3B Rebuild and Performance Notes

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the venturi and reference point makes me think of the differential pressure indication transmitters (DPIT'S) they install for calculating flow rate on some process piping in the patch. Depending on what they are being used on, they will also install a pressure transmitter and sometimes a temperature transmitter to get an exact quantity.

Anyway, I re-read your stuff, my thought is that the original design of this was to proportion fuel based on flow, nut it was for a NA engine, by design it doesn't incorporate air density. Not that it provides a solution to modifying the pump, but I suspect pumps built around turbo'd diesels would provide some idea's on how to run your air lines.

On my 91 cummins there is a line from the intake manifold to the top of the diaphragm cavity and the lower side which contains the spring is just vented to atmosphere, instead of observing flow like on the 3B it looks at boost pressure, in order to govern fuel. Perhaps the 3B diaphragm should run boost pressure to the top and atmosphere on the other (spring side), and then go to a different spring, perhaps even two springs, one smaller sized one inside to create a progressive rate and avoid run away.

Just my perspective.
 
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Cody

Your cummins is a boost compensated pump with a manually controlled governor. I belive it is also rotary which are a totally different animal from an Inline.
The boost compensator is static i.e., not moving under a no boost condition, spring preload keeps it at the minimum fuel delivery stage via the smoke screw on the very top of the pump. When under boost, the diaphragm is pushed downwards at a linear rate relative to boost level, moving the pin that controls the full load fuel limit set by the full load screw. however at each level of boost, the diaphragm position is relatively static. for example say 10Psi gets you 5mm of downtravel. It will hold at the 5mm postion until you increase or decrease the throttle or load. Not true for the 3B diaphragm system

The 3B pump does not have any provision for boost control. Youre correct, it was not designed for turbo applications. But in essence it works in very much the same way it would as an N/A system. The problem is there isnt a proper rise in fuel rate as boost increases. It's pretty much --> Set the max fuel screw to the highest you want to run, and that is the setting for all rpms, boost levels and load situations. Now when you add the mercedes spring, it adds more travel and decreases the force required to push the diaphragm to full load, allowing you to set the max fuel lower and still have higher full load fuel quantity than the same settings with the stock spring. Adding too much pressure to the backside would slam the rack fully forward, which is not ideal for a truck used daily. Yes, a spring could be installed on the front cavity, but it would be almost impossible to change a diaphragm with a spring over top of the fasteners holding the diaphragm to the rack. And you still have to regulate the idle with vacuum.

Now I hear what you re saying with the reversal of pressures, but you must understand that the diaphragm in the 3B is NEVER static. It never sits in a single position, even at idle. It moves the rack like a sewing machine needle, constantly back and forth in small increments, presumably because the airflow is constantly changing and not a static pressure/volume. This is why the manual throttling system conversions like posted above cant be used for daily driving. they dont hold an idle, and are very twitchy and overly sensitive. For a race truck, theyd be great.



Now on to yesterdays findings.....

I discovered the needle valve had a integral spring loaded bypass valve. So when it was fully closed, it still bled pressure due to the bypass.
So that would definitely screw things up. Made me go "well what the fu....."

After adding a second heavier spring and sealing it back up, I tried the valve as an in-line restrictor. Long story short, It gave surging and strange throttle behaviour at highway RPMs when closed off even the smallest amount. Not the best way to go, but i figured i should try it again with the valve sealed up.

Next i tried the valve again as a bleed valve, hooked up same as before (previous pictures). Opening it up in small increments and testing as I went. I ended up getting a nice "kick in the pants" from a stop, and it would really take off around 2300rpm. And NO SURGING or goofy throttle behaviour this time. Now opening it too much and these symptoms WOULD arise, but that was far beyond the amount I had opened it to start seeing the gains. Closing the valve completely also brought it back to stock operation.
Im pretty happy with it so far. gives a nice zip in first and second gear. More on this after more testing. Have a 1400km round trip starting tommorow, so will report results when I get back.

Cheers
 
yotahed said:
Now on to yesterdays findings.....


After adding a second heavier spring and sealing it back up, I tried the valve as an in-line restrictor.


Next i tried the valve again as a bleed valve, hooked up same as before (previous pictures). Opening it up in small increments and testing as I went. I ended up getting a nice "kick in the pants" from a stop, and it would really take off around 2300rpm.

Cheers
Click to expand...

A couple questions/clarifications:

You went to the heavier spring in the valve (bypass spring) or on the governor?

You have the bleed valve on the vacuum line for this last setup?

Any thoughts on using a regulator for bleeding out air, for better take off, and then a bleed valve to tune the upper range of power?

Thanks.
 
Bleed valve is tee'd in on the reference line.
This actually gives better take off and top end.
Using the valve as a regulator/restrictor doesnt work as well as the bleed valve setup.

I put the heavy spring in the needle valve by-pass to stop it from opening.

Sent with greasy fingers.
 
1200km and all is well.
Im pretty happy with the change with this little mod.
Power comes on really strong but predictable at low revs, levels out, and really takes off at around 2200-2500. No throttle surging under any conditions, but has a very slow and slight(1-2psi) fluctuation at part throttle on hills. Can hardly feel it, but I can see it on the guage.
It does slightly amplify the way it increases fuel as load is added when at a steady throttle position, i.e. going from a flat stretch to a hill.

I had turned the fuel up a 1/4 turn before leaving, and I saw 100F lower max egts and gained 100kms to a full tank of fuel. Egts came up slower as well. Dont ask me how or why, maybe a more efficient fuel quantity at certain rpms/load?

I havent checked with a quage to determine exactly how much pressure I am bleeding off, but it did lower the max boost by a 1 or 2 psi.
So in essence, I did create a boost leak. But I like the way it drives, not worried about losing a few psi.

Sent with greasy fingers.
 
Just a little update on the throttle mod,
I cranked up the fuel to full bore for a day or so, truck goes like stink, but EGT needs to be very carefully watched...
Seems the higher the fuel delivery, the more the effect if the valve is felt, I almost had to turn it right closed to stop digging into the snow right off idle up the trail. Ended up turning the fuel back down as well as closing off the valve for most of the trip.
Good for the highway/on-road, not so good for off road/snow wheeling. Unless you find a good open area to do donuts and chuck snow everywhere...

I have a question about the fuel arm movement.
When it is free to move to full, there is stronger spring pressure for about half the movement, and less to the max movement to the right. Im wondering which spring has no pressure on it at the max, the arm spring or the actual diaphragm spring. There is a very noticeable difference in spring pressure as you move it back and forth. I have a feeling its the one on the arm itself and not the diaphragm one....


Sent with greasy fingers.
 
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Which arm spring are you talking about? The shut off spring? I really like where this thread is going I must say. I'd put my 2cents in, but I never spent much time looking at the pump and fuel delivery. You might consider adding a plain ball valve shut off after the bleeder valve as you could shut it off and open it without having to dial in your exact needle valve settings again. Might save you sometime. I wish I lived closer to ya, but I'm in the valley. If your ever out here give me a shout.
 
Well when you take off the HAC module, or take the fuel screw out to allow the arm to move freely, It has spring pressure towards the back of the truck throughout the range of movement.
Its stronger from the full stop position to about 3/4 of the range before it hits the HAC mount(it may go even further if you took the mount off, dont know yet). The pressure lessens quite a bit there and I was worried about dislodging the diaphragm spring from the center and having it contact the leather instead of the metal center.
I guess the easy way would be to take the cover off and feel the difference to see whats what. Im pretty sure its the spring on the arm mech. itself since the rack only has around an inch of movement total and the diaphragm spring is still quite compressed when installing the cover-> fuel is at full load when not running. Maybe Im just being over technical.. :rolleyes:
I also noticed very little difference between that point(3/4 back) and the full out positions in terms of EGT, smoke and power overall. Im sure theres a difference, but its not huge. Smoke doesnt clear until around 10-12psi when set up that high. Blows black clouds when just blipping the throttle and makes it sound a lot meaner too. :hillbilly:
I really need to install my intercooler. Been sitting here for a year+ with all the piping. Just need to modify the hood latch mount bracket thingy to make the room....

Good call on the shut off valve, as you really only need to re-dial it in if you change your fuel delivery level. And shutting it off completely seems to work best for low traction situatiuons.

I may have a chance to start working at a diesel injection shop in the okanagan real soon, really lookin forward to actually getting instruction about this stuff instead of guessing all the time. Here's hopin, fingers crossed

cheers :beer:
 
Got my front mount intercooler installed today. Pretty tight fit but only clearance issues were an easily trimmed out grille. Took about 4 hours once I had all the fasteners and aluminium I needed to mount it up. Worked out fairly slick and is solid as can be.
No pics yet.
Still waiting on some silicone couplers in the mail.
Ill post up some pics tommorow when its light out and I have the grille off for paint/rock guard.
Im all giddy to test it out lol cant wait.

Sent with greasy fingers.
 
That sounds cool.... No pun intended. Be sure to tighten the snarf out of your clamps. It's surprising how much boost you can loose from a fairly small leak. Pressurizing the intake is even better then you know 100% if you are leak free. Are you still getting better mileage since the pump mod?
G
 
Just topped the tank off and yea, looks like im picking up about 50-90km per tank with around 7L left on fill up(1/16 tank on guage 80L tank) and ive been a little more heavy on the skinny pedal than usual too...

Sent with greasy fingers.
 
The intercooler pics

Bottom mounts lined up perfectly with stock holes in front xmember lucky!
I used some small Al tube for spacers to get the height I needed and fed allen head up through the bottom into a rubber washer and into the threaded boss on the IC.
Top was tilted forward a bit for clearance from the rad support/body xmember. I used some Al flat bar to both strengthen the area (i cut out a lot of sheet metal for the pipes and cut out the bottom grille/hood latch support) and provide a mounting for the top of the IC. Riveted in the bottom and bolts in the top. A twisted up peice of flat bar to the top threaded boss with a rubber and shes stiff as can be. I was going to put a 2nd top peice in but it doesnt need it at all. The bottom mounting holds all the weight and the top is simply to angle it forward a bit.
Last pic is the backside of the grille. Had carve out a bit in the middle and may have to move the turbo emblem...


Sent with greasy fingers.

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Thanks

Yea I thought it'd be a good size when I bought it 2 years ago. Seems the cats ass now. I really didnt know how I was gonna fit it until I started chopping away...
Looking forward to the hook up.

Sent with greasy fingers.
 
Boost controller and Reference line

"Was just wondering if we can use a manual boost controller on the reference line?"

-You could, but it would be very "jerky" in operation. The reference pressure would be blocked, resulting in boost throttling of the diaphragm until it opened. Once open, it would operate similar to stock, but I dont think it would work that well, or as well as a needle restrictor valve. With the the needle valve, you get a set flow for any given boost level, as opposed to the on-off function of a boost controller. But feel free to test it out. All good tech test info is welcome here,

"Also what would be the effect of moving the atmosphere reference line before turbo?"

This would give a similar effect to the boost throttling described earlier. Would be much the same as just disconnecting it and having it open to atmosphere, but worse, since you would now be be adding a bit of vacuum to the reference side under boost, multiplying the undesired effect.

One fellow I spoke to moved the reference line further from the throttle body towards the turbo and said he had good results, but I havent confirmed this with any testing. Not sure if it would make a large difference or not. But again, It's worth a look.
 
Nice job on the intercooler! Can't wait to hear how it effect's EGT's/power, etc. Also looking forward to more pics. Keep up the good work.
 
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