I have the upgraded secondary rail with 1600's. Should I move the 850's to the primary rail to replace the 550's or just leave the 550's there. The turbo is a T-78 and boost will be anywhere from 15-22psi.

 

You definitely need to replace the primaries. 850's might be *JUST* big enough but you might need more, I'm not too sure. Get some 1000cc to make sure.

 

Whoa, hold on a minute. I know some people run the 550/1600 setup with absolutely no problems. I think that is plenty of fuel, however I know other people go ahead and put the 850's in the 550's place. I think Poweraxel did this somewhat recently. I'm fairly certain he was running a T-51 with the stock 550's. I just want to know if I should use the 850's and if so, why?

 

850's are fine just have to re-tune the duty cycle of it at idle and under load.

 

550cc with possibly up to 22psi of boost? Eeek

 

.

 

yeah, i agree with kraft - 550 is probably not gonna cut it at 20+ psi.

the only advantage of 850's is simply more fuel/lower injector duty, nothing more.

 

I didn't. I just changed injector size. I'm not running any more rich than I was before. Some people however have had problems with their settings. Best to do it by individual car.

 

Thanks for all the feedback gents

 

I don't understand. Obviously, under high boost, he will have 550x2 + 1600x2 cc's available to work with. I thought that, for high power, only the total cc available mattered and that there might be some advantage from idle quality using lower capacity primaries.

What am I missing?

BTW, I love your handle. I'm Canadian myself. You should read this if you've never seen it:

http://www.bigrigindustries.org/cheesy/

 

Well I fear with only 550 cc primaries, the boost may get high enough that he would be leaning out before the secondaries come on line.

Hahhaa, thanks

 

The rule of thumb is basically the primaries are properly sized such that the engine would idle smoothly, while the secondaries will supply additional fuel for higher rpm, high load situations. So if you put a large injector, the engine would not able to idle at normal RPM, since the injector is supplying too much fuel, even with the shortest pulsewidth.

I also prefer using low impedance injectors because they have faster response compared to high ones, thus take less time for the injector to fully open.

It is possible to use a large high flow injector on the primaries if it's low impedance and can adjust the pulsewidth less than 1.3 ms. Just my .2 cents

 

You can't. The secondary's kick on when the primary's hit 40% duty cycle(stock settings for the PFC). Once the secondary's come on line, then the primary's take a back seat. They still fire, but they get out flowed by the secondary's.