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Author Topic: Whipple Blower by pass valve question  (Read 5509 times)
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ronnieroadster
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« on: November 05, 2014, 04:38:03 PM »

  On a Whipple screw type blower that has a bypass valve port located above the rotors can this valve be eliminated? The Whipple blower in question has a carb mount cast into the case on the top. On the back wall of the blower case is an opening where a bypass valve would be mounted. With the valve open that would allow air into the case below the carb and above the rotors wouldnt that case a lean situation?
 Since the use would be for Land Speed Racing not street use is there any reason why the opening in the case could not be just covered over?  huh
« Last Edit: November 05, 2014, 04:39:36 PM by ronnieroadster » Logged

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NathanStewart
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« Reply #1 on: November 06, 2014, 12:49:54 AM »

Most blower bypass valves that I've seen take air from the outlet of the blower and send it back to the inlet which keeps the blower from making boost.  It doesn't create a lean condition because you're not introducing any more air to the engine - you're simply taking the compressed air from out of the blower and "leaking" it back into the blower inlet.  It's a means to reduce parasitic loss and increase efficiency at lower throttle positions (cruising, etc) which isn't really a concern in a racing application. I'd just lock it shut.
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JimL
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« Reply #2 on: December 21, 2014, 11:33:58 PM »

Those bypass valves are a handy device.  The valve is controlled by vacuum, sampled after the throttle plate.  Any time there is less than atmospheric pressure, the bypass opens up to give a low restriction path from carb/throttle body into the manifold.  This is important because the rotors will begin recirculating air (and reheating) instantly when there is uneven vacuum ahead of the rotor inlet.  

The bypass valve makes sure that vacuum pressure is even on both sides of the rotors until you have enough throttle-open airflow to keep the rotors moving air in one direction, only.  

You can put a vacuum restrictor in the bypass control line to "ramp" into the blower flow as you get back on the throttle after each shift.  This could be useful if you use a carb with an accelerator pump.  A .023" wire feed welder tip (in that vacuum line) will give you about a second or two ramp on a butterfly type bypass valve, from 'open' to 'closed'.  That could help get the accelerator pump shot from the carb to the ports, instead of smeared through the rotor housing while the engine hickups and spits.

For a race engine, run the biggest bypass valve you can fit, especially when using a little more cam then the turbos dare.  A blower with bypass valve can use more overlap than a turbo, because it doesnt need to keep high exhaust side temps.  Its perfectly ok to cool those exhaust valves off (and the top of the pistons) at the end of the exhaust stroke. wink  They also like really cool head temperature, FYI.

  I only ever worked with the efi engine kits, so I dont know what you need to do to set that carb up.

Hope this is useful.
JimL

PS....forgot to mention.  Never try to control boost by opening the bypass valve under load at rpm.  The blower cannot survive reheating its own air, the engine will start detonating (at any rpm) and it will likely swell the rotors into the case.  We did open the bypass, for 800 milliseconds, during auto trans upshifts and just when the engine went on rev limiter on stick shifts (to let the driver know...shift or slow down!)

That stick shift trick is a bad deal in the hands of a CART champion driving a Pace Car on Press Day. embarassed  I made a big mistake by doing a quick electrical patch on a shattered Knock Sensor and sending him back out.  Sometimes we just dont think things through in the heat of the moment.
« Last Edit: December 21, 2014, 11:58:12 PM by JimL » Logged
Bob Drury
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« Reply #3 on: December 22, 2014, 12:02:36 AM »

  Uh, why not call Art Whipple and ask him?  (559) 442-1261.
                                            Straight from the horses mouth.......... Dead Horse  One Run, out.................
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Bob Drury
JimL
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« Reply #4 on: December 22, 2014, 12:08:17 AM »

Exactly right, and Whipple has a very good selection of bypass valves.. Good stuff.
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JimL
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« Reply #5 on: December 22, 2014, 10:28:29 AM »

Here is an example of a low vacuum bypass valve.

http://kennebell.net/KBWebsite/Accessories_pg/Bypass%20Valve/layouts/bypassvalves.htm

If you have much cam, you can smoke a blower waiting on the starter to you send you off.  Always remember that the gear case isnt sealed very well against vacuum, and you will suck the oil out of it every time you lift throttle at rpm...if you dont open the bypass.
« Last Edit: December 22, 2014, 10:31:23 AM by JimL » Logged
NathanStewart
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« Reply #6 on: December 23, 2014, 01:40:52 PM »

Interesting info Jim.  This is also from Kenne Bell which is where I think I gleaned the info I posted: 

During non boost driving, bypass valves reduce NOX emissions and allow the supercharger to operate at a cooler temperature by circulating compressed air (boost) back to the inlet. Note: This is NOT a concept unique to only Eaton kits. It is 25 year old techology. If the supercharger is located in front of the throttle body (blow through) as in the case of centrifugals, and the throttle body closes at high rpm, the compressed air has no place to go. The resulting back pressure and surge can destroy the supercharger. Since the centrifugal is driven by the engine crankshaft, the higher the rpm the greater the air flow and more severe the problem. Assuming the inlet air temperature into the engine is 100, the boost temp must be added making 170 the temperature the engine sees under 7 psi boost conditions (7 psi X 10 = 70 + 100 ambient = 170). In some cases the elevated air charge may not be desirable. For example, NOX emission increase with temperature. Since the bypass valve eliminates most of the work of compressing air, the supercharger's parasitic losses are also reduced under normal non boost driving conditions. During idling or part throttle non boost operation, the bypass valve is held "open" by engine vacuum (10"-22"Hg). This allows the compressed air in the supercharger to re-circulate or bypass to the inlet thereby lowering the temperature. When the throttle is opened and the supercharger is called on to produce boost, the bypass valve closes off the re-circulating air thereby forcing all the boosted air into the engine. Positive displacement superchargers (Twin Screw and Roots) are positioned downstream of the throttle body (suck through). If the throttle body is closed at high rpm, there is no surge problem as with centrifugals (blow through). Centrifugals react against the closed throttle blade(s). This deceleration won't harm the supercharger in any way. However, when coupled to an "idiot underhood filter" that sucks in 200 air (the equivalent to another 20 psi boost), the heat may be a problem for any supercharger - centrifugal, Roots or Twin Screw. We've said it before . . avoid exposed underhood filters in supercharged and non supercharged engines - unless you think that your engine likes all that hot air.

I've got an upcoming project that involves a 5.4L supercharged Lightning motor with a GT500 blower adapted to it.  Looks like the bypass valve does more than just what the above says.
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JimL
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« Reply #7 on: December 24, 2014, 12:29:16 AM »

Thanks for adding that Nathan.  Right down at the "molecular level" as they say, the blower rotors should not make pressure unless you absolutely know the air will flow THROUGH the rotors and not get dragged around and around inside them.  Thats why an engine that can make a lot of power (for its displacement) needs a bigger bypass valve that closes later.  Any time its not pumping pretty fast with throttle open, the blower needs to coast a bit.

At idle and very low throttle, low revs, the blower may be turning too slow to be effective (and the pulses get big enough to make your air flow sensing devices go crazy without bypass opening).  Another critical area when dealing with these blowers is the airflow through the air filter to the Airflow Meter, especially on the common "hot-wire" AFM.

Production air filter housings are carefully designed to keep the air flow through the hot-wire clean and even.  Most aftermarket air filter kits use straight through tubing between an air filter and throttle body, with the AFM inserted somewhere in the tube (pretty much wherever the stock wire reaches).  On various occasions, I mapped the airflow measurements on some of these.  I found big errors and "holes" in the measurement at various parts of the powerband except top end, and idle.

The best "correction", besides putting the good parts back on, is a section of intake tube about 3-4" before the hot-wire that has a pair of flat blades arranged in a T pattern.  The upper quadrant of the T can be about 1/3rd down from top of the tube circle.  The blades, about 2" chord length, straighten the airflow for two different scenarios: rapid airflow increase on the low end, when throttle is dumped open, and intake tract air spiral length that changes rapidly as the "tuning" gets right passing through the mid-range.  The section of tube with the T installed is clamped to rubber tube at each end.  This allows you to test air measurement at different orientation of the T.  Once you hit the right angle you will know, because all the "bog" and "lean surge" suddenly disappears.

Hot-wire AFMs are most sensitive (give the biggest rate of change per pound of air) at the lower airflows.  Near the top end of the AFMs designed capacity the measurement is much less accurate and responsive.  On a 300HP engine, that peak flow rate of about 30 lbs/minute may measure anywhere from 28-31 lbs/minute. The ECM doesnt care...its running pretty much on the "open loop power map" and says "whatever....heres a chunk of fuel, so you deal with it".  This is where some folks get in trouble with too-large capacity AFM and throttle body.  I was told that too-big carb can be trouble also, because it can get into too much airflow for mid-range circuit at those throttle settings.  I never messed with those, however, but it stands to reason that full power enrichment areas of throttle plate opening should match the real airflow the blower adds....its probably complicated.

The reason I mention that last AFM bit, is because you can have really strange things happen in the mid-range airflow measurement if something is odd with your air filter or intact tract.  One of the celebrity Celicas (I remember John Elway had that car, that year) was definitely weak on mid range acceleration.  The problem turned out to be one damaged clip (out of four) on the cover of the air box.  When the intake tuning started working in the midrange, the cover would pulse and the AFM measured less airflow.  After we replaced that damaged clip, the car ran perfectly.  Some of the aftermarket air filters (big, cone shaped) can get soft, over time, and the AFM will undermeasure every time you start getting into the strongest torque range of your engine design.

Intake tuning is no different on a blower engine, than on NA.  You still need to hit the tuned lengths for the powerband you are using.  If you get it wrong, you can get some heavy pulsing in the intake tract that gives a "shudder" feel at large throttle.  When I was working on the Turbo Highlander Hybrid we had some struggles with that.  Because the Atkinson Cycle on a Hybrid only runs with large throttle opening we had to run the turbo off the front three cylinders, only (otherwise, it stays spooled all the time).  The higher airflow, when we got on boost, was really showing some problems on the air flow measurement side.  The intercooler was scrambling the tuned length between the AFM and the cooler inlet, because the other side (the runner side) was seeing the intake "pump back" effect of Atkinson Cycle operation.  I moved the length of that inlet tract area out to 14" and it ran fine. 

Getting the EVAP system to work, purge the Charcoal Canister, and not throw codes...was a whole other animal.  Nature never intended your Charcoal Canister and gas tank to see boost pressure so high and so quick, as what a Hybrid does!  In the end, we made a lot of power for street use but we could not overcome two problems.  Every time you lifted throttle on a long downgrade, the Hybrid system shuts down the engine (normal).  The turbo started cooling and that delayed relight of the Catalytic Convertor (kiss of death for that project!). The other problem is that the tires wouldnt squeal when you started boiling them if you stabbed full throttle at 30mph.  Between the big electric motor, and the added push of the turbo V6, the tires just hissed (not even as loud as the intake noise).  Your first clue was vague steering and smoke coming out of the dash vents (the Heater-A/C plenum has drain flow open into the front wheel-well area on most cars).  I guess thats really operator error. wink

Now I am getting off track because this is about a fellows Whipple blower.  Thanks for your patience with another trip down memory lane! embarassed

Good night,
JimL
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JimL
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« Reply #8 on: December 24, 2014, 01:00:45 AM »

Forgot something for ronnieroadster and you, Nathan.  Back in the 70s emissions days, when most everything was carbs, there were devices used on some systems called "vacuum transmittng valve".  These could take a very small or finely calibrated vacuum signal and use it to turn on larger vacuum to another device, from a small storage tank that "saved high vacuum" gained on decel.  You often found small vacuum canisters here or there under the hood of some models.  I remember GM had a round black ball, about the size of a big softball....or maybe it was Ford...hmmm.

For this carburetor application, you might research those old systems to put together a positive control system method of that bypass valve, even in the event your cam is too lumpy.  If we cant find the old device, a vacuum signal control switch could operate a vacuum solenoid to get bypass at lower vacuum using a storage canister (fed by a one-way valve from the vacuum source).

In a worst case scenario, where you cant make and store enough vacuum, mid-80s Camry with Cruise Control had a small 12v vacuum pump in the engine bay.  I think other manufacturers did that, also.  That pump could pump down your storage canister and you would always have control even at higher altitude.

I really appreciate that you started this, and that Nathan jumped on board and helped out.  That roundabout brainstorming has handed me the solution for how to control the bypass valve for my Eaton r410 I am fitting on my 680cc V-twin.  Now all I need are some really old emissions manual....might have some in the garage attic.  Then I will need a friendly junkyard.

JimL
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JimL
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« Reply #9 on: December 25, 2014, 01:15:56 AM »

This might be useful....and cheap.

http://www.ebay.com/itm/ADJUSTABLE-VACUUM-SWITCH-KIT-700R4-200-4R-350C-6-22-SUPERIOR-K058-TRANSMISSION-/250987009002

  The electrical output/ground could switch a common VSV and it is adjustable for the vacuum switch point.  The three-port VSVs found on many junk cars will often have a normally-open and a normally-closed port arrangement.  I think I will plumb for "normal open" bypass valve, with a vacuum canister for supply.  That way if something goes wrong I will feel the power lag and see the boost drop off....and turn out.

Ronnieroadster....you might consider a dash switch to "short period" test with bypass on or off.  It could be useful during the debugging stage.  I am really ignorant of what happens on a carb when it goes from normal flow to blower flow.  The ability to cross-check will make it easier to decide what vacuum level is best for that transition.  I can envision a condition where too much vacuum in the carb (due to too much blower, to early) might backflood some carb circuits that would give a pretty long period of unstable running.

If that condition reached  into a detonation potential range, it might pe trouble.  Back in my carb days, as a dealer mechanic, we often had cars with partially plugged idle and low speed circuits.  This was common in the Spring, when cars that had been parked over the winter were brought out (many of us drove beater 4WD in Colorado winter and a good car the rest of the year).  The quick and effective way to get them cleared was to rev them up with the air filter off, and slap a folded up redrag over the carb mouth as we yanked full throttle.  The high vacuum sucked fuel backwards through everythng.  We would yank the rag off before the engine stalled and wait for it to clear as we gradually eased throttle back to idle.

You might find a little bit of that type condition could occur, depending on your bypass setup.  You are trying to make the result of every shift smooth, controllable, and predictable ramp up of power on the salt.

Anyway...This trans kit gadget could control them, though you might use a 5v power supply to run a TIP120 transistor to power or ground the VSV.  The vacuum sensing switch would only have to handle the low voltage, low current, off of the 5V limiter circuit, through a resistor to the base of the TIP120.  You only need a little over half a volt to turn those on.

   TIP120s can handle 10 amps at 12v, which are the type I used when I built the transistor-to-transistor logic circuits TRD needed  (prototype breadboards) to test control functions for various kits.  The production controllers were mass produced as PICs using final logic settings from those prototypes (too complicated for me).

Which reminds me....I still have one of the prototype controllers I built for the Camry V6 supercharger project, if I can find it.  Time to repurpose that thing for my bike.  Gosh...I think if it wasnt for this board, I wouldnt be able to remember anything, sometimes. cheers

JimL
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ronnieroadster
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« Reply #10 on: December 25, 2014, 10:30:29 AM »

 Here's my update on the bypass. Jon Bond supplied to me a bypass valve which is a direct mount to the Whipple. Sizing the outlet diameter of the bypass valve I matched that size with aluminum tubing that now directs the flow into the intake manifold I built.
   Quickfuel built me a proper sized carb for the new combination that has a dedicated vacuum port for the bypass valve. Once I'm underway on a run the bypass will of course close and since I run a manually shifted automatic I think there will be no overheating in the blower since the shifts are very quick.
   I like the idea the vacuum being completely controlled by the carb throttle plate position this should work fine. At the end of the pass when I lift off the throttle the vacuum signal will once again open the bypass keeping the blower temps in check until I shut the motor off. Seems simple enough looking forward to trying the new combination in the spring.
  Since my experience has been with GMC superchargers there was no need for the bypass valve. Thanks to everyone's input my learning curve with the screw type blower has been greatly advanced.  cheers
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Working in the shop I use the 'F' word a lot. No not that word these words Focus and Finish go Fast and Flathead Ford!
 ECTA  XF/BGRMR Record 179.8561
 LTA    XF/BGRMR  Record 186.946
 SCTA  XF/BGRMR Record 192.448
 SCTA  XXF/BGRMR Record 216.131 plus a Red Had
NathanStewart
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« Reply #11 on: December 30, 2014, 01:36:38 AM »

Thanks for the follow up Jim! Sounds like you've got quite a history behind you. We'll have to get together some time as I'd like to hear more of your stories.
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