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Discussion Starter #1
finally got around to hooking my gauges up in the car the other day and took it for a test spin... first off ive replaced the wires checked for vacuum leaks etc and still have the miss but it gets worse when motor warms up so im going to borrow a buddies known good dizzy and see if it fixes, if so i guess im going to try out a new mallory...

back on subject, just curious as to how much vacuum psi there is supposed to be drawn at idle, how long before boost #s start showing up in the positives, and if my miss might be causing the blower not to boost up to full potential... because im at around -20 on vacuum, seems to take a while for the boost to start showing up, and its peaking around 6psi but holding closer to 4. which with what i have read on a stock car the v3 should be around 6-8 psi, instant boost, and i have a 90mm maf, 42lb injectors, bunch of bolt ons, etc... also the car doesnt really seem any faster than it did before the blower instal....
 

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vacuum is measured in inHg (inches of mercury). 20 at idle is good vacuum. I make 10 at idle lol because of my cam.

but anyways better flowing parts will yield less boost. boost only shows when the engine is under a load. theres no set time its based on blower speed and efficiency
it should be positive as soon as you are at WOT then as the rpm rises it should also rise until it peaks
 

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load and rpm make boost in a centrifugal, not like a turbo or positive displacement supercharger. Your idle vac depends on your cam. Mine is around 10-12. I have no comment on you not feeling the car being any faster. With 4-6 you would feel it but not until 3500+. A ROUGH estimate is 10hp per # but that really depends on your combination.

An example with a v1. This chart sucks for reading boost because it is so small, boost is the barely visible pink line on the bottom chart. 11 peak at 6000 but it was only about 5 until roughly 3500-4000. Every combination is different though.

 

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With my Steeda cam I idle at 13. Just putting out some information to help.
 

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Discussion Starter #5
Well that kimdof sucks LOL I figured more airflow meant more boost... so since my peak is low after I get the miss figured out if it still peaks around 5-6 should I get a different pulley to get it up around 8-10? If so any idea what size?
 

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I make 4hg of vac tfs stg 2
 

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Well that kimdof sucks LOL I figured more airflow meant more boost...
An engine is a big air pump. The goal is to get a higher volume of air through the engine. With more air volume passing through, you can add more fuel and then get more power. Adding more fuel is the easy part, larger injectors and a pump and your done. How do you get more air in the engine? Some combination of more cubic inches, higher rpm, less restrictive intake/exhaust, higher compression, or force it in there via NO2 or with turbo/supercharger. The cam selection along with timing and specific A/F ratios are what ties the whole combination of parts together so you get the desired max/average/flat/low/high torque and HP curves you are looking for.

About that boost.. more boost or pressure in the intake = more airflow into the cylinders but on the same hand, more total airflow results in less measured boost. Does that make sense? Boost is the build up of what is left over that did not make it into the cylinders. Here is one way to look at it. With your mouth, blow through a narrow coffee stir straw, your mouth has a high pressure (boost) but there is a low flow at the end of the straw. If you could blow harder [insert joke here], your mouth pressure will go up and more airflow will go through the straw. Now blow through a paper towel roll. You have less pressure in your mouth but more air flow goes through the tube. Another way.. A car with stock E7 heads might gnerate 10 psi of boost, put on a nice set of heads and a cam and you may now only see 7 psi of boost but you will be making a lot more power because air flow went up. This is the reason you see small 4 cylinder engines running 15-25 psi and they are about equal in HP gain as a larger v8 only running 5-10. More cubic inches therefore less boost pressure needed to get the same gains in airflow. The 4 clyinder is the coffe stir and the v8 is the paper towel tube.
 

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^ nice!
 

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Discussion Starter #9
Ya the way you worded it makes sense nolife... restrictions are what makes boost psi diff... I was just tbinking of it from my diesel roots where more airflow usually makes more boost on Turbo ...

So would it be a good idea or bad to put a different pulley on it to up the boost some?
 

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Im not sure but you may have to have it retuned if you change the pulley. Maybe some one else will chime in that can answer that
 

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Discussion Starter #11
That wouldn't be an issue cause I'm going to ha e to anyways after I get the miss fixed ... and I'm sure it Prolly would throw off the a/f ratio...
 
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