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Discussion Starter · #1 ·
Kinda curious what peoples opinions are, and would make a good discusion. just like it sounds....how much boost do you thing is too much...for your engine that is.

Use me for an example; 5.4 DOHC (Navi based), just over 8.5:1 c/r, everything bottom end is forged (Manley H-beams, and pistons), Studs all the way around, SHM blower cams, billet oil pump, Sullivan intake...ect..

What would you say should be my maximum boost level...and why

Chris
 

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I tend to use the block, fuel system, and blower potential as the limiting factor. Boost is nothing more than a measure of restriction.

I am at 12 psi and 460 or so RWHP according to my cars weight and trap speed. For me on the stock block I would be scared to add any more boost even though my blower is capable of much more.
 

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Discussion Starter · #4 ·
Dark 5.0 - Do you mean the physical block or are you talking about the internals?


buddha - Lets say both. But to be realistic, lets focus on pump gas.

I should have posted also that my fuel system should not to be a limiting factor. I'm running; return style, sumped tank, two individually fed Bosch 044's plenty of fuel line size and 80lb injectors.
 

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All things being equal, the max boost you should run is right below the boost at which you have a failure.:rolleyes:

Sorry for the dumb comment, but I couldn't resist.
 

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On mine I am talking about the block its self. If the fuel system or block isnt a limiting factor it all comes down to blower potential and having an adequate valve train for a high boost application. I went to an NHRA event a couple of years ago were one of the imports was running 50 psi:eek:
 

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Discussion Starter · #7 ·
Blown 85 - hmmmm....if it were only that easy huh...lol. But your absolutely right!!!

Dark - Why do you thing the block itself is a concern? Im right there with ya, Ive seen tons of folks running crazy high boost numbers and that's why I posted this.

Trying to get alll the info we can out there from those who have the experience, and to try and figure what my max should be as well. Seems like it comes down to good parts for the obvious reasons (strength) and proper fuel management (tune)... but is it that simple, I doubt it. What additional stress is created by increased boost?
 

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Blown 85 - hmmmm....if it were only that easy huh...lol. But your absolutely right!!!

Dark - Why do you thing the block itself is a concern? Im right there with ya, Ive seen tons of folks running crazy high boost numbers and that's why I posted this.

Trying to get alll the info we can out there from those who have the experience, and to try and figure what my max should be as well. Seems like it comes down to good parts for the obvious reasons (strength) and proper fuel management (tune)... but is it that simple, I doubt it. What additional stress is created by increased boost?
I think he is saying the block is a restriction because he's still using the stock block which is known to fail over/around 500hp level.....
 

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when you blow the heads off the block, then you'll know it was too much. ;) Just ask the tractor pull guys.
 

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Discussion Starter · #10 ·
Well I surely hope to find out a cheaper way for those of us to figure this out.... lol. Any experts out there that will pass on some info here?
 

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Dark 5.0 - "Boost is nothing more than a measure of restriction." That is a very accurate statement. An engine is nothing more that an air pump the more air that will go through it the more power you will make. You can have a Novi 2000 on a 331 making 12 lbs then change the pulley and make 15 lbs and Dyno near the same hp. Where is the restriction? I would say in the intake and heads. The block and internals are a hp restriction. Some of the other guys were playing around saying that "the max boost you should run is right below the boost at which you have a failure" but that too is a very accurate statement. LOL
 

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Discussion Starter · #12 ·
Very true, however, although it is the measure of restiction 20psi is going to force more air into the chamber than 5psi. When you add the required amout of fuel you should be making more power just due to the extra volume of oxygen.
I guess I'm kinda looking more at when do people think the dynamic c/r is too much to support different fuels and parts, when do you thing you should o-ring heads, and what are the actual stresses imparted my additional boost...in a nut shell why is too much boost bad?
 

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To your original question, I wouldn't be afraid to shove 20 psi down the throat of my 331 with 93 octane with a bunch of meth for a little added safety margin.

IMO, there is no such thing as "bad" boost. It's simply that the equation gets a little more complicated as you increase the cylinder pressure. In other words, it's a lot easier to tune a car on pump gas making 10 psi, that it is a 2000 hp small block running race gas. The tune isn't linear for a lack of a better word.
 

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Very true, however, although it is the measure of restiction 20psi is going to force more air into the chamber than 5psi. When you add the required amout of fuel you should be making more power just due to the extra volume of oxygen.
I guess I'm kinda looking more at when do people think the dynamic c/r is too much to support different fuels and parts, when do you thing you should o-ring heads, and what are the actual stresses imparted my additional boost...in a nut shell why is too much boost bad?
IMO, there is no such thing as "bad" boost. It's simply that the equation gets a little more complicated as you increase the cylinder pressure. In other words, it's a lot easier to tune a car on pump gas making 10 psi, that it is a 2000 hp small block running race gas. The tune isn't linear for a lack of a better word.
at some point if you remove the mechanical restriction of the parts breaking, it all comes down to flow. 18 lbs of boost at say 130* is better than compared to 20 lbs at 220* so there is a such thing as "BAD" boost.

look at the article in the link below:

AFM - Pump Gas Brags
 

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at some point if you remove the mechanical restriction of the parts breaking, it all comes down to flow. 18 lbs of boost at say 130* is better than compared to 20 lbs at 220* so there is a such thing as "BAD" boost.

look at the article in the link below:

AFM - Pump Gas Brags
I'm not referring to the "quality" per say of the psi/backpresure. I'm sure what the OP is looking for is how much is too much. Obviously keeping ACT temps down is always a factor, which is why I mentioned adding meth to the mix.

At some point you need to look at the effeciency of the combination. You can spin the crap out of the blower, but at some point the efficiency could go south if the setup can't support the CFM of the blower.
 

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I'm not referring to the "quality" per say of the psi/backpresure. I'm sure what the OP is looking for is how much is too much. Obviously keeping ACT temps down is always a factor, which is why I mentioned adding meth to the mix.

At some point you need to look at the effeciency of the combination. You can spin the crap out of the blower, but at some point the efficiency could go south if the setup can't support the CFM of the blower.

I believe you just repeated my last post...:lol:
I think that we agree that there are to many factors to be exact on what he is asking, but after near 20 yrs BOOSTED I have melted pistons at 12 lbs (blower) 2 at 19 lbs (turbo) and 1 on the back bumper at 25 lbs (big thumper) at the time each of these amounts of boost where too much.
 

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Discussion Starter · #17 ·
I dont have a meth system but I am upgrading the blower to help reduce temps and increase effeciency. The only problem with that is room for the pulley. I'm pretty limited on space so getting a big enuf pully on the blower to keep boost down mght be a challenge. Pulley/boost math is frustrating!! You never truely know what your gonna get till you run it...
 

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I dont have a meth system but I am upgrading the blower to help reduce temps and increase effeciency. The only problem with that is room for the pulley. I'm pretty limited on space so getting a big enuf pully on the blower to keep boost down mght be a challenge. Pulley/boost math is frustrating!! You never truely know what your gonna get till you run it...
Well until you have used 1 pulley on your combination, then you can pretty accurately predict boost lb. With vortech, 1 pulley size is 1-2 lbs of boost. You can then calculate effieciency using the calculator: Support | Vortech Superchargers

IE: with my S trim, 7" crank pulley, 3.3" blower pulley and shifting at 6800, I am spinning blower at 49763.64
So for my set up, that is the max boost for this blower to remain effiecient. It is recomended to 50,000rpms. So rather I am at 14lbs or 18lbs.....this is it with this combo.

Performance Specs
Max Speed: 50000 RPM
Max Boost: 20 PSI
Max Flow: 1000 CFM
Max Power: 680 HP
Peak Efficiency: 72%
Performance specs apply to units equipped with standard gearcase.

Dimensions
Discharge OD: 2.75"
Inlet OD: 3.5"
Discharge ID: 2.38"
Inducer Diameter: 3.1"
Part Numbers and Prices listed below.

The industry standard supercharger

Straight cut spur gear
Available with straight or curved discharge and clockwise or counterclockwise rotation
Superchargers exceeding 6 PSI require a Vortech standard bypass valve or a Vortech Maxflow racing bypass valve.

Superchargers exceeding 10 PSI require a Vortech Maxflow Mondo or Maxflow racing bypass valve.

Cog belt drive systems are recommended for all heavy duty superchargers
 

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Discussion Starter · #19 ·
lol...for me its yes and no. I have run the P1 with a 3.22 on my current set up but havent run it beyond 4200 rpm, so I truley dont know what I would make for boost at peek but I am figuring it would be right about what the 4.6 2v was making.
We pegged the MAF around 4k so terminated the pulls, and put a 4500 limiter on it so I could still use the car and get some mile on the new engine. I was rushed getting it ready due to a suprise deployment so assumed the MAF would support it. I miscalculated how much air the new engine would move, and it bit me.
Things are going to be different this time, new MAF, stepped up injectors, and the upgraded blower.
 
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