FAQ: Return line vs other methods

turboengnr · 02-09-2005

I have been asked several time what fuel system is necessary for turbocharging your car. And there are several answers.

I will list what i have discovered works, then explain them later on.

I believe that the BEST way of doing the fuel system for your turbocharged or supercharged civic would be to:

1. run a return line
2. Get larger injectors
3. Get engine management (emanage, AEM EMS, Split Sec, etc)

Then the slightly cheaper, but still effective (to an extent) would be to

1. buy larger injectors
2. Get engine management

Some kits come with their own fuel systems. These system usually consist of several extra injectors with an injector controller. These are probably the cheapest way to go, but not necessarily the worst.

Another method of fuel enrichment is using a rising rate regulator.

I will now explain the how/why each method works......

The rising rate fuel pressure multipliers works by adding a set amount of fuel pressure as the boost rises. So basically as you make boost, the fuel system will increase the fuel pressure by a given amount (usually 12 psi) for ever 1 psi of boost.

The downfalls to this system are
1. you are limited on the amount of boost you can run. If the fuel system comes with a 125 psi fuel pump, you can only make that much pressure. So with our cars having a base fuel pressure of about 45 psi, we only have 80 psi of fuel pressure to play with. So with a 12:1 ratio, you are only able to run 6.66 psi of boost before you run out of fuel.
2. The fuel delivery is not exact. It does not deliver the same amount of boost for every psui it increases. As the pressure rises, the rate at which the flow increases tapers off. This means that when you increase the fuel pressure from 45 to 55 psi, it delivers X amount of fuel. Then from 55 to 65 psi it delivers X-Y amount of fuel. Then 65 to 75 psi it delivers X-Z amount of fuel. With each step, it increases the flow rate by less and less. Though it does not taper off very much, it makes its precision less than that of the other methods
3. The last reason is because it can damage your injectors. After running such high fuel pressure all the time, the internal discs inside the stock injectors can become warped or bent. This can cause several things: the injector can never close, or the injector will not be able to flow as much fuel as stock.

Adding additional injectors is a common method for fuel enrichment. This method takes several additional injectors and either injects them into the charge pipes, or behind the throttle body. The main drawback on this is the fact that our intake manifolds are made to flow air. NOT LIQUIDS. so the fuel has a chance to puddle in the manifold. If this happens, the fuel is not going into the cylinders, causing one or more cylinder to go lean. If the car has a lean backfire, it can physically destroy the intake manifold along with other parts.

Adding bigger injectors and an engine management is a good way to add extra fuel. By adding bigger injectors you allow the computer to do all of the fuel delivery in the way it was meant to be delivered.
With Bigger injectors, there is a lot of tuning. The car has to be tuned at idle, and at all vaccum and boost positions for every RPM setting. The larger injectors (if left at stock settings) will deliver much more fuel than stock. If you leave them this way you will most likely run rich EVERYWHERE. This means horrible power losses, misfiring, bad gas mileage, and rough idle. But when tuned correctly, the fuel delivery is EXTEMELY precise. And the power gains are the highest.

Adding a return line with bigger injectors does the EXACT same thing as the above, EXCEPT, you can do it with smaller injectors. This means that there will be less tuning required to make it idle and drive (non-boost) like normal.
Adding a return line with a 1:1 fuel pressure regulator will help in 1 way. As you make boost, your fuel pressure will rise to compensate. This does not increase the fuel pressure by lot like the other method, but in small moderation. You have to remember that for every psi of boost you add, it makes it that much harder for the injectors to deliver fuel. So if your running 45 psi of fuel pressure and 10 psi of boost, you only have the equivalent of 35 psi of fuel pressure under normal conditions. So when you increase the fuel pressure on a 1:1 ratio, you keep the equivalent amount of fuel going into the motor. This allows you to run properly sized injectors for your application.

i hope this helps you guys out. If i need to add anything else, please ask and i will update this post.

if you have any other questions, feel free to ask. there are a lot of talented and knowledgable people on here. So if i cant answer something, i am sure there will be someone that can.

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Pedro Lopes · 02-09-2005

I don't know how to thank you. Your awesome. Great post.

2K1Civic17"Gabe · 02-09-2005

Do you know anything about the TSI Fuel Management Unit? Great info, BTW. I havent heard much about TSI's, but I hear it really isnt bad at all. Pretty decent for low boost like 6. ANy opinions or recomendations? I will be installing the kit on a week or two.

turboengnr · 02-09-2005

if the TSI is the same as the Turbo Discounters, then it is an additional injector style setup.

those arent bad, but they arent the best. I am sure that with the lower boost settings (under 10 psi) your chance of breaking something is pretty slim.

HondaLuver · 02-09-2005

what if you put some 550cc injectors on a NA engine such as a k24a2 which will probably be turboed within the next 5 months... or are the stock injectors fine?

turboengnr · 02-09-2005

if you add injectors that are larger than what the computer is calibrated for, you will need tuning.

I would run the stock K24 injectors until you turbo the motor. It will save you some money in the long run by tuning it once instead of twice.

HondaLuver · 02-09-2005

what if u have kpro?

turboengnr · 02-09-2005

then you tell the kpro what size injectors you have and it should automatically compensate. Very nice unit.

HondaLuver · 02-09-2005

hummm.... interesting...

2K1Civic17"Gabe · 02-10-2005

Quote:

Originally Posted by turboengnr

if the TSI is the same as the Turbo Discounters, then it is an additional injector style setup.

those arent bad, but they arent the best. I am sure that with the lower boost settings (under 10 psi) your chance of breaking something is pretty slim.

Thanks a lot, I was starting to get worried. A new fuel system and methanol injection will be my first mods for sure. Just glad to hear that Ill be ok for a few months.

Peace

Havok2k1 · 02-10-2005

Added to the *NEW* FUEL section of the Turbo FAQ!

/shameless plug for people who read this to read the FAQ

AzNmiKex215 · 02-12-2005

Quote:

Originally Posted by turboengnr

if the TSI is the same as the Turbo Discounters, then it is an additional injector style setup.

those arent bad, but they arent the best. I am sure that with the lower boost settings (under 10 psi) your chance of breaking something is pretty slim.

so this method would work for ppl running relatively low boost? say 6-8 psi all the time, NO HIGHER. This is the case for most ppl with automatic trannies. So im assuming this is the most cost effective / and easiest solution?

One downfall to this is ive read the settings have to be set to where you live? Different climates make for different settings? aka CrewCheif vs. EternalBlue_Vic?

turboengnr · 02-12-2005

ALL fuel systems have to be tuned for where you live. There are no exceptions to that rule. Temperature, atmospheric pressure, humidity...... EVERYTHING will change the settings. Thats why you should always have your car tuned before driving it extensively when you have a mod done like this.

BudDyLeEBoOsteD · 02-12-2005

Awsome Post +1

02sleeper · 02-12-2005

awsome faq great job