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Discussion Starter · #1 ·
I have a Fiero with an L32 in it. From a dead stop going full throttle it seems to max out at only 5 psi boost. I thought superchargers gave immediate boost unlike the turbos that had to build boost.
 

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They do, you have an issue with your boost bypass, most likely. Many people keep the useless bypass solenoid connected which mainly performs a traction control. I'd post some pics of your vacuum lines and maybe screenshots of scans, if you have any.
 

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Discussion Starter · #3 ·
They do, you have an issue with your boost bypass, most likely. Many people keep the useless bypass solenoid connected which mainly performs a traction control. I'd post some pics of your vacuum lines and maybe screenshots of scans, if you have any.
The boost bypass is connected to vacuum and the solenoid has been removed. I had asked in another post about this and was told it was fine to run it this way, was that incorrect?
 

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make sure that ONLY the top port is connected to the vac port on the top of the blower, the lower port on the bbv MUST BE OPEN TO ATMOSPHERE if the bbv solenoid is removed... or as the engine heats up the air inside the actuator expands and holds the bbv open

make sure the bbv arm isnt bent and is touching the threaded stop on the blower case...if it isnt touching you need to loosen the bolts on the bbv actuator and adjust it downward.
 

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Discussion Starter · #5 ·
make sure that ONLY the top port is connected to the vac port on the top of the blower, the lower port on the bbv MUST BE OPEN TO ATMOSPHERE if the bbv solenoid is removed... or as the engine heats up the air inside the actuator expands and holds the bbv open

make sure the bbv arm isnt bent and is touching the threaded stop on the blower case...if it isnt touching you need to loosen the bolts on the bbv actuator and adjust it downward.
I'll have to check it in the morning but from what I remember I think the previous owner had vacuum hooked to the bottom port and the top port open. Would that be causing the low boost on takeoff?
 

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yup.
the actuator spring pressure holds the butterfly vavle closed, vacuum from idle/part throttle cruise behind the TB (before sc rotors) is supplied to the top chamber to force the spring to collapse and open the butterfly bypassing air from below the rotors to their inlet......

the OEM BBV solenoid is a normally open solenoid, leaving the lower port exposed to atmosphere 90+% of the time and when traction control requires a drop in power output the PCM switches the solenoid which connects the actuator lower port to positive boost pressure from the LIM and force the BBV open, dropping power.

you dont need the solenoid as most of us are control freaks and can control ourselves lol.

but that lower port must be vented to air....i have seen this issue often enough with swaps...people plug the port
 

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Discussion Starter · #7 ·
yup.
the actuator spring pressure holds the butterfly vavle closed, vacuum from idle/part throttle cruise behind the TB (before sc rotors) is supplied to the top chamber to force the spring to collapse and open the butterfly bypassing air from below the rotors to their inlet......

the OEM BBV solenoid is a normally open solenoid, leaving the lower port exposed to atmosphere 90+% of the time and when traction control requires a drop in power output the PCM switches the solenoid which connects the actuator lower port to positive boost pressure from the LIM and force the BBV open, dropping power.

you dont need the solenoid as most of us are control freaks and can control ourselves lol.

but that lower port must be vented to air....i have seen this issue often enough with swaps...people plug the port
Thank you for the information.
 

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Down ~5psi from what? And climbing from what number to what? It will start increasing from the regular level to a couple psi higher at the top of a gear as the heads restrict at higher rpm. (See Richard Holdener's YouTube videos of 3800 dyno charts and how the boost on the M90 acts.)

Do you have baseline data to compare to, or is this just when you've started looking at this value and it feels off for some reason to you? Troubleshooting is a process that requires knowing what the normal/good condition looks like prior to being able to evaluate any perceived issues. On top of that, getting remote help requires providing this level of information to us to understand your specific condition, setup, observations, expectations, etc. so that appropriate and helpful replies can be offered.
 

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Discussion Starter · #11 ·
Down ~5psi from what? And climbing from what number to what? It will start increasing from the regular level to a couple psi higher at the top of a gear as the heads restrict at higher rpm. (See Richard Holdener's YouTube videos of 3800 dyno charts and how the boost on the M90 acts.)

Do you have baseline data to compare to, or is this just when you've started looking at this value and it feels off for some reason to you? Troubleshooting is a process that requires knowing what the normal/good condition looks like prior to being able to evaluate any perceived issues. On top of that, getting remote help requires providing this level of information to us to understand your specific condition, setup, observations, expectations, etc. so that appropriate and helpful replies can be offered.
I was seeing that other people are getting close to the 10 PSI right from a dead stop and the tires are breaking loose. When I nail it from a dead stop it won't even chirp the tires and the boost is only up to about 5 psi. To get to 8 to 10 psi I have to be up to about 5,000 to 6,000 RPMs.
Also, I took the vacuum line off the boost bypass valve and there was no difference at all. I checked the arm on the valve and with the vacuum line off it's all the way down, and when I put the line back on it comes all the way up.
 

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Sounds normal. Under vacuum, it should be up to reduce the extra pressure going to the engine. It will actuate pretty easily as you get past ~25% throttle to close the bypass as vacuum turns to 0 and it now builds boost. This action, driven by the top hose to the vacuum tree, is meant to transition from efficient normal driving to boosted heavy throttle driving.

As for what it's doing under throttle, have you scanned it, or are you just now observing it as a new-to-you setup? Fieros don't tend to spin much (on purpose) with a basic L67/32 swap, at least without doing some dumb... Errr, spirited things that may find you in the ditch. I highly suggest starting to scan the computer and get some feel for what the car tells you it's doing.
 

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Discussion Starter · #13 ·
Sounds normal. Under vacuum, it should be up to reduce the extra pressure going to the engine. It will actuate pretty easily as you get past ~25% throttle to close the bypass as vacuum turns to 0 and it now builds boost. This action, driven by the top hose to the vacuum tree, is meant to transition from efficient normal driving to boosted heavy throttle driving.

As for what it's doing under throttle, have you scanned it, or are you just now observing it as a new-to-you setup? Fieros don't tend to spin much (on purpose) with a basic L67/32 swap, at least without doing some dumb... Errr, spirited things that may find you in the ditch. I highly suggest starting to scan the computer and get some feel for what the car tells you it's doing.
I just bought it late fall last year and didn't get to do much before putting it away for winter. Now that I've taken it out I'm just surprised that it has less "get up and go" than my turbocharged vehicles. I thought being supercharged it would have more grunt out of the hole.
 

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It's stock, from the sounds of it, so there's not enough grunt quite yet to snap necks. Upgrades are pretty easy to start doing, and making that thing into a death trap, depending on your desire to spend time/money/effort on getting more from it.

Also, many factory turbo cars have short gears compared to a 3800SC's 2.93's that go to ~50mph in 1st and ~95mph in 2nd. Many cars like Focus ST's, turbo'd Civics, Subies, etc. are almost out of gear by then, going into their overdrive gear. There's been studies showing that those short jerky gears tend to make people feel like they're accelerating quicker (despite the fact they can get to 3rd or 4th by the end of the block and barely be over the speed limit).

When you get a scanner to confirm your data is looking clean (no significant KR, single digit fuel trims, etc.), do a pull next to one of the cars you're thinking about. Don't overexpect a 250hp setup to beat 4-500hp+ modern hotrods just yet, but some of the normal ones in your range. That "bogging" feel is just traction demanding more torque someday, and I can assure you it's a blessing (as someone who's only had the FWD configuration forever... for now).
 

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Discussion Starter · #15 ·
It's stock, from the sounds of it, so there's not enough grunt quite yet to snap necks. Upgrades are pretty easy to start doing, and making that thing into a death trap, depending on your desire to spend time/money/effort on getting more from it.

Also, many factory turbo cars have short gears compared to a 3800SC's 2.93's that go to ~50mph in 1st and ~95mph in 2nd. Many cars like Focus ST's, turbo'd Civics, Subies, etc. are almost out of gear by then, going into their overdrive gear. There's been studies showing that those short jerky gears tend to make people feel like they're accelerating quicker (despite the fact they can get to 3rd or 4th by the end of the block and barely be over the speed limit).

When you get a scanner to confirm your data is looking clean (no significant KR, single digit fuel trims, etc.), do a pull next to one of the cars you're thinking about. Don't overexpect a 250hp setup to beat 4-500hp+ modern hotrods just yet, but some of the normal ones in your range. That "bogging" feel is just traction demanding more torque someday, and I can assure you it's a blessing (as someone who's only had the FWD configuration forever... for now).
Thank you for your help.
 

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first, the flat portion of the steel arm should be perpendicular to the BBV shaft, many times ive come across it bent and holding the bbv open or sticking it closed.

mosre spring pressure holding down the arm the more post TB vac required to open the butterfly and recirculate air.....not alot but its a little area under the curve.

btw, most i got outta a stock pulley gen5 SIII engine was 7.8psi measured with a real snapon mechanical gauge.

just removing the DP/cat dropped it to 6.5, pacesetters with a full 3" catback we rarely got over 6psi, 3.4 pulley got us back up to 8psi but wayyy more power than the 7.8psi of before

also make damn sure the rubber T under the sc snout that feeds the vac harness isnt rotted/soft and leaking.....slide it off the LIM nipple and look for the lengthwise crack or for it to crumble
 

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Discussion Starter · #18 ·
first, the flat portion of the steel arm should be perpendicular to the BBV shaft, many times ive come across it bent and holding the bbv open or sticking it closed.

mosre spring pressure holding down the arm the more post TB vac required to open the butterfly and recirculate air.....not alot but its a little area under the curve.

btw, most i got outta a stock pulley gen5 SIII engine was 7.8psi measured with a real snapon mechanical gauge.

just removing the DP/cat dropped it to 6.5, pacesetters with a full 3" catback we rarely got over 6psi, 3.4 pulley got us back up to 8psi but wayyy more power than the 7.8psi of before

also make damn sure the rubber T under the sc snout that feeds the vac harness isnt rotted/soft and leaking.....slide it off the LIM nipple and look for the lengthwise crack or for it to crumble
Thank you.
 
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