Mechanically adding a HPFP to my BMW, need gear reducer

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Mechanically adding a HPFP to my BMW, need gear reducer

Post by Aaron »

My BMW 335i has an upgraded low pressure fuel pump (LPFP), which is able to hold 65-75psi on e85 for a lot more horsepower than I'm making. The fuel lines and injectors can easily support quite a bit more power than I'm making. The weak spot is the high pressure fuel pump (HPFP), the same one that habitually fails. My first one failed at about 21,000 miles, but my new one is an updated version that supposedly lasts quite a bit longer (And is still doing great). Aside from reliability concerns, the pump is pretty much maxxed out at 485rwhp on e85. My pressure struggles to keep up between 2500-3000rpm at full boost, but past that the pressure climbs back up to desired and holds steady.

The HPFP is driven off an internal chain from the same shaft as the cam chain drive. This chain drives the HPFP, a vacuum pump, and the oil pump. It is driven at 1/2 engine speed. The pump itself is externally mounted, and has a keyed shaft that fits into the vacuum pump, which bolts to the engine case, and has a gear on it for the chain. The gear is easily removed.

My goal is to add a second HPFP, driven off of the crank pulley. This will nearly double my power capacity, in fact will more than double it, and will also reduce duty cycle on the OEM pump as under normal operation it only has to work 1/2 as hard. The pump is electronically controlled, and I'v got the electronics figured out, so long as my second pump is driven at 1/2 engine speed. This is where my problems begin.

I've got two options:

1) Drive off the factory serpentine belt. The OEM crank pulley is large, about 6" in diameter. In order to get 1/2 engine speed, I'd need a 12" pulley on the HPFP, which is obviously impractical. I've got room and the belt routing figured out to mount the HPFP, but with a 3" pulley it'd be at 2x engine speed, which won't work the electronics. It needs to be 1/2 engine speed. So I need a gear reducer that can handle the conditions present, last a considerable amount of time, have a 1/4 output ratio, and be fairly small and cheap (Cheap being under maybe $500?).

2) Add a second auxiliary crank pulley that is significantly smaller than the OEM one, maybe 1-2" in diameter, and run a second serpentine belt whose only job is to run the second HPFP. Although this sounds easy, it presents a number of difficulties. The OEM pulley is bolted on using 6 bolts, much like a flywheel. I'd need to machine a 2" long spacer that bolts to the OEM crank pulley, then the auxiliary pulley can bolt to that. This takes a lot of precise CNC work, which increases cost. Additionally, I'd need a way to tension the belt. I'd like to use an OEM rocking belt tensioner, but this increases cost and difficulty of designing.

Overall I like the 1st option best, assuming I can find a suitable gear reducer. And that is what I need help with. Anyone know anywhere I can find something like this? Google searching isn't being very helpful unfortunately. Thanks guys!
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Re: Mechanically adding a HPFP to my BMW, need gear reducer

Post by ericjon262 »

From what it sounds like you're working with, I would add a pulley to the crank, you could make a reduction box out of a set of timing gears off of another engine, or just underdrive the belt. the pro to the gear drive is you can run a bigger crank pulley for more belt contact, but if you run a cogged belt it shouldn't matter.

can you post any pictures or diagrams of what we are working on here? do you have an exploded view of the pump? I take it's a positive displacement pump? what type? gerotor? gear? piston? my big concern would be belt slippage, the pump won't do any good if the belt slips.
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Re: Mechanically adding a HPFP to my BMW, need gear reducer

Post by Aaron »

I'm pretty set on belt drive, and either way will have over 3/4 pulley wrap. I don't anticipate slipping problems, maybe ignorantly, but I don't. If I run an auxiliary belt I can just increase ribs, or go cogged, if it's an issue.

I don't want to build my own reduction set, I'd rather outsource that component. Of course this would mean I'm stuck with OEM belt style, but the OEM belt is a 7 or 8 rib belt, it's pretty wide.

OEM belt routing. New pump would go just to the right of the alternator. If I use OEM belt I will change belt routing to go up from the A/C compressor, back down to that idler. A/C belt wrap would be reduced from 3/4 pulley to 1/4 pulley, but I've seen several cars run less that than before without issue.

Image

OEm pump

Image

OEM vacuum pump, from the rear. HPFP bolts into this. My plan is to add a second vacuum pump as well, and use that as a dedicated PCV pump, which is good. Also eases inseall as the HPFP needs to be oiled, and picks up oil from the sealed connection to the vacuum pump, which gets oil from the timing chain housing area.

Image
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Re: Mechanically adding a HPFP to my BMW, need gear reducer

Post by ericjon262 »

Image


just to make sure I'm not crazy

1.crank
2.power steering pump?
3.idler
4.a/c compressor
5.idler
6.alternator
7.tensioner
8.water pump

3/4 wrap can be pretty hard to obtain, esp w/ smaller pulleys, and in this case, your drive pulley will have to be smaller to support a compact design. does your engine make peak torque in the band your having trouble in? I take it this setup is similar to GM SIDI where there is a low pressure in tank pump, and a high pressure engine driven pump, what's the low pressure pump discharge pressure? how is it regulated? I'm wondering if your high pressure pump is cavitating due to some kind of harmonic resonance or something are there any pictures of the high pressure pump taken apart? that might give some insight to the problem.
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ericjon262
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Re: Mechanically adding a HPFP to my BMW, need gear reducer

Post by ericjon262 »

looking at pictures of the pump, it appears to be gerotor type pump. but it's pretty much impossible to tell based on pictures of the outside of the housing. if there any room behind the existing pump?
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Re: Mechanically adding a HPFP to my BMW, need gear reducer

Post by ericjon262 »

looks like the pump is some kind of plunger type pump, so that kills my idea of making a shaft to go through pump 1 to drive pump 2 directly behind it.

Image
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Re: Mechanically adding a HPFP to my BMW, need gear reducer

Post by Aaron »

ericjon262 wrote:Image


just to make sure I'm not crazy

1.crank
2.power steering pump?
3.idler
4.a/c compressor
5.idler
6.alternator
7.tensioner
8.water pump

3/4 wrap can be pretty hard to obtain, esp w/ smaller pulleys, and in this case, your drive pulley will have to be smaller to support a compact design. does your engine make peak torque in the band your having trouble in? I take it this setup is similar to GM SIDI where there is a low pressure in tank pump, and a high pressure engine driven pump, what's the low pressure pump discharge pressure? how is it regulated? I'm wondering if your high pressure pump is cavitating due to some kind of harmonic resonance or something are there any pictures of the high pressure pump taken apart? that might give some insight to the problem.
#8 is another idler just to ensure good wrap on the crank belt. Water pump is electronic.

In tank LPFP pumps 70psi to HPFP, which bumps it up to anywhere from 700-2300, depending on load demand. During high boost/high power times, fuel pressure should be at 2200, but I'm dropping to 1700-1800. Once I get up around 4,000rpm the pump output increases of course, and the engine's demand hasn't increased, so fuel pressure comes back up and stabilizes. Although the pump is struggling, it's just because I've got it maxxed out. It's the weak spot in performance.

I'm not having "problems," the OEM pump is working perfectly as designed, I'm just maxxing it out. I hit peak torque right past 3,000rpm, but at that low of engine speed, the HPFP can't keep up with my fuel demand, and pressure drops.

I just need a second pump is all. Now I'm swaying back to an auxiliary belt, I think it'll be cheaper, plus alleviate the need for a gear reducer.
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Re: Mechanically adding a HPFP to my BMW, need gear reducer

Post by Shaun41178(2) »

What is the flow rating of the factory lpfp in lph? I see upgrades to a 255lph walbro. The factory is less than a 255?
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Re: Mechanically adding a HPFP to my BMW, need gear reducer

Post by ericjon262 »

nobody makes a higher capacity pump? it doesn't look too complicated, way less complicated than adding a second one.
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Re: Mechanically adding a HPFP to my BMW, need gear reducer

Post by The Dark Side of Will »

Checkout McMaster P/N 6481K74: http://www.mcmaster.com/#6481k74/=1466rpv

Any gearbox is going to require a machined adapter at each end for both mounting and drive, which is four adapters total. If the HPFP is lubricated by oil it gets through the vacuum pump, then any externally mounted pump will require externally supplied and externally returned oil.

How does it work with the electronics such that it has to turn a certain speed?
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Re: Mechanically adding a HPFP to my BMW, need gear reducer

Post by ericjon262 »

does BMW make a higher output DI engine?
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Re: Mechanically adding a HPFP to my BMW, need gear reducer

Post by The Dark Side of Will »

Ditto... is that the same pump that the turbo M3 uses?

Does the turbo M5, which is pretty much 600 RWHP on gasoline in cool ambient temps use a large pump of the same family or something completely different? Or does it use the same pump, just close to its flow limits on gasoline?

Who makes the pump? Bosch? Does that company supply other OEM's as well?
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Re: Mechanically adding a HPFP to my BMW, need gear reducer

Post by Aaron »

Shaun41178(2) wrote:What is the flow rating of the factory lpfp in lph? I see upgrades to a 255lph walbro. The factory is less than a 255?
I thought I made it clear this was a HPFP issue. In case I did not, this is a HPFP issue.
ericjon262 wrote:nobody makes a higher capacity pump? it doesn't look too complicated, way less complicated than adding a second one.
Nobody does, I imagine for a couple of reasons. First, these are already failure prone. My first one lasted like 20,000 miles. Second, they are computer controlled and I'm not sure how increased output would mess with that.
The Dark Side of Will wrote:Checkout McMaster P/N 6481K74: http://www.mcmaster.com/#6481k74/=1466rpv

Any gearbox is going to require a machined adapter at each end for both mounting and drive, which is four adapters total. If the HPFP is lubricated by oil it gets through the vacuum pump, then any externally mounted pump will require externally supplied and externally returned oil.

How does it work with the electronics such that it has to turn a certain speed?
Thanks, that is something like what I was looking for.

I'll probably seal the oil ports, and just have the vacuum pump and HPFP carry an internal oil that I change with oil changes. It won't be exposed to the combustion by products, but may still be exposed to high heat because of the pump, I'm not sure.

It it turns the OEM speed, you can just splice a second connector in, and control it that way. I'm not 100% sure on this, friend is taking the electrical side and says at OEM speed it won't be an issue.
ericjon262 wrote:does BMW make a higher output DI engine?
Yes, particularly the new M3/M4, but those pumps are not any better and are already close to being maxxed out stock. they are also not easily adapted.

The M5 uses an OEM dual setup, and they wouldn't be any easier to adapt.
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Re: Mechanically adding a HPFP to my BMW, need gear reducer

Post by Shaun41178(2) »

why can't you supply what the lp pump flows? I asked a simple question. do you not know? what did you upgrade it to?

if the hpfp can't keep up, then you are sol. Why not go hit up the m boards for help? Or did you call them all stupid there so now everyone laughs at you?

step it down to e47. its a much easier solution than what you propose.
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Re: Mechanically adding a HPFP to my BMW, need gear reducer

Post by ericjon262 »

that's a pretty complex little pump... looking at the diagram, I feel like I have a pretty good idea as to what is going on. looking at the design is kind of a bummer, because it looks like the only way to increase the pump's capacity is to bore out the plunger assemblies, but then you have to make new plungers too.

My concern with just adding a second pump, is that now you're supplying a double the fuel all the time. the pump regulates discharge pressure by recirculating fuel back to the pump suction, so by adding a second pump, you end up recirculating alot more fuel which could heat the fuel up quite a bit considering it's a positive displacement pump, and doesn't have a quench volume to cool it like it would recirc'ing to the tank. would it be a problem? not sure.

Here's another thought, can you speed the pump up? have a new gear cut that reduced the reduction ratio to say 1.5:1 instead of 2:1? it would require a new chain, as well as major disassembly of the front end of the engine, but a "bolt in" kit could be made to fit. the pump may need more NPSH to prevent cavitation at higher RPM, but the in tank pump should be able to keep up if you keep the fuel cool.

Edit: the reverse might also work, cutting a larger crank gear, assuming packaging works. it might be best to make the crank a little bigger, and the pump a little smaller at the same time, that way you might be able to keep the same chain. if you one for one swap teeth, it should use the same chain, and the chain guides would probably fit better that way too.
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ericjon262
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Re: Mechanically adding a HPFP to my BMW, need gear reducer

Post by ericjon262 »

Shaun41178(2) wrote:why can't you supply what the lp pump flows? I asked a simple question. do you not know? what did you upgrade it to?

if the hpfp can't keep up, then you are sol. Why not go hit up the m boards for help? Or did you call them all stupid there so now everyone laughs at you?

step it down to e47. its a much easier solution than what you propose.
you can't force liquid to go through a positive displacement pump. if the low pressure pump is supplying 255 LPH, but the high pressure only supplies 200 LPH, you're still only going to get 200 LPH.

I think the best bet is to cut new gears. if you're at, or close to, your power goals now, you should be able to overdrive the pump. if you intend to go significantly higher, then 2 pumps is probably a better solution.
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Re: Mechanically adding a HPFP to my BMW, need gear reducer

Post by Shaun41178(2) »

he didn't give any specifics on what pump he is using, nor what the hp pump can flow. Without certain details, all we can really do is guess. Of course if what he is trying to do hp wise, can't be accomplished with the lp pump, then it doesn't matter what the hp pump can do. Details he left out of his OP. Knowing aawrong, I am not taking anything he says for granted. He states his lp pump is good, but do we really know that? Just take his word without specifics?

either way, like I said, he should just go to e47 and call it a day. Or put a nitrous kit on it to supply more fuel.

What I find funny is that he claims his computer controls the HP pump, but I guess modifying the computer code isn't something he has considered to get back fuel in the 2k-3k rpm area.
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Re: Mechanically adding a HPFP to my BMW, need gear reducer

Post by ericjon262 »

did you read the first sentence in the thread that said the low pressure pump was already upgraded? also, it wouldn't make sense for the electric pump that spins at a relatively constant speed, to have a dead spot at 3000 RPM that doesn't continue above.
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Re: Mechanically adding a HPFP to my BMW, need gear reducer

Post by Shaun41178(2) »

ive already wasted enough time on this. He is a super smarty, he doesn't need our help.

mod move to proper section? other cars
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Re: Mechanically adding a HPFP to my BMW, need gear reducer

Post by ericjon262 »

here's a possible option, costs alot more though...

http://www.bimmerboost.com/showthread.p ... wer-record

last post was late 2015 though...
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