Thread: HPFP New Option
View Single Post
      04-20-2019, 01:52 PM  

Drives: BMW 135i, Ford F150
Join Date: Apr 2019
Location: Detroit, USA

iTrader: (0)

Originally Posted by adrien78 View Post
It has been said on the other forum, and it seems very interesting to me.

The "HDP5" fuel pump on N55 (BMW 13518604231 / Bosch 261520283) seems to run at 1.12cc but the "HDP5 Evo" version (BMW 13517642466 / Bosch 0261520258) runs at 1.2cc according to Bosch specifications.

XDI says their hpfp deliver 1.22cc, really close from the Evo version.

I don't mean bullshit but, in this case, why the Evo one would not be suitable to run more fuel and go 100% E85 ?
Let me take this point and explain in detail:

This is the most important part when comparing HPFPs for size / capacity / fuel flow etc.
And this is also the biggest misunderstanding in the aftermarket as well.
All piston/plunger style direct injection high pressure fuel pumps are driven by a cam lobe, either on one of the main engine cams or on auxiliary cam like in the BMW N55 and S55.

To all N54 guys, you have a rotary style Conti pump, this is all different for you !! I will try to explain in a different thread later.

The fuel flow capacity of a piston style HPFP is calculated very similar to engine air flow capacity.
Geometric size (displacement) x Volumetric efficiency

Same similarity for geometric size, it is bore and stroke and number of pistons (or number of strokes).

HPFP Volumetric Capacity = Piston Area X Stroke of cam lobe X Number of lobes per pump revolution

Let's take some time to think about this. Stroke of CAM-lobe and number of lobes. This has nothing to do with the pump itself, that we bolt on top of this.

Piston Area = (Piston Bore X Piston Bore X PI) / 4

Piston bore, this is the piston or plunger diameter. This is the only thing in the actual HPFP, that defines the volumetric capacity of an HPFP.
Now here the fact that nobody knows, all Bosch HDP5 variants have the same piston diameter of 9.0mm, even the HDP5 evo !!!
Our XDI-HPFP35 has a Piston diameter of 10.5mm and the XDI-HPFP60 has an 11.5mm piston diameter.

When Bosch states in their datasheets, that the HDP5 has a maximum delivery quantity of 1.12cmm and the HDP5 Evo has a maximum delivery quantity of 1.2cmm, that just means that this is maximum possible with any pump of this family (there is more than 200 variants in production worldwide).

The actual delivery capacity is defined by the lobe profile.

So where is the difference between HDP5 and HDP5 evo on the Bosch datasheet coming from now?
The HDP5 is in production since more than 10years, it was validated back in the day for the "biggest" cam-profile at the time, which is a 4-lobe design with 4.4mm stroke per lobe, let's call this 4x4.4-lobe. This lobe can be found in the Ford Focus RS, Mustang 2.3L EB and Taurus SHO (just some examples). This lobe design comes with some issues, you cannot spin the cam faster than 3250rpm (6500 engine rpm), or the pump piston will start to float (yes like a valve).

Here some math examples for the 4x4.4 lobe:

At the far left two examples you can find the 1.12cmm Volume that you see in the HDP5 Datasheet.
You can also see, that on the 4x4.4-lobe our XDI-HPFP35 has a capacity of 1.524cmm which is 36% more (guess where the name HPFP35 is coming from )
Our XDI-HPFP60 has a capacity of 1.828cmm on that 4x4.4-lobe (which is 63% more, same coincidence )

Now the same math for the brand new 4x4.7-lobe.
Bosch validated this one lately for the HDP5 evo, doesnt mean you cannot put the HDP5 on the same lobe, it was just not validated for it:

There is the 1.2cmm that Bosch claims for the HDP5 evo !
And again, if you bolt our XDI-HPFP35/60 on this 4x4.7-lobe, you have the same 36%/63% more capacity. This is valid for every lobe profile.

Now the one that we are all interested in, the BMW-N55 !!

Darn BMW !! They just gave us 3 lobes at 4.7mm stroke each
Why is that? Because they run the HPFP off the vacuum pump on an auxiliary cam-lobe and they spin more than 6500 engine rpm. Every OEM chooses the lobe-profile based on multiple criteria, rpm, package, fuel demand from power targets. There is all kinds of profiles from 3x2.5mm up to 4x4.7mm. Some OEMs even run 3x5.8mm.
Now you might think, why not change the camshaft, I know a guy that can grind cams. Believe me, that was the first idea we tried. That cam doesn't come out of the vacuum pump without damage.

Here the math for the BMW-N55 with all pump variants:

And there is the 0.897cmm that we claim in our XDI-HPFP35 datasheet for OEM-HPFP capacity and the 1.22cmm that we claim for XDI-HPFP35 capacity on N55 lobe.
Still no capacity gains with the HDP5 evo...

Before I explain why the HDP5 evo actually gains a little bit of flow, let me finish up with the capacity math.

The last example for this community that also nobody really knows, the S55.
You might think it is the same vacuum pump, just with two HDP5s...yes. Same lobe profile? NO !! The S55 has a 3x4.0mm lobe profile, smaller than the N55. For the given engine rpm and power targets, they chose to go with two HPFPs. This doubles up the HPFP capacity but with a risk of piston float and wear at higher rpm. Since they didn't need double the capacity for the power target, they reduced the risk for float and wear by reducing the stroke of the cam-lobe.
Here what that means in terms of HPFP capacity, for the ease of math I calculate with 6 lobes which equals two pumps on 3 lobes :

The HPFP volume / capacity of 1.527cmm that you see here with HDP5/HDP5 evo is what you get with the S55 dual HPFP setup.
This equals gains of 70% (yes just 70% not 100%) compared to the OEM-N55-HDP5 setup at 0.897cmm when you swap the S55 dual setup into the N55.
Worth mentioning here, that we achieve a capacity of 1.465cmm or 63% gains with one single bolt on XDI-HPFP60 on the N55 vacuum pump that the N55 comes with

I bet there is some guys doing the math already for the far right example.
Yes imagine what you could do with dual XDI-HPFP60s on the S55 vacuum pump !!!
This variant at 2.493cmm equals gains of 177% compared to HDP5 on single N55 lobe. Who is ready to build the engine for this baby ???

Still the open question, why do people see gains when mounting an HDP5-evo from the B58 on the N55 ?

It is the volumetric efficiency that Bosch has improved for the HDP5 evo!
If you look closely at the Bosch datasheet, you can see the minimum volumetric efficiency of 85% for the HDP5 vs. 90% for the HDP5 evo.
This means the HDP5 just delivers 85% of the possible 0.897cmm and the HDP5-evo delivers 90% of the possible 0.897cmm on N55-lobe.

And again this is not a general value, this HPFP-VE changes with load, rpm and lobe profile again. It is a generic value for the HDP5/HDP5-evo family.
To achieve this better VE, Bosch modified the internals of the HDP5-evo to optimize filling of the high pressure chamber in the HPFP and the overall flow through the different parts of the pump.

This being said, our XDI-HPFP35 has a 36% capacity advantage over the HDP5-evo. Even subtracting 5% for VE, we still gain 31% flow capacity overall. For all the B58 guys out there, we started working on your upgrade.
Attached Images

Last edited by XDI; 04-20-2019 at 02:32 PM.. Reason: forgot tags, details