boosted

charlie31603 · Post by **charlie31603** » Fri May 27, 2005 10:32 am

Ok. I'm very new to this and don't quit understand everything. My question is this. I have a Starion that is a 4 cylinder turbocharged. And I want to run the megasquirt on a custom mpi and get rid of the factory tbi. I did a search and I think I need a flyback board with low impedence injectors. So is that what I want to use on my engine. I didn't see if they have the size(65lb/hr) I need in high impedence. But I read the low impedence are the ones to use for the boosted vhicles. But I also have to use the flyback board inorder to use the low impedence injectors. Right? I just want to make sure I have everything that I need and it will work for me. This is going to be a daliy driver and is going to be raced every once in awhile. Boost is going to be 15psi for now but could go up to 25psi. Thanks in advance for the help! Adam

78Spit1500Fed · Post by **78Spit1500Fed** » Fri May 27, 2005 11:52 am

If the injectors are low impedance, you should use the flyback board. If they're not, you'll be fine with the circuit in the PCB.

The impedance of the injector is a function of the injector itself... the induction method (forced or natural) is of no consequense.

-Brian

charlie31603 · Post by **charlie31603** » Fri May 27, 2005 12:04 pm

Ok. I was reding this post http://www.msefi.com/viewtopic.php?t=68 ... =impedence. So I thought it was better to use the low-z injertors. But since I don't see my size in the price range I was going to go low-z anyways. But I just wanted to ask and make sure. Also if I'm going to use these injectors I need the flyback board. So that's just one more thing on my list. Thanks again! Adam

Brains · Post by **Brains** » Fri May 27, 2005 2:14 pm

We used a set of Siemens Deka Hi-Z injectors on a T76 turbocharged V8, and they're running quite well. The flow rate at the 4 bar rail pressure is somewhere around 65lb/hr, I believe they're rated 57 or 60lb @ 3 bar.
Memory is failing me

charlie31603 · Post by **charlie31603** » Fri May 27, 2005 2:32 pm

I know bar is boost. But what dose 1 bar mean in psi. Still a little new to forced induction. As far as injectors I was looking at these http://www.racetronix.com/17113814FM.html They seem like a very good price and it's the style I need for my intake. But let me ask you this. Are these going to be to big for a 2.6 liter four cylinder. Even though it has a bigger turbo that will push 600cfm at 15psi. The custom mpi with hard pipes for the intercooler. Custom 2.5 inch exhust. And the complete msd system. I heard if I go too small I run lean and over heat the injectors. But If I go to big I will not be use the injectors right and the spary patern will be crap. I don't know. This is my first fuelinjection car. All I had before were carbs. But I'm on the atkins deit now. lol. So If any one else want's to chime in to help, fill free. Thanks again for the help guys! Adam

Brains · Post by **Brains** » Fri May 27, 2005 2:57 pm

1 bar = 14.5 psi. So 3 bar = 43.5 psi, 4 bar = 58 psi

Probably the first thing would be to get an estimate of your fuel requirements. Google for a "brake specific fuel consumption" (BSFC) calculator. Punch in the values for your setup, and you should get a recommended injector size.

Its definitely better to run an injector that's bigger than you need. The caveat is being able to get the car idling smoothly with the small pulse widths necessary at low RPM. I don't think those injectors will pose much of a problem in that regard.

charlie31603 · Post by **charlie31603** » Fri May 27, 2005 3:22 pm

Ok. I'm lost now. lol. I found a calculator thingy. But I don't know how to use it. I put 65 for the flow rate. And 350 for the brake horsepower. And it came up with 0.18xxxxxxxxxxx. I don't know if that's right. I don't even know if I did it right. And I don't even know what it means. lol. Here's the link http://www.webcalc.net/calc/0756.php. I think i'm in over my head. If you can teach me what I'm doing. That would be sweet. Thanks. Adam

Brains · Post by **Brains** » Fri May 27, 2005 3:50 pm

Its not that bad once you get past all the terms and numbers. Still doing the same old thing we did with carbs, just related to new words and digits.

Try this link instead: http://www.witchhunter.com/injectorcalc1.htm

Use the 2nd calculator down the page and you'll find the right size injector. A couple notes:
1. Shoot for around 80% max injector duty cycle. Above that they tend to heat up.
2. Shoot for the max flywheel horsepower you intend to hit on this or any near future combos. Buy the parts once

3. If the fuel pressure your car runs is different from 3 bar (43.5 psi) you'll want to take the number from this calculator, and enter it into the flow rate calculator at the top of that page.

charlie31603 · Post by **charlie31603** » Fri May 27, 2005 4:44 pm

Ok. I'm still a little lost. It's this whole BSFC. I still don't know what it is or what I should change it to. Also I don't know what the feul pressure will be at 25psi. Because I don't have the car running. The rest of it I get. 400hp, 4 cylinder and 80% injector duty. If I use the .50 that's on the caculator when you load the page it says 62.xx lb/hr, for the injector. If I use the .60 like it says for the turbo applacations. It gose up to 75 lb/hr I think. I'm just confused. Do they make a BSFC book for dummies. LOL. Thanks again for the help. I'm gettting some of it. Adam

Brains · Post by **Brains** » Fri May 27, 2005 4:50 pm

BSFC is simply a measure of fuel usage. For our sake, don't worry about relating it to anything specific -- you just pick a number based on application. Turbo cars should pick something in the .60 range, typically.

Quoted from Edelbrock:
http://www.edelbrock.com/automotive/spo ... ech_1.html

Brake Specific Fuel Consumption
Brake Specific Fuel Consumption is the ratio of fuel consumed (in lbs. per hour) to horsepower produced. This ratio is a direct indicator of how efficiently the engine converts fuel into power. Most factory gasoline type engines run approximately a .50 to .55 Brake Specific Fuel consumption (BSFC) range while a highly efficient normally aspirated race engine operates at approximately a .40-.45 BSFC.

* Most common turbocharged or supercharged engine configurations run in the .55 to .60 BSFC range.

* For Methanol powered applications the BSFC is doubled (i.e. turbo/methanol: 1.10-1.20).

These factors should be considered when sizing & selecting injectors for your particular application.

charlie31603 · Post by **charlie31603** » Fri May 27, 2005 5:29 pm

So the BSFC has nothing to do with the how much the fuel pump flows or what the injectors flow, correct. It just determens what a tipycal(sp?) motor would consume, right. So it takes a turbo motor .55 or .60 lb/hr for the motor to make that one horespower. So to make my motor to have 400 hp. It would need 68.75 or 75 lb/hr at 43.5 psi. So I would just get the 75 lb/hr to make it on the safe side. Now. I know my car is not going to make that much power right now. So is that big of an injector going to effect my drivabilty. Thanks!! Adam

AmericanFrog · Post by **AmericanFrog** » Wed Jun 01, 2005 11:44 pm

Ummm, hate to be a pain, but isn't 1 bar = 1 barometic pressure, or 14.7 PSI or 100 kpa, at sea level (HS physics class comming back to me)

1 bar = 1 atm = 14.7 psi = 100 kpa = 760 torr (mm of hg) = 29.92" of hg

I think that's right

don't wantany error in any's calcuations that are that large (these numbers are not exact, but iirc, all of those are within 1.5%)

Devilman · Post by **Devilman** » Fri Jun 03, 2005 4:32 pm

Sorry to hijack slightly, but Im wondering, does RPM have any relation to BSFC?

surely an engine developing 300bhp @ 12000rpm would be using a lot more fuel than a motor developing 300BHP @ 6000rpm? or doesnt it work like that?

Just trying to get a feel for when I setup my Gixxer Turbo.

Thx.

renns · Post by **renns** » Fri Jun 03, 2005 4:39 pm

AmericanFrog wrote:Ummm, hate to be a pain, but isn't 1 bar = 1 barometic pressure, or 14.7 PSI or 100 kpa, at sea level (HS physics class comming back to me)

1 bar = 1 atm = 14.7 psi = 100 kpa = 760 torr (mm of hg) = 29.92" of hg

I think that's right

1 atm = 14.696 psi, which is 101.325 kPa. 1 bar is exactly 100 kPa (which converts to 14.5 psi), a bit less than the 'std' atmosphere. Hence the slight discrepancy between 14.5 psi and 14.7 psi numbers.

If really bored, go here: http://www.engineeringtoolbox.com/pressure-21_587.html

Roger.

whittlebeast · Post by **whittlebeast** » Sat Apr 15, 2006 7:28 am

These sheets ignore lots of thing like injector opening time, squirts per engine cycles, 2 stroke / 4 stroke and RPM. Lots of other info on this sheet.

Try http://www.ncs-stl.com/fuel/ReqInjectors03.xls

AW

Uncle Bob · Post by **Uncle Bob** » Sat Apr 15, 2006 8:39 pm

Devilman wrote:Sorry to hijack slightly, but Im wondering, does RPM have any relation to BSFC?

surely an engine developing 300bhp @ 12000rpm would be using a lot more fuel than a motor developing 300BHP @ 6000rpm? or doesnt it work like that?

Just trying to get a feel for when I setup my Gixxer Turbo.

Thx.

work is work. HP is HP. Your two example are too generic to answer them in detail, but in general, 2 EFFICIENT engines will have the same BSFC's for both your examples. The question is, are they both efficient?

There is a lot of factors in BSFC, and its hard to quantify without measuring it for real. The main thing to keep in mind is, its moreso a tool for getting in the ball park for your application, and its definitely better to overdo it than under do it!

But if you want more detailed info on injector sizing for a giving motorcycle size, the turbo'd busa boards would be the best resource for that, assuming you can get HP, injector size and pulse widths at peak output from members.....might be a challenge.