What engine modifications ? Updated January 14th, 2001. Updated January 8th, 2003.

When tuning a Cosworth engine (YBT or YBP) the amount of tuning done is generally divided into stages from 1 to 5. From stage 3 and 4 and onwards it seems like the differences in what the tuners do increases, and so does the difference in price.

Generally the RS Cosworth engines are very easy to tune, especially the YBT, which has a bigger turbo than the YBP, a hybrid turbo, sized midway between the Garrett T3 from the Sierra Cosworth and the Garrett T4 from the Sierra Cosworth RS500. This hybrid is therefore named T034B, (also referred to as the Garrett T35). This enables the YBT to produce a higher turbo boost when tuned than the YBP which has a Garrett T28 turbo, with faster response at lower revs and less turbo lag. The T25 is the smallest turbo mounted on any Cosworth car. Smaller than the T3 of the Sierra Cosworth.

The Cosworth engines will stand up to a lot of tuning as long as they are not abused. When trying to preserve a Cosworth engine for as long as possible it is a good idea not to rev it above 3000rpm, and not put too much load on it before it has reached normal operating temperature. Then after hard driving it is smart to let it idle for a few minutes so that the heat from the turbo can get transferred to the cooling system. This is to make sure that the oil in the turbo bearings won't boil away because of the extremely high temperature in the turbo after hard driving. If the oil boils away it will leave carbon deposits in the bearings and destroy them very fast. The oil passages in the turbo, may also become clogged by the deposits, ensuring the turbo will get very little or no any lubrication at all. It is also recommended because other parts of the engine can reach very high temperatures, and therefore needs cooling down slowly and evenly.

When reading this keep in mind that it's all actually very simple. To get more power: Get as much air into the cylinders as possible each time the intake valves open, add suitable amounts of fuels, and then try to make the engine last by making it stronger. Because it is the fuel that makes the power, and the more fuel the engine can burn (effectively) the more power the engine has got.

Stage one: This is the basic level of tuning which usually consists of a new chip (ep-ROM) only. This will reprogram the engine to run with a higher boost pressure and will probably give somewhere around 270-280 hp , depending on which company does the tuning. One can of course buy a bigger (3") exhaust system already at this stage, which will probably give an additional 10-15 hp. 270-280hp is still the max amount of power the engines will safely produce without changing any mechanical parts. More power can can be produced but then the engine will not get enough fuel from the original injectors and fuelpump and this will lead to enginedamage.

Stage two: To get more power than stage one produces you need to get more fuel into the engine than the original injectors and fuelpump can supply and therefore you need bigger injectors (Green Bosch 803) and a high flow fuel pump. Another ep-ROM (chip) is also required. At this stage one needs to modify the exhaust system too, either by removing the first catalytic converter or by switching to a complete 3" exhaust system. The complete 3" system will give an additional 10 hp compared to only removing the front catalytic converter. This will give less backpressure and increase the engines ability to "breath". Just removing the first catalytic converter after the turbo will generally give around 5% increase in power, which will mean around 17 hp at this stage. Another reason for removing the cat is that it might melt from the extra heat produced by this conversion, and then restrict the exhaust even more than it would when intact. Changing to a bigger exhaust system will also decrease the spool-up time of the turbo and increase the responsiveness off the engine.It's also a very good idea to change the fuel pump for a new 195 ltr/hr unit, as the original fuelpump won't supply enough fuel to the new injectors when the engine is used to it's full capacity. It seems like some tuning companies skip this step, but I wouldn't. For added safety (to be sure that the headgasket won't blow out) it might be a good idea to change the headgasket for a new Group-A headgasket or a WRC-style multi-layer steel headgasker. Those are stronger than the original and will take the additional load from the tuning. A 3-bar map sensor is needed so the ECU can control the higher boost levels. A cone and trumpet airfilter assembly will give a bit more power and better response. A stage two tuning as described here will give anywhere from 320 to 340 hp. An additional oil breather kit might also be a wise investment as the higher boost used at this stage will increase the amount of combustion gases that passes the piston rings and finds it's way to the crankcase. This leads to an increase in pressure in the crankcase which the original breather system might not get rid of. A new oil breather kit usually consists of one or two new breather ports in the engine (either on top of the cam cover or in the crankcase), and an oil separator that separates the oil from the air and recycles the oil back to the crankcase. The original system simply dumps the pressure and oil into the inlet just after the airfilter. This might not be good as the amount of oil increases with increased tuning and engines are supposed to burn fuel, not oil.

Stage three: All the modifications of a stage 3 tuning kit as described here will give around 375 hp. Here, some rebuilding of the engine is required as the strain from the output of of such a conversion can destroy the standard engine. A definitive must is a new headgasket: A multilayer WRC metal headgasket will stand up to almost anything. An ARP stud and nut kit, instead of the original head bolts, to keep the cylinder head securely fastened to the engine block. It will increase the torque you can apply to the head and it will increase the control you have over the torque. A modified cylinder head with improved flow is required to get all that fuel and air fast into the cylinders. Off course a new chip and complete 3" exhaust system is needed. The 195 ltr/hr fuelpump will still give the new and even bigger injectors (light blue Bosch) enough fuel. To control it all a 3 bar map sensor is required so that the engine management system can sense at which pressure it is working. ( A map sensor is a Manifold Absolute Pressure sensor, that senses the pressure in the inlet manifold). At this point it might also pay of to install a bigger intercooler which will cool of the increased amounts of air from the turbo. The air will also have a higher temperature because it has been compressed more than it would have been in a standard engine. A new intercooler might give around 30 extra hp at this stage. As the boost pressure is increased even further it will give an even bigger advantage to have a bigger intercooler. An intercooler from the Sierra RS500 will be adequate for just about anything

Stage four and above: 420 - 600 hp ... This is expensive and will require a total rebuild of the engine. Which will include balancing of every engine part, polishing, new bearings and new seals. A modified cylinder head with improved flow, WRC headgasket, new camshafts with higher lift and longer duration, bigger hybridturbo, even bigger injectors (or the 8 injector setup found on the RS500), adjustable Vernier camshaft pulleys to accurately time the camshafts, bigger intercooler and generally everything mentioned for stage 2 or 3 three. Very expensive and not that great for road use as the powerband of the engine starts quite high in the rev-range.

General tips for increased reliability: From stage three and up a new gearbox should be considered as the original will not stand up to the load from the engine. Maybe it will if one always takes it very easy on first and second gear, and never does race-starts. The reason for this is that the original MT75 gearbox is made for roaddriving and thus have helical gears so that they will run smooth and quite, and the car does have 227 hp and not 350++. So: One needs a stronger gearbox, or more correctly; stronger gears. A set of straight cut gears from Quaife or a complete gearbox is the way to go. It will make a lot of noise though. If one has enough money for stage four or above tuning I suppose a seven speed sequential transmission with 3 electronically controlled diffs is the thing to go for. A new clutch is a good idea from stage two and onwards, as one can very easily wear out the original one if one is a little careless. I think a carbon/carbon racing clutch from AP-Racing would be a good choice. Another good idea when tuning (no matter what stage you're at) is to install a better engine breather system with more ports and an oil separator. This because of the increased piston blow-by that will occure when the engine is tuned. This will result in a increase in crankcase pressure which can lead to oil leakage or gasket failure. Relocation of the dumpvalve to the cold side of the intercooler will improve response and prolong the life of the valve because of the lower temperature. A new group-A dumpvalve will also decrease the probability of a failure, which will lead to loss of boost pressure. From stage two a waterinjection system would increase the power even more, go to my waterinjection page to read more.

Exhaust sytem: The original double exhaust system with three catalytic converters that comes with the Escort Cosworth is quite restrictive. To begin with it will not allow the turbo to spin up as fast as it is capable of. This increases the time before the turbo reaches the desired boost level. At high revs the catalytic converters will restrict the gas flow even more. If the engine is tuned it will created more heat than standard, which in turn can melt the cats, blocking the exhaust even more. If going for more than 270hp a complete 3" exhaust system will increase performance a lot. I have installed a Mongoose 3 inch stainless steel exhaust sytem. I didn't think it would make any real difference apart from the sound and that it will outlast the car, but it really did. The throttle response is quite a bit quicker and the max overboost increased by one line on the boost gauge. And it accelerates better. But it adds quite a bit of noice. A tuningcompany I have been in contact with has tested the Mongoose 3" exhaust system and found it to give 18 hp extra on a standard car. Here you can read how to install a 3 inch exhaust system on your Cossie without any problems, on the how-to page.

If you think there's something incorrect or missing in this page: Don't hesitate, just send me a MAIL! Back to www.wrc-cosworth.org