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'Justin Mcaulay'
4-Cylinder Dump Valves


The system has been successfully fitted to 4 Lotus Esprit models, the 2.2 litre Chargecooled Esprit SE, S4 and S4s and the 2.0 litre Chargecooled GT3.The unit is a piston type valve open not re-sirc type, which mean the pressurised air is release making a SWOOSH sound and not recirculated.

Fitting takes about 45 mins. A 13mm spanner, a screw driver and some snips are needed for assembly. Full instructions are included with help and advices available via email.

The Esprit will pull better up through the gears with reduced turbo lag.The turbo will also spin up quicker when back on the throttle as it will now keep spinning. This kit will also protect your turbo from wear, by releasing pressure which would normally stall the turbo causing increase wear and tear.

The kit costs only £155.

Email justin@meanmachine.co.uk for your Esprit Dump Valve


Customer View

I just got my turbo dump valve from Justin through this morning, whipped it open to be confronted by scary drawings of the inlet manifold in bits with gaskets everywhere. When I stopped shivering I found that the instructions were just a five or so line paragraph on a seperate sheet of paper and the scary diagrams were just to show you where a specific pipe was! Phew!

I undid the chargecoolers bolts as suggested only to find that one mount had sheared off anyhow, saving me some work. Not that it mattered, hardly rocket science. I undid the jubilee clips and yanked the old hose off, marvelled at how much oil was inside, and stuffed the dump valve hose on. Did the jubilees up again, removed the small black vacuum pipe from the front left of the engine and popped the tailor-made bit in Justin's kit into its place, then reconnected the removed hose onto the T-piece provided.

While doing so I thought I'd unplug the sensor on the chargecooler (the charge air temperature sensor I assume) to avoid damaging it, while doing so I snapped the bloody retaining clip off, rats! After connecting the hoses back up I just jammed the sensor lead back in, seemed OK.

Total time about 20 minutes including head-scratching time.

I took it for a spin and was very quickly surprised at the noise, it sounded like someone opening a bottle of coke at first, I thought it would take some getting used to and as it turned out I'd bloody well better get used to it because it goes off every time I come off the power. The more welly you give it the louder and sharper the Fssst! sound is.

While driving the "Check Engine" light came on --- oh shit! I glanced over my shoulder at the charge air temperature sensor and yep, it had fallen out. I drove cautiously home and applied lashings of cable ties. Sorted.

More confident now and wearing my normal driving shoes, I gave it some welly and fffut fffutted down the road at great speed, and yes indeed as I had hoped the power takeup when changing gear is much better, I whack it into gear and glance down to see the needle just reaching "1" on the boost gauge, much quicker than before. In fact any occasion when I slack off the power then come back on is much quicker than before, the car felt much more spritely.

After a while however I began to smell a strange smell, which triggered the visions of the engine catching fire or exploding that I always get when screwing around with my car. After a short period of sweating and gnashing of teeth I remembered what the smell was --- burning brakes. I took the hint and slackened off.

So it's working great, my granny could fit it (and she's dead) and it doesn't cost much. Not bad. When coming off the power the valve opens and the air starts coming out, but as soon as you go back on, the valve shuts and the pressure starts to build again. This means that when performing heroics with the gearchange you can get it down to a short ffp! rather than the more longer drawn-out ffffffssssssss that you get when driving like my granny (yes the dead one).

So, nice bit of kit, well made, does the job, easy to fit, cheap. Thanks Justin!

The only issue I have now is that because of the amount of oil in my air intake due to worn engine/thin oil, I'm expecting it to deposit
significant oil in parts of my engine bay that normally wouldn't get hit! Will see how it goes.

Ian Rawlings
1989 Esprit SE


What's a Dump Valve?
(blow off valves)
by Anthony Hyde

there are numerous names for compressor relief valves fitted to turbocharged engines. They all open under engine vacuum, and close firmly when positive (boost) pressure is present in the inlet manifold (or plenum chamber). A small diameter hose connects between the inlet manifold and the valve, with pressure changes opening or closing the valve accordingly.

With the valve closed under boost pressure, a sudden throttle lift-off between gear changes creates an instant *vacuum inside the inlet manifold which pulls the valve open, momentarily venting boost pressure.

* Vacuum (negative pressure) is formed in the cylinder bore when pistons decend on their "intake stroke". Vacuum transfers to the inlet manifold, and increases when the throttle plate is closed.

There is a difference between a CBV (compressor bypass valve) and the BOV (blow-off valve) and this is described below. The additional terms 'Dump valve' and 'Vent valve' would fit into the BOV catagory.

The Bosch style valves are a CBV (compressor bypass valve) style, are open most of the time under engine vacuum (idle, cruise, throttle lift-off), but close firmly under positive (boost) pressure. This open style returns the air quietly to the turbo compressor inlet.

A number of BOV's (blow-off valve) feature an adjustable spring design to keep the valve closed under idle, cruise and boost conditions (eg 0.5 bar). Sudden throttle lift-off (eg 0.8bar) opens this style of valve to vent the pressurised air to atmosphere (wooshtssh).

Cars and trucks without a vent valve emit a high shrill-whirr sound, as the compressor back cuts the air. Listen to a turbo truck between gearchanges.

Why vent the pressure? - Primary reason is to reduce strain on the compressor turbine wheel due to compressor surge. Between shifts, or sudden throttle lift-off, the turbine is still spinning fast (but slowing) pumping air at the closed throttle plate, as well as placing strain on the intercooler, hoses and fittings. A CBV/BOV keeps air from flowing backwards over the compressor wheel, allowing the turbine to continue spinning freely. When back on the throttle, boost pressure quickly rises again with little lag. A suitable valve location is just before the throttle plate.

A CBV should be used with Bosch K-Jet injection, as being a closed system, a loss of air for which fuel has been metered by the movement of the airflow sensor plate, can result in an over-rich condition and possible backfire. A CBV is found on many "OEM" original engine manufactured EFI turbo systems.

A BOV is suited to an EFI system that use a MAP (manifold absolute pressure) sensor. As the MAP sensor source is inside the plenum chamber in the inlet manifold, relieving air before a closed throttle (throttle lift-off) will not affect running.

Whether you decide to vent/wooosh to atmosphere with a BOV , or quietly back to the turbo compressor CBV, magazine tests have shown little performance difference between the two, other than the aural sound.

Press Play to hear the Dump Valve again


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