Supercharger
Joined: Sep 2004
Posts: 6,223
Likes: 4
From: Orange County, CA
I cant comment on FMUs.
With regard to capping boost another more simple method can be used. On the inlet side a restrictor can be used to mechanically limit the airflow in to the supercharger. In my case im planning on using a 20psi pulley on a C38 rotrex and then using a 14psi limiter. Ive seen a similar method used on a c30 with good effect.
With regard to capping boost another more simple method can be used. On the inlet side a restrictor can be used to mechanically limit the airflow in to the supercharger. In my case im planning on using a 20psi pulley on a C38 rotrex and then using a 14psi limiter. Ive seen a similar method used on a c30 with good effect.
Would someone with an engineering background be able to tell us which is more efficient and which is less stress on the blower?
Registered User
Joined: May 2010
Posts: 1,408
Likes: 1
From: Columbia, South Carolina
just gonna throw this out there... 6psi top off while using oh say a 12 psi belt would make sense but would it have a point? i could just use the 12 psi for 12psi peak and spank that guy thats basicaly restricted his supercharger... i suppose if we could find a blow that would spin for 20psi and set up a max psi of say 10 or 12 it would make it more useful for our applications...
Registered User
Joined: May 2009
Posts: 1,308
Likes: 1
Originally Posted by razzele' timestamp='1312020002' post='20830370
I cant comment on FMUs.
With regard to capping boost another more simple method can be used. On the inlet side a restrictor can be used to mechanically limit the airflow in to the supercharger. In my case im planning on using a 20psi pulley on a C38 rotrex and then using a 14psi limiter. Ive seen a similar method used on a c30 with good effect.
With regard to capping boost another more simple method can be used. On the inlet side a restrictor can be used to mechanically limit the airflow in to the supercharger. In my case im planning on using a 20psi pulley on a C38 rotrex and then using a 14psi limiter. Ive seen a similar method used on a c30 with good effect.
Would someone with an engineering background be able to tell us which is more efficient and which is less stress on the blower?
Yes, we could, but that would require doing math!
I'll stick to half-baked internet theory instead...One thing to consider... If you spin the blower up to really high boost levels, you have to make sure your blowoff valve is big enough to handle it. Otherwise it won't vent enough air to keep you outta boost when you're cruising. I am suspicious that this is what's happening to my car because I used a long hose to route the blowoff under the fender. I'm not sure it is really letting all the air out fast enough now due to drag inside the hose, and I need to do some testing. I'm not talking about the boost limiter valve (which caps boost at a set level), I'm talking about the blowoff that keeps you outta boost when you're not on the gas.
Another thing to consider... Same thing, if you run the car up to redline and then jump off the gas to shift, your blowoff needs to be able to vent all that air or you'll get compressor surge (air trying to escape past the compressor wheel). That's bad news for the S/C.
The thing I'm wondering is if you use a restrictor on the SC intake, does that effectively move the choke line on the compressor map? And what are the ramifications of operating the SC in a choked condition on a regular basis?
The other thing I'm wondering is, if your blowoff doesn't vent fast enough, could the restrictor make compressor surge even worse if the air can't get back out?
Inquiring minds want to know...
Community Organizer
Joined: Jun 2007
Posts: 31,070
Likes: 566
I've lost count on how many threads there are floating around on this topic. The latest one with probably the most useful information is from a friend of mine locally who does have an engineering mind and was contemplating the restrictor idea vs the bleed off one. This thread wasnt that long ago, I'll see if I can find it and post a link, or I'll ask him to post in this thread. But just so you know, we all end up just wanting more power and so this kind of topic usually dies with that desire and the cycle continues with the next batch of newbs 
Be neat if someone would actually implement and see it through though, just for the sake of doing it, either method and making it work, I know it can.
Here you go guys.
https://www.s2ki.com/s2000/topic/822...#entry19625841
Be neat if someone would actually implement and see it through though, just for the sake of doing it, either method and making it work, I know it can.
Here you go guys.
https://www.s2ki.com/s2000/topic/822...#entry19625841
Registered User
Joined: May 2009
Posts: 1,308
Likes: 1
Hilarious. And here I was all worried that a 3.5" CAI pipe would be too restrictive..
Good link, and the links in that thread was good too.
On another note, I became suspicious that maybe my BLV wasn't working because they might have welded it on without drilling a hole first. Checked it just now and the hole is there. Spring pressure is pretty mild too; I can move the ball with my finger. Meanwhile I loosened it a bit and now it's stuck. Can't seem to fully unscrew it or tighten it back either.. Grr.
Good link, and the links in that thread was good too.
On another note, I became suspicious that maybe my BLV wasn't working because they might have welded it on without drilling a hole first. Checked it just now and the hole is there. Spring pressure is pretty mild too; I can move the ball with my finger. Meanwhile I loosened it a bit and now it's stuck. Can't seem to fully unscrew it or tighten it back either.. Grr.
Joined: Nov 2008
Posts: 1,347
Likes: 1
From: Pittsburgh, PA
Hilarious. And here I was all worried that a 3.5" CAI pipe would be too restrictive..
Good link, and the links in that thread was good too.
On another note, I became suspicious that maybe my BLV wasn't working because they might have welded it on without drilling a hole first. Checked it just now and the hole is there. Spring pressure is pretty mild too; I can move the ball with my finger. Meanwhile I loosened it a bit and now it's stuck. Can't seem to fully unscrew it or tighten it back either.. Grr.
Good link, and the links in that thread was good too.
On another note, I became suspicious that maybe my BLV wasn't working because they might have welded it on without drilling a hole first. Checked it just now and the hole is there. Spring pressure is pretty mild too; I can move the ball with my finger. Meanwhile I loosened it a bit and now it's stuck. Can't seem to fully unscrew it or tighten it back either.. Grr.
I bet it deformed the BLV from welding on it
Former Sponsor
Joined: Oct 2007
Posts: 28,698
Likes: 38
From: Mooresville, NC
just gonna throw this out there... 6psi top off while using oh say a 12 psi belt would make sense but would it have a point? i could just use the 12 psi for 12psi peak and spank that guy thats basicaly restricted his supercharger... i suppose if we could find a blow that would spin for 20psi and set up a max psi of say 10 or 12 it would make it more useful for our applications...
Yeah pretty pointless to do it under 12 psi. I have thought about doing this but I am at 12 psi now and not sure if I want to run more boost than I am currently. I would then do a 15-16 psi pulley and bleed off after 12-13 so I can get some nicer midrange gains and stay at a safer max boost level.
Joined: Apr 2009
Posts: 6,036
Likes: 4
From: FAR BEYOND THE WHEEL...
In regards to the restrictor plate... What good is more boost at a given RPM if you are cutting the CFM ?
Yeah you make the boost quicker, but you are making less power per psi when compared to an unrestricted setup, right?
Yeah you make the boost quicker, but you are making less power per psi when compared to an unrestricted setup, right?
Joined: Oct 2003
Posts: 11,949
Likes: 474
From: MAHT-O-MEDI
Just an idea for a low boost application..say about 6 PSI.
Since a supercharger is based off the Cranks RPM. The faster it spins the more boost it builds, which makes us choose a pulley based on the amount of boost we want. Using a smaller pulley than intended would build too much boost than we would like at redline. SO..could we use a 12 psi pulley which would build 6 PSI a lot more earlier and cap off the boost with something similar to a wastegate before it hits the intake manifold?
Since a supercharger is based off the Cranks RPM. The faster it spins the more boost it builds, which makes us choose a pulley based on the amount of boost we want. Using a smaller pulley than intended would build too much boost than we would like at redline. SO..could we use a 12 psi pulley which would build 6 PSI a lot more earlier and cap off the boost with something similar to a wastegate before it hits the intake manifold?
Or you could get a roots kit and be done with it.
Joined: Jun 2008
Posts: 1,593
Likes: 75
Originally Posted by mrscbw' timestamp='1311961601' post='20828353
Just an idea for a low boost application..say about 6 PSI.
Since a supercharger is based off the Cranks RPM. The faster it spins the more boost it builds, which makes us choose a pulley based on the amount of boost we want. Using a smaller pulley than intended would build too much boost than we would like at redline. SO..could we use a 12 psi pulley which would build 6 PSI a lot more earlier and cap off the boost with something similar to a wastegate before it hits the intake manifold?
Since a supercharger is based off the Cranks RPM. The faster it spins the more boost it builds, which makes us choose a pulley based on the amount of boost we want. Using a smaller pulley than intended would build too much boost than we would like at redline. SO..could we use a 12 psi pulley which would build 6 PSI a lot more earlier and cap off the boost with something similar to a wastegate before it hits the intake manifold?
Or you could get a roots kit and be done with it.
As the OP already stated, the down side to doing this is the supercharger is spun much faster than necessary which is wasting power.About the intake restrictor. It will limit POWER as the restrictor limits airflow; power is a function of airflow. So if you have a flat power curve, you have a decreasing torque curve as rpms increase. Boost is one of the main variables determining torque. The boost and torque curves follow each other for the most part. So, if your torque is decreasing, then your boost is decreasing too.
So, with a centrifugal blower with an inlet restrictor, you'll end up with your max boost in the midrange until the air flow chokes. Then the boost level will decrease with increasing engine rpms. You will not have a flat boost curve.
If you want to try to limit boost by venting excess air, I think I would just get a Tial wastegate valve and put it between the turbo outlet and IC (reduces mass flow of air thru IC allowing the IC to cool the air that is going thru it better). Wastegates are designed to vent off flow to maintain a certain pressure. So that seems to be exactly what you want.