Is there a rule of thumb for limits on increasing fuel injector size before exceeding the computers fuel mapping ability to adjust? Is this question totally off target? I must admit ignorance about EFI systems. While I have had the desire to learn more about them, I just now find myself with the need. I have been fortunate enough to enjoy about 700K of mopar EFI ownership usage miles (me & the wife for 20 yrs) with never a problem so I have never had to learn.

The reason: 1989 Dodge Daytona 2.5L Turbo 5 spd, 200K + miles. The wifes old car. This car has been sitting for about 7 years and had developed a miss when parked. My daugther has had her eye on the car since she was 5 and is now nearing 15 and will get her license at 16.

I fired it up a few weeks ago and put it in the barn to start a restoration on it including rebuilding the engine, replacing the turbo (never failed but has lotsa miles on it), as well as anything else the car needs. Thinking it much better to iron out any bugs now rather than discovering them and trying to work through them with a fresh engine I traced the miss to a bad injector.

I have been reading a lot over on Turbo-Mopar.com and a little on TurboDodge.com of which I will join shortly. However, having great respect for the knowledge on this board I wanted to ask some general questions here. From that reading I discovered Forward Motion Inc. which has a set of 30lb/hr injectors at a comprable price to stock replacements.

My delima right now is do I buy a set of these, or stick with the stock injectors? I would like to be able to increase the power marginally, but since this is the daughters first car, dependabilty and fuel consumption are the highest priorities. Besides that, the wife has already stated that the car is already fast enough for a new driver. While I can't argue with that, the ability to tune it up a bit as she grows is appealing. From what I understand, the abilty to dependably add boost requires the abilty to add more fuel. My daughter wants to very much be involved in the restoration and is helping out already, which is a thrill and opportunity for me. She is a bit of a gear head and I'm lovin that.

Any advice, thoughts, or recomendations of source material (reading) is greatly appreciated. Right now I am in the stage of identify the needs / target of the build and then research the best way to achieve that, but I find myself having to buy a set of injectors at this point.

I'm a old gear head that has some knowlegde on internal combustion motors and their operations, gas motors need a certain amount of fuel, air and ignition spark to function correctly, the better the tune the better the perforamnce. the EFI that I have work on, not many, need all the inputs to make the most power, adding bigger injectors will add more fuel if you leave the same computer, fuel controller settings the same and it will not make more power due to not having more air to go along with the additional fuel If you want to turn the boost up on the turbo then you will need more fuel along with the additional air from the turbo. I'm thinking like your wife right now, fix what is broken and start aquiring parts for a lot better motor for when,and if, the daughter has the skill to handle more power Niether one of my kids wanted to drive my hotrods, we lived in the desert in SO CA and they both got into offroad motorcycles and three wheelers, no drag cars My middle grandson on my duaghter side wants to drive my 10 second Duster at the track, not sure if he has the skill yet, Maybe soon

Before buying injectors try removing them & soaking them overnight in a bowl of Berryman B12 then apply 12v to the coil & blow them out with compressed air..... Usually makes for a very cheap fix...

Thanks 1_Wild. That is something I will have to remember. However, this injector seems to be open on the coil. Apply 12V and no click. I'll give that a shot though just the same. Can't hurt.

Cab_Burge,
I get your point and wondered if the computer would keep the larger injectors from over fueling until boost is turned up supplying the air side of things. My daughter has been driving a little bit around here for the last couple of years (on private roads only) and is giving indications of having good sense. I will build the engine once and do it right on the internals to ensure that it is strong enough to handle additional power either way. I'm not talking that much. The factory rating was 150 HP and the injectors noted are good to 185 HP. I did say increase the power marginally. That still won't put it to the levels that many new 4 bangers are available with.

Thanks for your input!

Bigger injectors are nice for future upgrades however the stock speed density system will not just let you drop them in and everything be fine. You'd need a tune for the injectors...

Ohm the coils, if the resistance is the same chances are the pintle is gummed up due to the old fuel.... It may clean..

changing to new larger injectors won't help you, the computer will just run them at the same flow rate as your getting now just at a lower duty cycle. with a turbo you probably have 30 lb/hr injectors in there already. going to a 35 lb/hr injecor will buy you a little room for upgrades but not something your going to use until you really start developing power. head porting, bigger turbo, intercooler, etc. i would wait and get the injectors when you are ready to upgrade that way you can buy the right size for the power level you want to make later.

if the car has been sitting a bunch of years it would be good to send the injectors out to get flow matched and cleaned professionally. on a boosted application its more critical to make sure that each cylinder has all the fuel its supposed to hence the flow matching.

here is a link to some light reading on injectors
injector info

DO NOT increase fuel injector size without purchasing a recalibrated computer. There are vendors on the turbo boards who will do this but it's really not necessary in your application. The stock computer will do up to about 14lbs of boost, which the stock injectors will be able to fuel. Since your 2.5 T1 is only rated at 150hp and 9psi for 10 seconds, then 7psi the rest of the run, upgrading fuel injectors would be a waste. These cars already run rich enough at full throttle. The larger injectors are just going to pour even more fuel in at full throttle and cause you a drop in fuel efficiency during warm-up.

You want to get more power out of the car? First scrap the entire stock exhaust. Stock exhaust on these things suck, the stock tail pipe necks down to like a 1 7/8 compression bent, I would do a 2.5" mandrel bent system from the turbo back. Second, add in an intercooler like the 2.2 T2's had. Doesn't have to be a stock intercooler, but if you can find one, they fit in nicely. After adding in an intercooler, convert it to a manual boost controller and set it at 13psi. These mods will get you close to 200hp, with a lot of torq and will help mpg a little if you can keep your foot out of it.

Here's the math: Assume your engine has a brake Specific Fuel Consumption (BSFC) of 0.5 lb /hp-hr. Figure your desired horsepower. Say it's 200 hp. Duty cycle of injector should be kept under 80%, so at 80% your four injectors are 4 x 30 x 0.8 = 96 lb / hr. Divide by 2 and you get 192 hp. As your engine will probably be under 0.5 BSFC, meaning the engine puts out more power per unit of fuel, because it's computer tuned, you can probably get your 200hp.
But, if you are looking for more than that, you need bigger injectors.

On a personal note, most kids wreck their first car, so I'd say the combination of a first time driver and more than 200hp in a small car is dangerous. Let her prove she can handle it before souping it up.

R.

not sure about the turbo 4 cylinders, but I can say for fact that the JTEC computers (trucks/vans/jeeps/SUVs) have 2 modes...open loop and closed loop.

I would imagine the little 4-cylinder turbo is the same...I can't see why it would be any different, unless the sheer age of the system outdates closed loop mode, and the computer only runs pre-set tunes.


anyway, in closed loop, the computer is reading the O2 sensors in the exhaust, and will adjust the duty cycle of the injectors to fine tune the AFR to reach 14.7 for maximum economy. bigger or smaller injectors will not affect this, as the computer will see the exhaust being rich or lean and will adjust the tune accordingly.

However, closed loop only activates once the engine is warmed up and at operating temp, and when at part throttle cruise, idle, etc.

when the motor is cold, or you go WOT, closed loop turns off, and the computer goes to "open loop" mode, and will run a pre-calibrated fuel table, and if you change injector sizes without re-tuning the computer, then when you're in open loop, you WILL change the AFR.

You'd be surprised how much HP the stock injectors can handle before they reach 100% duty cycle and you have to upgrade.

ON the 5.2/5.9 series V8s, there's a lot of guys making 400-450 crank Hp using stock injectors, with just a re-tune of the factory computer.

I built a 5.9 with edelbrock heads, headers, single plane intake, and a 55x52 mm 2bbl TB (venturies are oval shaped) His combo is between 425-430 crank Hp, and we were not anywhere near maxing out the injectors to the point of having to go bigger.

FWIW, look for a set of reman injectors on ebay. Set of 4 shouldn't be more than $50 or so.

This gives you an injector that's been electrically tested, exterior cleaned ultrasonically, flowed with cleaner, and new o-rings and filter screen.

The 80's fwd mopar EFI systems don't operate any different than the 90's mopar OBD-1 v8 efi jtec computers, so 70cuda383 is correct.

I should add that these computers top out at 14.7psi in stock form. The reason for this is the stock 2-bar map sensor can only read that high. Any higher than that and you hit overboost cutout and the computer cuts fuel and spark. The stock injectors are easily capable of fueling your 2.5 right up to 14.7. Usually guys only upgrade injectors when they upgrade their computer to one recalibrated for a 3-bar map sensor, which will do nearly 30psi of boost.

Thank you all so much for your feedback! Moparts Rocks!

This is exactly the kind of advice I was looking for. People with first hand knowledge. I will stick with stock injectors. And yes, I will be keeping the tune stock until my daugter proves she can handle more.

Thanks again!