Well, it turns out that my 850s in secondaries are low impedence so I need to get new secondaries. I'm thinking if I should stick to 850s or get bigger ones since I'm looking to bump up the boost up to 12-13 psi. I'm running a upgraded turbo but don't know the spec... it made 285rwhp@10psi. So I'm assuming that I'll probably make low 300s with the boost bumped up but to be on the safe side, I want to have enough fuel to support 350rwhp safely. So what size injectors do I need for this? Do I need to upgrade only secondaries or both primaries and secondaries? Thanks in advance for you help

 

you are going to need 3775cc/min of fuel at least to support that. you can divide it any way you like as long as you don't starve the engine while only running primaries(<3800) 850 in primairies and 1050 in secondaries. or something close to that.

 

i just sent my 550cc high imp. injectors off to RC Engineering to get bored out to 850's. just doin my secondairies right now. i'll go 720 primaries later.

 

I've seen 400rwhp done with 550 primaries and 1600cc secondaries. The 1600cc can be had for less money than most 720's or 850's

 

what ECU are you running??

if stock with piggy back go with 4x 720 or so. you'll want bigger primarys.

if standalone. 550 / 1600 is common now.

who ever said you need 800 / 1000 to make 350hp doesn't know anything.... 4x720 is good for 400RWHP.

 

550/1600 is generally enough up to about 525 or so rwhp.

 

It sounds like you haven't taken the max safe duty cycle of 80-85% into account. By my calcs four 720's will only support 390fwhp (~330rwhp).

With stock primary injectors you'd need at least 1000cc/min secondaries to support 350rwhp, but as Scott mentioned you need to be careful of running out of flow below 3800rpm, as the stock primaries can only support ~150fwhp on their own.

 

BDC made 408RWHP or something like that with 4x720 and haltech. but ya it was over 90% duty and I think higher fuel pressure....

 

Well, I spoke to my mechanic and he already started working on my car and got my fuel system ready already... He just put in new 850s in so I have 550/850 combo. He said he would start next week when the parts all come in... oh well. I guess I'll just shoot for about 300rwhp or a bit more for now. I have Microtech ECU btw.

 

FWIW, I saw 90% peak duty cycle on my 720x1600 setup at 19psi and 467 RWHP... That was a peak reading and certainly not sustained. this was also with a 10.8 AFR, which is also a bit rich. I would want more fuel to do over 500...

 

well, i'm getting my information from RC Engineering. I guess they don't know anything about fuel delivery.

 

You gotta remember RC Engineering wants you to spend more $ than you have to probably

 

Bigger injectors aren't necessarily better, and if you add two more aux injectors with a fuel pump running them at 80% duty cycle two more 550's will give you that kind of HP.
People these days, however, are running 1600's as aux injectors, and then adding two more 1600's. An ECU upgrade and a new fuel pump can also be helpful.