Author Topic: Main jet and nozzle size  (Read 594 times)

Offline masracingtd1167

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Main jet and nozzle size
« on: May 11, 2019, 01:21:01 PM »
Is there a formula to use when going to a bigger nozzle ? right now I am running a .037 nozzle with an .88 main jet . If I go to a .040 nozzle is there some sort of formula to figure out what size main to use just to get it close to the same ?   

Offline dreracecar

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Re: Main jet and nozzle size
« Reply #1 on: May 11, 2019, 03:47:37 PM »
should have the entire system flowed to get a baseline

Offline fuel749

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Re: Main jet and nozzle size
« Reply #2 on: May 12, 2019, 06:28:05 AM »
If you're systems been flowed and you're confident with the numbers head on over to Spuds page and use his calculator.  And because he's so nice to provide the free info it couldn't hurt to buy the parts from him. I've used his info several times and always came out with a xxxx good starting point.

Offline denverflatheader

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Re: Main jet and nozzle size
« Reply #3 on: May 12, 2019, 06:51:02 AM »
Bill - a nozzle change with larger holes from .037 to .040 requires less pressure to maintain your engineís current fuel tune-up.  Part of the formula needed for calculating your new main pill starting point is your present fuel pump output.  Both fuel749 and dreracecar suggestions are good ones to accomplish the calculation.

Your question and sharing your current .088 main pill actually reminded me of FIEís Technical Article regarding main pill sizes.  Your proposed nozzle change should allow you to move from a .088 main pill to a .100 or larger.  According to Spudís Technical Article, thatís an excellent decision on your part for tuning methanol.  Spud has much useful information in his Library, and compares a ďbig benefitĒ of selecting a main pill area between .100 to .130 for methanol which promotes a 6% - 8% area (i.e. diameter) change using .005 main pill increments (e.g.  .100, .105, .110 etc.).

To make tuning your methanol engine easier, please read Spudís Technical Article, the last paragraph that starts with ďIdeally,Ē hereís the link (thank you Spud):
     
http://www.fuelinjectionent.com/bigpumpmyth.php


p.s.  nice formula presentation
          \/      \/      \/
« Last Edit: May 13, 2019, 06:07:29 AM by denverflatheader »

Offline coupemerc

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Re: Main jet and nozzle size
« Reply #4 on: May 12, 2019, 02:47:52 PM »
Bill,

You can calculate the approximate new main jet by converting everything to area. I calculated a .100 for your new jet size.
Here's how...
Presently the % fuel out of your pump that you are returning back to the tank is Area Main Jet/(Area Main Jet + Area Nozzles).
Area Main Jet is (.7854)(.088)(.088)= .0069821 in2
Area Nozzles is (.7854)(.037)(.037)( 8 )= .0086017 in2...I'm assuming you have 8 nozzles.
The % fuel you are returning back to the tank is .0069821/(.0069821+.0086017) = .44 or 44%

So now...
Area new Nozzles is (.7854)(.040)(.040)( 8 )= .01005312 in2
Set the Area new Main Jet/(Area new Main Jet + Area new Nozzles)=.44
or Area new Main Jet = (.44)(Area new Main Jet) + (.44)(Area new Nozzles)
or (.56)(Area new Main Jet) = (.44)(.01005312)
or Area new Main Jet =(.44)(.01005312)/.56
Area new Main Jet = .00789888

Diameter of new Main Jet is .1002 or a "100" Jet

Hope that helps!
« Last Edit: May 12, 2019, 02:51:12 PM by coupemerc »

Offline dreracecar

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Re: Main jet and nozzle size
« Reply #5 on: May 13, 2019, 08:15:36 AM »
Bill - a nozzle change with larger holes from .037 to .040 requires less pressure to maintain your engineís current fuel tune-up.  Part of the formula needed for calculating your new main pill starting point is your present fuel pump output.  Both fuel749 and dreracecar suggestions are good ones to accomplish the calculation.

Your question and sharing your current .088 main pill actually reminded me of FIEís Technical Article regarding main pill sizes.  Your proposed nozzle change should allow you to move from a .088 main pill to a .100 or larger.  According to Spudís Technical Article, thatís an excellent decision on your part for tuning methanol.  Spud has much useful information in his Library, and compares a ďbig benefitĒ of selecting a main pill area between .100 to .130 for methanol which promotes a 6% - 8% area (i.e. diameter) change using .005 main pill increments (e.g.  .100, .105, .110 etc.).

To make tuning your methanol engine easier, please read Spudís Technical Article, the last paragraph that starts with ďIdeally,Ē hereís the link (thank you Spud):
     
http://www.fuelinjectionent.com/bigpumpmyth.php


p.s.  nice formula presentation
          \/      \/      \/

Question,  If you open the nozzle area (19%) you wind up with a pressure drop, add to that an increase in the mainjet/return which also drops line pressure, that you would lose volume and run leaner??.  Would not reducing the main increase the nozzle pressure, thus increasing fuel volume thru the larger nozzles??


Don't know why the OP is changing the nozzles unless the nozzle area of the 37's is below the volume needs of his motor and the 40's put him in the proper range??

Offline denverflatheader

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Re: Main jet and nozzle size
« Reply #6 on: May 13, 2019, 09:40:07 AM »
Hi dreracecar - Iíll use an extreme example to illustrate:  As I understand for Bill, heís wanting to maintain a matching amount of fuel passing through his engine during the same time period using either a .037 or .040 nozzle. 

Please picture an empty swimming pool, then filled with a garden hose and it takes 10 hours to fill.  Now picture the same empty swimming pool, filled with a larger fire hose and you want it to take a similar 10 hours to fill.  To accomplish, you would reduce the water flow pressure.

In Billís tune-up, with a larger .040 nozzle (firehose), you would decrease pressure to maintain the same volume of fuel moved through his engine with the .037 nozzle (water hose).

Iíll mention again what both you (dreracecar) and fuel749 suggested is what I would do first.  Without knowing the status of your fuel pump, and if itís just marginal doing the job, making a change could create other troubleshooting issues.  It may work fine initially, and with a change push it beyond itís capability and maybe you go lean.

Offline dreracecar

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Re: Main jet and nozzle size
« Reply #7 on: May 13, 2019, 11:45:30 AM »
There has to be purpose for change and that's what is missing in the first post.

  I already own a water hose to fill my pool, and I don't need to buy a fire hose to fill my pool with the same volume of water. Also consider that the faucet and plumbing has a small ID, so attaching a larger dia hose to it is not going to fill the pool any faster unless I find a faucet that will flow more and the garden hose at some point becomes a restriction

Offline denverflatheader

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Re: Main jet and nozzle size
« Reply #8 on: May 13, 2019, 12:42:02 PM »
Yes, I donít know why the change either.  Maybe a reason will be added.

Offline wideopen231

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Re: Main jet and nozzle size
« Reply #9 on: May 13, 2019, 01:14:12 PM »
 Bill,
  Few ways to get your answer and simplest is Spuds calculator. I will show you pressure with both changes. .037 to .040 is big jump in nozzle sizes. It will require larder bypass becuase the pressure required to get fuel to motor will be far less. My guess its its a SWAG w.o a lot of the s part. .010 to .015  bigger bypass depending on pump size. I normally run a 7.0 (+/-) 80A on injected stuff. Hence the less scientific part.

 Unless you have problem getting enough fuel thru .037's which shouldn't be unless pump issue. OR? You are tilting the can quite a bit? IMO you would just be lowering pressure in system and I like higher pressure system better. Thats my 2 cent and its probably over valued at that.

I have some flow sheets for nozzles if it helps. They are based on 150 psi. At 150 psi a .037 flows .3237 gpm  a ,040 flows.3660 gpm. So that would be roughly(no calc. handy) .34 gpm difference. If know pressure you can figure flow  using that and new flow = old flow (my #)x sq root of new pressure dived(yours) by  old pressure(150). Or just go to SPuds calculator its lazy way out and works w/o headache later. Oh yea I am not nice enough to do the math for you like some show offs did.LMAO

Ok guys go a head I am sure something wrong there. I know it but normally screw up putting it down..
« Last Edit: May 13, 2019, 01:30:31 PM by wideopen231 »
Relecting obama is like shooting right foot because it did not hurt enough when you shot left foot

Offline masracingtd1167

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Re: Main jet and nozzle size
« Reply #10 on: May 15, 2019, 03:03:33 AM »
Thanks for all of the reply's ! The reason I thought a bigger nozzle would be better for my tune up when running a small amount of nitro ! The alcohol tune up with the .037 and .088 main is just about perfect ! My plan is to go to a little bit bigger amount of nitro and thought this might be a better way to do this !

Offline msundstrom

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Re: Main jet and nozzle size
« Reply #11 on: May 15, 2019, 06:42:28 AM »
What percent are you now ?

Offline dreracecar

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Re: Main jet and nozzle size
« Reply #12 on: May 15, 2019, 11:21:44 AM »
Then just change the nozzles and leave the main jet alone to see where you are at, Alc is a sloppy fuel, it will still  run when fat because it only burns what it needs.  The big issue is having enough spark to light it, a 1.7 vertex is marginal, and should be closer to a 3.5 Mad III, and silly to go bigger unless you have a larger mag already

Offline masracingtd1167

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Re: Main jet and nozzle size
« Reply #13 on: May 15, 2019, 12:55:33 PM »
I think that my ignition could be a limiting factor at some point . I use a 7al3 and so far it has been fine .When I was spraying it with nitrous I was running a good amount of alcohol as well with a secondary pump . I closed the gaps up to .020 and had no issues and it has been fine with up to 20 percent so far !At some point I do plan to put a mag in it but my budget is not quite ready !

Offline wideopen231

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Re: Main jet and nozzle size
« Reply #14 on: May 16, 2019, 03:14:44 AM »
how much nitro? According to those nitro notes you have been reading.No need to change till passing 30 %. Plus go to spuds tune up calculator. It has a line for nitro% .Just play with numbers and see what it shows. I am sure its not perfect but probably dang(just for you Glen) close. Running my set up thru system  program shows my 7 gpm pump good till about 55% with bigger nozzles and keeping my main above .100(personal preference). Spuds calculator has be come a go to toy when bored at night and just want to educate myself some on ideas.LOL
Relecting obama is like shooting right foot because it did not hurt enough when you shot left foot