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 What should my boost be?

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kylan_13
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PostSubject: What should my boost be?   Sun Feb 25, 2018 7:27 pm

Hi, I think my boost is suspiciously low for my mods. Also it seems to fluctuate. The only airflow mods I have are 1.8 ratio rockers, cat delete, and specter air filter/gutted airbox. With a 3.25 S/C pulley I'm getting only 9psi and other times 11.5psi. It seems like the boost builds up at higher rpms usually but not always. I thought maybe my belt was slipping so I tried a 3.4 S/C pulley and I got 7.8psi to 9.5psi. Is that much fluctuation normal? Is it normal for boost to be lower at low rpm and higher at high rpms? What size S/C pulley do people start experiencing belt slippage usually?
On my stock sized belt I'm using a 3.5 tensioner pulley and a 3 idler pulley which puts me between the tensioner range marks. I've tried putting on a new tensioner but it did not help. I also noticed my belt was very dirty so I tried cleaning it. I used brake clean and a bunch of towels which got a lot off (idk if using brake clean on the belt was ok but I have a new belt just waiting to be put on so I'm not worried). cleaning the belt also did not help. I have also tested the boost actuator which I believe is good. It pushs the flap all the way down when I give it gas. I have also drove for a short period with the lever blocked all the way down, it did not raise the boost. I know this is probably dumb but I blocked off the egr with plates to see if maybe my boost was escaping there but it did not raise the boost either.
As you can probably tell I'm grasping as straws at this point, this is getting very frustrating. Idk what else it could be. I don't believe I have any large enough vacuum leaks to bleed off boost, my fuel trims and AFR look fine. I believe my belt was so dirty because of a oil/coolant leak, could my belt be the problem even though I tried to clean it off? Thank you in advance for any help/ideas.
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albertj
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PostSubject: Re: What should my boost be?   Sun Feb 25, 2018 9:29 pm

See if you can determine how well the vacuum modulator on the SC is actually working. And if there are any leaks in the vacuum circuit to it. If you can pull/replace any vacuum connector easily, you probably should assume it leaks.

All that said, I suspect your boost levels are OK. See the following:

http://www.fiero.nl/forum/Archives/Archive-000001/HTML/20120111-2-112318.html

http://www.3800pro.com/forum/superchargers/32650-how-much.html
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kylan_13
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PostSubject: Re: What should my boost be?   Mon Feb 26, 2018 1:30 am

Thank you albertj. I will double check my S/C actuator and the vacuum lines tomorrow. Also note that I don't hear any squeaking or squealing from my belts(hopefully indicating no slippage). Just to clarify is a 2 psi variation from low rpm (9psi) to high rpm (11psi) normal? I thought it should basically stay the same at any rpm.
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kylan_13
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PostSubject: Re: What should my boost be?   Sat Mar 03, 2018 7:45 pm

So my belt was slipping. I marked the S/C pulley and belt with a colored pencil. After starting the engine a couple times those marks did not line up anymore. I didn't even drive, I just started the engine for a few seconds! This was with a 3.4" S/C pulley and a brand new belt. It's weird though because I don't hear any noise coming from the belt even though it is slipping. I guess I'm going to need a belt wrap kit or an 8 rib belt system. Is there any info about making those work on our cars? I searched but didn't find much.
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AA
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PostSubject: Re: What should my boost be?   Mon Mar 05, 2018 1:40 am

You can minimize belt slip by upgrading your idler and tensioner pulleys to 3.5" dia. See this thread for details:

http://rivperformance.editboard.com/t36-faq-upgrading-serpentine-belts-pulleys

Boost depends on RPM, load, and weather conditions. Most of the time the engine operates in vacuum. At some point you cross into boost (0 PSI) and eventually top out at 6-8 PSI on a stock engine.

I have roughly the same mods as you (+headers) and top out at 13-15 PSI on a 3.4" pulley with the 3.5" idler/tensioners. Once hit 16 PSI on the dino at 6 grand. You can boost a bit more with the E85, but IMO bump the timing to a hotter table before boosting beyond the 3.4". Just my 2.

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kylan_13
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PostSubject: Re: What should my boost be?   Sun Mar 11, 2018 7:18 am

Thanks AA. Please excuse me for being dumb. I've thought about my method for determining belt slip and it maybe flawed. I marked my belt and supercharger pulley with colored pencil thinking that when ever that part of the belt landed on the pulley it should line up every time, but that might be wrong. The belt would have to be exactly a whole multiple of the pulley size such as 10 times. if it was 10.1 times then it would only line up once out of ten times. all the other times it would not line up. long story short now I'm back to square one, thinking why is my boost low/fluctuating? Could my supercharger just be getting worn out? This problem has been driving me crazy, I just want my power. My boost does go up if I put a smaller pulley on so should I just forget about it being lower than normal? 3.4"pulley=8psi-9.5psi and 3.25"pulley=9psi-11.5psi for my car rite now. Also note my boost did not change from using a stock sized belt with the 3.5" tensioner to a brand new smaller belt with the 3" tensioner (both put the tensioner mark in range). Thanks for letting me vent to anyone that will listen/help.
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kylan_13
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PostSubject: Re: What should my boost be?   Thu Mar 22, 2018 6:08 am

Ok, just to clarify I was being dumb and getting worked up for nothing. I cant believe I didn't think to look at my data scans from the past. I was getting the same boost number like 4 years ago and the boost did climb as the rpms went up. So I don't think anything is wrong with my boost levels. also just to clarify now that I've seen how the egr works boost can't leak out through it since the intake port is before the supercharger. Sorry for being dumb, let me know if I should edit/delete my nonsense.
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