First off want to thank @Goose_ss4 for making this project possible, without guys like him who are willing to take some risks to help further development of performance idi parts I wouldn't be able to make half the parts I do. I would also like to thank Justin Anderson who has been very helpful in answering some of my own questions as we put this pump together.
So, db4/db2 hybrids have always been a real hush subject, with not a lot of info out there on what goes into some of these firebreathing rotary pumps, hopefully with this thread I can shed some light on some of the benefits of going with a 4 plunger pump, what it takes to build and calibrate a db4, how I plan to improve on this style pump and finally our results on the stand.
First off, lets talk about db2s and the drawbacks of these injection pumps. Our injection pumps only have two opposing .310" plungers, which is the largest plunger ever put into a db series pump. Fuel displacement is made by these opposing plungers taking the pump's transfer pressure and forcing it through passages in the head to each injection outlet. The amount of fuel delivered is mostly controlled by three things; transfer pressure, plunger stroke, and metering valve position. Transfer pressure is inlet fuel that is further pressurized by the transfer pump and fed to the plungers. This pressure is delivered in a curve based on rpm and is regulated by a bypass spring in the front of the injection pump. We can increase this pressure to increase fuelling, but only have a marginal amount of room for improvement since past 130-140 psi we start seeing the pump's housing flex and can seize the head in the pump. The metering valve is the "gate" for this transfer pressure, as the governor or throttle input commands more fuel this gate opens more to allow more fuel to flow to the plungers. At low rpm/low load situations the metering valve does all the control for fuel delivery since the plungers can only be limited to so much fuel, and transfer pressure can only be brought down so low without loosing the proper advance at idle. Lastly that leaves the plunger's stroke, which is controlled by the leaf spring and the profile of the cam ring.
Here you can see the shoe and roller removed to reveal one of the plungers:
And with the shoe and roller installed, you can see how the leaf spring (adjusted by the fuel screw) limits the travel of the plungers by contacting the edge of the shoe stopping the plunger from travelling its full stroke while the roller can still freely ride the profile of the cam ring:
There are multiple sizes of leaf springs that can be used in a rebuild, for my 90cc spec I use a stage three leaf spring and no leaf spring for anything higher.
Here you can see how the cam ring sits and how the driveshaft can spin inside the cam ring, with either roller riding the inside lobes of the cam ring. Each hump is an injection event, and valley is a fill point. below the cam ring is the advance piston and cam pin that can move the cam ring a few degrees back and forth to alter the timing that the injection event occurs. For the most part, at wot the cam ring is stationary.
There are hundreds of cam rings for various applications that these pumps are built for, obviously a cam ring with deeper valleys will allow for more displacement, but the 7.3 db2 cam rings have been best I have seen for performance. I am hoping to have my own cam ring developed later this year.
The biggest drawback with any of these rotary pumps is their inability to supply fuel at high rpms. You can see with this fuel curve of my latest 150cc db2 that despite our best efforts to limit fueling down low and increase fueling in higher rpms, the designs of these pumps really looses it's efficiency past 2500 rpms.
Compare that graph to a typical specification for a na 7.3 and you can see how much work has been put into trying to hold the fuel curve at higher rpms, with it following about the same curve as stock up to 3000 rpms, just with double the fuel and instead of the fuel dropping off at 3300 rpms, it keeps pulling hard to 4000 rpms where airflow and turbos can really use the fueling.
7.3 na calibration spec example: http://www.stanadyne.com/dealerportal/ssi/Navistar/04826.pdf
Im really happy with the results of that 150cc db2, but with anything we are always pushing the limits for more. Im pretty confident thats the limit that a db2 can safely make with still the original .310 plungers and stock cam ring. The next step of course going to a four plunger pump.
So we started putting parts together for this db4, theres many four plunger db series pumps out there, but very few were 8 cylinder and none were ever an on road pump. The head and rotor I chose to use was an extremely rare 6.5 detroit marine application pump. From what little I could gather on these they seemed to be rated at 370-450hp and they seem to be most common in northern europe. This brought many challenges to the table, one being that the pump number DB2831-5722 was a dead part number, talking to many grey beards at stanadyne we were able to find a part number for the head and rotor for that pump that had been superseded three times before we came up with a good part number. Next problem was getting one, theres no cores available from my sources so we got pricing on a new head and rotor, stanadyne said they had none in stock and that it was made to order that it would be coming from europe and would be up to a two week wait. For the h&r, plungers, leaf springs and shoes along with the parts to do a regular rebuild, we were looking at over 2 grand in parts before we could even spend time on the bench trying to make this work. I got the costs to @Goose_ss4 and he gave us the go ahead.
So, fast forward a few weeks and we've got the parts to put our db4 together. Detroit's rotate opposite from our idis, so we could either use the db4 cam ring and flip it so that it is setup for the correct rotation or we could use the 7.3 cam ring in its normal rotation. We compared db4 cam ring to our db2 7.3 cam ring and found that the 7.3 cam ring had much more lift than the db4 design, so weve opted to use that. With the rotation issue fixed we started inspecting our "new" head and rotor. We noticed the plungers were pretty stiff in their bores, and needed tapping from a brass punch to remove. I talked to justin about this and he confirmed the same thing with the db4 heads hes gotten. Seems stanadyne is selling old parts that have been on the shelfs for who knows how long and claiming they are brand new made to order, kinda a disappointment but at least we have what we need.
Looking at the spec for the marine 6.5 we found some interesting things. These use a smaller orfice plate test nozzle and are set to open at 3000 psi. Main fuel spec is only 120 cc of fuel, which is still much more than any db2 stock spec, but less than you would expect for that power level. Of course pressure is a measurement of restriction so testing with the 7.3 orfice plate and pop pressures we should expect to see a good increase in fueling.
We assembled the pump with leaf springs bottomed out but still installed, with the highest fuel calibration shoes in place, with the 7.3 cam ring and 7.3 cam pin. Went through our idle fuel and hot cranking fuel adjustments first and were able to get things within spec. Noticed right away this pump is very noisy, but with twice as many rollers as a 7.3 pump its to be expected. Brought the rpms up to test our main fuel and got 110cc, brought rpms up more to test 2000 rpms and had a pop and the room went silent, pulled the pump down and the cam pin had clean snapped, so the cam ring was rotating with the driveshaft making no fuel displacement. After talking with Justin he recommended using the db4 cam pin with the 7.3 cam ring, the db4 cam pin is much larger and would require machining the extremely hard cam ring but should be able to hold things together to make some big fuel. This next week were going to be reassembling the pump with the larger pin and spending another day on the test stand, Ive got some tricks I want to try to get more fuel out of the pump in the higher rpms and adding more adjustment to the pump to be made on the truck for driveability, as well as some things that will get added on after the pump is done to allow for transfer pressure to be externally monitored with the pump installed.
Just wanted to get this thread going early so I can answer any questions before we get the results in later this week, since once we're on the stand we dont have much time to answer questions as the numbers roll out
Wes
So, db4/db2 hybrids have always been a real hush subject, with not a lot of info out there on what goes into some of these firebreathing rotary pumps, hopefully with this thread I can shed some light on some of the benefits of going with a 4 plunger pump, what it takes to build and calibrate a db4, how I plan to improve on this style pump and finally our results on the stand.
First off, lets talk about db2s and the drawbacks of these injection pumps. Our injection pumps only have two opposing .310" plungers, which is the largest plunger ever put into a db series pump. Fuel displacement is made by these opposing plungers taking the pump's transfer pressure and forcing it through passages in the head to each injection outlet. The amount of fuel delivered is mostly controlled by three things; transfer pressure, plunger stroke, and metering valve position. Transfer pressure is inlet fuel that is further pressurized by the transfer pump and fed to the plungers. This pressure is delivered in a curve based on rpm and is regulated by a bypass spring in the front of the injection pump. We can increase this pressure to increase fuelling, but only have a marginal amount of room for improvement since past 130-140 psi we start seeing the pump's housing flex and can seize the head in the pump. The metering valve is the "gate" for this transfer pressure, as the governor or throttle input commands more fuel this gate opens more to allow more fuel to flow to the plungers. At low rpm/low load situations the metering valve does all the control for fuel delivery since the plungers can only be limited to so much fuel, and transfer pressure can only be brought down so low without loosing the proper advance at idle. Lastly that leaves the plunger's stroke, which is controlled by the leaf spring and the profile of the cam ring.
Here you can see the shoe and roller removed to reveal one of the plungers:
You must be registered for see images attach
And with the shoe and roller installed, you can see how the leaf spring (adjusted by the fuel screw) limits the travel of the plungers by contacting the edge of the shoe stopping the plunger from travelling its full stroke while the roller can still freely ride the profile of the cam ring:
You must be registered for see images attach
There are multiple sizes of leaf springs that can be used in a rebuild, for my 90cc spec I use a stage three leaf spring and no leaf spring for anything higher.
Here you can see how the cam ring sits and how the driveshaft can spin inside the cam ring, with either roller riding the inside lobes of the cam ring. Each hump is an injection event, and valley is a fill point. below the cam ring is the advance piston and cam pin that can move the cam ring a few degrees back and forth to alter the timing that the injection event occurs. For the most part, at wot the cam ring is stationary.
You must be registered for see images attach
There are hundreds of cam rings for various applications that these pumps are built for, obviously a cam ring with deeper valleys will allow for more displacement, but the 7.3 db2 cam rings have been best I have seen for performance. I am hoping to have my own cam ring developed later this year.
The biggest drawback with any of these rotary pumps is their inability to supply fuel at high rpms. You can see with this fuel curve of my latest 150cc db2 that despite our best efforts to limit fueling down low and increase fueling in higher rpms, the designs of these pumps really looses it's efficiency past 2500 rpms.
You must be registered for see images attach
Compare that graph to a typical specification for a na 7.3 and you can see how much work has been put into trying to hold the fuel curve at higher rpms, with it following about the same curve as stock up to 3000 rpms, just with double the fuel and instead of the fuel dropping off at 3300 rpms, it keeps pulling hard to 4000 rpms where airflow and turbos can really use the fueling.
7.3 na calibration spec example: http://www.stanadyne.com/dealerportal/ssi/Navistar/04826.pdf
Im really happy with the results of that 150cc db2, but with anything we are always pushing the limits for more. Im pretty confident thats the limit that a db2 can safely make with still the original .310 plungers and stock cam ring. The next step of course going to a four plunger pump.
So we started putting parts together for this db4, theres many four plunger db series pumps out there, but very few were 8 cylinder and none were ever an on road pump. The head and rotor I chose to use was an extremely rare 6.5 detroit marine application pump. From what little I could gather on these they seemed to be rated at 370-450hp and they seem to be most common in northern europe. This brought many challenges to the table, one being that the pump number DB2831-5722 was a dead part number, talking to many grey beards at stanadyne we were able to find a part number for the head and rotor for that pump that had been superseded three times before we came up with a good part number. Next problem was getting one, theres no cores available from my sources so we got pricing on a new head and rotor, stanadyne said they had none in stock and that it was made to order that it would be coming from europe and would be up to a two week wait. For the h&r, plungers, leaf springs and shoes along with the parts to do a regular rebuild, we were looking at over 2 grand in parts before we could even spend time on the bench trying to make this work. I got the costs to @Goose_ss4 and he gave us the go ahead.
So, fast forward a few weeks and we've got the parts to put our db4 together. Detroit's rotate opposite from our idis, so we could either use the db4 cam ring and flip it so that it is setup for the correct rotation or we could use the 7.3 cam ring in its normal rotation. We compared db4 cam ring to our db2 7.3 cam ring and found that the 7.3 cam ring had much more lift than the db4 design, so weve opted to use that. With the rotation issue fixed we started inspecting our "new" head and rotor. We noticed the plungers were pretty stiff in their bores, and needed tapping from a brass punch to remove. I talked to justin about this and he confirmed the same thing with the db4 heads hes gotten. Seems stanadyne is selling old parts that have been on the shelfs for who knows how long and claiming they are brand new made to order, kinda a disappointment but at least we have what we need.
Looking at the spec for the marine 6.5 we found some interesting things. These use a smaller orfice plate test nozzle and are set to open at 3000 psi. Main fuel spec is only 120 cc of fuel, which is still much more than any db2 stock spec, but less than you would expect for that power level. Of course pressure is a measurement of restriction so testing with the 7.3 orfice plate and pop pressures we should expect to see a good increase in fueling.
We assembled the pump with leaf springs bottomed out but still installed, with the highest fuel calibration shoes in place, with the 7.3 cam ring and 7.3 cam pin. Went through our idle fuel and hot cranking fuel adjustments first and were able to get things within spec. Noticed right away this pump is very noisy, but with twice as many rollers as a 7.3 pump its to be expected. Brought the rpms up to test our main fuel and got 110cc, brought rpms up more to test 2000 rpms and had a pop and the room went silent, pulled the pump down and the cam pin had clean snapped, so the cam ring was rotating with the driveshaft making no fuel displacement. After talking with Justin he recommended using the db4 cam pin with the 7.3 cam ring, the db4 cam pin is much larger and would require machining the extremely hard cam ring but should be able to hold things together to make some big fuel. This next week were going to be reassembling the pump with the larger pin and spending another day on the test stand, Ive got some tricks I want to try to get more fuel out of the pump in the higher rpms and adding more adjustment to the pump to be made on the truck for driveability, as well as some things that will get added on after the pump is done to allow for transfer pressure to be externally monitored with the pump installed.
Just wanted to get this thread going early so I can answer any questions before we get the results in later this week, since once we're on the stand we dont have much time to answer questions as the numbers roll out
Wes