Calling all FI gurus....(Let's Talk Compression)
 

As some of you know, I'm preparing to go FI soon with my G. I already have my kit purchased (Greddy twins) now I'm in the process of slowly picking up my supporting parts.

I read this thread here about our stock motor and its high compression not being favorable for FI.

In the thread a couple people are mentioning that swapping out the head gasket is a good idea while the motor is out to help lower its compression level.

I don't know much about this. What do you guys think? Is it ideal to do at this time or should I bypass and focus on the head gasket when I decide to build the motor down the line?

Leave the motor alone, and tune the afr and timing to work with the stock compression.

op, where did you buy your kit from and who are you planning on installing/tuning the kit?

^ this

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+2

:werd: +3

Thanks guys. I'll leave it alone and take the extra money to set aside for the motor build.

Jonnylaw, I bought the kit from a member here for a good deal a few months ago. I have someone local in mind who's really good that I'd like to install the kit and tune. If for some reason he weren't free there are a couple places I can go as well.

^^You will get different opinions on the frs. Some will say it is possible/safe to do at stock block power levels. Others will recommend the frs so safety/reliability/consistency in fuel delivery and ease of tuning.

If you plan on building your motor later down the line than a frs might be good to do now.

Thanks Jonny. I'm still considering something like the CJM stage 0. It's not that expensive either.

Why don't OEM cars come with fuel return setups built in? Do any factory turbo cars come with fuel return systems?

my 1993 Geo prizm has a return fuel system. it all depends on the engineers.

yep, some of the older Infinitis used a fuel return system, then they changed to a regulator setup on the later models.

4 main reasons. Lower emissions, better fuel mileage, more power for a given amount off fuel & lower manufacturing costs.

In 99% of all normal motor operating conditions the motor only needs very little of the fuel that is supplied to the fuel rail. The rest is returned to the tank.
As the under hood temps rise during operation, so too does the fuel temperature due to the constant recirculation.

Now a gallon of gas is a gallon of gas wether it is at @ 35deg or 95deg, but that expanded 95deg gallon has less BTU's (energy output) than a chilled 35deg gallon.
Modern non return fuel systems keep the fuel cooler. Cooler fuel = less evaporation & they also have a fuel temp sensor in the tank that allows the ECU to further refine the signal to the injectors.

^^ you have that right on.

so an identical setup without a frs will get better gas mileage than the same setup with a frs?

In normal operation Yes.

Not a great deal better but with the EPA regs & marketing, every bit counts

Having said that, I dont think gas milage & emissions is the 1st thing on the mind of FI Z owner

Would that equate to a 1 mpg difference or more?

I know it may be hard to quantify, but I am wondering how much better mileage I would be getting had i opted for only a rising rate fuel pressure regulator as opposed to a rfs.

But will the fuel delivery be more consistent/reliable, especially in high rpms, with a fuel return system as opposed to just a regulator when F/I?

you cannot have a FPR without a return line. The only way to increase FPR is to control the amount that is going back to the gas tank.

Call Larry @ SP

/thread