Injectors for Colin's 32V Cams
12-15-2010, 05:34 AM
#16
Former Sponsor
The stock injectors are "turds" when it comes to changing fuel pressures. They will quit "atomizing" the fuel and simply squirt. as the pressure rises. If you are going to change injectors, make sure you specify EV6 injectors. They respond well to pressure changes and have the correct spray pattern for our two valve engines.
You can run an EV6 injector all the way to 7 bar and still get a good injector pattern and spray atomization". You will never need more fuel for a 5.0 928 naturally aspirated engine than a 24 pound EV6 injector.
BTW..if you need bigger injectors....you also need a bigger fuel pump. An "044" pump fits really well...you just need to upgrade the power supply with an additional relay.
You can run an EV6 injector all the way to 7 bar and still get a good injector pattern and spray atomization". You will never need more fuel for a 5.0 928 naturally aspirated engine than a 24 pound EV6 injector.
BTW..if you need bigger injectors....you also need a bigger fuel pump. An "044" pump fits really well...you just need to upgrade the power supply with an additional relay.
12-15-2010, 10:38 AM
#17
Drifting
I'm realistically hoping for an approx 50hp increase, so somewhere in the region of 380-400 Crank HP, which is at the upper end of the 24's range. 30's will comfortably handle the HP, however I don't know how they would behave around idle, would the duty cycle be too short leading to rough idle?
12-15-2010, 10:52 AM
#18
Race Car
Data point: Sue's GT with headers, x-pipe and 2.5" dual exhaust, otherwise stock, is 346 rwhp. (That's like 75hp on me, plus a lower rear end, it's embarassing). Injectors are 24# 4-hole Ford/Bosch injectors, no half-rate injection (threshold moved above redline), max pulse-width is around 8.2 ms at 6500 rpm with AFR ariound 13:1.
Normally (for an S4/GT/GTS) the injectors fire once per revolution up to 5100, and then every second revolution. The reason is that it takes time to open the injectors (0.94ms is what the LH uses as opening-time), and cycling half as fast means less time lost to overhead.
With 24# injectors the injector pulse-width (open-time) is shorter, and the opening-time for newer injectors is quicker-- 0.85ms. So firing once per revolution all the way to redline is fine. I am not sure that it buys any horsepower, but seems more sensible.
And most folks recommend a max injector duty-cycle of around 80%, they need some off-time. The 8.2ms I quoted above is the number from the ST2, which includes the opening time. So the real open-time is approx 7.3ms, and at 6500 RPM that works out to 79% duty cycle.
If you are looking at max HP for a given injector, that is probably at 100% duty-cycle at spec'ed pressure which is less than our stock pressure. So add HP for higher pressure, deduct for 80% max duty cycle, probably a wash. But it also looks like our 346 is close to the max for 24# (without half-cycling).
Normally (for an S4/GT/GTS) the injectors fire once per revolution up to 5100, and then every second revolution. The reason is that it takes time to open the injectors (0.94ms is what the LH uses as opening-time), and cycling half as fast means less time lost to overhead.
With 24# injectors the injector pulse-width (open-time) is shorter, and the opening-time for newer injectors is quicker-- 0.85ms. So firing once per revolution all the way to redline is fine. I am not sure that it buys any horsepower, but seems more sensible.
And most folks recommend a max injector duty-cycle of around 80%, they need some off-time. The 8.2ms I quoted above is the number from the ST2, which includes the opening time. So the real open-time is approx 7.3ms, and at 6500 RPM that works out to 79% duty cycle.
If you are looking at max HP for a given injector, that is probably at 100% duty-cycle at spec'ed pressure which is less than our stock pressure. So add HP for higher pressure, deduct for 80% max duty cycle, probably a wash. But it also looks like our 346 is close to the max for 24# (without half-cycling).
Dan
'91 928GT S/C
475hp/460lb.ft
12-15-2010, 12:57 PM
#19
Rennlist Member
But I think the 0.69 ms opening time is too short, in either case. The opening time is both voltage and pressure-dependent. The injectors run at about 12.0 volts (after LH and wiring drops), and 55 psi vs. the spec'd 39 psi. So for the A302, the offset at 12 volts is 0.781, times 1.0279 for 55 psi, is 0.837 ms. The AA302 is quicker, 0.751 x 1.0296 = 0.77 ms.
The AA302 specs are here and the A302 specs are here (www.fordracingparts.com).
I found an article in a Mustang forum which explains the terms used in the specs, here.
Bottom line, I don't think it matters if Sharktuner's opening-time parameter is exactly right, because any differences will be taken care of in the fuel map after tuning. However, if you have a good fuel map and want to change injectors, then you can pretty much nail it without retuning, if you tweak the opening-time appropriately. I did that empirically when I changed from stock 19# to the A302 24# injectors, by changing ST2's injector selection to 24# and then fiddling with the opening-time parameter until the fuel was correct at idle-- that's where the 0.85ms number came from. The map was then right on, over the full range. Then I dug into the injector spec's with Rob Edward's help and found that I was only off 0.01 ms, which was pretty amazing. Maybe there is some science here, after all
12-15-2010, 02:22 PM
#20
Drifting
Having the correct opening time is for driveability at lighter load. The more closely you know exactly how much fuel you got vs what was expected minimizes errors that have to be fixed with closed loop feedback. It will make very little difference on absolute power.
12-15-2010, 04:10 PM
#21
Race Car
As far as I know, the SharkTuner value in the fuel parameters page is for opening time in ms at 13.1V. The LH brain probably has a table or function that scales that value based on actual measured voltage. I don't think it is correct to use a 12V value in that field. Seems to me for the A302's the number would be 0.71ms @ 13.1V w/ 55psi regulator.
Dan
'91 928GT S/C 475hp/460lb.ft
Dan
'91 928GT S/C
475hp/460lb.ft
