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Discussion Starter #1
How much spring pressure do you need on the seats and over the nose at 28Lbs boost . 9000rpm . SBC
 

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Not sure what it is . But i would think it is around 520 lobe lift . It is a 55mm cam with 937 lifters and a 850 wheel .
 

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That's the problem. I bought this engine used. The engine builder will not give me any specs. The spring that is there is a Manley 448 Installed at 2.100. They all test good 360 , but I have a miss at 7300 and up under load in sec and third gear . Sounds like it is on a rev limiter bs3 box and a 7531 . All limiters are turned of . Cylinders all leak down good 2-4% Crank trigger air gap is .065 and dist Is phased at 20* Plug gap is 18 and they are 5671-9 I am at a loss Not sure where to go now.
 

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That's the problem. I bought this engine used. The engine builder will not give me any specs. The spring that is there is a Manley 448 Installed at 2.100. They all test good 360 , but I have a miss at 7300 and up under load in sec and third gear . Sounds like it is on a rev limiter bs3 box and a 7531 . All limiters are turned of . Cylinders all leak down good 2-4% Crank trigger air gap is .065 and dist Is phased at 20* Plug gap is 18 and they are 5671-9 I am at a loss Not sure where to go now.
The cam might have grind # on front or back. Even if the spring test 360 coil bind is important. You never get true lift everything together i have like .040 coil bind with way more boost. That is good pressure if setup right and the cam has soft lobes. I always run 30-40 more psi than what the cam calls for because they wear. I would check crank trigger wires for interference or plugged in backwords. i have my trigger gapped .045...I would check grounds and check msd to coil wires for interference maybe wind them up.
 

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What ratio rocker are you using with that cam. If you are a 1.7 then you are not bad but if they are 1.8's then you are extremely close to coil bind with that 2.100" installed height.
 

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Discussion Starter #12
It does not go to coil bind . That is good . You can here the miss on the top end . It will not pull up top .
 

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400 pounds at seat to keep you from blowing valves open ans boost does play a role in what spring to use.
Actually has a very modest impact. There are dynamics going on on both sides of the valve not just one side.

Many years ago when I was running a 394" SBC with 2.10 titanium intake and running through the tramps at 9300 rpm I ran in the 260 lbs seat and it never missed a beat.

If you've got over 300 seat that's plenty in my experience.

Now a BBC is another story.

Blessings............Ron
 

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I've never understood the argument that boost plays a role in spring pressure requirement. The boost is on both sides of the valve.
 

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That's the problem. I bought this engine used. The engine builder will not give me any specs. The spring that is there is a Manley 448 Installed at 2.100. They all test good 360 , but I have a miss at 7300 and up under load in sec and third gear . Sounds like it is on a rev limiter bs3 box and a 7531 . All limiters are turned of . Cylinders all leak down good 2-4% Crank trigger air gap is .065 and dist Is phased at 20* Plug gap is 18 and they are 5671-9 I am at a loss Not sure where to go now.

Had same type problem when ignition went out. Would free rev or burnout fine, but under load it would start bangin and popping like it was on a limiter at about 5k. I would change coil and msd and see if it fixs it. Maybe borrow one from a friend?
 

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You do have compensate for boost,, if you have 28 psi trying to push the intake open then you need 28x the surface area in square inches more spring pressure'' a 2.25 valve will have 3.5 square inches of surface area,, 3.5x28psi = 98 psi more than you would run on a na engine.. Some will say to subtract out 1bar {1 atmosphere, or about 15 psi} would leave you with 83 psi more seat pressure..
But,, I doubt spring pressure is your problem in this case. Sounds like an ignition problem,, you might check the injector opening time under configuration,, if you have bosch it should be .80 from 13.9v up.. Billet atomizers can be less..
 

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if you have bosch it should be .80 from 13.9v up.. Billet atomizers can be less..
My classic is setup using .60 in configuration with 160 injectors. I've never played with this but i'm having trouble tuning AE vs Map engine going lean in and out of throttle or on the brake. I know people always shoot for 400lbs on the seat no matter what. My cam only calls for 280 closed seat and it is very radical for a boosted 360 SB. I have it setup 350 with very little coil bind clearance. My engine is close to 40 psi i feel aggressive cam lobes are worse and longer rocker ratios are a plus where i'm a 1.72 with a dual spring.
 

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This is handy,,depends on what fuel pressure you are using {more pressure = more time}. From what I have seen 350-400 on the seat of a boosted sb engine seems fine up to 9500 rpm provided the valve train geometry is correct.. We have noticed when the springs get weak the engine doesn't misfire, just won't rev as high and looses high rpm power..
 

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My classic is setup using .60 in configuration with 160 injectors. I've never played with this but i'm having trouble tuning AE vs Map engine going lean in and out of throttle or on the brake. I know people always shoot for 400lbs on the seat no matter what. My cam only calls for 280 closed seat and it is very radical for a boosted 360 SB. I have it setup 350 with very little coil bind clearance. My engine is close to 40 psi i feel aggressive cam lobes are worse and longer rocker ratios are a plus where i'm a 1.72 with a dual spring.
When we had classic fast used 1.0,, with 160 Bosch,, don't know why but always ran fine,, we did have a customer that has his set at .50 and it ran like there was a limiter set at 5000..
I have always had my Gen 7 set at .80 with the billet atomizers and ran fine,, but after studying this chart {downloaded of the Holley EFI web site} I will try less..
Injector phase angle has an effect on proper tune also...
 
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