return fuel system necessary for RC 750's? / accessport injector scaling
 

I have an 03 5at G35 at 60k miles and have had a couple previous FI setups but have not gone above 440cc injectors/walbro 255 on this platform yet so i'm not sure if I will have any issues with my next planned setup.

I have all the FI parts on the side right now and have not installed them.

Procharger at 9 psi (26/39 pulleys)
supporting engine mods:
RC 750cc injectors
treadstone 340lph fuel pump
5/16 motordyne spacer
stillen HFC
M2 3" HR y pipe
oem midpipe and muffler
Cobb Accessport
OEM plenum/runners with all castings smoothed out
transgo VB mod and trans cooler

many suspension mods/no exterior mods

I have been reading into it for the past few months but have not really found any definitive answers on this and was wondering when/if a return fuel system is necessary. I plan on aiming for 400whp with this setup and do not plan to ever go for more than that. I just want a fun daily driver but will rarely ever use the power honestly. I just don't want to run into any idle issues with these injectors.

I also have not seen any threads on people doing custom maps using the Accesstune race software(which I have). I know it can do injector scaling but I have not seen any examples of it done for the VQ35 platform. I have seen the calculations for GTR's and subis but it also does not specify in the pdf for the g/z about the calculation/tables just briefly mentions it so I was wondering if anyone knows specifically about this.

I have installed/uninstalled all these parts on the G myself with a previous setup so I plan to do the install myself, then use accesstune race to scale the injectors so I can drive it to a nearby shop for dyno tuning.

Any help would be appreciated.

To Start, Your Fuel pump and injectors are over kill for 400whp

600cc and walbro 255 will work just fine for 400whp

A FRS will make tuning much easier, especially Idle and part throttle.

So, NO a FRS is not required for 400whp, But, it a Fuel System and components need to be matched.

Hope this helps…..

TimRod

Definitely helps! I know its overkill but when I bought the injectors a while back I was planning on a 12 psi build but I decided to settle for 9psi because i don't want to try and deal with the belt breaking issues and would like it to be semi-reliable. I got a good deal on the fuel pump so I just picked it up at the time aswell.

Think I should be fine keeping these components though and just tuning with the cobb? Or would having the FRS make that significant of a difference for daily driving? I would prefer to just use the components I already have if possible and not have to buy anything more that may be unnecessary if I can avoid it.

You will be fine without a RFS ~400whp. I think the 750cc's are a bit overkill and not sure the Cobb Accessport can handle them. Most people go DW 600cc's since they are drop in.


OldManZ350, have you tried the new 300+lph pumps? (Aeromotive, DW, Treadstone.. etc)

I will never consider a walbro 255 again in a build even if they gave it to me for free.

Thanks for all the input. hopefully the accessport can handle it. I guess I will try to scale the injectors in accesstuner once I complete the install and see how it goes then determine if it will need the RFS to run smoothly.

Ya, I have a DW300

Accessport can handle it, have a friend with a TT 370z with it and runs great.

Thanks for the input! I also posted a specific post in the uning forum asking about injector scaling in accesstuner race. Im not sure if the 370z/350z software is the same or not as the gtr and subi maps seem completely different.

What size injectors is your friend running on his 370z and does his run very smoothly at a normal idle rpm's and cruising speeds?

just found a really good deal on a FPR so I may just end up piecing my own return system together if i end up buying it, to be safe and help lower the idle fuel pressure to run smoother. besides the oem FPR plug from cjm ill just pick up high pressure SS fuel lines from rail to FPR and FPR to the tank and a gauge to go with it as well as the fuel rail adapter. really a pretty simple system and inexpensive if I get a good deal on the FPR since thats the most expensive part.
Also what line length is needed from the engine bay to the tank?

The Walbro 255lph is noisy and has a high rate of failure. I love my DW300.

just figured id share my dyno results today. finally had time and was able to get properly tuned. switched from cobb to uprev due to a few more features such as starting enrichment and better support. peak hp was 369

@jdm-v35
Did youbhave to use spacers to make the RC injectors fit correctly? If so, where did you buy them?

You should be able to buy them from RC...when I used to use RCs they came with the bigger spacers...

I do have the spacers but I got them with the injectors. I have heard people have to grind the fuel rails or plenum but mine fit just fine. As said, you probably have to call RC for the correct sized spacers.