Mondragon

Hi guys,

I am approaching the final satages of my engine rebuild. what i need to know is what size injectors to run in the 3.2 manifold for around 600hp at the fly wheel?? Also i have been reading a fair bit about BOV's but am unsure what to do for my set up with the 3.2 manifold? any advice would be appreciated.

Alex...

Chet 930

I think 55lbs injectors will be enough but I'm not sure.......Stephen at www.ImagineAuto.com would know better than I.

Bruce M.

That's what I have (the manifold and the horsepower) and I run 72 lb Indys. The advice I got from those in the know was that the 55 lb Bosch's would be working too hard for that kind of power.

125shifter

55 lbs may be a little small. I've got a Tial BOV welded to the pipe from the compressor to the intercooler.

Geoffrey

55lbs is too small at stock 3.8bar fuel pressure. Bosch injectors are very well made and you can run them at a base fuel pressure of 5 bar and it will for you in tht 550-600hp range. At that hp level, I generally install 72lb/hr injectors although they are not as well made as the Bosch. You do have options here.

Chet 930

Thanks for clarifying guys. I kinda thought they might be borderline. So what range do the injectors come in?

Bruce M.

Bosch doesn't make a 72 lb injector, which is the next step up. Dunno if it makes a 90+ lber, but that's getting pretty big....

Mondragon

Thanks guys for all the info! looks like ill be using the 72 lbs/h items. wish you guys would talk in metric like the rest of the world :-)

srf506

We ARE the rest of the world! ;-)

125shifter

Here are some calculations: http://www.injector.com/injectorselection.php

I think our BSFC is around 0.6 to 0.65

DonE

The 55lb Bosch injector is a good injector - but you will need to use a fuel system that provides higher fuel pressure to keep the duty cycle within limits. This will be a cost consideration since new rails, regulator, dampers, pumps, filter and lines get very expensive. So what do you get for all that money? Very good injectors that have great low end drivability and can provide top end performance.

I have 72lb Siemens injectors that can provide high fuel rates at stock pressures. I've retained the stock 3.2 rails, damper, regulator, pumps, filter and lines to keep costs down, but the big injectors don't like low-end work. For example, the at idle, my injectors are on 1.3ms. The min (usable) injector on-time for the Siemens is around 1.15ms - I've found that's too close for a good idle. Also, in-town drivability is not as good as it could be.

Something else to keep in mind, is the ECU you choose. Different mfgr's use different inj drivers (software and firmware).

Geoffrey

I'd disagree with Don a little here. Any good current ECU has injector drivers sufficient to control larger injectors down to under 1ms of injector pulse width, including the Electromotive Tec III. The Bosch injectors allow for a leaner idle air fuel ratio due to the better design, spray pattern, and quality of the inejctor over a Siemens, not because the ECU's injector drivers can't control them properly. You can get great drivability with large injectors, particularly if you use a fully sequential injection system and take advantage of the injector timing paramaters.

The only caviat would be an ECU that only used saturated injector drivers where the larger injectors are generally peak and hold injectors. The two are not directly interchangable. However, most aftermarket ECUs can handle either peak and hold or saturated injectors so you should be fine.

If you want to retain the 55lbs injector, there is a direct replacement for the 3.2 fuel pressure regulator available that is an adjustable rate rising rate fuel pressure regulator and can be set for higher base fuel pressures than stock 3.8bar. The stock fuel pumps and lines are sufficient for higher than stock fuel pressure.

DonE

Point taken. My ECU comment was based on conversations with only 3 ECU makers. They told me about their drivers and software. I may have misunderstood their comments but they were consistent.

Also as you know, I run fully sequential with the TEC3r and these large injectors, but can not get, what I would call, good idle and off idle performance. If I had this to do all again, I would reduce the size of the inj to gain low-end drivability and increase the line pressure. At top end (according to the software), I am only running 68% duty cycle.

Geoffrey

Don, it may have more to do with the injector battery compensation parameters (if your ECU has them). This compensates for the injector dead time based on current draw and battery supply voltage. On a bench you can use a scope and measure the dead time and program a proper battery compensation which would be the difference between the injector effective pulse width and the injector actual pulse width.

DonE

It does - thanks. And, I have access to a scope to measure.