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4-Cyl. Esprit Turbo Upgrade
by Dermot O'Hare

Dermot’s Latest Mods
(1) Re-Plumping of the Dump Valve Exhaust Gas
Many people including myself are opting for the recirculation type dump valve, supplied by Justin McAulay (justin@meanmachine.co.uk; dumpvalve.html). The is no difference in performance between the recirculating and non-recirculating versions. However, by re-routing the exhaust or “dumped pressure” back into the inlet system this has the effect of silencing the system and thus lowered the loudness of that whoosh….

Oil Mist Catch pot
High performance engines and race cars all routinely fitted with catch tanks to collect oil mist that is produced by pressurisation of the sump. Of course, in the Esprit Lotus decided to plumb the exit of the crankcase breather pipe back in to the airbox. The result is that oil mist is fed back into the engine. The effect of oil mist in the air intake is to dramatically increase the potential for engine knock by lowering the effective octane level of the air/fuel mixture. Oil is not as volatile as petrol and the effect is the explosion that pushes the engines piston down is not as violent which equals less power. Oil vapour also encourage the engine to 'Pink', when the engine 'Pinks' then there is a sensor on the engine 'Knock sensor' that detects this and retards your ignition timing to prevent pinking happening again. Again this retarding of the ignition timing by the ECU reduces power. The solution is to fit an oil mist catch pot and blank off the hole in the airbox. The Mocal catch pot is a nice small (1L) alloy tank, it comes in a range of colours and has a fill indicator and breathable top

I found by trial and error that it could be mounted on the side of the airbox. Correct location on the side of airbox means it does not interfere with either the spark plugs or direct ignition module and the engine cover does not have to be modified. Some new hose is then required to complete the plumbing back to the crankcase breather. Keeping a variety of extra hoses on hand is always a good idea. That way when you need to replace the breather hose or the radiator hose you will have the parts on hand and can complete the job quickly.

NOTE: When I looked in my airbox and the air intake hose to the turbo there was significant oil build up. That can only be coming from the crankcase or turbo oil seals.


(3) Turbo Upgrade
The 1990-1993 SE and 1993-1996 S4 were fitted with a Garrett T3 with a 50 trim compressor wheel. It has a maximum flow rating of 30 lbs/min at a pressure ratio of 2.2 (1.2 bar boost) with 58% efficiency.

The 1994-1996 S4s was fitted with a Garrett T3 with a 60 trim compressor wheel. It has a maximum flow rating of 34 lbs/min at a pressure ratio of 2.3 (1.3 bar boost) with 64% efficiency.

There are some fantastic articles written by John Welch on Esprit Turbos. If money was no object his WC Engineering Ceramic Ball Bearing Turbo would be the way to go.


The bottom line is that once you start producing a very free flowing engine setup; air filter, ram air mod, exhaust mod, de-cat pipe the turbo then become the weak link in the system. The turbo in the S4 cannot flow enough air at the top end, the result is that the inlet temperature (MAT) raises very dramatically and boost drops away. In fact there is a condition in which increasing the boost will actually produce lest power.

Having decided to “mod your turbo” the main problem is deciding what to do to it. If you get this wrong, talk to the wrong people you will end up getting a system that is great for mach 1 but has massive turbo lag. VERY FEW PEOPLE KNOW WHAT THEY ARE TALKING ABOUT.

I talked to a lot of people and decided to go for the following modifications to my T3-50 turbo:

(i) 360 deg thrust bearings.
(ii) slightly bigger super 48 compressor wheel with different angle (+housing).
(iii) high performance wastegate capsule (stiffer spring + bigger diam.).

The compressor wheel has the blades at a different angle of attack.

plus full re-balancing of the whole assembly.
This was all arranged by:

This should offer modest increase in airflow and good response.

Over last weekend Justin came up for the weekend and instead of going to the film shoot and we decided to change the turbo over ourselves. The book time is 4 hrs. It took us about 10-12 hrs with some extra help from Richard Cambers and his Dremel tool, carbon discs and chisel.

I did not get time to try the car out yet in the dry, I will be reporting back in the coming week and showing it of at Stoneleigh next weekend. Dermot


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