Blow off Valve
Discussion
Hi Alan,
Have a look at:
www.espritfactfile.com/Procedures.html
There's a couple of articles on there about this.
Regards
John
PS, Any joy with the gear shift problem yet?
Have a look at:
www.espritfactfile.com/Procedures.html
There's a couple of articles on there about this.
Regards
John
PS, Any joy with the gear shift problem yet?
Thanks all. So far no joy on the gearbox problem. It appears that most of the b.o.v's are designed to go on the chargecooled cars. Have e-mailed justin (from the stuff on this site) but it appears his set up is for chargecoolers only. Any way round fitting to a carb/non chargecooler car????
Alan
Alan
Blow off valves are relatively simple, especially the non-recirculating type. Seems like you could find one with a threaded fitting on the intake side, drill and tap your aluminum intake pipe to accept this fitting and simply screw it in. If you want to use the quieter recirculating type, you would need to run a hose back into the turbo inlet hose or air box.
I asked this question too. Jim Lotusguy tells me that on my carbed turbo, there is already a BOV factory fitted which lotus call a dump valve.
Have you done any other mods on your motor?
Is yours a carbed or fuel injection?
Are you going to Donnington this weekend, if so which day?
Cheers,
Dave Walters
Have you done any other mods on your motor?
Is yours a carbed or fuel injection?
Are you going to Donnington this weekend, if so which day?
Cheers,
Dave Walters
Ummmm Dave...
superdave said:Jim Lotusguy tells me that on my carbed turbo, there is already a BOV factory fitted which lotus call a dump valve
BOV (Blow Off Valve) Is the American name for it
Dump Valve Is the English name for it
They are exactly the same thing, and not just a name made up by lotus (like Charge Cooler)
www.lotusespritworld.co.uk/EMaintenance/dumpvalve.html
Child0fthecorn said:Ummmm Dave...
superdave said:Jim Lotusguy tells me that on my carbed turbo, there is already a BOV factory fitted which lotus call a dump valve
BOV (Blow Off Valve) Is the American name for it
Dump Valve Is the English name for it
They are exactly the same thing, and not just a name made up by lotus (like Charge Cooler)
I think you know what I meant. I was merely trying to explain that a dump valve is already fitted on a carbed Turbo. This info came from Lotusguy (Jim MacFadden). There's no need to split hairs hey.
Cheers,
Dave Walters
www.lotusespritworld.co.uk/EMaintenance/dumpvalve.html
Sorry Dave, didn't mean to split hairs or anything, just trying to help out. its the way you said "...there is already a BOV factory fitted which lotus call a dump valve" lead me to wrongy assume that you thought only Lotus call them Dump Valves, a simple misunderstanding
superdave said:I think you know what I meant. I was merely trying to explain that a dump valve is already fitted on a carbed Turbo. This info came from Lotusguy (Jim MacFadden). There's no need to split hairs hey.
apologetic Tony
(PS. I didn't know that Lotus factory fitted BOV's to Carbed Turbos, is this true? I haven't seen it mentioned anywhere)
Hi all,
Seems a little further clarification is in order. A Blow-off Valve (BOV) and a Dump Valve (used on Lotus Carb Turbos) are different animals.
A Dump Valve is a basic pressure relief valve and is sometimes called a Pop-off Valve. Have you ever seen or used a household pressure cooker. That little device on top of the lid that vents steam pressure to keep the pot roast from being blown all over the ceiling is, in essence, a Dump Valve.
A boost Dump Valve monitors the pressure within the plenum upstream from the throttle plates and vents when the boost pressure reaches a pre-set limit.
It is not a smart valve, it's oblivious to throttle position, intake manifold pressure/vacuum or turbo rpm. The Dump Valve "single mindedly" monitors plenum pressure and vents excess pressure without consideration for other factors. When the plenum pressure drops below the preset limit, the valve closes again.
The Dump Valve will vent during full throttle conditions anytime the boost pressure exceeds the preset limit for whatever reason. It will also vent
when the throttle is closed abruptly during a boost condition. When the throttle closes the turbo output suddenly has no where to go, and the plenum pressure spikes. The Dump Valve will open if/when the spike exceeds the preset limit, govern by the spring in the valve, and close again when the pressure drops and is overcome by the spring pressure again.
The Dump Valve opens a large orifice sized to quicly vent excess pressure. But when it closes again, the turbo is still spinning and quickly pressurizes the plenum back above the preset limit, so the Dump Valve opens again at least partially. The cycle repeats until the turbo slows to the point at which it can no longer pressurize the plenum beyond the limit. The cycle occurs rapidly and seems more like a "flutter". The fluttering vent cycle is what produces the characteristic "Horsey Noise".
A Blow Off Valve is similar to a Dump Valve, but adds an external control circuit and vents the plenum in response to throttle position. A Throttle Position Switch (TPS) could be used to actuate the BOV, but on older carburetted, non-ECU engines, the BOV typically monitors manifold vacuum downstream from the throttle plates since closed throttle = high manifold
vacuum. A vacuum port is located in the side of the intake manifold where it will be 1) immediately downstream from the throttle plates when they are
fully closed and 2) upstream from the plates as soon as they are cracked open. A vacuum line runs from that port to a diaphragm in the BOV.
When the throttle is closed, the port applies high vacuum to the BOV diaphragm to open the valve and vent plenum pressure. When the throttle is cracked open, the throttle exposes the port to plenum pressure, killing the vacuum at the diaphragm and closing the valve. Hence, the BOV operates in response to throttle position, venting the plenum when the throttle is closed. It remains open/ venting as long as the throttle remains closed. Typically the BOV does not cycle or flutter, so the usual sound is one smooth whistle... no flutter.
If the throttle is slammed shut when the turbo is fully spooled up and at full boost, the sudden high back pressure condition can physically damage
the compressor wheel, and will definitely cause the turbo to rapidly slow down. Then when the throttle is opened again, the turbo will have to accelerate again before achieving full boost. The result is "turbo lag".
The BOV vents the plenum back pressure, allowing the turbo to keep spinning at high rpm, and preventing the damaging pressure surge.
The Dump Valve is a pressure relief / over-boost protection device, whereas the BOV is a throttle-sensitive plenum vent.
The waste gate is quite different in that it does not vent plenum pressure. It vents exhaust gasses, by-passing the turbine wheel in order to control
the amount of boost produced in the first place. Dump and Blow-off valves limit boost "after" it's delivered to the plenum.
The wastegate and Dump Valve both monitor "plenum pressure" and act to control and limit available boost levels. The Blow-off valve monitors "throttle position" (manifold pressure) and vents the plenum to kill any boost present at times when boost is not wanted (closed throttle). Hope this better explains the two. Happy Motoring!...Jim '85TE
Seems a little further clarification is in order. A Blow-off Valve (BOV) and a Dump Valve (used on Lotus Carb Turbos) are different animals.
A Dump Valve is a basic pressure relief valve and is sometimes called a Pop-off Valve. Have you ever seen or used a household pressure cooker. That little device on top of the lid that vents steam pressure to keep the pot roast from being blown all over the ceiling is, in essence, a Dump Valve.
A boost Dump Valve monitors the pressure within the plenum upstream from the throttle plates and vents when the boost pressure reaches a pre-set limit.
It is not a smart valve, it's oblivious to throttle position, intake manifold pressure/vacuum or turbo rpm. The Dump Valve "single mindedly" monitors plenum pressure and vents excess pressure without consideration for other factors. When the plenum pressure drops below the preset limit, the valve closes again.
The Dump Valve will vent during full throttle conditions anytime the boost pressure exceeds the preset limit for whatever reason. It will also vent
when the throttle is closed abruptly during a boost condition. When the throttle closes the turbo output suddenly has no where to go, and the plenum pressure spikes. The Dump Valve will open if/when the spike exceeds the preset limit, govern by the spring in the valve, and close again when the pressure drops and is overcome by the spring pressure again.
The Dump Valve opens a large orifice sized to quicly vent excess pressure. But when it closes again, the turbo is still spinning and quickly pressurizes the plenum back above the preset limit, so the Dump Valve opens again at least partially. The cycle repeats until the turbo slows to the point at which it can no longer pressurize the plenum beyond the limit. The cycle occurs rapidly and seems more like a "flutter". The fluttering vent cycle is what produces the characteristic "Horsey Noise".
A Blow Off Valve is similar to a Dump Valve, but adds an external control circuit and vents the plenum in response to throttle position. A Throttle Position Switch (TPS) could be used to actuate the BOV, but on older carburetted, non-ECU engines, the BOV typically monitors manifold vacuum downstream from the throttle plates since closed throttle = high manifold
vacuum. A vacuum port is located in the side of the intake manifold where it will be 1) immediately downstream from the throttle plates when they are
fully closed and 2) upstream from the plates as soon as they are cracked open. A vacuum line runs from that port to a diaphragm in the BOV.
When the throttle is closed, the port applies high vacuum to the BOV diaphragm to open the valve and vent plenum pressure. When the throttle is cracked open, the throttle exposes the port to plenum pressure, killing the vacuum at the diaphragm and closing the valve. Hence, the BOV operates in response to throttle position, venting the plenum when the throttle is closed. It remains open/ venting as long as the throttle remains closed. Typically the BOV does not cycle or flutter, so the usual sound is one smooth whistle... no flutter.
If the throttle is slammed shut when the turbo is fully spooled up and at full boost, the sudden high back pressure condition can physically damage
the compressor wheel, and will definitely cause the turbo to rapidly slow down. Then when the throttle is opened again, the turbo will have to accelerate again before achieving full boost. The result is "turbo lag".
The BOV vents the plenum back pressure, allowing the turbo to keep spinning at high rpm, and preventing the damaging pressure surge.
The Dump Valve is a pressure relief / over-boost protection device, whereas the BOV is a throttle-sensitive plenum vent.
The waste gate is quite different in that it does not vent plenum pressure. It vents exhaust gasses, by-passing the turbine wheel in order to control
the amount of boost produced in the first place. Dump and Blow-off valves limit boost "after" it's delivered to the plenum.
The wastegate and Dump Valve both monitor "plenum pressure" and act to control and limit available boost levels. The Blow-off valve monitors "throttle position" (manifold pressure) and vents the plenum to kill any boost present at times when boost is not wanted (closed throttle). Hope this better explains the two. Happy Motoring!...Jim '85TE
(PS. I didn't know that Lotus factory fitted BOV's to Carbed Turbos, is this true? I haven't seen it mentioned anywhere)
Tony,
Lotus did fit a 'Dump Valve' (Lotus Part # C910E0928F) to the carb'd cars. This valve is located on the rear of the plenum and also serves as the mounting point for the fuel regulator which sits directly on top of it. If you don't know where to look, you probably won't ever notice it. It is a simple spring loaded piston type valve.
Since the carb'd turbos are calibrated to produce 8.0 and 8.5 PSI of boost, the spring is rated higher than that. When the throttle plates close (as when decelerating or shifting gears), this pressure spikes and overcomes the spring pressure and the valve opens. I recalibrated my wastegate to allow 10 PSI of boost, and that still is not sufficient pressure to open the valve. This means that the pressure spike in the plenum upon deceleration exceeds 11 PSI.
It's primary function is not to prevent overboost as in a typical application. It's purpose is to control the fuel pressure regulator by venting the plenum pressure which, combined with the microswitch actuated by the throttle spindle, signals the fuel pressure vacuum solenoid to switch from providing boost to the fuel pressure diiaphram to vacuum supplied by the #1 cylinder. This drops the fuel pressure from 5.0 PSI to 3.5 PSI.
Once the turbo spools back up, producing boost, the system reverses itself to apply higher fuel pressure to the carbs. Hope this helps. Happy Motoring! Jim '85TE
Nope unfortunately thats not me, I haven't got an Esprit yet still looking around collecting all the information I can so I can get a good one first time round and not get burnt by lotus ownership. Its best to go in with both eyes open I find
superdave said: Hey tony, your surname isn't Stapleton by any chance? are you the guy who going to Donnington on Sunday with John Roberts?
and thanks for explain that to us Jim, I've saved it now so I can go back to it if I need to.
Tony
Thanks for that, Jim.
I've learned something and it is appreciated. Without the forum I wouldn't know about the finer things of Esprit life, such as crossgate cables and red hoses. It makes ownership so much less painful.
Without the forum I would assume that all Esprits had a crap gearchange and would no doubt ultimately change the car without realising that the problem can be fixed.
Who would assume that a 20,000 mile car could have a knackered linkage, without knowing about cable stretch and red hose problems?
Three cheers for the Esprit forum....
Hip Hip......
I've learned something and it is appreciated. Without the forum I wouldn't know about the finer things of Esprit life, such as crossgate cables and red hoses. It makes ownership so much less painful.
Without the forum I would assume that all Esprits had a crap gearchange and would no doubt ultimately change the car without realising that the problem can be fixed.
Who would assume that a 20,000 mile car could have a knackered linkage, without knowing about cable stretch and red hose problems?
Three cheers for the Esprit forum....
Hip Hip......
Child0fthecorn said:Nope unfortunately thats not me, I haven't got an Esprit yet still looking around collecting all the information I can so I can get a good one first time round and not get burnt by lotus ownership. Its best to go in with both eyes open I find
superdave said: Hey tony, your surname isn't Stapleton by any chance? are you the guy who going to Donnington on Sunday with John Roberts?
and thanks for explain that to us Jim, I've saved it now so I can go back to it if I need to.
Tony
Unfortunately Tony, I didn't do enough research when buying my first Lotus. Didn't even know about the different models. Also didn't know about this forum until after I bought my motor. Now looking back my car wasn't the model is wanted but i've been a little lucky as it appear to be a sound cars with regular maintainance. It had interior cosmetic damage/wear and I didn't like the wheels. I knew that I could change this myself.
Would have gone for the SE if had a choice but this one came up pretty cheap and right before Christmas, there were no takers, so I had to oblige. At the time wasn't seriously looking for an Esprit, it's a sore talking point in our household. It took the wife a week to talk to me. Over a month and a half to even sit in it!.
Now Iam on the Lotus ladder, it's easier now to trade up to an S4 as soon as I have the funds. For the time being I can enjoy driving this one which Iam over the moon with. It's pretty fast enough for me and drives well.
I think that if I had done the research, it would be another year or two before I bought the right one!
There is another way of looking at it. I prefer to have two years experience now driving this one as life is not a rehersal, I could be dead in two years.
Hope that'll get you thinking now and go and buy one.
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