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Dump Valves.

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I have x2 HKS Dump Valves fitted to my V8 Esprit. I was about to hook up a turbo boost guage and tap into the vacuum pipe which connects both of these DVs together. However, I have just noticed the pipe isn't connected to anything and have no idea where and what it attaches to?

Looking at the 20th picture down (4th from the bottom), the pipe seems to vanish into the plenum


Thanks very much!

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It does what you've said, it connects into the plenum.

That way as you close your throttle and the butterflies close, the resistance to air flow creates a pressure differential, with the engine side higher than the turbo side of the butterflies. That's the trigger for the dump valves to open and dump the rest of the boost until pressure equilibrium is nearly achieved (spring in the dump valve requires there to be a small amount of pressure differential else it is closed).

So, tap into that pipe and you're at inlet manifold pressure.

Tap into one of the pipes from the turbos to the butterflies ad you're reading available boost.

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Cheers Andy...

I have been back down to the car, still can't see where on the plenum it connects to - anyone got a picture or instructions?

Thanks again!

I guess the mechanic must have knocked it out when replacing the turbos, water pipes etc.


I found it, cable is supposed to go under the right hand airbox and taps into (using a tee-piece) into the pipe which connects to the boost solenoid valve...

What is worrying - the red pipe which would normally conenct to the solenoid valve was hanging off :D

Wiith this pipe not connected to the plenum, would this have caused any issues?


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Sounds like you figured it out. Yes the dump valve vacuum line goes under the plenum and tees off the hose in the back of the plenum. Now having the vacuum line to the boost solenoid off will result in uncontrolled boost. Meaning your wastegates will remain closed and you'll boost as much as the turbos will give. Not good.

Edited by gmendoza

'03.5 Final Edition Esprit ~ 5.7lbs/hp

mildly modded - 430rwhp, 353rwtq

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That might explain why I was not getting any over-boost code and/or limp mode with both my wastegates being seized :D ..... (see my other thread).

One turbo already replaced and the other getting done now.

I also bought a boost gauge, getting this fitted tomorrow.


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  • 3 months later...


Max. boost is about 0.75 bar, so there are no factory installed BOVs.

The problem with a BOV is that it doesn

Edited by mike_sekinger

1996 Esprit V8, 1998 Esprit V8 GT, 1999 Esprit S350 #002 (Esprit GT1 replica project), 1996 Esprit V8 GT1 (chassis 114-001), 1992 Lotus Omega (927E), 1999 Esprit V8SE, 1999 Esprit S350 #032, 1995 Esprit S4s, 1999 Esprit V8 GT (ex-5th Gear project), 1999 Esprit V8SE ('02 rear)

1999 S350 #002 Esprit GT1 replica

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  • 2 weeks later...

My little red boost control pipe fell off (discovered shortly after and fixed out of fear) and it really shows you what the engine can do and how de-tuned it is...I was getting wheelspin in all five gears up to 90mph. Admittedly it was wet, but, I was using Kevin(GTO)'s tall gearbox with LSD so that's BOTH back wheels spinning at 90mph with a 5th gear ratio which would be 24mph taller than standard (sixth gear if you like) What a pity the standard gearbox would break a week later if expected to cope with this much power. Even a Murcielago driven a few weeks later didn't feel as quick.

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