DTT Assassin not pumping!

[bjytech]

That pump is interesting but it only flows 28GPH at its "low" pressure setting of 45psi it seems.

[rancherman]

I saw 340 lph, which is almost 90 gph. Not sure how much they choke the pump down THAT testing. would that be free flow?

Just because it's rated @ 45 psi, doesn't mean it HAS to run that hard. We'd still run a bypass.. just like in a mechanical or any aftermarket FASS, or Airdog.

Between an auxiliary bypass, and the overflow, It should run plenty volume @ 16-17 psi.

*theoretically*...

I remember years ago, when we were running the drag cars, and the simple 'blue holley' fuel pump was the standard of the day. we'd run a pressure regulator INLINE, just before the carb. Dumbest thing, They (holley) used the regulator as a downsteam use regulator. Meaning any fuel needed, must go past a spring and ball. Didn't work for crap when vapor lock kicked in.

Then, someone came out with a stand-off regulator, which 'teed' into the line.. BEYOND the carb, which meant there was always liquid fuel running past the banjo on the carb. This meant the fuel pressure the lil blue holley ever 'saw' was whatever the regulator was set at. 6-7 lbs.

[rancherman]

http://www.lingenfelter.com/mm5/graphics/00000001/L710020000%20high%20pressure%20EFI%20fuel%20pump.jpg

This shows the 340 lph, @ 3 bar, which is ~ 42 psi.

[bjytech]

I saw 340 lph, which is almost 90 gph. Not sure how much they choke the pump down THAT testing. would that be free flow?

Just because it's rated @ 45 psi, doesn't mean it HAS to run that hard. We'd still run a bypass.. just like in a mechanical or any aftermarket FASS, or Airdog.

Between an auxiliary bypass, and the overflow, It should run plenty volume @ 16-17 psi.

*theoretically*...

I remember years ago, when we were running the drag cars, and the simple 'blue holley' fuel pump was the standard of the day. we'd run a pressure regulator INLINE, just before the carb. Dumbest thing, They (holley) used the regulator as a downsteam use regulator. Meaning any fuel needed, must go past a spring and ball. Didn't work for crap when vapor lock kicked in.

Then, someone came out with a stand-off regulator, which 'teed' into the line.. BEYOND the carb, which meant there was always liquid fuel running past the banjo on the carb. This meant the fuel pressure the lil blue holley ever 'saw' was whatever the regulator was set at. 6-7 lbs.

Woops you are right, I was looking at the wrong line (amps)  

Edited January 8, 2015 by bjytech

[ISX]

I switched jobs and we use a lot of air and I had never heard any compressors running.  I finally saw it today.  Its a twin screw compressor about the size of a washing machine and about as loud.  Couldn't believe they were that quiet.  

 

I would get that little walbro for my truck.  One guy tested (link mike previously posted) and he's only getting 35GPH out of the cam lift pump.  That means 90 sound like plenty.

 

I'm told a 12mm pump can flow up to 650cc-ish, if every trick in the book is done to it.  That actually equates to 185GPH.  I'm not sure how much a stock one flows.  Probably half that. 

[bjytech]

If I remember correct I read somewhere a while back that a stock 180 pump only flows around 200cc weather that is a correct number or not I don't know as there was no flow bench numbers presented to back it up.

[ISX]

That's probably about right.  

 

For anyone who wants to know this cc crap, it is calculated per 1000 revolutions, per cylinder.  So in 1000 revs at max fuel, one cylinder would receive 200cc's of fuel.  

 

Easy way to convert to GPH pump to flow it would be to get it back to per revolution.  200cc/1000revs = 0.2cc's per rev. per cyl.  Hmmmm now I see where I screwed up.  I then multiplied by 6, but in a given revolution of the engine, only 3 cylinders fire.  So since we are using engine revolutions, multiply by 3.  0.2 x 3 = 0.6 cc total per engine revolution.  With a 3000RPM limit, multiply by 3000 and you have 1800cc's of fuel needed per minute.  Multiply by 60 to get an hour...= 108,000 cc's.  Then multiply by 0.000264172052 to get gallons.... = 28 GPH.  

 

Or....and this will only work on 6 cylinder engines at 3000RPM....take rated cc times 0.14265290808.

 

Meaning the 650cc absolute max of a 12mm pump would only need 92GPH.  But I think this 650 is heavily modded. The mm3 on the data plate actually calculates out to the cc rating because its showing mm3 per stroke.  Since cc is rated per 1000 strokes, the conversations cancel out and it just happens to be the same number.  So my data plate says 103 mm3 per stroke, which means 103 rated cc.  Meaning 14GPH is all I need.  I'll have to play with the numbers some more and see how legit that is.  

[rancherman]

Sounds about right.. industry standard has been about 4.5 gph per 100 hp. 18 gph should be pretty dang close to 400hp.

Your last paragraph is a commonly missed factor I've read in CF.. people have forgotten those 1000 strokes equate into 2000 ENGINE revolutions. Good catch ISX.

I wonder if Walbro has an exploded view of this pump somewhere?

Edited January 8, 2015 by rancherman

[bjytech]

That's probably about right.  

 

For anyone who wants to know this cc crap, it is calculated per 1000 revolutions, per cylinder.  So in 1000 revs at max fuel, one cylinder would receive 200cc's of fuel.  

 

Easy way to convert to GPH pump to flow it would be to get it back to per revolution.  200cc/1000revs = 0.2cc's per rev. per cyl.  Hmmmm now I see where I screwed up.  I then multiplied by 6, but in a given revolution of the engine, only 3 cylinders fire.  So since we are using engine revolutions, multiply by 3.  0.2 x 3 = 0.6 cc total per engine revolution.  With a 3000RPM limit, multiply by 3000 and you have 1800cc's of fuel needed per minute.  Multiply by 60 to get an hour...= 108,000 cc's.  Then multiply by 0.000264172052 to get gallons.... = 28 GPH.  

 

Or....and this will only work on 6 cylinder engines at 3000RPM....take rated cc times 0.14265290808.

 

Meaning the 650cc absolute max of a 12mm pump would only need 92GPH.  But I think this 650 is heavily modded. The mm3 on the data plate actually calculates out to the cc rating because its showing mm3 per stroke.  Since cc is rated per 1000 strokes, the conversations cancel out and it just happens to be the same number.  So my data plate says 103 mm3 per stroke, which means 103 rated cc.  Meaning 14GPH is all I need.  I'll have to play with the numbers some more and see how legit that is.  

That 92 GPH for 650cc @3000 RPM has me a little confused, I read some information from a guy that really knows his stuff about the 12v's (Seth Haley) and he said for a P7100 set at 500cc to have a lift pump that would support 143 GPH @ 4000 RPM. Now going of the calculations you have for 500cc @ 4000RPM you would only need 95 GPH. Just something I noticed and was wondering about.

 

Edit:

Was just thinking after I posted this and I think I know why the calculations are different. Running 500cc @ 4000 RPM and feeding the injection pump 95 GPH you would be at 0psi because it would be using all the fuel the lift pump could feed it. Right?

So you would need a pump rated for Higher flow at the pressure you want to run.

I'm just kind of thinking out loud now. Plus I like getting into the technical details/calculations for this stuff.

Edited January 8, 2015 by bjytech

[rancherman]

I think you got it byjtech ^^^^

That 92 gph is what is being actually injected.. and of course we'd need more to make sure there was pressure to properly fill the pump. @ 4000 rpm, you'd need pretty good pressure to get the rack filled to the end.

Found those twin screw pumps on ebay, 229 bucks. http://www.ebay.com/itm/NEW-WALBRO-GCL624-330LPH-RACING-FUEL-PUMP-INLINE-amp-KIT-UNIVERSAL-7-00228-51-/171286801265?_trksid=p2054897.l4275

No real mention of this exact pump on CF, but there is a lot of guys running walbro's inline and the 392's

[ISX]

Yes I think pumps are rated at 0psi.  So at the required 25psi minimum, a 143GPH@0psi pump probably fits the bill at 25psi.  

[Ilikeoldfords]

Well we've got another issue with this DDT pump. They finally got the fuel pressure gauge hooked back up. At idle, it's sitting at 12psi to the VP. Nothing wrong there. At 2000 rpm's, the 30psi gauge is pegged. Apparently the pressure regulator isn't working at all!!! Any ideas on what to do with that? I'm so far not to impressed with this particular mechanical pump.

[rancherman]

Well we've got another issue with this DDT pump. They finally got the fuel pressure gauge hooked back up. At idle, it's sitting at 12psi to the VP. Nothing wrong there. At 2000 rpm's, the 30psi gauge is pegged. Apparently the pressure regulator isn't working at all!!! Any ideas on what to do with that? I'm so far not to impressed with this particular mechanical pump.

 

 

You're  right... something  in the  bypass  circuit is  not  right.    either the   valve itself (are  we   looking at another  plastic ball and  spring scenario here??)   the return line back to tank might be  kinked or  full of   ice or   just too dang small..  

Apparently  the  pump is   doing it's  job!   can't  complain  there.    Now   getting the ducks in a row   downstream   shouldn't be  THAT  impossible!

 

Truthfully?     any time  I see a   bypass  valve  on  any  hydraulic  system  that can't   keep a  lid on  upper pressure,  but  keeps   minimum  ok    means   1 of  2  things.

 

Either   the  pump  is just  barely making enough  pressure  at the low speed,     and  the  bypass valve  is  completely shut down...      and  when the   rpm's  go up  is  the only time  the bypass    starts to open..  This means  the  bypass is   set too tight.

OR   the  bypass   itself is  too dang  small (or   return circuit)  to handle the   volume going back to tank.

 

Start  by   adjusting  the   upper limit  at   high rpm.       Set the   bypass to your   desired  pressure   @  2500    and  see  what  it  goes  back down to  @ idle.  Keep track of   psi  at   various   rpms  from  1000   up to     3000   and   report back!! 

 

That'll  tell us   what's  going on   within  your  set up.

 

If  I  was  looking at this  scenario  in my truck.     let  say   I got the upper  limit   set  good,   but  at  idle it  drops  to  say,  8-10 lbs.       I'd  run it.      after all,   how many   hours  are spent  idling??      Not very dang many.    With all the  talk of   'flow equals  pump cooling'  no one,  has EVER proven  when  the  pump  is  'cooked'.    NO ONE.     ( either  idle  with less than  8  lbs,  or    going down the road   @less than  12)    RUN TIME  data  would  suggest  the later.    

 

Lets  step back and  look  at  an electrical  pump  system.    We all have  read  where    Idle is   X psi,    and  WOT  is  about  the same or  just  a  tad less.  Makes  sense,   the  output of the  electric pump  is   the same,   and  IT'S  bypass is the  variable.

Here,  we have  a   mechanical pump that is  proportional  to  engine speed.  If  getting    a  minimum is impossible,   even with  bypass totally closed,  then  SPEED UP THE  PUMP WITH  THE  SMALLER  PULLEY.       

I think  most  guys  would   see the  2 options  in the pulley dept  offered by   DTT   as      the smaller  high speed as  'racing'  or  high engine rpm.... quite the opposite!    If  you are just a  DD,   where   sub  3000 rpm is  the norm..  this is  where  I'd  use the  high speed  set up!

So  in YOUR  situation,   check your  return circuit first,  make sure it's  unrestricted. check and double check the  routing!!!  make sure you have the  hoses  on the  correct  nipples!   bypass  has 3 nipples,  fuel in, fuel out to vp, and fuel returned to tank.   Then   take your bypass apart and see if  it's not  jammed with  debris.   One blob of  thread sealer would  ball up the whole show..

Set your   bypass to   your  preferred  pressure  @  2000-2500 engine speed.   Tell us  what it  drops  down to  when idling.

 

Edited February 5, 2015 by rancherman

[Ilikeoldfords]

I will have to see if they can check the regulator out. I don't know if the ones that come with the Assasins are adjustable pressure-wise. I will have them double check to make sure the return line is free flowing as well. Thanks for the help!!

[rancherman]

'shim adjustable'  

[Ilikeoldfords]

Ok guys. The high pressure was an easy fix after all. My bro had the pulleys swapped. There is a big pulley and a smaller pulley. He had the big pulley on the crank which caused the pump to run twice as fast as it needed.

Got them swapped around and the pressures are just about where they should be!!

[Texas CTD]

Ok guys. The high pressure was an easy fix after all. My bro had the pulleys swapped. There is a big pulley and a smaller pulley. He had the big pulley on the crank which caused the pump to run twice as fast as it needed.

Got them swapped around and the pressures are just about where they should be!!

 

Good to hear.

 

Whenever I swapped pulleys, it always changed my overall pressure, where either both (idle/WOT) were too high, or too low.

But it depends on regulator spring tension as well.