Hi all,
Following on from my supercharger build plans I had a thought the other day I need sanity checking.
My first thought was that if I am making my own supercharger (potentially) then I may have to spin the compressor faster. Reasons being:
1) To gain additional efficency and therefore have excessive boost. This excessive boost, I was thinking can be bled off with the use of a BOV or
recirc. This is not impossible unusual as you can get them adjustable to do exactly that and dial in the required boost.
2) I will not have a butterfly pre SC and therefore if I let of the throttle during braking or gear change it will damage my throttle bodies.
3) The final reason I would like one is because if I oversize the compressor then it will reach my desired boost earlier in the rev range. If the
boost is bled off then potentially it will platau boost level and give me more turbo characteristics and less peaky SC characteristics. I have read
about this and it has been proven that if you are willing to waste a little energy at the top of the rev range you can gain hugly in the middle range,
where the 4age 20V suffers.
I dont like the idea of a BOV, noisey and wastefull of the energy used to create the boost. I was thinking that using a recirc AFTER the intercooler
will get either;
a) compressed air in front of the compressor therefore reducing energy required to maintain the boost levels;
or
b) release cold compressed air into the compressor intake air stream, the compressed cool air will decompress (due to the other end of the tube
obviously being open to atmos) and therefore cool intake air further;
or
c) do nothing and be just as wastefull as a BOV.
Another question, the recirc valves that I have seen seem small capcity and look like they will restrict air flow. Surely the heat will build up
through this as the rush of high pressure air flows through the smaller tube. If this is the case will it recirc heated air? I may consider using 2 to
double capacity and therefore reduce heat recirc into SC intake.
Discuss, and if so try to reference 1,2,3,a,b,c so I can get constructed thoughts.
Cheers!!!
Biz
Why have throttle bodies after the S/C, dump these and just run a big T/B in front of the supercharger with a bypass so excess boost is fed back into
the inlet after the T/B.
It's what eaton do, why make things hard at the outset, when you have your foot hard down the bypass is shut and only compressed air goes in.
People do have T/B's after the S/C to sharpen the response but it does lead to other problems unless well balanced, start simple and see how
it's goes.
Corky Bells book on forced induction is available free as a PDF on the internet which should help.
[Edited on 18/11/13 by mark chandler]
quote:
Originally posted by mark chandler
Why have throttle bodies after the S/C, dump these and just run a big T/B in front of the supercharger with a bypass so excess boost is fed back into the inlet after the T/B.
It's what eaton do, why make things hard at the outset, when you have your foot hard down the bypass is shut and only compressed air goes in.
People do have T/B's after the S/C to sharpen the response but it does lead to other problems unless well balanced, start simple and see how it's goes.
Corky Bells book on forced induction is available free as a PDF on the internet which should help.
[Edited on 18/11/13 by mark chandler]
You don't need an additional throttle body if you already have ITBs. Your BOV or recirc valve idea will not work, these devices are attached to
the plenum so when you back off the throttle they open. They are there to stop compressor stall and are not strictly necessary on a supercharger.
Most OEM turbo installs have dump valves on the Turbos which has a spring installed that is rated at a certain PSI (typically 0.7Bar) which is the
'safe' boost for the engine. The ECU will control the valve and hold it shut until the required boost is achieved and the spring only comes
into effect if the ECU loses control for the turbo for some reason.
I suggest you size the supercharger to fit your application rather than getting complicated with dump valves etc.
I know nothing, but there is a thread about recirc/BOV on the V8 forum
http://www.v8forum.co.uk/forum/viewtopic.php?t=12180
quote:
Originally posted by jeffw
You don't need an additional throttle body if you already have ITBs. Your BOV or recirc valve idea will not work, these devices are attached to the plenum so when you back off the throttle they open. They are there to stop compressor stall and are not strictly necessary on a supercharger.
Most OEM turbo installs have dump valves on the Turbos which has a spring installed that is rated at a certain PSI (typically 0.7Bar) which is the 'safe' boost for the engine. The ECU will control the valve and hold it shut until the required boost is achieved and the spring only comes into effect if the ECU loses control for the turbo for some reason.
I suggest you size the supercharger to fit your application rather than getting complicated with dump valves etc.
recirc or BOV valves are not designed to manage boost only to dump pressure when you lift off. You could try a bleed valve which would open at a set
pressure.
Bleed Valve
They are nasty things though
[Edited on 19/11/13 by jeffw]
quote:
Originally posted by jeffw
recirc or BOV valves are not designed to manage boost only to dump pressure when you lift off. You could try a bleed valve which would open at a set pressure.
Bleed Valve
They are nasty things though
[Edited on 19/11/13 by jeffw]
The work by tapping into the plenum (can be the line to the BOV but doesn't have to) and have a spring which is tensioned by a screw. There is no control over the boost by the ECU or the engine so it is a cheap 're-map' which has been know to seriously damage engines when people get greedy....