Nismo 555cc Or 740cc

[Peter]

Hi Everyone,

I am looking at upgrading my fuel injectors on my R33 (Series 1) RB25DET and not sure whether to go for the Nismo 555 or 740s.

Is there any disadvantage of using the 740s, even though my current application doesn't come anywhere near using their full potential? Why I am asking this question is that the 555 and 740s are similarly priced, and I thought that rather than buying bigger ones in the future, I would get them now.

Any issues regarding idle, drivability, fuel consumption etc?

Relevant supporting mods are:

-Power Intake

-Z32

-Nismo Fuel Pump

-Power FC

-3" Exhaust

-FMIC

-EBC

Thanks!

Peter

Edited July 30, 2009 by Peter

[joeyjoejoejuniorshabadoo]

740's

i'm pretty close to running out of puff on my 555's with 320ish rwkw

[Peter]

But with my current "lower end mods", would having the bigger 740s on be detrimental in anyway? (ie idle, drivability, fuel consumption?)

Thanks,

Peter

[frankiman]

it could have an impact on fuel consumption,

but if they are tuned properly, the difference should be minimal

[R31Nismoid]

Well what future mods do you have planned?

You dont even have a turbo yet by your mod list... 550's will do well over 300rwkw, so unless you want more, dont get 740's.

As for economy - you dont own a modified turbo car, and then worry about how many km's to a tank

[skylinecouple]

Have to agree here. You would stick with the 555's if 300kws is where your headed but otherwise the 740's if your going for a monster that can't put the power to the ground anyway. 350kws or over is just stupid in a street car so decide now where your headed. Though 740's would come in handy should E85 make a big entrance to fueling in the future.

740's are a little more difficult to tune but if the tuner knows what he's doing should achieve a good result.

[Black R34 GT-T]

Daily: 555cc

Weekend + Alot of money for big power in future: 740cc

The car seems like your daily so i would say 555cc

[djr81]

Broadly I have always said that 1cc of injector in a six will get you 1 rwhp. Depends on AFR's too obviously.

So 555 will allow about 555rwhp at the upper limit of the duty cycle (where you don't want to be). So back it off 10% & you still get 500rwhp or 375rwkW.

[Krishy]

I have got 740cc's running in my car at the moment.....New turbo is on its way and only looking to push about 270rwkw or so.....

The only reason i got my 740cc's was because i picked them up in fuel rail for $600 delivered....and 555's were at the same mark....it doesnt really hurt having bigger injectors well 740's compared to 555's....if you can afford it then 740's are a good investment as you might wanna chase up more power in the future....do as it suits you mate

[rob82]

740's

i'm pretty close to running out of puff on my 555's with 320ish rwkw

550cc Injectors at 3bar base pressure will support 350rwkw on pump98 (BSFC=0.55) - so I would be checking your fuel flow or the tune or your regulator!!!

550cc Injectors at 4bar will support 400rwkw on E85 (BSFC=0.6).

Can you see yourself making more horsepower than this???

I would always select the samllest injector for the required horsepower in allmost all situations.

[discopotato03]

My opinion only , if the price is the same and there is no real disadvantage , the 740's leave more possibilities open .

The Nismo 740 is a single pintle injector with a four hole wafer in front of it so the spray pattern is supposed to be very good for an injector that's twice the size of the std 370's .

To me going this way means you have the capacity to make high power outputs with all of the rest of the fuel system running in factory type regulation - provided the fuel pump can keep up . Won't need adjustable FPR's and it can all look factory standard .

I think the real question is can the engine management system run largish injectors and have fine control of them .

I think it was Sk that told me the computer has to have a fair amount of processing power to have fast accurate control of injectors particularly at light loads and lowish revs - normal round the burbs stuff . People say PFC's cope fine with them .

I bought 555's and then 740's because I got interested in the possibilities of E85 - still in their boxes .

Cheers A .

[Peter]

Thanks for all the replies...I think discopotato03 summed up my question better than I originally asked it...

At the moment the price difference between the 555 and 740s is $6.27 per injector or $37.62 for all six....buggar all really...so my way of thinking is that if I can get bigger, for basically the same price - why not?

It was mentioned that the 740s are slightly harder to tune...are there any other disadvantages?....(because besides that, people seem mixed in their views - some people say go for the smaller injector - why?)

If my car will drive basically the same with the 740s or 555s, I might as well go for the 740s as it leaves more possibilities open in the future...

I am more than happy for alternate views...

Thanks!

Peter

Edited August 1, 2009 by Peter