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Stu
Dodge Dakota
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10/07/2005
19:48:44
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 Subject: Boost
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Can somebody give a comparison as to how much pressure 6 lbs of boost is?
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Craig
Dodge Dakota
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10/07/2005
22:00:43
| RE: Boost
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Well, I would highly recommend the bood Supercharging,Turbocharging, and Nitrous Oxide by Earl Davis and Diane Perkins-Davis. It can fill you in on a lot of good info about the power adders.
I don't know how much this will help you, but one way to think about 6 PSI of boost, is this:
Assuming the factory compression ratio on your garden variety 3.9/318 is about 9:1, and you add 6 PSI of boost to the motor, your compression ratio at max boost is now 12.7:1.
That's one way of thinking about it anyway.
6 PSI is not a lot of boost. If you put your hand on the outlet side of the blower, it might feel like a strong breeze at the best.
Bear in mind that HOW you supercharge or turbocharge an engine determines a lot on what sort of wear and tear you add, and how much power you actually add. Assuming a Roots blower, you have the vast majority of your boost available to you at lower RPMs. Roots blowers are generally more expensive and under normal circumsttances are at a disadvantage of forcing you to use a low profile intake with short runners (effectively decreasing the air velocity entering the engine)
A centrifugal supercharger produces most of it's boost above 3000 RPM. The good news is that when you're below that, you're not really putting much strain on your motor. The bad news is that when you're below 3,000 RPM, you make yourself a sitting duck. Centrifugal blowers are the cheapest, easiest to maintain, easiest to install, and can produce the most boost per dollar. But they don't look like much under the hood.
A turbocharger is a different animal. Why you would turbocharge if you're only looking for 6lbs of boost is totally beyond me. Turbocharging give you the most bang, but unfortunately it's for the most buck of almost any other power adder out there.
I would put a 6PSI supercharger kit on my daily driver- maybe even 8-9 PSI kit. Nothing beyond that though, beyond that you're going to start eating into your drivability/reliability. Remember that you might still want to burn premium gas with 6PSI of boost- you don't want to induce detonation and knocking into the formula- that's a good way to ruin your day.
I hope I haven't bored you to death with a long lecture if you alread know this stuff. If I have, please accept my apology, if not, you can thank me later. :-)
Good Luck!
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Stu
Dodge Dakota
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10/08/2005
07:30:06
| RE: Boost
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would 6 lbs boost (pressure) fill a simple 10" balloon?
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Craig
Dodge Dakota
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10/08/2005
21:32:28
| RE: Boost
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I really don't know. First of all, I think the issue is how fast it could fill that balloon. PSI is a measurment of how much matter you can pack into a given ammount of space. I'm not sure the balloon would serve as a valid analogy.
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GraphiteDak
GenIII
10/08/2005
22:29:37
| RE: Boost
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When I read a article "the truth about boost" (strongly recommended) it is funny about the PSI of boost = power mumbo jumbo.
Something to think about.
You can have an engine that flows really well with it's intake/exhaust/cam setup and make a LOT of power only showing 10 PSI of boost on the gauge.
You can have another enging that is UNeffecient at bringing in air and show 15 PSI on the gauge and actually make LESS power than the other engine at 10 PSI.
Boost on the gauge is the EXCESS air that is not being introduced into the engine.
So amount of boost doesn't exactly proportional to power.
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Craig
Dodge Dakota
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10/09/2005
14:52:31
| RE: Boost
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And like I said above, the boost has a lot to do with compression ratio, which determines a lot about how much power, and how efficient your engine is. Boost is actually a measurement of what's backed up behind the intake valves, but basically you're correct- it's what's not in the engine. On excessively high boost engines (say 35+ PSI), it starts to become a problem where the turbo boost starts forcing the intake valve open, DECREASING efficiency. For that reason, heavier valve springs sometimes must be used in extreme applications.
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stu
Dodge Dakota
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10/09/2005
20:28:48
| RE: Boost
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If 6lbs boost is backed up behind the valve then there is 6lbs boost going into the valve when that valve opens thus giving the guage an acurate reading of the pressure going into the valve?
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Craig
Dodge Dakota
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10/09/2005
22:10:01
| RE: Boost
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That might be a simplified way of thinking about it. It's actually somewhat more complicated.
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stu
Dodge Dakota
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10/13/2005
20:09:56
| RE: Boost
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So how much pressure is 6 lbs boost?
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N56629
Dodge Dakota
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10/13/2005
21:49:47
| RE: Boost
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6 pounds?
Is that a trick question?
Just like any compressor, you have to know how much airflow you will have at a given pressure. The air compressor in your garage may only put out 3 or 4 cfm at 100 pounds but the compressor on a car may put out 1500 cfm at 6 pounds.
You can easily fill a tire with one but not the other. You can supply plenty of air to run an engine with one but not the other even though you have more pressure.
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Craig
Dodge Dakota
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10/13/2005
22:44:15
| RE: Boost
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He's asking for something simpler than that, but I don't know how to give it. There is no way I can think of to quantify 6 PSI in terms of real life experience. My suggestion is get a book on supercharging, and read about it.
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1hotkadota
Dodge Dakota
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10/14/2005
15:52:50
| RE: Boost
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The volume of what ever your filling, in this case a cylinder, will determine what the volume of air @ 6psi will be. The two will be related.
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