turbo and induction system

[andy b]

Ok i have bought a laid up since 2002 82 turbo, i have got the engine now on 4 can someone in simple terms explain about the waste gate operation and what is the bolt on ali hose connection on the plenum box it has a spring loaded nylon plunger inside it. i do not have any hoses on this is it connected to any thing. also from the engine breather it has a flexible pipe going to the inlet side of the turbo is as simple as that with no oil trap, i have looked at other posts and it looks as if i need to learn a lot more i just thought the turbo just forces in fuel, the more i have read the more i realise i don't know, especially the part where you are pulling hard at full rpm and you shut the throttle to change gear as i have read the turbo is well spinning and the pressure has to go some where.

the manual ant much help

andy b

[Bibs]

http://auto.howstuffworks.com/turbo.htm

The turbo forces in air, not fuel. Have a look through ^ that for basic turbo operation.

[trackmagic]

Andy,

Good luck on your new project. If you haven't done so already you need to invest in a parts and service manual. In it you will find exploded view(s) of all the major components and the service manual explains in pretty good detail all the functions you are interested in.

On your 82 Esprit the wastegate is spring loaded to keep the valve shut. When the turbo produces boost, the line from the turbo to the wastegate will eventually push the valve open. In order for it to be functioning properly the wastegate valve needs to move freely and the diaphragm inside needs to seal properly.

Best,

Jeff

[andy b]

Thanks Bibs

But it would help me with a more specific insight to my 82 turbo system it looks pretty basic but when i run the car on the road i do not want to melt anything. as some of the post's i have read i really don't want a disaster.

[Simon350S]

The last part of your post explains the function of that alloy bit on the plenum.

When the throttle shuts, the excess boost is vented out past the nylon plunger. There is no hose connected to it, it just vents into the engine bay. Make a horsey fluttering kinda noise when you change gear or lift off the throttle. Just make sure the nylon plunger is free to move as if it gets stuck you can start having problems.

Also check to make sure you are not overboosting on your dash guage as if you are it can cause serious internal failure of the engine. Common cause could be the wastegate diagphram holed. The wastegate is fitted between the end of the exhaust manifold and the turbo. You'll see it hanging down underneath the manifold like a little darlek.

The engine breather has no filter so your all good there as well.

Post up some pics of your car then

Edited August 7, 2011 by Simon350S

[910Esprit]

I reckon that device is a simple pressure release valve and does not do anything in normal service. The plenum is full of all kinds of fuel fumes. oil vapour, etc (as the crankcase is recirculated into the inlet). It would be highly questionable (illegal?) design to vent this to atmosphere (explosive and polluting). This can also be evidenced by examining the outlet from the valve. Mine is bone dry with zero contamination of the engine bay. Flutter noise is a combination of compressor stalling and wastegate operation - well thats my opinion!

[andy b]

well it does look a bit odd to a new owner with a car that has been worked on and not completed the car was supplied with a big box of leftover bits hence my question

thanks people.

[molemot]

O-kay...the alloy thingy on the plenum is, I believe, intended to deal with extreme overpressure situations...backfiring etc. whereupon it vents the overpressure to atmosphere. Possibly also with the overpressure resulting from a gearchange at max boost. It has no hose fitted and, as has been said, is serviceable as long as the innards move.

The wastegate is the thingy hanging down from the exhaust manifold extension piece. One of the exhaust pipes comes from it, and there is a small diameter copper pipe feeding into it from the compressor side of the turbo. This pressurises the diaphragm on the wastegate and, when the boost pressure reaches the limit as determined by the spring in the wastegate and the thickness of the aluminium spacers, the wastegate diaphragm moves and opens the wastegate valve, allowing the exhaust gas to bypass the turbo turbine and thus limits the boost pressure. The crankcase is vented directly to the turbo compressor air inlet, and there are two other connections.....one from the oil gallery via a Goodrich braided hose to deliver oil to the turbo, and a convoluted stainless drain to convey this oil back to the sump. It's about the simplest possible turbo system.

Keep a weather eye on the boost gauge...if the wastegate diaphragm gets a hole in it, or the wastegate valve seizes in it's valve guide, the boost will rise to higher levels than the innards of the engine can readily deal with and holey pistons can result.

[andy b]

brill thanks andy b

[Simon350S]

I reckon that device is a simple pressure release valve and does not do anything in normal service. The plenum is full of all kinds of fuel fumes. oil vapour, etc (as the crankcase is recirculated into the inlet). It would be highly questionable (illegal?) design to vent this to atmosphere (explosive and polluting). This can also be evidenced by examining the outlet from the valve. Mine is bone dry with zero contamination of the engine bay. Flutter noise is a combination of compressor stalling and wastegate operation - well thats my opinion!

Always appreciate an opinion but in this instance it's very wrong.

Sorry mate and don't mean to sound patronising but that valve does exactly as I explained.

[910Esprit]

No it doesn't - Block it up and test your car out.

Edited August 9, 2011 by 910Esprit

[molemot]

Let's not get to handbags at dawn, chaps!! Back in my early days with the supercharged MG TC, the inlet manifold incorporated what was termed an Explosion Valve...now THERE'S a name to conjure with....and it was very much the same sort of thing as the valve on the side of the plenum on the turbo. The TC had a "suck through" supercharger system, which sucked the mixture through a 1 3/4" SU carburetter, compressed it in the vane type Shorrocks blower, and then squirted the resulting compressed mixture at about 6psi into the manifold. The Explosion Valve was there to deal with backfires and other overpressure situations....and pretty desperate they could be, too, considering the inlet was full of an explosive compressed mixture! This, plus the Lotus parts list description of "Dump Valve" makes me think that the ally dongle on the side of the plenum is intended to dump overpressure during high performance gearchanges or backfires. Without the valve, damage to the turbo compressor could result. Blanking it off would probably result in no obvious change, as it only gets used "in extremis".

[910Esprit]

No handbags, just opinions... Thats my point John, its an 'emergency' valve irellevant to normal use. I agree that its function could be to cope with 'explosion' type events in the induction system. Reasoning:

There is no way the manufacturer would vent the closed loop crankcase ventilation to atmosphere on each gearchange under boost! (not even legal for FIA?)

There is no oil contamination on the bellhousing, where the outlet is directed (what kind of s*** design would that be?

The part number is identical for LC and HC - i.e. it is not a closely calibrated part - and not tied to the closely controlled wastegate calibration (which it would need to be to perform the suggested function)

There is no reference to its function in the manual which suggests its not part of any normal fueling

As a single valve BOV (a dump valve venting to atmosphere) it would make a very characteristic hissing/wooshing noise

A fluttering noise, familiar of our carb turbos, is the noise of a stalling turbo - precisely as there is no BOV/Dump valve in normal circuit.

[molemot]

This has got me fascinated...Lotus, being Lotus and a penny pinching lot (as we all know from working on them!) would surely not have fitted this Dump Valve unless it had a defined purpose. If it could be left off with impunity..they'd have binned it. Blow off valves do still dump the excess pressure to atmosphere ( apart from being banned by the FIA) and I think that some experimentation to find the pressure at which the valve opens might be in order. Things intended for explosion protection would, I think, have a pretty strong spring and thus a high opening pressure....if it was intended to dump excess turbocompressor pressure when the throttle butterflies slam shut, then the spring would be weaker and the valve operate above normal boost pressure, but not vastly so. Thing comes off easily enough....maybe a task for tomorrow!!

[910Esprit]

Good man! I await further developments....

[Simon350S]

Got a spare sat in the garage, seem to remember being able to blow it open reasonably easily. If I find it I'll check.

Right. Just checked and carried out a very scientific test. I pushed it with my thumb and it easily opened.... And then stayed open!

Clearly it needs a clean but I'm off out for the day.

Its definitely not a strong spring, took very little effort to open.

[AJay]

HI chaps it is a mechanical BOV or blow off valve. it was a mechanical overboost protection device. it is designed to operate at 10psi which is not a lot of pressure it you use your thumb, however it should close as soon as you release the pressure unless the piston is sticking. Under normal driving it should not operate, however it can operate under spirited driving on the overrun when the throttles are snapped shut while at full boost, i'e changing gear... you will get a spike of over 10psi... it should sound like the number 7 bus with a psssssss as you change gear... It was replaced with an electronic over boost switch on the HC engine set at 10.5 PSI this information has been supplied to me by Dave massey (Lotus technical) a number of years ago...

Hope this helps

[andy b]

velly intelesting chaps car is coming on well checked and refitted the air con rad today i have to run new pipes to the compressor next, i rang paul matty's cheif mechanic and he tells me to remove the inner sill to get access remove the door rubber peel back the carpet and drill out rivets. sounds easy,

andy b

[Roger 912]

The garage that fitted my EFI lost the Lotus dump valve and in its place fitted one from another vehicle. This one is also bolted on to the plenum but has a connection to a vacuum pipe. As soon as the foot is lifted off the gas pedal, the vacuum opens the dump valve and a lovely fizzy noise greets my ears as the excess plenum pressure is dumped.