School me on hydro steering
- Thread starter Mkyhmltn
- Start date
It depends on what size cylinder you want to run and what your orbital displacement is. Your cylinder size determines the total volume of fluid you will need to go lock to lock, and your orbital (steering control unit) displacement will determine how many turns of the wheel it will take to go lock to lock. Now the ambiguous part is how fast can you possibly turn the wheel? This is what will determine the flow rate tou need in order to not out run your pump. Based on averaged stopwatch tests I did turning a wheel that had zero resistance and a suicide ball, I would say .375 seconds per turn is about as fast as you can possibly turn the wheel. Probably closer to .5 seconds per turn for a wheel with some resistance and no suicide ball.
So using those numbers, here is an example:
Lets say you have a 2.5" diameter, 8" stroke double ended cylinder with 1.5" shafts. You also chose an orbital (steering control unit) with a 160cc displacement.
The cylinder has an effective volume of 25.1ci (area of the diameter minus the area displaced by the shaft, multiplied by the stroke). Since this is a double ended cylinder the volume is the same regardless of which direction you are steering.
160cc = 9.76ci, so the number of turns lock to lock would be 25.1ci/9.76ci = 2.57.
So lets say you can turn the wheel at a rate of .375s/turn. Therefore it would take you .964s to go lock to lock and move the entire volume of the cylinder. Thus, 25.1ci = .109 gallons, which works out to .113 gallons per second, which then becomes ~6.8 gpm. This would be a high end number that I would consider the upper-end limit of pump you could use. Using the .5s/turn number you would only need ~5.1 gpm which would be much more realistic. Of course if you use a smaller displacement orbital (steering control unit) you will have more turns lock to lock and would be able to use an even smaller pump. Using the same cylinder above, but with a 125cc orbital (steering control unit), which would result in 3.29 turns lock to lock, and assuming .5s/turn, you would only need a ~4 gpm pump.
The Billavista hydraulic steering article is excellent, and I would highly suggest that you read it: http://www.billavista.com/tech/Articles/Hydraulic_Steering_Bible/index.html
So using those numbers, here is an example:
Lets say you have a 2.5" diameter, 8" stroke double ended cylinder with 1.5" shafts. You also chose an orbital (steering control unit) with a 160cc displacement.
The cylinder has an effective volume of 25.1ci (area of the diameter minus the area displaced by the shaft, multiplied by the stroke). Since this is a double ended cylinder the volume is the same regardless of which direction you are steering.
160cc = 9.76ci, so the number of turns lock to lock would be 25.1ci/9.76ci = 2.57.
So lets say you can turn the wheel at a rate of .375s/turn. Therefore it would take you .964s to go lock to lock and move the entire volume of the cylinder. Thus, 25.1ci = .109 gallons, which works out to .113 gallons per second, which then becomes ~6.8 gpm. This would be a high end number that I would consider the upper-end limit of pump you could use. Using the .5s/turn number you would only need ~5.1 gpm which would be much more realistic. Of course if you use a smaller displacement orbital (steering control unit) you will have more turns lock to lock and would be able to use an even smaller pump. Using the same cylinder above, but with a 125cc orbital (steering control unit), which would result in 3.29 turns lock to lock, and assuming .5s/turn, you would only need a ~4 gpm pump.
The Billavista hydraulic steering article is excellent, and I would highly suggest that you read it: http://www.billavista.com/tech/Articles/Hydraulic_Steering_Bible/index.html
- Joined
- May 22, 2020
- Member Number
- 1120
- Messages
- 5,023
That's some great tech there guys :rolleyes:
This is supposed to be a hardcore tech forum and your response to the guy is to whip out his credit card? If he wants to try and build a better understanding of a hydraulic steering systems and perhaps put together his own steering, what's the problem with that? Perhaps Howe has the best steering kit around and you couldn't possibly build your own setup for cheaper (I doubt that), but there are plenty of people who put more time ,money, and effort into building things themselves just for the challenge or enjoyment of doing so.
Let's teach people how to fish instead of telling them to just go buy a fish.
- Joined
- May 19, 2020
- Member Number
- 244
- Messages
- 1,117
You asked a HUGE question. Ask something specific and you'll get answers.
School you?
Go drive a tractor and look at how it works. Tractors are pretty easy to see all the parts.
You need a pump. orbital valve and a cylinder. Pipe it up and bamm, don't kill anybody.
I simply said that a call to Howe is a schooling in hydro steering. And it is. Every single time I've talked to them it turned into a lesson and I learned a ton. That's knowledge I didn't have and can't be taken away.
One thing with Howe, they don't want to just sell you a ram. They want you to know the exact distance your steering moves first, then they'll add stops in the ram so that the ram and knuckles stop at the exact same time. Less chance of parts breaking and gives a hard point at which the bypass opens. They also mentioned running the lines to the cooler as long a possible. This adds capacity to the system and the longer lines do add a bit of cooling.
Talking to the folks who do this stuff for a living at the highest levels of motorsports is never a bad thing.
I am not the OP there Tiger, and I am well aware of the shortcomings of the OP's post.
Certainly, talking to Howe or any of the other companies is not a bad idea at all. I just got the impression from your post that you were telling him to just go buy a complete system instead of answering his question about pump size.
i was
Thank you for the answers and the link to learn more. Didn't mean to start a shitshow, was just trying to see what people are using and where to get answers and knowledge about a subject that I am new to so I want to do it right the first time.
The gm p pump works, but its crapshoot if you can get a good one from the parts store. Dad has an original from the 80s and works flawless, even after being ran empty and on whatever fluid is slick.
I don't think they like high rpms tho, he runs a sbc so it's done at 3grand.
Depending on what you expect this works very well.
P pump limits out at 7k pump shaft rpm, if you can keep it fed with fluid. It's good for flow but not tolerant of overpressure. But most stockers and reman'd cores are getting old now, and as noted, parts store remans are hit or miss because they can get away with it--a P pump is overkill for most stock vehicles so a half-ass rebuild is still "good enough".
As to OP, yes, you can run hydro on a P pump. Proper way to start is with steering force and stroke needed, then size the cylinder, from there size the valve, then from there, to the pump. Starting with the pump is backwards of how it "should" be done. So... OP... How big are you planning here, weight, tires, axles, usage, etc.?
Its a smaller buggy on toyotas and 39.5's. 4.3 and havn't decided on trans yet, but leaning towards keeping the W56. Dual cases with 2.28 and 4.7 gears. 4.88 gears in the axles right now but probably going to 5.29, I will figure that out after I get it driving. Taking my time on it, not looking to have it ready till spring.
so who is this Howe person? they on here? they have a page? kinda wonderin where their shop is..
cool.. thanx
I'm surprised nobody mentioned PSC. They are the "other" hydro company. (I really don't know of any others that are diy.) They have allot of good tech on their site. I built mine buying key parts from them and the rest at Fastenal.
I hate to say this, but there's a thread on pisrate that has good additional info. I think it was written by "Hydrodynamic". He is on this site now and maybe he could copy his thread or post here. (He really knows his shit on this subject)
I hate to say this, but there's a thread on pisrate that has good additional info. I think it was written by "Hydrodynamic". He is on this site now and maybe he could copy his thread or post here. (He really knows his shit on this subject)
So am I the only guy that hasn’t been super enthused with Howe?
You could ask if the sky was blue and start a pissing contest shitshow any day of the week.
Probably not. There's always folks who didn't have a great outcome with any company.
Hey OP, single or double end ram?
When building my rig I went with a psc single ram and psc orbital. I had read and reread bilavistas bible article. I went to autozone and bought a p pump for an 80’s ford van. In his article he mentioned that they had the highest output of stock pumps. It has worked flawlessly for years. I ran my return line to a cooler in back. This allows the fluid to cool down even on hot days. I ran a fan that is to kick on when fluid in the cooler is too hot. It has never kicked on. I agree with the crap shoot at auto part stores. I bought the same pump for my sons rig and it didn’t work half as good.
All these years in and people are still approaching the problem from the wrong direction. Steering is purely a math equation and BII did a bit of it. But still didn’t start with the two most important numbers. Vehicle weight tire size and scrub radius + the type of terrain trail wheeling on requires deciding on how many pounds of output force from the ram is going to be sufficient for your needs.
By now it’s been done enough that there is a general rule of thumb to go by. Some people get away with a scabbed together POS system that others absolutely will not get away with.
So when picking components that are all going to have work together you need to decide how many pounds of steering force you need FIRST. Then, how quickly you want it to be able to steer second. (see BII’s calculation on orbit valves) The rest can come in a few different orders. Cost, life span, are also factors that can vary wildly. There is a simple algebraic equation to run through and starting with a p-pump is like starting with a wrong answer first and reverse engineering your X-Y-Z numbers.
Each part has a two factor consideration. The output force of the ram is determined by the cubic inch of fluid displacement and the pounds of pressure the pump can put out. The speed of the ram will be determined by the volume the pump can put out at rated pressure. The fluid controller (orbit valve) has to also be able to handle the pressure and the fluid volume. The pump should be the last part decided on based on the volume of the ram and pressure required, VS the turns lock to lock as BII penciled out.
If you insist on sticking with the p-pump you can probably make a tractor supply ag ram and northern hydraulics orbit valve work, but no one is going to find that to be optimal. I use this analogy because I’ve seen a ton of starter builds with that exact cheapo setup. By starting with the p-pump you will find that it’s going to be slow to turn, and you are going to be met with resistance trying to turn the steering wheel. That setup seems to go with Toyota axles and Iroks like peanut butter and jelly. If that sounds like an insult, it is, sorry not sorry.
So lets get into real numbers. I’m not going to show my work because I don’t have time but you can easily verify these on your own. Unmodified p-pumps put out around 1200 psi at 2 ½ gpm. You can get more pressure out of them by modifying the relief but you’re not going to change the GPM DIY at home. A fixed vane pump is generally moving its full volume by 2000 rpm and shouldn’t be turned over 6000 rpm. Howe, PSC, Steerco all make turned up p-pumps but I can tell you from experience they are still lacking in life span and performance compared to their TC and CBR pumps. Howe doesn’t even want to sell p-pumps but they’re in the biz of making money so if you insist you have to have one they will sell them.
The cheap AG ram with a p-pump has a push force of 5890# and pull is 4698# as a single ended ram always has more pounds of push than pull, pull being the direction of the ram body being pulled back over the ram shaft. That same ram with a pump putting out 1600 psi is now going to have a push force of 7854# and pull force of 6264#. Because of the diameter of the ram you are getting thousands of pounds of force change from only hundreds of pounds of pump pressure change. Meaning the cheapest part of the system can make the largest amount of change.
https://www.pscmotorsports.com/motor...sc-sp1200.html For the general trail wheeler I recommend this pump from PSC. I run them on race cars and rock crawlers both, with double ended rams and single ended rams both. It’s rated at 1600 psi and 4 ½ GPM which is sufficient for a 2 ½” DE ram and effortless 2 ½ turn steering at the steering wheel. If you want to run a 3” ram and have it be that fast you are going to need the CBR or gear pump to put out that kind of GPM. They do sell 1600 PSI p-pumps but the volume rating is “high volume” not giving us an actual GPM rating. We race U4 with people who run the hi-vo P-pumps on full hydro buggy’s and they are a short lifed alternative to the TC and CBR pumps.
The most popular size of rams seems to be 2 ½” and that is because they fall squarely in the range of output pounds of force most rigs weighing from 3,000 to 5,000 pounds need to perform adequately. PSC and trail-gear rams have a larger ram shaft than howe or surplus center which is harder to bend, but also has less output pounds of force than the other two because of the difference in displacement. So a howe or surplus center 2 ½”x8” ram with 1 1/4” shaft with a good 1600# pump will put out 5890 pounds of force at the ram. A psc or trail-gear 2 ½”x8” ram with 1 3/8” shaft has 5478 pounds of output force. The psc ram will have a quicker action with the same CC of orbit valve all other things equal because it has less fluid displacement. All 4 of those rams with a good pump will have enough force to steer the tires and in time tear apart the stock steering knuckles on a Toyota axle. Most Dana 60’s with 40’s and 2 ½” rams will seemingly last forever in that configuration assuming the 5500 to 6000 pounds of output force.
Just because I’m already here we can explore the competition and rear steer part of the equation. With the same 1600# pump a 3”x10” ram with 1 3/8” shaft puts out 8934# of output force. Vehicles weighing in excess of 6000 pounds, vehicles with 44” and larger tires, or most trail rigs with a rear steering axle are going to find that a 2 ½” ram is going to fall short of having enough output force to adequately control the vehicle at all times. This is where the 3” ram takes over. With the killer aftermarket and giant superduty front end components available now. Parts can live through giant tires being steered against crazy obstacles and still steer because of that 9000# of output force. With CBR and even gear pumps being used the 9.5 GPM needed to quickly fill the volume required is there. The scott’s custom LLC gear pump is set for 2000# making a 3” ram capable of 11,167 pounds of steering force which will either steer the tire or move the rig, or even rip the center out of the wheel.
By now it’s been done enough that there is a general rule of thumb to go by. Some people get away with a scabbed together POS system that others absolutely will not get away with.
So when picking components that are all going to have work together you need to decide how many pounds of steering force you need FIRST. Then, how quickly you want it to be able to steer second. (see BII’s calculation on orbit valves) The rest can come in a few different orders. Cost, life span, are also factors that can vary wildly. There is a simple algebraic equation to run through and starting with a p-pump is like starting with a wrong answer first and reverse engineering your X-Y-Z numbers.
Each part has a two factor consideration. The output force of the ram is determined by the cubic inch of fluid displacement and the pounds of pressure the pump can put out. The speed of the ram will be determined by the volume the pump can put out at rated pressure. The fluid controller (orbit valve) has to also be able to handle the pressure and the fluid volume. The pump should be the last part decided on based on the volume of the ram and pressure required, VS the turns lock to lock as BII penciled out.
If you insist on sticking with the p-pump you can probably make a tractor supply ag ram and northern hydraulics orbit valve work, but no one is going to find that to be optimal. I use this analogy because I’ve seen a ton of starter builds with that exact cheapo setup. By starting with the p-pump you will find that it’s going to be slow to turn, and you are going to be met with resistance trying to turn the steering wheel. That setup seems to go with Toyota axles and Iroks like peanut butter and jelly. If that sounds like an insult, it is, sorry not sorry.
So lets get into real numbers. I’m not going to show my work because I don’t have time but you can easily verify these on your own. Unmodified p-pumps put out around 1200 psi at 2 ½ gpm. You can get more pressure out of them by modifying the relief but you’re not going to change the GPM DIY at home. A fixed vane pump is generally moving its full volume by 2000 rpm and shouldn’t be turned over 6000 rpm. Howe, PSC, Steerco all make turned up p-pumps but I can tell you from experience they are still lacking in life span and performance compared to their TC and CBR pumps. Howe doesn’t even want to sell p-pumps but they’re in the biz of making money so if you insist you have to have one they will sell them.
The cheap AG ram with a p-pump has a push force of 5890# and pull is 4698# as a single ended ram always has more pounds of push than pull, pull being the direction of the ram body being pulled back over the ram shaft. That same ram with a pump putting out 1600 psi is now going to have a push force of 7854# and pull force of 6264#. Because of the diameter of the ram you are getting thousands of pounds of force change from only hundreds of pounds of pump pressure change. Meaning the cheapest part of the system can make the largest amount of change.
https://www.pscmotorsports.com/motor...sc-sp1200.html For the general trail wheeler I recommend this pump from PSC. I run them on race cars and rock crawlers both, with double ended rams and single ended rams both. It’s rated at 1600 psi and 4 ½ GPM which is sufficient for a 2 ½” DE ram and effortless 2 ½ turn steering at the steering wheel. If you want to run a 3” ram and have it be that fast you are going to need the CBR or gear pump to put out that kind of GPM. They do sell 1600 PSI p-pumps but the volume rating is “high volume” not giving us an actual GPM rating. We race U4 with people who run the hi-vo P-pumps on full hydro buggy’s and they are a short lifed alternative to the TC and CBR pumps.
The most popular size of rams seems to be 2 ½” and that is because they fall squarely in the range of output pounds of force most rigs weighing from 3,000 to 5,000 pounds need to perform adequately. PSC and trail-gear rams have a larger ram shaft than howe or surplus center which is harder to bend, but also has less output pounds of force than the other two because of the difference in displacement. So a howe or surplus center 2 ½”x8” ram with 1 1/4” shaft with a good 1600# pump will put out 5890 pounds of force at the ram. A psc or trail-gear 2 ½”x8” ram with 1 3/8” shaft has 5478 pounds of output force. The psc ram will have a quicker action with the same CC of orbit valve all other things equal because it has less fluid displacement. All 4 of those rams with a good pump will have enough force to steer the tires and in time tear apart the stock steering knuckles on a Toyota axle. Most Dana 60’s with 40’s and 2 ½” rams will seemingly last forever in that configuration assuming the 5500 to 6000 pounds of output force.
Just because I’m already here we can explore the competition and rear steer part of the equation. With the same 1600# pump a 3”x10” ram with 1 3/8” shaft puts out 8934# of output force. Vehicles weighing in excess of 6000 pounds, vehicles with 44” and larger tires, or most trail rigs with a rear steering axle are going to find that a 2 ½” ram is going to fall short of having enough output force to adequately control the vehicle at all times. This is where the 3” ram takes over. With the killer aftermarket and giant superduty front end components available now. Parts can live through giant tires being steered against crazy obstacles and still steer because of that 9000# of output force. With CBR and even gear pumps being used the 9.5 GPM needed to quickly fill the volume required is there. The scott’s custom LLC gear pump is set for 2000# making a 3” ram capable of 11,167 pounds of steering force which will either steer the tire or move the rig, or even rip the center out of the wheel.
Last edited:
Nice to see you posting in here; lots of good info. So do you have any good resources for determining how much steering force you need? Obviously if you have driven enough setups in different rigs you can get a pretty good idea of what you need, and you could also try to back it out mathematically making some assumptions, but is there some kind of reference you can share?
Also, any idea roughly how much steering force your run of the mill factory steering box provides? I haven't been able to find any information online, and I am curious how comparable an assist setup I've got in mind would be to a full hydraulic system.
Here is my setup for a go fast four seat buggy on 40" with a 6.0LS, 4l80, 241/205, super duty axles with 45 degree steer front axle only.
PSC XR series
XR CBR race pump is 11.3cc = .689ci with -12 suction and -8 pressure with no relief or flow control valve, this means the pump has full flow and output so it requires an adjustable external relief valve which sends any overloaded oil through the cooler and back to the filter reservoir, this means there is no hot oil looping inside the pump which can cause wear, PSC recently switched to the billet CNC housing over the forged or cast housings so they are much more robust. Flow should be 3gpm at 1000rpm and 15gpm at 5000rpm. The pump needs a two piece pulley to set the right spacing for use on the LS 6.0 truck motor, I’m running the @Goatbuilt CBR pump bracket so it’s easy to install the pump either way but the two piece pulley allows for installing a the pump first and bolting on the pulley second.
The PSC CBR XR pump is 11.3cc/rev = .689ci/rev
The pulley size is close to the crank pulley guessing 1:1, if over or under driven, flow will change
at 4000 rpm 11.93 GPM
at 2000 rpm 5.97 GPM = 1 second lock to lock if the wheel could turn fast enough, 2.64 turns
at 1000 rpm 2.98 GPM
External relief valve - The external relief valve is inline after the pump that will dump oil to the filter/reservoir if the pressure is backed up and reaches the set point. These are adjustable and since the race pumps do not have a warranty because they have no built in safety bypass, some thought needs to be put into how high you really want to set the relief setting. If you set the pressure high at idle but then rev it up to red line while in use you will be over pressure because pressure relief valves have some resistance. This also goes for cold oil vs hot oil settings, were viscosity will change pressure due to resistance. Ideally you want to set the pressure to be below what PSC says is the MAX (1800 PSI) when your at red line and full flow with cold oil. That would be worst case conditions.
XR race ram in 8” stroke 2.5” bore for a couple reasons over the standard ram.
1st. it has a welded one piece rod so the rod and piston can not come unscrewed and it gives it more strength
2nd it comes with four clamps instead of two and the body has notches so the cylinder can not slide in the clamps
3rd it has a super shiny nickel coating and machined emblem with easy to service anodized caps so it will resist corrosion and look good longer and be easier to work on
4th when you factor in the cost of the welded rods and two extra clamps included it is not much more to get the better body
PSC/Eaton orbital was a hard decision on output choices, I dug around for as much info and opinions as possible to balance steering wheel size, wheel rotations lock to lock, and input force. I chose the 156cc over the 185cc unit as it should have lighter input and less response for non seasoned racers learning to drive including myself and boys who will learn to drive the buggy before they learn to drive a street legal car. Right now I have a 14” wheel and might go down in size if needed. I intend to run an extended rod from the wheel to the orbital with a support rod end or bushing to make the mounting more universal.
XR race reservoir is really advanced and well engineered when it comes to fluid dynamics in hydraulic systems.
The suction is -12 and the dual returns are -8. The suction can pull from the filter or oil supply equally. The filter is being feed from the return flow so the filter is flowing right back into the suction, this term can be called supercharging where the oil does not need to go back to a reservoir to stir up air and get pulled into the suction during agitated reservoir conditions like off camber sideways or zero gravity whoops. The oil in the reservoir does not see use once the system is full and all the air is purged to the high point, if you have a single ended rod then you will need some reservoir oil for volume changes.
The return ports enter into a tangential area so any entrapped air is forced out under centrifugal force into larger bubbles and can work its way up into the top of the reservoir where it can say out of the working oil.
The filter is a common Napa spin on filter with high capacity and precise filtration media. With the bottom down design during filter changes the contaminated oil can can only drip down and not into the reservoir.
The reservoir top has a recessed o-ring for a liquid tight seal and a anodized cap with top port to run excess air out of a breather during thermal expansion.
The cooler is a Thermal Transfer MA-4 with 8" or 10" Spal fan. The core is 8" x 8" x 2.5" and the overall is 10.5 x 9.7 x 2.6 with #16 SAE ports. The MA series is similar to the bar and fin style oil coolers sold by Griffin, CBR, and Triton which are commonly used for transmissions or engine oil coolers.
The MA-4 is rated at a 10psi pressure drop at 20GPM.
100ETD = 180* hot entering oil - 80* cooling ambient air.
It can remove 18,000 BTU/H @ 100 ETD or 7HP worth of heat if the hot oil is 180 and the outside air is 80.
It can remove 9,000 BTU/H @ 50 ETD or 3.5HP worth of heat if the hot oil is 130 and the outside air is 80.
PSC XR series
XR CBR race pump is 11.3cc = .689ci with -12 suction and -8 pressure with no relief or flow control valve, this means the pump has full flow and output so it requires an adjustable external relief valve which sends any overloaded oil through the cooler and back to the filter reservoir, this means there is no hot oil looping inside the pump which can cause wear, PSC recently switched to the billet CNC housing over the forged or cast housings so they are much more robust. Flow should be 3gpm at 1000rpm and 15gpm at 5000rpm. The pump needs a two piece pulley to set the right spacing for use on the LS 6.0 truck motor, I’m running the @Goatbuilt CBR pump bracket so it’s easy to install the pump either way but the two piece pulley allows for installing a the pump first and bolting on the pulley second.
The PSC CBR XR pump is 11.3cc/rev = .689ci/rev
The pulley size is close to the crank pulley guessing 1:1, if over or under driven, flow will change
at 4000 rpm 11.93 GPM
at 2000 rpm 5.97 GPM = 1 second lock to lock if the wheel could turn fast enough, 2.64 turns
at 1000 rpm 2.98 GPM
External relief valve - The external relief valve is inline after the pump that will dump oil to the filter/reservoir if the pressure is backed up and reaches the set point. These are adjustable and since the race pumps do not have a warranty because they have no built in safety bypass, some thought needs to be put into how high you really want to set the relief setting. If you set the pressure high at idle but then rev it up to red line while in use you will be over pressure because pressure relief valves have some resistance. This also goes for cold oil vs hot oil settings, were viscosity will change pressure due to resistance. Ideally you want to set the pressure to be below what PSC says is the MAX (1800 PSI) when your at red line and full flow with cold oil. That would be worst case conditions.
XR race ram in 8” stroke 2.5” bore for a couple reasons over the standard ram.
1st. it has a welded one piece rod so the rod and piston can not come unscrewed and it gives it more strength
2nd it comes with four clamps instead of two and the body has notches so the cylinder can not slide in the clamps
3rd it has a super shiny nickel coating and machined emblem with easy to service anodized caps so it will resist corrosion and look good longer and be easier to work on
4th when you factor in the cost of the welded rods and two extra clamps included it is not much more to get the better body
PSC/Eaton orbital was a hard decision on output choices, I dug around for as much info and opinions as possible to balance steering wheel size, wheel rotations lock to lock, and input force. I chose the 156cc over the 185cc unit as it should have lighter input and less response for non seasoned racers learning to drive including myself and boys who will learn to drive the buggy before they learn to drive a street legal car. Right now I have a 14” wheel and might go down in size if needed. I intend to run an extended rod from the wheel to the orbital with a support rod end or bushing to make the mounting more universal.
XR race reservoir is really advanced and well engineered when it comes to fluid dynamics in hydraulic systems.
The suction is -12 and the dual returns are -8. The suction can pull from the filter or oil supply equally. The filter is being feed from the return flow so the filter is flowing right back into the suction, this term can be called supercharging where the oil does not need to go back to a reservoir to stir up air and get pulled into the suction during agitated reservoir conditions like off camber sideways or zero gravity whoops. The oil in the reservoir does not see use once the system is full and all the air is purged to the high point, if you have a single ended rod then you will need some reservoir oil for volume changes.
The return ports enter into a tangential area so any entrapped air is forced out under centrifugal force into larger bubbles and can work its way up into the top of the reservoir where it can say out of the working oil.
The filter is a common Napa spin on filter with high capacity and precise filtration media. With the bottom down design during filter changes the contaminated oil can can only drip down and not into the reservoir.
The reservoir top has a recessed o-ring for a liquid tight seal and a anodized cap with top port to run excess air out of a breather during thermal expansion.
The cooler is a Thermal Transfer MA-4 with 8" or 10" Spal fan. The core is 8" x 8" x 2.5" and the overall is 10.5 x 9.7 x 2.6 with #16 SAE ports. The MA series is similar to the bar and fin style oil coolers sold by Griffin, CBR, and Triton which are commonly used for transmissions or engine oil coolers.
The MA-4 is rated at a 10psi pressure drop at 20GPM.
100ETD = 180* hot entering oil - 80* cooling ambient air.
It can remove 18,000 BTU/H @ 100 ETD or 7HP worth of heat if the hot oil is 180 and the outside air is 80.
It can remove 9,000 BTU/H @ 50 ETD or 3.5HP worth of heat if the hot oil is 130 and the outside air is 80.
Last edited:
That is a loaded question when you get into the reservoir design. If a reservoir has a quick return path where the oil does not mix in the main compartment and the system is balanced it can reduce restriction and "supercharge or pressurize" the supply line to the pump so the fluid has less of a chance of cavitation at higher flow rates. By not mixing the oil in the main compartment it also keeps air from entering the circulating oil stream. Having air in the reservoir and shaking the oil up and down while driving can enter air into the suction if the oil is circulating through the reservoir. By keeping the main compartment completely full and having a overflow tank, the chance is almost eliminated. The main compartment or the overflow tank can have a pressurized cap and filter to keep pressures higher to further eliminate the low pressure that causes cavitation. The bubbles need to be large to float up and get out of the system so non pressurized systems help with this. If the air is mixing and the oil has air bubbles then the restriction does not need to pull a full vacuum it only needs to expand the already present air bubble and then rapidly compress it small again and slam the quick compressing oil against the metal surface causing damage. The less reaction with air entering also helps with keeping the oil cleaner and dryer. A sealed reservoir helps with this as well.
With this being said I plan to run the reservoir completely full and have a vented overflow tank with a filter. As the system comes up to temp the expanded oil will purge out the air at the top of the main reservoir and pull in oil when cooling.
The problem with the math side is, it starts with a number of assumptions and guesses. I'm not saying don't do the math, in fact, quite the opposite. But understand the why behind.
Here's how it's "supposed to be done":
Step 1: Calculate kingpin torque
Kingpin torque = (vehicle weight on steered axle) x (Coefficient of friction) x square root ( (tire width^2 /8) + (kingpin offset^2) )
Double kingpin torque result if the axle in question is driven
Step 2: Calculate cylinder force
Force = kingpin torque / steering arm length (this is easy)
Step 3: Determine cylinder size
Measure stroke
Calculate needed area: piston area = Force / system pressure
Cylinder piston radius = square root (piston area / pi)
Bore size = radius x 2
If you're using a single ended cylinder, you subtract the rod cross section on the retract side, and need to calculate for the weak side.
Step 4: Calculate cylinder volume
Volume = pi x radius^2 x stroke
Step 5: Select steering valve displacement
Volume / turns desired = valve displacement
If you're using a single ended cylinder, you do this twice as retract will be faster than extend, and you need to make sure you have close-enough to what you want both directions.
Step 6: Calculate pump flow
Valve displacement in cubic inches x desired spin rate in RPM / 231 = pump GPM
Backing way back to step 1...
We have to assume vehicle weight on the axle because the vehicle usually isn't built when we're doing this.
We change the weight loading dramatically going up/down hill.
We can guess at the coefficient of friction, and it changes with terrain.
The tire width changes dynamically with loading, with terrain, and with air pressure.
So we roll into this with a bunch of assumptions right at the start. Most have found that a bore size around 2.25-2.5 works for light rigs, 2.5-3 for heavy rigs, and go from there. If you expect to yank the wheel back and forth like a drifter or rallyguy, you're going to need a lot of pump to keep up with that. If you're a crawler and don't expect it to be streetable, a lot less pump is acceptable. For me, I run parallel CB pumps because they're cheap, easy, durable, they work, and if they stop working, I can get more halfass rebuilt ones at every autoparts store and decent-used ones at most junkyards. And by running two, I don't really care if it's a halfass rebuilt one, because I'm not asking any one pump to do more than it was designed for. Mounting two pumps can be a pain, but I'm OK with it.
For OP, I'd probably go with about a 2.5" cylinder, a 125-160cc valve depending on your preference, and you can run that off of a healthy P pump if you're crawling and not rallyracerguy. If you want to be rallyracerguy, you'll want more pump than what a stock P pump will deliver.
Here's how it's "supposed to be done":
Step 1: Calculate kingpin torque
Kingpin torque = (vehicle weight on steered axle) x (Coefficient of friction) x square root ( (tire width^2 /8) + (kingpin offset^2) )
Double kingpin torque result if the axle in question is driven
Step 2: Calculate cylinder force
Force = kingpin torque / steering arm length (this is easy)
Step 3: Determine cylinder size
Measure stroke
Calculate needed area: piston area = Force / system pressure
Cylinder piston radius = square root (piston area / pi)
Bore size = radius x 2
If you're using a single ended cylinder, you subtract the rod cross section on the retract side, and need to calculate for the weak side.
Step 4: Calculate cylinder volume
Volume = pi x radius^2 x stroke
Step 5: Select steering valve displacement
Volume / turns desired = valve displacement
If you're using a single ended cylinder, you do this twice as retract will be faster than extend, and you need to make sure you have close-enough to what you want both directions.
Step 6: Calculate pump flow
Valve displacement in cubic inches x desired spin rate in RPM / 231 = pump GPM
Backing way back to step 1...
We have to assume vehicle weight on the axle because the vehicle usually isn't built when we're doing this.
We change the weight loading dramatically going up/down hill.
We can guess at the coefficient of friction, and it changes with terrain.
The tire width changes dynamically with loading, with terrain, and with air pressure.
So we roll into this with a bunch of assumptions right at the start. Most have found that a bore size around 2.25-2.5 works for light rigs, 2.5-3 for heavy rigs, and go from there. If you expect to yank the wheel back and forth like a drifter or rallyguy, you're going to need a lot of pump to keep up with that. If you're a crawler and don't expect it to be streetable, a lot less pump is acceptable. For me, I run parallel CB pumps because they're cheap, easy, durable, they work, and if they stop working, I can get more halfass rebuilt ones at every autoparts store and decent-used ones at most junkyards. And by running two, I don't really care if it's a halfass rebuilt one, because I'm not asking any one pump to do more than it was designed for. Mounting two pumps can be a pain, but I'm OK with it.
For OP, I'd probably go with about a 2.5" cylinder, a 125-160cc valve depending on your preference, and you can run that off of a healthy P pump if you're crawling and not rallyracerguy. If you want to be rallyracerguy, you'll want more pump than what a stock P pump will deliver.