injection event theory

F

fnschlaud4620

New member
Joined
Nov 13, 2007
Messages
356
Hello all,

I would like to start a discussion about what actually happens when we do mods to our injection pumps and injectors and stuff...

I have a few questions....

When is the greatest pressure developed in the injection pump, is it when the pump is pushing fuel through the injectors?

If we leave injector alone (say a control) and do mods like DV and more rack travel(p7100) we add more volume of fuel to be pushed through the same size injector effectively increasing the pressure in the pump??

I have read that a p7100 injects all of its fuel in 40* of crankshaft rotation, If pop spring pressure is lowered will the event last longer say 43* like adding duration of injector on time on a common rail truck? But I hear that a quick injection rate cam makes more power because it puts more fuel in when we need it.....?????????

For example If you had stock 160 pump and some 5x18 injectors you would have low pressure and poor atomazion and low power and lots of smoke

And say you had 13mm full race pump and some stock injectors you would have so much volume through a small injector there would be too much pressure in the pump and wipe out the pump cam.

so is there a mathmatical formula to calculate the perfect injector size for a given pump output volume?? so the pressure is there for good atomazation?

If I am way off here please help me out

Thanks
 
fnschlaud4620 said:
I have read that a p7100 injects all of its fuel in 40* of crankshaft rotation, If pop spring pressure is lowered will the event last longer say 43* like adding duration of injector on time on a common rail truck? But I hear that a quick injection rate cam makes more power because it puts more fuel in when we need it.....?????????

so is there a mathmatical formula to calculate the perfect injector size for a given pump output volume?? so the pressure is there for good atomazation?Thanks
Click to expand...

I'm not sure on the injection time to 40* crank rotation number...I'm sure someone who has spec's out the various P7100 cams (possibly smokem) has that info for sure...

As for adding "duration", the injection of fuel cycle begins with port closure (in a pump controlled injection timing system- non-cp3) and so I would have to say that by lowering the pop-off pressure, even significantly, couldn't change the "duration" by as much as a degree of crank rotation...the ramps on even stock P7100 cams are rather steep, so the pop off pressure would have much little if any effect...

As for the perfect mathematical equation...a lot of it comes from experience, and beyond that relying on others with the experience already...:Cheer:
 
I don't know if it has anything to do with the pumps but I can tell you this. With my two 215hp pumps the 5 x 16 injectors have a lope and governor springs will not do anything to fix it. With the 180 pump I had on I was able to adjust the spring tension to remove the lope, no such luck on the 215 pumps. Is this something to do with the v-groove plungers fuel delivery rate in the 215 pump? That's my uneducated guess. Weston, what's your thoughts?
 
Weston,

Do all injection pumps found in 12V's (160, 175, 180, 215) come with reversal-inhibiting cam designs? Leaving very little time to fill the space above the plunger with fuel. Or are they assymetrical or symetrical?

I believe the 848 pump I just picked up is this way.

I could provide some numbers for this pump which I have on the bench, but I don't know if it has the same cam profile as a normal pump or not?
 
GOT-Torque said:
Weston,

Do all injection pumps found in 12V's (160, 175, 180, 215) come with reversal-inhibiting cam designs? Leaving very little time to fill the space above the plunger with fuel. Or are they assymetrical or symetrical?
Click to expand...

They are all (in pickup engines) the anti-reversal cam lobe design...and yes, they do leave minimal fill time
 
Went out and looked at it again just eyeballing the plunger and using a degree wheel. It only dwells at BDC of the stroke for about 50 degrees. After the injection, it dwells at TDC of the stroke for about 200 degrees...

I imagine a quick rate cam has a steeper lobe for injection (during a smaller amount of crank rotation) and then immediately returns to BDC for the rest of the revolution to aid in fill time?
 
So speaking in injection pump rotation degrees, fill ramp and return ramp were 70 degrees, plunger at BDC for 50 degrees, and at TDC for 170 degrees?

Are quick rate cams just regrinds of these stock cams? Since all the material is there already to create a steep symmetrical lobe? Or are billet pump cams required?

Back to the topic at hand, I would guess the highest pressure developed in the pump would be just prior to the injector popping open. I would think of it as a pressure relief valve, the pressure should never get higher than the pop pressure of the injector.

Unless of course you consider the case of a huge pump with stock injectors, you know the setups that wipe the cam lobes of the pump cam... I would imagine those setups may have a bit higher pressure...
 
So what are the degrees that the pump cam leaves fill time or BDC and gets to TDC? Just because the cam stays at TDC for 170 degrees the fuel should already have been injected. Or am I reading your results wrong?

It would seem to me that we can make a better gain by regrinding our pump cams to inject a larger volume of fuel faster, and in a shorter peroid of time. I would have to think that any camshaft regrinding facility could do this and there would be more benifits than spending money on a valvetrain camshaft.
 
fnschlaud4620 said:
So what are the degrees that the pump cam leaves fill time or BDC and gets to TDC? Just because the cam stays at TDC for 170 degrees the fuel should already have been injected. QUOTE]

Westons numbers showed 70 degrees from BDC to TDC (injection cycle), however some of that movement would be taken up by the delivery valve rising up (overcoming the spring pressure) until the DV should has cleared the outer piece allowing fuel to flow. Even though fluid is considered noncompressible, I would imagine a piece of the pump rotation and plunger lift would be needed to raise the pressue in the injection line and injector to the needed pop off pressure. Also the last 5 or 10 degrees is just the plunger slowing to a stop at TDC so injection quantity there would be very small (IMO).
Click to expand...
 
fnschlaud4620 said:
It would seem to me that we can make a better gain by regrinding our pump cams to inject a larger volume of fuel faster, and in a shorter peroid of time. I would have to think that any camshaft regrinding facility could do this and there would be more benifits than spending money on a valvetrain camshaft.
Click to expand...

Yes, you will gain fuel delivered and it will deliver it quicker, thus making more power...however, you can't just do a pump cam swap in your backyard like you can a valvetrain camshaft...unless of course you have the Bosch tools and test stand in your backyard as well :hehe:
 
well I have heard of these backyard test stands, And I believe that you work at an injection shop, so post up some pics of these special tools.....

usually if there is a will there is a way....
 
fnschlaud4620 said:
well I have heard of these backyard test stands, And I believe that you work at an injection shop, so post up some pics of these special tools.....

usually if there is a will there is a way....
Click to expand...

:rockwoot:...I like your enthusiasm...

I'll snap a couple pics on the camera phone this afternoon and get them up tonight...they really and truly wouldn't be that hard to make...but the calibration side of things is all on you guys :hehe:
 
Smokem said:
Francis, injector sizing plays directly into your application, setup, and supporting modifications.
Click to expand...

Yes, I know a little about that, I have talked with you about some 5x16s, but I am just trying to understand the pump better how it works and what is really happening. I am not saying that I will go out and get my cam cut, but I get tired of reading threads that say what injector and 10 guys say use brand XXX and 10 say use brand YYY and 10 say use brand...... I just want a little more mathematical or scientific method to make decisions. I understand that experience plays a big part.
 
CTDYoungGun said:
:rockwoot:...I like your enthusiasm...

I'll snap a couple pics on the camera phone this afternoon and get them up tonight...they really and truly wouldn't be that hard to make...but the calibration side of things is all on you guys :hehe:
Click to expand...

I would find a good and cracked gutted 53 block with a 12v front cover to mount the pump on. Throw an old cam and gear on to drive the injection pump gear weld a PTO flange to the cam gear. Hook it up to our 4960 and find some chemistry test tubes. Maybe I would even rig it all up on a pallet so it is portable. I believe If I read up on it it could be done. I have a few friends that work at Northwest fuel injection in Ohio.
 
Smokem said:
What other information are you looking for? What would you like this thread to cover information wise? I'll see what I can do to help.
Click to expand...

Well, I don't know if there is any more info. I guess when I started this thread I assumed there would be a formula to calculate flow out the injector based on volume and pressure in the pump, I think that everything being posted is great info. I am just ignorant in comparison to many on here when it comes to pumps. What I need to do is find an old 160 core and completely tear it down to understand things better. Thanks for the help guys
 
most 13mm pumps with a quick cam are around 20* degrees pump rotation. the pump shop i deal with is workn on 16mm short stroke pump talkn around 16* fuel delivery nice for the high rpm horse power
 
You must log in or register to reply here.
Back
Top