Anyone want to have a TB/inj. discussion?

[uglyDougly]

  Here are two graphs of 4 1098 injectors that I just tested today.

  Hope it actually posts!!

  Doug



[attachment removed after 60 days by system]

[-SeabrookTrickBagger]

  How about a wrap-up on the subject of injector sizing?

1) Determine the rear wheel HP of your build.
2) Multiply that by 1.15 or more to get crankshaft HP
3) Divide CS HP by the number of injectors to determine the HP per injector
4) Using a fairly conservative BSFC, like .550 lb/HP/hr, multiply the HP/inj X .55 to get the injector static flow requirement in lb/hr
5) Divide the static flow requirement by .80 which is the 80% duty cycle recommended to get the lb/hr you will want
6) Find the static flow or maximum flow rating of the injectors in question and determine at what pressure they are rated, typically 3 Bar
7) If the injectors are rated at your fuel pressure (3 Bar for M-M bikes, 4 Bar for Delphi) chose an injector that flows more than the calculated value 5) above
If the injector is rated at 3 Bar and you are using a 4 Bar Delphi system, multiply the 3 Bar rated static flow by the difference of the square roots of the two pressures, in this case it is 2 (sqrt of 4) divided by 1.732051 (sqrt of 3) = 1.154701
9) Then chose an injector that flows more than the calculated value

  Does that make sense?

  Doug

BTW, thanks for the synopsis.  Yes, it makes sense.

[-SeabrookTrickBagger]

While we can do all the calculations we need to do, don't we need to consider the choices made by the ECU software creators?

I am still curious if the software creators for the FI ECUs somehow use a 3 bar or 4 bar calculation in their software:  did they choose one when they wrote the program?  In other words, if you put "5.3" in the parameter "gps injector size" slot, is the ECU making its calculations to achieve the HP you entered in parameters, say 135 CS HP, at 3 bar and adjusting the calculations for the specific bike the unit is installed in such as a delphi 58 to 62 psi bike?  In other words, does the ECU want you to enter industry standard, 3 bar, in the parameter slot of injector flow rate or the true operating pressure injector flow rate of your injector/bike?  I asked Schroeder about this, and he said "it does not matter."  Kinda think it does matter, BWTFDIK.  In my case, it is the difference between 5.3+ gps at 3 bar and 6.1 gps at 4 bar.  FWIW, the bike starts and runs a heck of a lot better using 5.3 than 6.1 numbers in parameters which leads me to think the DTT TCFI IId software is using 3 bar for its software calculations and MAYBE making software adjustments for the actual operating pressure of the specific bike (which adjustment would be nothing more than the square root calculation posted by Doug).  My injectors were flowed at 6.1gps at 58 psi by Marren.  Again, WTFDIK.

[-SeabrookTrickBagger]

Doug,

BTW, would using a .55 BSFC instead of .5 BSFC would, for example, be the difference between a 5.39 gps injector and a 5.91 gps injector or about 5 lbs/hr on a 137 CS HP engine?  FWIW, another posters suggested use of an 85% duty cycle splits the difference between these two "extremes."

[uglyDougly]

   STB, I don't know that Marren resizes them, but they do match them. Ed from The Dyno Difference, bought a set for his 124 and they rated them just like the Yellow IWP069s.

 The injector sizing in the software is used to calculate the pulse-width, smaller injector value, longer pulse-width and vice-versa, why Chris would say it doesn't matter, I don't know except that you really need to put the value range in that works.

 Right around the turn of the century (the most recent one) EMC used to resize the M-M side-feed Weber injectors for $69.
 The company traded hands (I think because the guy who was doing the resizing, disappeared) and the new ownership didn't like to do the old ones, but they were re-sizing the Pico injectors.

 I purchased a few of the last of the oversized side-feeds from them and then Dan Fitzmaurice sent me a box full of M-M crap with a few more of the O.S. ones.
 Because they were reamed with teeny-weeny carbide reamers, the pulsed flow of these things is all over the map. I'm not sure if I can even get a matched set for my own pile.

  I think everyone who's doing tuning these days (the ones who actually calculate the injector requirements) are using somewhere around 80%. 'They' have been saying that for years, whomever 'They' is.

 When I'm doing a bike that revs to 11,000 RPM I'll give myself more head-room but the reality is, you don't always have many choices. Adjustable fuel regulators work for that.

 The MotoGP bikes are using 10 Bar pressures and high flow peak-and-hold injectors to keep the duty cycle within acceptable limits at 20,000 RPM. They need 32 bit processors to break the time into high enough resolution at those speeds.

  STB, if you put the wrong numbers into an equation yo umay get the result you want but not the result you need.

  That .55 BSFC is about how efficient you designed your engine. If you can improve the BSFC by 10% that's good. That's not saying that I have any idea what the actual BSFC of the engines I'm tuning is, but 'They' say (this is the engineering fraternity) that .5 BSFC is near the best you can get with an Otto Cycle engine.

  The BSFC number has to know how much friction your engine has as well as the drive-train losses. Ron has an engine dyno and he has a good idea of what they make at the crank but he has to calculate what the friction losses are.

   Maybe the saving grace of this whole injector sizing thing (since we're really not accounting for a lot of the losses) is that the the Dynojet reads so high, the equation actually gets it close.

  Having absolutely no idea about most of what goes on with our engines, I'm constantly amazed at how well a few equations actually work.

 Doug

[-SeabrookTrickBagger]

Well said.

Marren did send flow sheets to me when I ordered the injectors at my desired flow rates at the desired pressure.  I don't know how they do it, but.........  .  I might take another look at that flow sheet.

Understood ------- about .5 and .55 BSFC.

[-SeabrookTrickBagger]

Since I don't do what you do for a living, making mistakes is part of my learning process.  As Brig. General Prather told me years ago:  It is not the mistakes you make son, it is how you recover. 

I certainly make at least my share of mistakes and I post many of them on this website for all to see.  Fortunately, or unfortunately, my mistakes are well thought out.  And, those mistakes lead to discovery of reality, as in this instance.

Injectors:  When I built my engine several years ago, I did all the calculations, fairly close to what Doug suggests.  I came up with a need for injectors at 6.1 gps, flowed at 58 psi which I figured was the right thing to do since that was HD fuel pressure.  I really did not know, but it seemed correct to flow them at that pressure.  No HD mechanic in this area knew HD FI from Shinola. 

I contacted Marren and told him what I wanted.  He told me the flow rate would be too high.  I suspected he was factorin' when he should have been usin' gazinta since the flow at 43psi would be lower than that at 58psi.  So, I told him thanks but do it anyway.  He told me he did:  I got flow sheets and injectors flowed at 58 psi with a yield of 6.1gps.   Since these injectors are "electrically controlled" I suspected you just changed the voltage or some such thing and the flow/output changed.  ......... the basis of my misunderstanding started here...... .

Today, I looked for my flow sheets.  I called Marren, too.  He sent injectors to me that are 5.29 at 43psi.  Upon this foundation of "error" I built my knowledge base:  injectors could be custom flowed.  I am not an engineer or a professional mechanic or tuner; just an afficianado with a bit of curiosity and scars on my hands, having left my flesh on engines from Briggs and Stratton up to blown alcohol engines, reminding me of why I do what I now do for a living even though my dreams at 8 years of age were to be a motorcycle mechanic.

I am pleased on several levels, one is Doug telling me that flowing injectors is largely a mechanical process and the other is that Marren did send what he knew to be the correct injectors to me since 6.1 gps flowed at 58 is about 5.3gps at 43psi even though he did not explain to me that he could not do what I asked him to do (0513HD).  (The flow sheets are a bit of curiosity, but I can live with them).  I am also pleased to learn a bit more about injectors even though all this learning is at some personal expense.  I guess "how you recover" is where it is at.

[uglyDougly]

   This has been a very civil discussion and interesting too. Remarkable.

   Thanks to everyone who offered info and questions.

   Ed, do you really want to talk about throttle size? Really?

    Doug

[ederdelyi]

Doug,
Well, I don't have a problem picking appropriate carb or TB sizes for a given application, but a lot of other folks sure seem to. Since the title was TB/inj I thought the next step would be TB size and it's effect on engine power/driveability ... it's up to the rest of those out there who may be lurking and hopefully learning.

I can easily let this thread go at this point with no problem :>)

[Scramjet]

What about the knock down, drag out TB thread that was just finished recently in the Twin Cam section?

The moderators just got done cleaning up the floors from that discussion.

I would hope this thread does not go there.

B

[ederdelyi]

Musta missed that one ... or ignored it. Like I said, I can easily forget I even mentioned it, I know how to size carbs and TB's. If the thread is really done maybe someone should ask that the thread be locked ... it's not my thread or my decision.

[uglyDougly]

  Cooler heads prevail.
  Let's call this a wrap?

  Doug

[ederdelyi]

 

[axtell]

chickens??

[uglyDougly]

  instigator!!