Citroen BX 16v Rotrex compressuer
Posted: July 11th, 2012, 1:41 pm
Right something a little different to what we’re used to reading about here. Having read Guy’s latest book (several times) and him saying to me “Oh Ian I love Superchargers” when visiting his works one day .I think its only right that I publish some of my work here with the Rotrex Superchargers. While the Lada project is on temporary hold as its in Leeds having an new Exhaust system fitted, I’ve found myself with a few days spare to turn my attention back to my previous project. It was pushed outside due to failure of the Flow Diverter valve on the Hydraulic system when I tried to reverse it down the drive for the first time. I’d simply ran out of time/patience and money with it after that and its sat outside for around a year waiting for me to get the interest back again.
This is a car I’ve owned for about 5 years but only set out to supercharge it in 2010 having stumbled across the core components on an internet auction site to do this sort of conversion.
For those who don’t know Rotrex are a Danish Firm which manufactures small compact belt driven centrifugal superchargers. These are very compact units around the size of an alternator therefore are generally easier to retro fit into engine bays and have some advantages over conventional blowers. One of the main benefits is the way it can be applied with relative ease and without major changes to the standard components and layout in the vehicles engine bay. The AFM (Air Flow Meter) is still used in the intake of the Rotrex. The best circuit is to have the throttle positioned upstream of the supercharger,(i.e before the intake) this then will minimise the work the supercharger has to do and therefore should reduce fuel consumption under part load due to the thin air situation around the impeller at throttle angles less than 90 degrees
The simpler approach and the one I used to get started was to keep the throttle housing on the manifold which ket it simple, however to do this I have fitted a re circulation valve (dump),this is so at low engine speeds the impeller in the charger at engine overrun/deceleration doesn't back up air in the compressor housing and cause any racket. This in simple terms means that the dump valve will prevent surge in the discharge pipe work by allowing air to recirculate back to the intake under vacuum condition pretty much identical to a turbo system really.
You can depending on the model, gearing and physical size of the compressor wheels get gains of up to 100% power but the model and application I have will typically tend to see around 50% increase in power. So on a 160bhp Peugeot Mi16 engine I should be seeing around 240bhp.
Now I’ll apologise in advance as I know most people that use this forum are bias towards the Fiat/Lancia products, but for the sake of the supercharger conversions please bear with me.
I’d thought long and hard about the Rotrex conversion and did a lot of research and to my horror discovered that knowbody seemed to have any idea how to workout what the optimum compression ratio needed to be (Guy Please tell us the correct way if you know, I still don’t). I’d decided/guessed that the best way to factor in maximum performance and reliability was to get the Comp ratio down to around 9:5:1. from 10:4:1. Now this may sound silly but I wanted to know why Volkswagen had seen fit to lower the comp ratio on their 1.8 G60 engine from the normally aspirated 1.8 GTI engine when essentially it’s exactly the same engine?. They must have know something I don’t. I then spoke to GMC motorsport in Scotland who are an authorised Rotrex dealer and they said that its fine to run the Sp30/74 on the Mi16 engine and leave the comp ratio as standard (but That they’ve never tried it!). they advised me the comp ratio wants to be no lower than 9:0:1 in any application as you will loose to much drivability at the bottom end, I asked what formula they use to work this out and they didn’t seem to want to tell me.
I think its probably ok to run 0.7-0.8 bar on the comp ratio 10:4:1.....but you will need a powerful live ECU which is capable of retarding the ignition enough under load and a huge intercooler to keep the air charge temp as low as possible and Fuel with octane additives….maybe, any thoughts?
By far the easiest way to reduce the comp ratio is to get a later engine with the DFW code as opposed to the earlier D6C high comp engine (both still 1.9cc) The later engine had a slightly more modern Bosch level 4.1 motronic 3 row ECU which ran a knock sensor and a air charge temparture sensor and a catalitic convertor. This engine ran a reduced comp ratio of 9:7:1 which is ideal really when you do the maths. I struggled to find one of these engines but I did manage to managed get a set of DFW pistons, these have a 0.85mm shorter crown than the D6C ones. I also Commissioned another company In Scotland… Hiflowheads to build me one of their full blown stage 5 head force inducted heads which has 35.05 inlet valves with 6mm stems and 30.7 exhaust valves with 7mm stems. These are cut with 3 angle valve seats which recesses them further into the combustion chamber reducing the compression ratio even further. They had the CC figures from a similar head and had done the calculations which I’d based my engine on, So now 9:5:1 is the optimum ratio ideal on 98 ron pump fuel and standard ECU They is and MF2 piggy back triggering two auxillary injectors from a 2 bar map sensor under boost.
So a stand alone engine management system is where I’ll be going once I’ve got the engine functioning correctly on its original management. I purposely omitted to modify this area for the time being in an attempt not to bog down the BX project to the point of never getting it going again. I’ve learned in the past that its better to do things in stages as you also learn a lot from running a car between the stages of tune rather than going from standard to mental in one go. I’ve also learned that a lot of the time most of the stuff you plan isn't necessary or needed.
I have a spare Omex 600 management system I could use on my BX but for the time being getting it up and running on standard management with a piggyback auxiliary injector driver is the more sensible option. I’d like to see how it performs on the rolling road before I go down this route. I actually think that if I do decide to take it to the next stage of tune I’ll go to the Netherlands with DP-engineering who do lots of turbo/supercharger conversions on Peugeot and Citroens and go for a plug and play Vems system with MAP, Pieter there says that my car with such a high spec could easily achieve 300 bhp but only time and money will tell
So some pictures of this stage 5 head which apparently has been designed to work with forced induction in mind. I’d like to know what Guy thinks of this, I did briefly mention it to him and he thought the concept didn't sound right butwith more info would have a look. Apparently so I was told by Highflow heads one of the only screw ups Peugeot made with this engine was the design of the exhaust ports and the exhaust manifold, On flow test the exhaust ports flow around 120 CFM which is ok but as soon as you add the manifold into the equation it drops down to about 65 CFM which is dire. Peugeot corrected the problem with the later 2.0 XU10J4 adding Siamese ports per cylinder. They copied this design on my 1.9 head to combat this problem as much as possible. Its also had a big big valve conversion to improve flow with Inconnel Inlets at 35.05mm and Inconnel exhausts at 30.70 which is the absolute max you can go to on the Mi16 head
I’ve also fitted a set of Kent Vs34 twin valve springs and titanium retainers This is supposed to prevent any blowback on valves under boost, these are also more suitable for the long duration cams needed for getting the torque in the right area.
I've also fitted the obligatory kent adjustable pulleys and a set of Sierra Cosworth 57X exhaust manifold studs.
From an application point of view it took months of thinking and fiddling on to get it all in. For example I had to move the radiator up 3 inches and forward about 2,Therfore had to raise the header tank aswell I've had to find the room for all the intake and discharge pipe work as well as 2 oil coolers a intercooler a charge cooler, charge cooler radiator and a electric fan plus not compromising anything that was already there before I started, its been difficult I must say. Having a sound background in Classic car restoration/welding as well as equipment like lathes, milling machines tig welders etc always proves invaluable when you're doing this sort of thing.
However there has been a lot more work getting all this in the BX than I first thought they would be. Anybody who knows hydraulic Citroens knows that the Hydraulics and associated components are everywhere on a BX so making a supercharger system thats a professional fit is difficult and expensive.
Just a couple of points to note in the Pictures:- The lap angle on the Supercharger belt should be ok due to the low resistance of it.....it being centrifugal of course. If it was a roots or screw it would have to be a toothed belt. The timing belt tensioner attached to the sump is designed to get extra tension on the charger pulley to prevent slipping
Let me have all your thoughts good and bad
Ian
This is a car I’ve owned for about 5 years but only set out to supercharge it in 2010 having stumbled across the core components on an internet auction site to do this sort of conversion.
For those who don’t know Rotrex are a Danish Firm which manufactures small compact belt driven centrifugal superchargers. These are very compact units around the size of an alternator therefore are generally easier to retro fit into engine bays and have some advantages over conventional blowers. One of the main benefits is the way it can be applied with relative ease and without major changes to the standard components and layout in the vehicles engine bay. The AFM (Air Flow Meter) is still used in the intake of the Rotrex. The best circuit is to have the throttle positioned upstream of the supercharger,(i.e before the intake) this then will minimise the work the supercharger has to do and therefore should reduce fuel consumption under part load due to the thin air situation around the impeller at throttle angles less than 90 degrees
The simpler approach and the one I used to get started was to keep the throttle housing on the manifold which ket it simple, however to do this I have fitted a re circulation valve (dump),this is so at low engine speeds the impeller in the charger at engine overrun/deceleration doesn't back up air in the compressor housing and cause any racket. This in simple terms means that the dump valve will prevent surge in the discharge pipe work by allowing air to recirculate back to the intake under vacuum condition pretty much identical to a turbo system really.
You can depending on the model, gearing and physical size of the compressor wheels get gains of up to 100% power but the model and application I have will typically tend to see around 50% increase in power. So on a 160bhp Peugeot Mi16 engine I should be seeing around 240bhp.
Now I’ll apologise in advance as I know most people that use this forum are bias towards the Fiat/Lancia products, but for the sake of the supercharger conversions please bear with me.
I’d thought long and hard about the Rotrex conversion and did a lot of research and to my horror discovered that knowbody seemed to have any idea how to workout what the optimum compression ratio needed to be (Guy Please tell us the correct way if you know, I still don’t). I’d decided/guessed that the best way to factor in maximum performance and reliability was to get the Comp ratio down to around 9:5:1. from 10:4:1. Now this may sound silly but I wanted to know why Volkswagen had seen fit to lower the comp ratio on their 1.8 G60 engine from the normally aspirated 1.8 GTI engine when essentially it’s exactly the same engine?. They must have know something I don’t. I then spoke to GMC motorsport in Scotland who are an authorised Rotrex dealer and they said that its fine to run the Sp30/74 on the Mi16 engine and leave the comp ratio as standard (but That they’ve never tried it!). they advised me the comp ratio wants to be no lower than 9:0:1 in any application as you will loose to much drivability at the bottom end, I asked what formula they use to work this out and they didn’t seem to want to tell me.
I think its probably ok to run 0.7-0.8 bar on the comp ratio 10:4:1.....but you will need a powerful live ECU which is capable of retarding the ignition enough under load and a huge intercooler to keep the air charge temp as low as possible and Fuel with octane additives….maybe, any thoughts?
By far the easiest way to reduce the comp ratio is to get a later engine with the DFW code as opposed to the earlier D6C high comp engine (both still 1.9cc) The later engine had a slightly more modern Bosch level 4.1 motronic 3 row ECU which ran a knock sensor and a air charge temparture sensor and a catalitic convertor. This engine ran a reduced comp ratio of 9:7:1 which is ideal really when you do the maths. I struggled to find one of these engines but I did manage to managed get a set of DFW pistons, these have a 0.85mm shorter crown than the D6C ones. I also Commissioned another company In Scotland… Hiflowheads to build me one of their full blown stage 5 head force inducted heads which has 35.05 inlet valves with 6mm stems and 30.7 exhaust valves with 7mm stems. These are cut with 3 angle valve seats which recesses them further into the combustion chamber reducing the compression ratio even further. They had the CC figures from a similar head and had done the calculations which I’d based my engine on, So now 9:5:1 is the optimum ratio ideal on 98 ron pump fuel and standard ECU They is and MF2 piggy back triggering two auxillary injectors from a 2 bar map sensor under boost.
So a stand alone engine management system is where I’ll be going once I’ve got the engine functioning correctly on its original management. I purposely omitted to modify this area for the time being in an attempt not to bog down the BX project to the point of never getting it going again. I’ve learned in the past that its better to do things in stages as you also learn a lot from running a car between the stages of tune rather than going from standard to mental in one go. I’ve also learned that a lot of the time most of the stuff you plan isn't necessary or needed.
I have a spare Omex 600 management system I could use on my BX but for the time being getting it up and running on standard management with a piggyback auxiliary injector driver is the more sensible option. I’d like to see how it performs on the rolling road before I go down this route. I actually think that if I do decide to take it to the next stage of tune I’ll go to the Netherlands with DP-engineering who do lots of turbo/supercharger conversions on Peugeot and Citroens and go for a plug and play Vems system with MAP, Pieter there says that my car with such a high spec could easily achieve 300 bhp but only time and money will tell
So some pictures of this stage 5 head which apparently has been designed to work with forced induction in mind. I’d like to know what Guy thinks of this, I did briefly mention it to him and he thought the concept didn't sound right butwith more info would have a look. Apparently so I was told by Highflow heads one of the only screw ups Peugeot made with this engine was the design of the exhaust ports and the exhaust manifold, On flow test the exhaust ports flow around 120 CFM which is ok but as soon as you add the manifold into the equation it drops down to about 65 CFM which is dire. Peugeot corrected the problem with the later 2.0 XU10J4 adding Siamese ports per cylinder. They copied this design on my 1.9 head to combat this problem as much as possible. Its also had a big big valve conversion to improve flow with Inconnel Inlets at 35.05mm and Inconnel exhausts at 30.70 which is the absolute max you can go to on the Mi16 head
I’ve also fitted a set of Kent Vs34 twin valve springs and titanium retainers This is supposed to prevent any blowback on valves under boost, these are also more suitable for the long duration cams needed for getting the torque in the right area.
I've also fitted the obligatory kent adjustable pulleys and a set of Sierra Cosworth 57X exhaust manifold studs.
From an application point of view it took months of thinking and fiddling on to get it all in. For example I had to move the radiator up 3 inches and forward about 2,Therfore had to raise the header tank aswell I've had to find the room for all the intake and discharge pipe work as well as 2 oil coolers a intercooler a charge cooler, charge cooler radiator and a electric fan plus not compromising anything that was already there before I started, its been difficult I must say. Having a sound background in Classic car restoration/welding as well as equipment like lathes, milling machines tig welders etc always proves invaluable when you're doing this sort of thing.
However there has been a lot more work getting all this in the BX than I first thought they would be. Anybody who knows hydraulic Citroens knows that the Hydraulics and associated components are everywhere on a BX so making a supercharger system thats a professional fit is difficult and expensive.
Just a couple of points to note in the Pictures:- The lap angle on the Supercharger belt should be ok due to the low resistance of it.....it being centrifugal of course. If it was a roots or screw it would have to be a toothed belt. The timing belt tensioner attached to the sump is designed to get extra tension on the charger pulley to prevent slipping
Let me have all your thoughts good and bad
Ian