Need Help Selecting Fuel Injectors for car

[Ryan @ UD]

hello,
Ok, I did the calcuations and i have determined that i need 87 cc injectors for my 600cc mortorcycle engine if it is to make 60HP.

Could you help me determine if this is around the size i need. Also, i'm trying to figure out where i can find injectors this small. I was thinking mortorcycle, but i haven't been able to find very many on ebay and they don't list the size.

thanks

[Ryan @ UD]

hello,
Ok, I did the calcuations and i have determined that i need 87 cc injectors for my 600cc mortorcycle engine if it is to make 60HP.

Could you help me determine if this is around the size i need. Also, i'm trying to figure out where i can find injectors this small. I was thinking mortorcycle, but i haven't been able to find very many on ebay and they don't list the size.

thanks

[KU_Racing]

Ryan:
several things:
1) is 67 cc/min the rate you calculated the motor would use fuel at at a perfect 14.7:1 ratio? if so, re calculate using a ratio of about 12.5:1. when you tune an engine, you want the fuel ratio to be richer than stoich to avoid engine damage and keep things cool.

2) is the rating you calculated the exact flow requirent the injectors have to meet? In other words, did you allow for any error in your calculations? If so, you are definately going to want much larger injectors than your calculations show.
Here is why:
Say you do all of your calculations, and you decide that at WOT, your engine need 90 cc of fuel per minute to make your target power. That assumes perfect ignition timing and a 14.7:1 fuel ratio.
If you want your engine to not explode during endurance (an admirable goal in my mind) you are going to have to richen the mix. Say you tune to a 12.5:1 fuel ratio. Now you need 101 cc per minute of fuel to keep things interesting.
So logic would say that you want a 101 cc injector to supply that much fuel. This, however, is incorrect.
If you use an injector that is capable of supplying no more than the minimum amount of fuel your engine requires, that injector will be held open indefinately as long as the throttle is open. While this doesnt seem to be a bad thing, this will cause injectors to lose their internal seals, as well as making it incredibly hard for the fuel pump to maintain fuel pressure. Also, since the intake valve is only open every other crank revolution, you will be spraying fuel when the valve is closed and air is not moving. Instead of mixing with the intake charge, the fuel will go through the stagnant air and puddle on the intake walls and floor. This means your engine will run lean- and lean means hot, and hot means danger.
So basically, you want an injector that can provide the same amount of fuel in half the time- this way the injector is only open when the intake charge is moving past it, and it will deliver the precise amount of fuel at the right time. This logic says a 200 cc injector is more like it.
So in all odds a 200 cc injector will get the job done. There is one more thing to remember about injectors- an injector that flows more than in needed is MUCH better than one that doesnt flow enough. When an engine is tuned, you dont tell the ecu how much fuel you want- you tell it how long to hold each injector open during the intake phase. The ECU does not know injector size- in other words, if you run two different injector sizes on the same fuel map (a map with the same injector pulse widths on it) the larger injector will deliver more fuel. You want to be on the larger injector side of the equation- not because you want to use more fuel, but because it is easier and safer for the motor. When the motor is tuned, it is better to run a high flowing injector at a short duty cycle, say 30%, than it is to run a low flowing injector at a high duty cycle, such as 80-90%.

im sorry if i got too complicated, but i hope this helps.

[Ryan @ UD]

KuRacing,
First off, thank you for your help so far,

Let me explain how i cam to this number, i used this equation out of my book " How to tune and modify engine mangagment systems"

the equation is
Flow rate = (hp*BSFC)/(Number of Injectors * Max Cycle)

FR = (60HP*.45)/(4*.8) = 8.43 lbs

Basc = break specific fuel consumption, recomends .45 for NA

Max cycle = duity cycle of injectors, i used .8 becasue you should load them over 80% or they will overheat the coil.

This Equation leads me to belive that i am calcuating the amount of fuel i will need when the engine is at it's peak power, thus when it will need the MOST amount of fuel.

I understand your logic and i plan on finding an injector this is sized slightly larger than this or in reality what ever i can find. But, if you go tooo big you will have problems with fueling the engine at idle and at low RPM's

Also, for my injector firing order, i plan on atleast doing injection every other revolution. However, i am not that far yet, i think i'm going to use the megasqurt computer to control my spark and fuel, but i haven't purchased anything yet, nor have i any clue how the sensor will hook up to this.

[KU_Racing]

Ryan,
first off, I hope I am helping- that is my goal!

About the book you are using- is it designed for tuning a street car? Try to find out if it is not obvious. I am sure that many of the guys that will read this post can attest that tuning a race motor is not like tuning a street car. After all, whether you have thought about this aspect or not, you should be thinking of this motor as a full bore race motor- it cant break during endurance, but you also dont have to make it last 20,000 miles. So I would reccommend bumping up the BSFC in that equation. The book specified that for NA. If it means NA street car, you will definately need to step it up.
You are right that if you go too big you will have low RPM fueling problems, but in order to see problems like that you would have to oversize the injectors by a HUGE amount.
As far as ECU's go, I would not reccommend the megasquirt- you will get better control out of a PE or MoTec if you can afford it. I am not sure if the Megasuirts are capable of sequential injection or not.

[Ryan @ UD]

hey again,
the book does not really say, but all their examples are for street cars. this is also the area where I have the most experiance in this field.

Since this is the first time U of D has attempted this i have little information to go off of and little funding to achive what little results are possible.

The engine i am working with has 30,000 miles and was manufactured in 1990. I personaly haven't even heard how well it runs, but i was told it did when we bought it.

ok, back on subject, i would assume that the goas are the same for a street car that your tunning and for the race engine, the goal is to make as much HP as possible, right? however i do see your point.

Thanks, for the advice on the ECU, I don't know how much the other two cost, i have read a lot about the motec, but i've seen little about the PE, I'm assuming these are worth the extra cost and headaces. Do they cost a lot more?

[drivetrainUW-Platt]

what engine, Honda F2? Thats what we have, but ours is stock bore and the first time we tore it down after getting it from the junkyard it still had the crosshatch in the cylinder walls, so it hasnt seen much run time...30,000 miles seem high for a bike, may be worn out and hinder your performance.

[pengulns2001]

60hp out of a 600cc motor is really REALLY weak, even a stock one should make more than that so i would bump that number in your calcs too... remember your equation is 60hp at the crank not at the wheels

[sr16ve]

you should also calculate the flow/rate needed using a lower duty cycle. at 80 percent the injector is almost at it's maximum recommended flow and the fuel does not get atomized as well as when the injector is at say 60% or so

[KU_Racing]

mike is right- 30,000 is a lot from a bike motor. Id break your down and inspect it- after all, that is free.

The PE ECU is about 700 if I remember right. The MoTec is probably the best you can buy, but it is WAAAY more expensive. Plus the guys from PE are really nice, and they come to the competition to give tech support to teams with their units. If i remember right, they actually loaned a unit to a team that needed help the night before. penguins is right too- at the flywheel, you should be shooting for 90 hp or more. I believe the stock F4i makes in the 110-120 range stock.

[kozak]

IT'S AN '89 YAMAHA FZR, IT MADE 90HP TO THE WHEEL I THINK.

[Ryan @ UD]

looking at stock HP doesnt' make much sense, with the restrictor it will have a much lower VE. This i was told will make the motor preform much more like a 250 cc motor from what i was told. That is why i'm using 60 hp, maybe thought 80 HP max is more accurate, and would leave room to grow. Right now it looks like the smallest injector i can find is 104 cc so i know they do make them small.

Also, Kozak, i have the title to the Bike and it say's it's a 1990 and it also states the milage when purchased.

Tearing appart an engin is not free, it takes time and you need new gaskets then. At this point in the game, that does not concern me, i know the engine ran, if it needs rebuilt, i don' thave the money to do that so there's no real point.

KU racing, thanks for the infor on the PE ECU. I will be looking into that.

[Dan G]

Ryan, these two pages/calculators might be of help. Like you said, the VE on our engines will vary.

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

http://www.bgsoflex.com/pwcomp.html

[KU_Racing]

just remember ryan- if you do all the calculations and set up so that your engine will make 60 hp, the maximum power you will make is 60 hp. On the other hand if you give it the parts to make 110 hp..... you get the idea.

[Ryan @ UD]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by KURacing:
just remember ryan- if you do all the calculations and set up so that your engine will make 60 hp, the maximum power you will make is 60 hp. On the other hand if you give it the parts to make 110 hp..... you get the idea. </div></BLOCKQUOTE>

WoW, yeah, if that's the case, then i want to make 1000 HP!

This is an understandable approach to designing the fuel system if taken into context.
When caluclating for a "subpar setup" probably will only yeald modest results. It will be harder in the futrue to go faster if i design to go slow.

Dan, thanks for the links, i like the second one, it however is telling me that i need to go smaller than i had originaly calcuated, it does take into account VE wich is nice. I'm starting to think around 130 cc's is where i should be at for a size that will be able to meat any future goals.