what is the correct formula for trying to figure out proper injector size for more hp on a 89 turbo?

 

if you have to think about it they're not big enough.

really

 

read other peoples list o' mods and it'll give you a good idea.

but for a starter we need to know the turbo you want to use. from that we can figure out how much air yours sucking. then you'll need 1/12 as much fuel. add 20% flow to keep your injectors below an 80% duty cycle. then you'll need a fuel pump that moves enough volume at the at your boost level plus your base pressure (40psi). anything bigger then a walburo pump and you'll need to upgrade your FPR and your FPD.

 

Go to the "Fuel Injector Worksheet" at the bottom of this web page.
http://www.rceng.com/technical.aspx

Here is a general guide:

HP = Horsepower at the flywheel

Number of Injectors = 4 if you are using the same size of injectors for both primary and secondary. Otherwise, enter 1 and that way the calculator will give you your total required flow. Then you can figure out what combination of the fuel injectors would meet that requirment.

BSFC = .55 for NA, .64 for low boost, .70-.80 for high boost.

Maximum Duty Cycle = .80

Fuel Pressure = 37psig for the stock FPR, or enter your custom value if you have an aftermarket FPR.

 

One I found a while back that is fun to play with:
http://rx7.com/cgi-local/2ndgencalc.cgi

 

the smaller the injector the better it is for fine tuning. 550cc injector = 0.0091 cc per millisecond. 1600cc injector = 0.0267cc/ms, smaller injectors will also atomize the fuel better, not much more horse power but you'll gain like 10-15km to a tank.

try not to make your secondary injector more then twice the size of teh primary, like a 550primary and a 1600secondary, this combination tends to create hesitations when you roll into throttle, depending on your EMS and tuner.
go with a 550 and 1000, or 860 and 1600. and if your running a large frame turbo use 1000 and 2200cc. thought people do make 1600 and 1600cc work.

 

Haha. This is cool. Thanks.

 

i want to get to 350 hp but i want to do the math. Haha

 

70-80 for high boost. Are you refering to stock injesctors are is that not a factor?

 

whats the stock pressure in 89T fuel system rails when fuel is runing in them?

 

That one is nice for a quickie calculation, but it doesn't factor-in BSFC or fuel pressure. It also doesn't compensate for dead time, but neither does the RC calculator.

The fuel injectors do not matter all that much, although a professional tuner could reduce BSFC with a nice set of injectors and a standalone EMS. The main factors are the quality of the tuning, the quality of the components (turbo, engine, exhaust, intake, intercooler, etc.), the boost level, and the type of porting. Most of the people on this forum who self-tune their engine with a piggyback and have overdriven OEM or crummy Ebay parts will end up with a higher BSFC. Professionally-built and tuned engines will have a lower BSFC. Since there are so many factors involved, it is difficult to estimate the value for your particular engine. Also, BSFC varies with engine rpm and load.

The acceptable range is 34.1 to 39.8 psig, which averages to 36.95 psi, which is why I used the 37psig number earlier.

 

^ Wont the psig numbers change once the fuel pump is upgraded?

 

Not if the FPR is doing its job. In some cases, such as with a pump like a Walbro 255, a stock FPR can be overrun, which will drive fuel pressure up.

Solution? Aftermarket FPR or a pump that is more suitable.

 

Hmmm. Well ii have a supra pump waiting to be put in. While we are on here and discussing injectors for power. Before i upgrade the turbo i was thinking about getting a boost controler and getting more power out of the stock tiurbo. How much power would i be looking at with the boost tuned to 11 or 12psi?

 

What determins low boost and high boost. What psi is the line drawn between low and high?

 

I gave generalized references on purpose because the BSFC depends on the tuning. There is no solid relationship for which x amount of boost = y amount of BSFC, but in general the higher the max boost the higher the BSFC.

You are probably beginning to see why I recommend professional tuning.

 

^ I do but i still want to learn this.

 

So after having done the math at rceng it turns out I need 750cc all around. I called my tuner to tell him this and he told me I can just do 1100 for my secondaries.

 

A better question would be How reliable is the stock turbo at 11-12 psi? Will i have boost creep? Answer: leave it at a safe limit until you upgrade.

 

the stock turbo I've seen reach as high as 13psi but it falls out of efficiency near redline and drops back to 10psi. so i'd say 10psi is the highest you want to run a stock turbo.

 

http://fc3spro.com/TECH/FM2W/power.htm

You can figure the same by entering "1" for the number of injectors. This will give you the total cc/min required, and then you can figure out what combination of injectors will meet this minimum number. For example, if the calculator comes up with 3000cc/min, that means you can use 4x750, or 2x550 + 2x1000, or 2x460 + 2x1100, 2x1600 primaries and block off the secondaries, 2x550 + 2x550 + 2x460 additional injectors, etc.

Some people modify this by using "2" if they will always use matched pairs. For example, if the calculator comes up with 1500cc/min, that means you can use a primary/secondary combo of 750/750, 550/1000, 460/1100, etc.

 

^ This was actually going to be my next step. Get the lump sum then devide. Cool im on the right track.

 

AS far as the turbo goes im getting it ported with the build. Im already creeping at 10psi without it dropping it just stays there until i let off ofcourse. Speaking of which does anyone make an upgraded waste gate actuator for the stock turbo? I want to run a boost controler when its ready.