Cooling down with water injection

Why water injection?

The water injection concept has been around for a very long time & has been used on supercharged piston engine aircraft, rally & formula 1 cars etc. LMG first used water injection in the late 80's to suppress pinking on normally aspirated MGB's running 10.5:1 flat top pistons with high compression ported cylinder heads. Before the introduction of intercoolers Saab used water injection on their successful rally winning 99 turbo, requiring a large water tank reservoir, and offered a tuning kit for their turbo road cars allowing boost & power to be reliably increased from 145 to 160 bhp and beyond. With the re-introduction of superchargers for MGA, MGB & T types the use of water injection has become more important again, a necessity in fact as under load using a reasonable boost level & with the demise of 5 star petrol it is imperative to avoid harmful explosion of compressed fuel & air instead of an efficient slow burn.


With modern forced induction setups intercoolers reduce the increased temperature of the incoming charged air by around 70-90 degrees C on some engines to around 275 degrees C. This provides cooler denser intake air charge for a greater expansion of power within the combustion chamber thus allowing for higher boost without the need to run lower compression or have knock sensitive sensors retard the ignition, all of which sap power! With high running boost 6-12psi (the legendary & record breaking MG EX135 used 26 psi producing 194bhp from 1087cc in 1938) the use of both intercoolers & water injection may be required without significantly raised octane level, but these cooling aids do not increase power & torque in themselves but allow greater power & torque to be achieved safely with increased ignition advance! (see graph courtesy of ERL) One advantage water injection has over intercoolers is that there is no loss of boost when fitted. All intercoolers, especially the less modern ones, will reduce the maximum boost available by approx 3-4 psi so if running a low boost blower this could be significant. That's why with the MX5 specialists tend to fit the larger M62 supercharger red-lining at 17280, producing considerably more boost than the M45 on their 1.8 & 2.0 ltr engines.

Water & methanol injection

Water injection is a high pressure mist spray & we have tested systems varying jet size, location, pump & boost on 1800 & 2000cc standard & mildly tuned MGBs using our special cam profile.Water has a high latent heat content which allows heat to be absorbed. Using methanol 50:50 water mix may be a bit extreme for road use but it raises octane levels & importantly lowers further the incoming air temperature but is corrosive as it harms the oxide coating that protects aluminium, but less so as a mix with moderate use.If going to use a mix we recommend using less methanol such as a 30:70 ratio to water which should eliminate the risk of it becoming flammable in use. Methanol with its 116 octane, high flash point (petrol low flash point) & with its specific gravity absorbs water & will reduce or eliminate detonation in all but very extreme conditions caused by those very high combustion temperatures. It is also used as water injection anti-freeze: 13% added will protect down to -7 & 24% added protects to -18 degrees C. The 'T' type MG workshop manual recommended the use of varying mixes of fuel for different supercharged stages on tune, typically 50% methanol, 20% petrol & 30 % benzol & up to 80% methanol, 10% petrol & 10% benzol as a petrol mix. Ethanol 95% pure as a 50:50 mix (not recommended for use with some pumps) & even isopropyl alcohol which already contains 30% water can be used as an alternative to just water injection. However, methanol is the cheapest & the most effective for high performance & even may reduce the tendency for the engine to 'run on' but our mild road camshaft seems to be the most effective solution to 'run on' supercharged or in mild road normally aspirated applications. Water for most uses is more than adequate as a pinking suppressant but must be distilled otherwise the very small jets 0.3-0.6mm in size will chalk up & will require stripping down for the tiny water vanes cleaned within the jet.

Different water jet sizes

Water consumption & practicalities

Distilled water is available in 5 & 20ltr containers (approx £15.00 for 20ltrs) & these systems can use a fair amount of water in short space of time. We found that just using one of the smallest jet sizes fitted (0.04mm) before the throttle body/carburettor where no siphoning is possible used 2ltrs of water within 80 miles fast road use using one of the high pressure pumps required to atomise the jet of water. That is a rate of over 24ml per mile & has a capacity to pump 140ml+ per minute if required. With a mix of normal & fast road use 200 miles is possible. In truth on a road going 'B' with 6psi boost the water injection system only needs to be used for sustained high speed work 'under load' regulated by a pressure sensitive switch set at desired boost level. (vac switch INS hg used for normally aspirated engines) A manual on & off switch is best fitted in case the pressure switch should ever fail & also if you wish to shut down the system to conserve water. It is best just to let the engine rev freely with little throttle to experience the willing engine & the return of reasonable fuel & water consumption. We tested this using a standard MGB late washer bag which holds 2.1 ltrs & fitted a low level warning sensor to avoid running the pump dry & potential engine damage. The big problem with water injection is that ideally a gallon reservoir is needed to avoid regular topping up but there's just no room for that size in any MG engine bay!?

Testing & performance gains

Our test results have mainly been carried out on a 2000cc MGB using Champion N9YC & the cooler running N6YC, pulling easily the MGC axle gearing with the Eaton Rootes type positive displacement third generation M45 (45cu in) blower with the Moss inlet manifold adaptor & fitting kit. Factory set 3-4psi @9877rpm using 5500 engine rpm & up to 7psi @12375rpm of which a very useful 80% of max boost can be produced at low engine 3050 rpm under load giving terrific mid range torque & mile crunching runs! We also run 200psi engine compression (standard 'B' compression 175psi) & 1.62" inlet valve size, tuftrided & balanced bottom end, & importantly our special stage 1 camshaft with suitably matched ignition advanced curve. Boost levels are affected by other considerations such as valve overlap, duration, combustion temperature, altitude, engine capacity, cylinder head etc so results will definitely vary. Heat soak can be a problem if using anything other than a cool running cam & the 'B' head is not really the ideal one to blow. For those who wish to run hotter cams & special heat shield is available but there is ample power available without further tuning. We would advise using 100 octane if uping the boost & currently have been using Shell's V power with Castrol valvemaster +. Alternatively use larger injection jets set to operate earlier if running 95 or 97 octane.


A good head releases pressure

We hope soon be testing a Peter Burgess cylinder head using 10-12psi boost (not recommended with a standard 'B' head) at the superchargers redline of 14760 rpm. To ensure the special head works well the ratio of the exhaust gases to inlet valve diameter needs to be in the region of 90%. They carefully unshroud the larger exhaust valve to increase the flow capabilities of the exhaust to ensure all the high pressure exhaust gases escape & importantly help to draw down the next induction charge. So hopefully this should be the icing on the cake! It is likely we may need extra water injection cooling & intend to fit two 0.3mm jets into the inlet track at 90 degree angle with check valves to stop siphoning. Fitting here may offer more efficiency than a larger single jet operating through the supercharger, or a combination of smaller jets may optimise the system so we are not necessarily expecting water use to be any higher.

The best pump for the job

We have decided in future to use the aquamist electro-magnetic pump which has enough delivery suitable for most 4 cylinder engines. Although the pump is more expensive & not as powerful as the diaphragm type offered by so many others, it is quiet, small, neat & has that quality feel about it. The high psi stainless steel construction RSR pump may be better suited to a 6 or 8 cylinder engine & has the advantage of not requiring the use of check valves if running jets at the manifold but this is by far the most expensive at around £395.00.

Above all it's been great fun working on a setup which further improves the performance of the 'B' series engine - taking it to another level!

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For advice on fitting water injection,superchargers & engine preparation please contact us:

Russell Lloyd