ALFAGTV6.COM

[Barry]

I have been toying with this idea for some time now...I used to make these in the old days for the 4 cyl nord engines....

I am now making a prototype for my Giulietta`s engine..

Let me tell you,the interferance fit of the gerotor to shaft is very tight...I destroyed a gerotor trying a puller..then I found out the gerotor and cage are made from a very porous cast iron material..

While machining it on the lathe,clouds of burnt oil coming off the job..
My wife also had a puppy as the friggin oil ran out in the oven while heating it up to shrink back on the shaft!!

Any how,here a start of the process..

[Barry]

I reckon the additional volume will be about 25%..A lot I know,but its the same I did with the 4cyl pump..

Im not looking at more presure,(its got way enough..)but volume...

[Barry]

To tie up the two parts,ive machined a housing from ally.I slotted the housing and then clamped both halves within it.Ive trued everything up and will now drill 5x 1mm holes in each of the 5 lobes and stick a cellock pin down each.All this must take place within the jig..

[MALDI]

Naive question: How can you pump more volume without increasing the oil pressure? The only way I can see to do it is to enlarge the oil galleries in the block. (Or decrease the viscosity of the oil...) It seems as if a pump with 25% more volume would produce 25% more pressure (oil being virtually incompressible) if the oil shaft rotates at the same rate.

(Just trying to learn a little something, that's all).

[Barry]

Maldi,The release valve and spring rate remains the same,so if it opened at ,say 100psi std.,it will do so again with the additional flow.
Now,if the additional flow is greater than the the volume the overflow can handle,the pressure will rise proportional to the restriction...

[MALDI]

I see now, thanks!

[Zamani]

Barry,

I still think along with the increase flow you wil see increase pressure as well. Because area is the same, and flow is increased, pressure must also increase. I could be wrong though but P=F/A should be applicable in this scenario.

Mats?

[Mats]

That's why there is an overflow valve.

[Zamani]

Mats,

Say if the oil pump can overwhelm the overflow valve by a huge margin, lets say it can pump infinity gpm or gph or whatever unit you wanna use.

Then how is pressure still gonna be constant (even if you have an overflow valve)?


Although Barry did says this:

"the pressure will rise proportional to the restriction..."

This makes sense.

[MD]

Something is fishy in Denmark

[la_strega_nera]

Mats,

Say if the oil pump can overwhelm the overflow valve by a huge margin, lets say it can pump infinity gpm or gph or whatever unit you wanna use.

Then how is pressure still gonna be constant (even if you have an overflow valve)?


Although Barry did says this:

"the pressure will rise proportional to the restriction..."

This makes sense.

OK, I have messed around with a hydraulic pump setup a bit... we were pumping 3500psi, and pumpimg 97% of the flow through the overpressure bypass valve on the pump (fixed speed/volume pump, adjustable bypass, driving a very small hydraulic actuator (8mm diameter), it was about a 5hp pump)

So, High volume pumps. Coming from 2 years of playing with an engine that has a fairly ordinary oiling system, and where one of the worst things you can do to it is fit a HV pump, i know a bit about this (A High volume pump on a hard revving 351 Cleveland without oiling restrictors will see the rockers covers full of oil and the sump dry :S).
The trick is, up untill the break pressure of the bypass valve, it'll pump more oil volume into the galleries and bearings, resulting in a higher pressure untill the pump bypass pressure.
For instance, the standard rule of thumb for operating pressures is in the order of 10psi pressure per 1000rpm. Ie 50psi @ 5000rpm, 60 @ 6000.

Now, theoretical example, pump outputs a pressure curve that'll be something like 10psi/1000rpm for the brearing tolerances etc in the system. The bypass may be set at 60psi (theretical example of a break pressure). So it'll start bypassing @ 6,000rpm, and only provide 60psi @ 7,000rpm... This pump will be supplying adequate volume for the engines requirements.

If you then upgrade the pump volume, it may supply 11psi/1000rpm, but if the relief valve is still set at 60psi, all you're doing is using up power spinning the pump and pushing oil through the relief valve..
If you shim the bypass, or fit a stiffer spring to the bypass in order to raise the bypass pressure, you might now see 10psi per 1000rpm all the way to 8,000rpm.
However, if the pump lacks the volume to cope, it'll taper off in pressure gain at higher rpms... ie maybe only 70psi @8000rpm.... in which case, now is the time to go to a bigger pump.

Ben

[Micke]

A good explanation.

My €0.05 is that the OE pump is doing OK as long as the oil is not warm and driving conditios are good. In my GTV I see a drop in pressure when oil gets hot (~140 degrees). At idle there's not much pressure at all. That is when the bigger pump really helps.

I'm interested in this kind of mod. Actually I hope to find a dry sump pump for a price less than outrageous and go for that instead.

[la_strega_nera]

A good explanation.

My €0.05 is that the OE pump is doing OK as long as the oil is not warm and driving conditios are good. In my GTV I see a drop in pressure when oil gets hot (~140 degrees). At idle there's not much pressure at all. That is when the bigger pump really helps.

I'm interested in this kind of mod. Actually I hope to find a dry sump pump for a price less than outrageous and go for that instead.

You can get 5 stage Barnes pumps ex NASCAR from alot of vendors on Ebaymotors.com for very reasonable prices, one of my friends bought one for $550 US and its in perfect condition except from a tiny bit of 200mph sandblasting on the very front.

The Pump in my GTV seemed fine, I did a 20-25ish minute run at between 5 and 6000rpm in 5th gear in my GTV in 35degree weather in SouthAustralia many years back, no drop in oil pressure, nothing.

[Barry]

Thought I should at least post a pic of the finnished aricle..If anyone wants to see the insides,ill post...

[Barry]