injector question for m20 turbo

[e30leigh]

hi there guys.

was woundering what injectors everyone is running?

as stock injectors are 19.5 lbs-hr (204ish cc's)

i was thinking 37ish lbs-hr (390ish cc's)

for injectors would be enough? i say this as this is a common mitsi gsr size and there are plenty of them available to me here.

so i wanted to know what others are running? also i was looking around but cant seem to find what the impedence is on the factory injectors? i dont have a set to measure which is lame.

also found this site which was good for some quick calculations

http://www.rceng.com/technical.aspx

which according to 37 lbs-hr is right on 355hp... right what im aiming for.
seeming its at 80% duty cylce it gives room to squeeze as well.

[jaywood]

Well, what EMS are you running? If you're using motronic to tune, 30lb is the max. If you're doing a standalone system, go bigger. 37lb is too small

[The Humjet]

355hp at the flywheel is what I think they mean. They should be good for 12psi with a well sizes up turbo. I doubt you could make 355whp on that level of boost.
Also if you are planning to run them on the motronic it can be done. Miller can tune via the W.A.R chip for injectors up to 50lb/hr in size.

[e30leigh]

i was intending to keep motronic. simply for cost reasons. ive been looking into it and they seem rather tunable. but i havnt done heaps of research into them just yet.

i may not make 355hp. thats fine. id like to but im not exactly sure what they are capable of. i may fit a more aggressive cam and just see what i can get out of them. also looking into map vs maf sensor options. id rather map as its tidier.

but i think i will go with the 37 lbs injectors. they are cheep and available. if i struggle ill source larger ones. i think an aftermarket rising rate fpr will be a must as well.

[sayed ali]

My friend uses the stock motronic and a custom chip + MF2 Fuel controller with two 450cc injectors (42 lbs)

He is at 25 psi making near 350hp ..

So I think you need to get a larger injectors

What are you planning to do with the motronic?

[The Humjet]

I'd get a ready built plug and play MS by either whodwho or blueapplesoda. If your gonna keep motronic because your budget doesn't allow to afford proper tuning. Then I would forget about running a nice fat cam like I mentioned earlier and tune with a standalone with that money instead. Tuning your car should be your no.1 priority before building motors with forged internals and having the latest ball bearing turbo.
For low boost tuning on motronic is possible. But its so much easier and better with a standalone ems. It doesn't have to be megasquirt check out some local brands see what these tuners work with. But megasquirt is very easy to get up and running.
Also you don't need an rrfpr with megasquirt.

[jaywood]

25 psi and he's only making 350 hp?



Definitely go Megasquirt op. After the RRFPR, chip, and all the other odds and ends, you could have already bought a pnp MS system from whodwho

[ak-]

You usually get bigger injectors for the application and detune them for yours.
Motronic is definitely tunable, you just have to find someone who can do it.

[sayed ali]

25 psi and he's only making 350 hp?



Definitely go Megasquirt op. After the RRFPR, chip, and all the other odds and ends, you could have already bought a pnp MS system from whodwho

^^
+1

Megasquirt is the way ;)

[efficient]

going to bump this. this is just an example
I was wondering if big injectors are bought like lets say 60lbs and i only plan on running like 8psi. i plan on buying megasquirt down the road. can those injectors be detuned to run properly or would it not work?

id like to see 300whp

[cleanasse30]

going to bump this. this is just an example
I was wondering if big injectors are bought like lets say 60lbs and i only plan on running like 8psi. i plan on buying megasquirt down the road. can those injectors be detuned to run properly or would it not work?

id like to see 300whp

You don't really "de-tune" injectors, you determine the duty cycle for a given point on the fueling map and the computer opens the injector for a given amount of time. The problem becomes when you get injectors that are large and for high horsepower, it becomes more difficult to tune for idle because more fuel is sprayed per percentage of duty cycle.

For instance if you had a stock injector that was at 10% duty cycle at idle it means the injector is open for 10% of one cycle of the engine. Say you put in injectors that flowed 3x as much as stock, you would need to lower the duty cycle to flow the same amount of fuel as the stock injectors. So for simplicities sake lets say your duty cycle at idle is now 3%. This means that now the larger injector is only open for 3% of one cycle of the engine. This causes problems with cheaper injectors because they aren't as precise as more expensive injectors. If the margin of error on a cheap injector is +/- .5% of duty cycle it makes a much larger difference at 3% duty cycle than at 10%.

Thus larger injectors will give you a worse idle (to a certain point) because the increments between percentage points of duty cycle are larger. Cheaper injectors further compound this problem by having larger margins of error which makes a larger difference at lower duty cycles.

That's probably a longer explanation than you were looking for but I hope it helps you understand how injectors are controlled by the EMS and why larger is only better to a point.

General rule of thumb is that the most you should run an injector is at 85% duty cycle, so you need to size your injectors by calculating how much fuel is needed at a duty cycle of 85% for the target horsepower you want to make. I believe there are online calculators that will give you a decent guess as to what size you would need, but somewhere in the 42-50lb range should work for 300hp.

[efficient]

Its a real good explanation. Thanks! Never really understood it until now.

[Cayoncrusier93]

You don't really "de-tune" injectors, you determine the duty cycle for a given point on the fueling map and the computer opens the injector for a given amount of time. The problem becomes when you get injectors that are large and for high horsepower, it becomes more difficult to tune for idle because more fuel is sprayed per percentage of duty cycle.

For instance if you had a stock injector that was at 10% duty cycle at idle it means the injector is open for 10% of one cycle of the engine. Say you put in injectors that flowed 3x as much as stock, you would need to lower the duty cycle to flow the same amount of fuel as the stock injectors. So for simplicities sake lets say your duty cycle at idle is now 3%. This means that now the larger injector is only open for 3% of one cycle of the engine. This causes problems with cheaper injectors because they aren't as precise as more expensive injectors. If the margin of error on a cheap injector is +/- .5% of duty cycle it makes a much larger difference at 3% duty cycle than at 10%.

Thus larger injectors will give you a worse idle (to a certain point) because the increments between percentage points of duty cycle are larger. Cheaper injectors further compound this problem by having larger margins of error which makes a larger difference at lower duty cycles.

That's probably a longer explanation than you were looking for but I hope it helps you understand how injectors are controlled by the EMS and why larger is only better to a point.

General rule of thumb is that the most you should run an injector is at 85% duty cycle, so you need to size your injectors by calculating how much fuel is needed at a duty cycle of 85% for the target horsepower you want to make. I believe there are online calculators that will give you a decent guess as to what size you would need, but somewhere in the 42-50lb range should work for 300hp.

Deka #60's would be a bad choice if a smooth idle is desired?

[cleanasse30]

Deka #60's would be a bad choice if a smooth idle is desired?

They would probably be fine, I was just trying to illustrate that choosing a 100lb injector for low boost wouldn't be the best idea. Size you injector for your intended power goals.

[bobross]

They would probably be fine, I was just trying to illustrate that choosing a 100lb injector for low boost wouldn't be the best idea. Size you injector for your intended power goals.

Incorrect. Mostly because power goals always end up increasing

As long as you have full control over injector output, use the biggest/highest quality injector you can get your hands on.

I have 2 1.8l cars running 1000 &1300 cc injectors with no issue. Both cars idle better than stock. 2000cc injectors in hand going into a 2.8L (also currently all motor)