I'm confused about this whole fuel system upgrade...
 

So, my Z has been in a tuning shop for a week now getting tuned... I received a phone call from my tuner yesterday that I'm gonna have to upgrade to a twin fuel pump setup. My goal is about 550+whp with 14~16psi on a pump gas. It's a pretty realistic goal and I thought my fuel setup was good enough for the goal.. Here is my fuel setup: HKS 1000cc injectors, CJM stage 1 fuel return system, Walbro 255lph fuel pump.

I went with this setup because most of the shop built 550+whp vehicles have similar setup. So, what gives??? I know tuners have different safety margins and mapping philosophies, but the tuner told me my fuel setup is not even close. He told me that fuel pressure starts to drop at 8~9psi on a high speed run..:icon11: This totally throws me through the loop...

Now, this tuner was formally trained in Japan and he tunes variety of dragster GTRs and drift competition purpose silvias here in Korea. So, I trust his skills and he thoroughly checked out the hardwares for a week before he proceeded with the mapping sessions. So, the equipment/installation failure is out of the equation.

I contacted Charles at CJM to order the twin pump assembly. I hope this fixes my problem. Please hurry Charles! :D

This is a little off topic, but I thought it was interesting, so I'll share this with you guys. Tuner made an interesting change to the HKS 1000cc low impedance injectors. He did NOT like how F con v pro was using its built-in resistors to drive the low impedance fuel injectors. He said he saw too many F con v pros get fried because resistors within a F con v pro get so hot. So, he ripped out a resistor pack from a racked GTR on his yard and turned off the low impedance driver of the f con v pro. He mentioned that Motec has an internal temp sensor, so it controls its own heat, but F con v pro doesn't. Therefore more heat problem with F con...

who installed your walboro pump? it may be leaking internaly in the fuel pump "bucket" assembly. i remmember when i installed my CJM return system with the 255lph pump there was a o ring in the installation that was in question. if installed improperly it would have leak by only at higher pressure output. i think sentry65 and bartenz had the same problem.

It seems like your tuner knows what he is doing. Good to see some info re pitfalls of FCON. I know alot of EMS's love to advertise features that in practice are basically useless (im not saying this is one of them!).

Hmm... Good point! I'll ask my tuner to look into this.. How did you fix this problem?

If you goal is 16PSI you will be more that fine with the fuel setup you have right now!!

Our Stage II kits have been taken over 600rwhp dynojet.

What type of dyno is he tuning on? Either way, at only 8-9psi of boost with the APS turbos, something isnt right to be maxing out the fuel system.

It could be an internal leak in the pump assembly which has been encountered before as mentioned by Sentry and possibly Barzten if i remember correctly... I believe they replaced their entire pump assembly in effort to eliminate the issue if memory serves me right

Argh! I just spoke to my tuner 5min ago. He is going to look into this. Meanwhile, are we good to go on the twin pump assembly by this Friday Charles?

I agree with whats posted. You shouldn't be maxing out that set-up. I also think that the HKS 1000cc injectors are overkill for you goals. I only say that because they are very expensive and should only be purchased if going past the 650whp mark. Just my .02

I agree with phunk there is something wrong, my system is similar to yours

1000 RC injectors
Fcon
CJM Stage 2 system
Walbro pump

and I am not even close to running out of fuel at 550 RWHP it could easily go much more before running out of fuel.

He is running the stage 1, so his limiting factor would be the factory supply hardline. I believe its stated on CJM's website that the oem hardline can be a restriction as low as 500rwhp. So potentially he could need the stage 2 upgrade.

However I agree, he should not be needing a twin pump setup to reach 550rwhp.

I know it's off the topic.. But which shop in Korea did you go??

I have a single walbro and the CJM stage 2 rfs and I am making 565whp.

JET

Thanks for the inputs guys.. I had more talks with my tuner and others who are familiar with Japanese tuning scenes and I begin to sense that 8~9psi pressure drop was just an attempt at persuading me to upgrade to twin pump setup. I got the feeling that tuner is just not comfortable with my single pump setup as my japanese friend, who is into tuning, told me that in Japan, anything over 500whp, they usually go with external multiple fuel pumps setup. This is probably how my tuner was taught and practiced for a long time.. so I guess I have to respect that since I'm not planing on changing my tuner. Even if I go to other tuner, he probably will be japanese and he'll probably say the same thing... This is very interesting to say the least.. Different tuning cultures and philosophies...

Charles/phunk, I sent you an email.
Jay

There are two main shops I use in Korea. One shop put together my engine+twin turbo kit and the other shop is tuning my car. Both shops are racing teams and they don't usually take street cars... Name of the former is Griffin racing team and the latter is MK who established Korea's only official drift competition, DDGT.

I don't understand where your friends are comming from. If fuel pressure is stable then there is no need for a second pump. You defeinetly need the stage 2 upgrade. That wil lget you stable. I'd listen to whatever Charles is telling you. If anyone, he knows what he is talking about.

JET

It's all good and well to listen to your tuner and give him want he wants. I understand that.

But I'd still be concerend with the issue at hand. Slapping the twin pumps in without fixing the current problem is like throwing a capacitor into a car stereo.. Just a band aid.

Just paid for the CJM twin pump assembly.. So, goodbye to the stock fuel bucket if it was leaking internally... problem no more. I'm gonna setup a huge @$$ custom fuel lines, so no more stock fuel line to worry about.. My wallet is lighter now, but everybody's happy this way..:icon22:

Different tuning methodologies and cultures are always hard to comprehend.. I think this tuner wants full safety net.. "Even if one pump fails, still got another"... kind of safety... I'm also dumbfounded as well because I feel the same way as you, but I'm not about to argue with my tuner... It's not like I can just walk away from him and go to another tuner..

With this fuel setup, I might as well move up my WHP goal D@MN IT! 650whp here I come! I was planning on getting the methanol+water injection system this summer anyways...

not really, you cant buy a better quality low impedance injector than the hks 1000cc. will he need the full potential of the these injectors.. probably not, but when you are running a car pushing 15psi or more and producing close to 600whp, that is not the time to skimp on the quality of the fuel system and especially on the final part that actually provides to the fuel to your engine. when you are already 20k + into the build project, saving $500 on injectors is not really a concern.

i wish i could help somehow leeboy, good luck fixing this issue.

650whp? Be careful what you wish for!

JET