3D%20616.32).


X2

Since there is no mention of cam specs, engine compression, valve sizes, intake type, and ignition on the OP's engine, my thought is also a carb that is too large for the combination of the above mentioned items.

Bill S.

saltshaker 03-25-2022 05:00 AM
I have a 750 do on my 428 I’m using 75/83’s … my suggestion is to get it chassi dyno tune
the tuner can adjust the air bleeds to correct the air fuel ratio and play with the squirters so it won’t hesitate off the line. I use Nickerson Performance in Pa and my Cobra runs like it’s fuel injected
Jon

DanEC 03-25-2022 05:21 AM
The 15 - 16” vacuum and 550 hp from a 428 sounds a bit inconsistent to me, but maybe if you have a good roller lifter cam. Should still pull past 4500 rpm and far more. It’s hard to beat a vacuum operated secondaries 750 for responsive street use. The engine gets the air flow it demands and no more.

Soundkillr 03-25-2022 06:28 AM
Quote:
Originally Posted by mrmustang (Post 1504673)
X2

Since there is no mention of cam specs, engine compression, valve sizes, intake type, and ignition on the OP's engine, my thought is also a carb that is too large for the combination of the above mentioned items.

Bill S.
Understood. Thanks for the suggestions guys. Im all ears. Unfortunately for me I dont have the internal specs. Im going to have to assume they are out of the box edlebrock performer rpm heads and performer rpm intake.

Ignition is msd 2 and black coil. Coil cap plugs and rotor All new...just for the sake of taking that off the table as an issue.

I dont doubt a dyno is the way to go...but im hoping to get it closer than what it is. It runs fantastic all the way around...no hesitation except for the top end wot and runs out of power at 4500. It will still pull above that...but its just out of power at that point.

mrmustang 03-25-2022 12:16 PM
Quote:
Originally Posted by Soundkillr (Post 1504677)
Understood. Thanks for the suggestions guys. Im all ears. Unfortunately for me I dont have the internal specs. Im going to have to assume they are out of the box edlebrock performer rpm heads and performer rpm intake.

Ignition is msd 2 and black coil. Coil cap plugs and rotor All new...just for the sake of taking that off the table as an issue.

I dont doubt a dyno is the way to go...but im hoping to get it closer than what it is. It runs fantastic all the way around...no hesitation except for the top end wot and runs out of power at 4500. It will still pull above that...but its just out of power at that point.
750CFM DP is recommended, as you can only jet and tweak the 850CFM DP so much.


Bill S.


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