Discussion
There is no cheaper rack than the one already in the car, so if it's not leaking you might as well keep it.
I can't remember how well it worked (it was over 20 years ago) but when I was at Harrogate HC I worked on a cerbera where the owner wanted to gear down the steering and also make it lighter. The factory sent me some longer steering arms for the front hubs and a couple of pump outlet adaptors. The adaptor has a small hole drilled in it which is presumably the first oil pressure control point for the system.
This infers that you could potentially increase the amount of assistance by having your existing adaptor drilled slightly oversize?
I can't remember how well it worked (it was over 20 years ago) but when I was at Harrogate HC I worked on a cerbera where the owner wanted to gear down the steering and also make it lighter. The factory sent me some longer steering arms for the front hubs and a couple of pump outlet adaptors. The adaptor has a small hole drilled in it which is presumably the first oil pressure control point for the system.
This infers that you could potentially increase the amount of assistance by having your existing adaptor drilled slightly oversize?
WTF Certainly don't find it lighter than either my Boxster or Touareg.
Interesting to hear about the adaptor mods will do my best to find something on that as it seems a low cost option as long as the, presumably, the increased pressure would not cause problems with the rack seals.
Scooby rack seems a popular retrofit so interesting to hear it makes for lighter steering. Is it geared differently or is it due to the level of assistance?
I believe Lloyd Specialist Developments did a variable rate electric conversion - anybody know anything about it?
Interesting to hear about the adaptor mods will do my best to find something on that as it seems a low cost option as long as the, presumably, the increased pressure would not cause problems with the rack seals.
Scooby rack seems a popular retrofit so interesting to hear it makes for lighter steering. Is it geared differently or is it due to the level of assistance?
I believe Lloyd Specialist Developments did a variable rate electric conversion - anybody know anything about it?
RedFI said:
OK so that's the comedy answer out of the way.
I was hoping for something more constructive re the existing setup or the Subaru rack or maybe converting to electric. Do any of these make much difference and does anyone have experience?
I'm sorry you see my suggestion as a joke but it's simple maths, increase the length of the lever (in this case the steering wheel) and less effort is required to move the load.I was hoping for something more constructive re the existing setup or the Subaru rack or maybe converting to electric. Do any of these make much difference and does anyone have experience?
phillpot said:
I'm sorry you see my suggestion as a joke but it's simple maths, increase the length of the lever (in this case the steering wheel) and less effort is required to move the load.
Thought you were pulling my leg - yes appreciate levers but do not want to spoil the look of the interior with a big wheel if there is an out of sight solution.
Any vehicle with traditional hydraulic power steering can be made super light, to find out more on this solution speak with Steering Developments in Hemel Hempstead as they're the experts in doing this and will explain the process/cost.
http://www.steeringdevelopments.co.uk/products/dri...
The trouble is as you increase speed the assistance they've added remains, and that's exactly what you don't want with a sports car, it's also largely unnecessary for most people even with reduced strength as at speed steering typically isn't that heavy at all, I'm guessing all you're looking for is an increase in assistance at low speeds and especially when parking?
If that's the case what you want is something that offers variable assistance, for this electric power assisted steering systems (EPAS) are your best bet. With EPAS systems there's typically two ways to achieve this variable assistance, either speed sensing (you already have this signal as a chimaera has an electric speedo), or torsional load sensing.
If you have a Canems engine management system the existing speed input signal can be applied to the pulse width modulation (PWM) map, calibrated correctly the PWM output is then used to increase and decrease the assistance the electric power steering motor applies directly to the steering column.
As EPAS systems provide assistance directly to the column not the rack I see no reason why you couldn't use such a system in conjunction with a traditional hydraulic power rack, the electric motor is effectively just giving you stronger arms. Talk to Lloyd Specialist Developments about the Canems option as they've converted a number of manual rack Chimaeras to electric power steering so have a tried and tested recipe, my guess is they could easily replicate on a power rack Chimaera and configure the system to only give assistance below a pre-defined road speed.
If you don't have a Canems engine management system there's nothing to say torsional load sensing is any worse or better than speed sensing, there are many companies offering stand alone speed or load sensing steering ECUs designed for classic cars so you really don't need to change your entire engine management system unless ditching the old 14CUX system and smoother running are also on you wish list which is well worth considering by the way.
DC Electronics in Essex manufacture a range of very nice motorsport grade EPAS steering ECUs and can also supply a range of compatible motors too, DC have lots of experience in this field and probably hold the greatest knowledge on the subject of retro fitting EPAS in the UK so they're definitely worth a call.
http://www.dcemotorsport.com/Home/EPAS
I would also talk to EZ Power Steering in the Netherlands as they're considered the European experts in classic car electric power steering conversions:
http://www.ezpowersteering.nl/158/Home.html
Ezpowersteering have developed their own tweaks to an existing OEM quality CAN BUS steering ECU so it can be used on classic cars, an interface has been developed that simulates the signals for engine speed, road speed and steering angle of the CAN BUS which traditionally regulates the ECU on the OEM application, they've also done an EPAS conversion on Chimaera so like Lloyds they will have mounting bracket drawings and know their way around the job.
http://www.ezpowersteering.nl/type/161/144/TVR_Chi...
To be honest there are many other companies offering electric power steering and there are a lot of kits offered in the USA, do keep in mind if you choose a company to fit a kit and they've never fitted an EPAS system to a Chimaera you'll be paying for them to learn on your car, here are two UK companies again worth calling to see what they can offer.
http://simonebirchall.co.uk/index.html
http://litesteer.com/products/classic-vehicles/
So lots of options, if I were you I'd make up a list of questions and ring all of the above asking them the same questions, I'd start with Steering Developments as they have specific experience in making hydraulic systems lighter and that'll likely be the most cost effective solution in your case as you already have a traditional hydraulic power rack, and who knows they may have a way of speed/load varying the assistance?
I'd then move on to phoning all the EPAS companies, this will give you a feel for what's on offer and who genuinely knows the subject inside out. As previously mentioned do keep in mind if you use a company like Lloyds & EZ who've fitted an EPAS system to a Chimaera they will have already done the development, design and packaging work specific to your car which means you'll likely get a better job completed quicker and for less money.
Dave.
http://www.steeringdevelopments.co.uk/products/dri...
The trouble is as you increase speed the assistance they've added remains, and that's exactly what you don't want with a sports car, it's also largely unnecessary for most people even with reduced strength as at speed steering typically isn't that heavy at all, I'm guessing all you're looking for is an increase in assistance at low speeds and especially when parking?
If that's the case what you want is something that offers variable assistance, for this electric power assisted steering systems (EPAS) are your best bet. With EPAS systems there's typically two ways to achieve this variable assistance, either speed sensing (you already have this signal as a chimaera has an electric speedo), or torsional load sensing.
If you have a Canems engine management system the existing speed input signal can be applied to the pulse width modulation (PWM) map, calibrated correctly the PWM output is then used to increase and decrease the assistance the electric power steering motor applies directly to the steering column.
As EPAS systems provide assistance directly to the column not the rack I see no reason why you couldn't use such a system in conjunction with a traditional hydraulic power rack, the electric motor is effectively just giving you stronger arms. Talk to Lloyd Specialist Developments about the Canems option as they've converted a number of manual rack Chimaeras to electric power steering so have a tried and tested recipe, my guess is they could easily replicate on a power rack Chimaera and configure the system to only give assistance below a pre-defined road speed.
If you don't have a Canems engine management system there's nothing to say torsional load sensing is any worse or better than speed sensing, there are many companies offering stand alone speed or load sensing steering ECUs designed for classic cars so you really don't need to change your entire engine management system unless ditching the old 14CUX system and smoother running are also on you wish list which is well worth considering by the way.
DC Electronics in Essex manufacture a range of very nice motorsport grade EPAS steering ECUs and can also supply a range of compatible motors too, DC have lots of experience in this field and probably hold the greatest knowledge on the subject of retro fitting EPAS in the UK so they're definitely worth a call.
http://www.dcemotorsport.com/Home/EPAS
I would also talk to EZ Power Steering in the Netherlands as they're considered the European experts in classic car electric power steering conversions:
http://www.ezpowersteering.nl/158/Home.html
Ezpowersteering have developed their own tweaks to an existing OEM quality CAN BUS steering ECU so it can be used on classic cars, an interface has been developed that simulates the signals for engine speed, road speed and steering angle of the CAN BUS which traditionally regulates the ECU on the OEM application, they've also done an EPAS conversion on Chimaera so like Lloyds they will have mounting bracket drawings and know their way around the job.
http://www.ezpowersteering.nl/type/161/144/TVR_Chi...
To be honest there are many other companies offering electric power steering and there are a lot of kits offered in the USA, do keep in mind if you choose a company to fit a kit and they've never fitted an EPAS system to a Chimaera you'll be paying for them to learn on your car, here are two UK companies again worth calling to see what they can offer.
http://simonebirchall.co.uk/index.html
http://litesteer.com/products/classic-vehicles/
So lots of options, if I were you I'd make up a list of questions and ring all of the above asking them the same questions, I'd start with Steering Developments as they have specific experience in making hydraulic systems lighter and that'll likely be the most cost effective solution in your case as you already have a traditional hydraulic power rack, and who knows they may have a way of speed/load varying the assistance?
I'd then move on to phoning all the EPAS companies, this will give you a feel for what's on offer and who genuinely knows the subject inside out. As previously mentioned do keep in mind if you use a company like Lloyds & EZ who've fitted an EPAS system to a Chimaera they will have already done the development, design and packaging work specific to your car which means you'll likely get a better job completed quicker and for less money.
Dave.
certainly on the two cars I have driven I only really have experience of two cars with scooby racks on .. one has a nice weight to it, lighter than the tvr PAS system but still feels nicely connected to the road (I'm not a fan of heavy steering anyway)
the other is very very light, and also the tyres catch on full lock.
maybe people are fitting different versions of rack ?
the other is very very light, and also the tyres catch on full lock.
maybe people are fitting different versions of rack ?
I did study this subject a bit at college years ago so I'll try and remember and relay the basics of what I was taught about traditional hydraulic power steering systems, to be fair hydraulic was all we had back then as EPAS simply didn't exist in the early 1990's.
A traditional hydraulic power steering system has a number of valves doing different jobs, in simple terms these valves are either located in the rack or in the pump. In the rack itself you have a power steering control valve that detects the amount of torque the driver is applying to the steering wheel using a torsion bar arrangement. This movement opens or closes an angle limit valve thus directing power steering fluid (ATF) to the appropriate side of the piston (driver steering left or right), to be clear for safety reasons you really don't want to mess with the power steering control valve
You then have a power steering relief valve which is built into the power steering pump and controls the maximum pressure the pump can generate no matter how fast it spins, as the engine spins faster so does the pump pulley so you need the relief valve or you'd soon end up in an over pressure situation and blown ram seals. It works in the exact same way as the relief valve on your engine oil pump and just like upping your engine oil pressure you can add shims or mess with spring tension on your power steering relief valve.
But again this is not advisable as you run the very real risk of over pressurising the system with disastrous consequences, years ago I stupidly did this mod on a Manitou forklift with a lazy carriage lift speed and it blew the ram seals giving me a nice high pressure hydraulic fluid shower... lesson learned! On hydraulic plant you raise engine speed to increase pressure, many HIAB equipped trucks have a solenoid linked to the diesel engine injector pump to automatically increase engine speed when you operate the crane.. more on this later.
Back to hydraulic power steering systems there is also a flow valve in the pump this is different to the pressure relief valve, while pressure and flow have a relationship the two are of course very very different. As the name suggests the flow valve regulates the flow ie the volume of fluid directly acting on the ram, this influences steering feel/weighting and is where the OP should focus his attention if he's looking to increase assistance.
Now for the interesting bit, in more modern hydraulic PS pumps the flow valve got a bit smarter, PS system designers fitted what is effectively a mechanically intelligent flow valve known as a droop valve, a droop valve is designed to limit flow at higher pump pulley speeds which has the effect of weighting the steering up at higher engine speeds. Droop valves work to reverse the natural engine speed governed volume increase as typified with hydraulic plant mentioned earlier, droop valves are how manufacturers gave us what they called variable power steering assistance which became common in the 1990's and long before EPAS arrived on the scene.
While a great idea for improving the feel of hydraulic power steering systems the trouble with droop valves are they are engine speed governed not road speed or load governed which is what you really want, I have no idea if the Range Rover PS pump has a droop valve but I very much doubt it does, my guess is as the pump was designed in the late 1980's it would have been fitted with a more basic and traditional type flow valve.
So if the OP wants to increase the assistance of his Chimaera power rack he shouldn't be looking at the rack itself, and he should avoid the increasing pressure approach, the way do get a bit more assistance is to play with the flow valve, or better still fit a more modern PS pump with a tunable droop valve. However, there are risks and steering is not something you should be taking risks with, the OP's TVR power rack will possibly be 20 plus years old and parts to service it are hard to source, indeed I believe some parts are completely unavailable which is exactly why people fit the Subaru rack.
If you want to stick with your hydraulic rack and need more assistance from it I'd talk to Steering Developments in Hemel Hempstead as they are the experts, Steering Developments will almost certainly know what type of flow valve is inside your Range Rover P38 power steering pump and will either be able to tune it or more likely be able to offer a more modern pump that contains a better variable pulley speed droop valve arrangement that again they can tune to give the OP lighter steering at low engine speeds but that will weight up nicely as the engine/PS pump pulley spins faster.
While it's not going to give you the superior road speed or load sensing variable assistance this droop valve tuning approach should still work well enough as parking is typically done at engine speeds below 1,500rpm, however the real question is how long an old and largely unserviceable TVR PS rack will last with far greater flow thrown at it when you're parking? So if you're not keen on the EPAS option then perhaps the ultimate variable assisted hydraulic power steering system for a TVR Chimaera is the Subaru rack paired with a modern PS pump containing a droop valve that's been carefully tuned by Steering Developments in Hemel Hempstead.... and my bet is that's exactly what they'll recommend.
It's probably a lot cheaper than fitting an EPAS system too which would be in the region of £2,000 plus if fitted by a professional, at a guess having a new or re-manufactured Skooby rack fitted with a more modern PS pump tuned by Steering Developments could easily be half the cost of an EPAS system and there would be no ECU's or wiring up a high amp electric motor required
A traditional hydraulic power steering system has a number of valves doing different jobs, in simple terms these valves are either located in the rack or in the pump. In the rack itself you have a power steering control valve that detects the amount of torque the driver is applying to the steering wheel using a torsion bar arrangement. This movement opens or closes an angle limit valve thus directing power steering fluid (ATF) to the appropriate side of the piston (driver steering left or right), to be clear for safety reasons you really don't want to mess with the power steering control valve
You then have a power steering relief valve which is built into the power steering pump and controls the maximum pressure the pump can generate no matter how fast it spins, as the engine spins faster so does the pump pulley so you need the relief valve or you'd soon end up in an over pressure situation and blown ram seals. It works in the exact same way as the relief valve on your engine oil pump and just like upping your engine oil pressure you can add shims or mess with spring tension on your power steering relief valve.
But again this is not advisable as you run the very real risk of over pressurising the system with disastrous consequences, years ago I stupidly did this mod on a Manitou forklift with a lazy carriage lift speed and it blew the ram seals giving me a nice high pressure hydraulic fluid shower... lesson learned! On hydraulic plant you raise engine speed to increase pressure, many HIAB equipped trucks have a solenoid linked to the diesel engine injector pump to automatically increase engine speed when you operate the crane.. more on this later.
Back to hydraulic power steering systems there is also a flow valve in the pump this is different to the pressure relief valve, while pressure and flow have a relationship the two are of course very very different. As the name suggests the flow valve regulates the flow ie the volume of fluid directly acting on the ram, this influences steering feel/weighting and is where the OP should focus his attention if he's looking to increase assistance.
Now for the interesting bit, in more modern hydraulic PS pumps the flow valve got a bit smarter, PS system designers fitted what is effectively a mechanically intelligent flow valve known as a droop valve, a droop valve is designed to limit flow at higher pump pulley speeds which has the effect of weighting the steering up at higher engine speeds. Droop valves work to reverse the natural engine speed governed volume increase as typified with hydraulic plant mentioned earlier, droop valves are how manufacturers gave us what they called variable power steering assistance which became common in the 1990's and long before EPAS arrived on the scene.
While a great idea for improving the feel of hydraulic power steering systems the trouble with droop valves are they are engine speed governed not road speed or load governed which is what you really want, I have no idea if the Range Rover PS pump has a droop valve but I very much doubt it does, my guess is as the pump was designed in the late 1980's it would have been fitted with a more basic and traditional type flow valve.
So if the OP wants to increase the assistance of his Chimaera power rack he shouldn't be looking at the rack itself, and he should avoid the increasing pressure approach, the way do get a bit more assistance is to play with the flow valve, or better still fit a more modern PS pump with a tunable droop valve. However, there are risks and steering is not something you should be taking risks with, the OP's TVR power rack will possibly be 20 plus years old and parts to service it are hard to source, indeed I believe some parts are completely unavailable which is exactly why people fit the Subaru rack.
If you want to stick with your hydraulic rack and need more assistance from it I'd talk to Steering Developments in Hemel Hempstead as they are the experts, Steering Developments will almost certainly know what type of flow valve is inside your Range Rover P38 power steering pump and will either be able to tune it or more likely be able to offer a more modern pump that contains a better variable pulley speed droop valve arrangement that again they can tune to give the OP lighter steering at low engine speeds but that will weight up nicely as the engine/PS pump pulley spins faster.
While it's not going to give you the superior road speed or load sensing variable assistance this droop valve tuning approach should still work well enough as parking is typically done at engine speeds below 1,500rpm, however the real question is how long an old and largely unserviceable TVR PS rack will last with far greater flow thrown at it when you're parking? So if you're not keen on the EPAS option then perhaps the ultimate variable assisted hydraulic power steering system for a TVR Chimaera is the Subaru rack paired with a modern PS pump containing a droop valve that's been carefully tuned by Steering Developments in Hemel Hempstead.... and my bet is that's exactly what they'll recommend.
It's probably a lot cheaper than fitting an EPAS system too which would be in the region of £2,000 plus if fitted by a professional, at a guess having a new or re-manufactured Skooby rack fitted with a more modern PS pump tuned by Steering Developments could easily be half the cost of an EPAS system and there would be no ECU's or wiring up a high amp electric motor required
as you were 
well nothing your going to change safely on the stock TVR set-up thats going to aid assistance apart from checking its operating A1 anyway apart from the mentioned larger steering wheel Gassing Station | Chimaera | Top of Page | What's New | My Stuff