Fuel Injector Size?

[INFINITI Q45]

I am looking at upgrading my fuel injectors-for better flow, and wanted to know if any know the size limit for a 1994 Q45? I will have a new hp ECU installed befor the injectors will be. I like the Apexi injectors so far, and they start at 440cc and go up from their. What are the big injectors limitations? Besides getting an overly rich fuel mixter. Would 650cc size require any thing besides high performance chip & a air intake?

[Q45tech]

The stock 370 cc units never have a higher than 60% duty cycle under even the overly rich oem program....10millisecs out of possible 16.6]

Stock they can provide 70 x0.8 or 56 HP [x8= 440] per injector - given enough air flow from a super/turbo charger.

Oem injectors provide way more fuel than the engine can use with any external mods.

[RobertsnewQ]

Here's how you calculate injector size (in lbs/hr) needed:

( H * B ) / ( C * D )H = horsepowerB = B.S.F.C.C = number of cylindersD = duty cycle

Use .70 for the BSFC of a 4-valve short stroke engine like the VH45DE. Use .80 for duty cycle, since you should never exceed this with any injector.

Plugging in the Q's estimated stock numbers gives you:

( 300 * .7 ) / ( 8 * .8 )210/6.432.8 lbs/hr.

to get cc/min, multiply by 10.5, so 344 cc/min.

Stock injectors are 366 cc/min (same as SR20DET), which means they are good enough for stock plus 6% or so.

The Duty cycle reported by consult is calculated indirectly and I would not assume it was correct. Duty cycle stock at the rev limit under HIGH LOAD (like on a dyno) will be closer to 70%

Oh, and just installing larger injectors won't do anything for you. You have to reprogram the ECU to account for them or your car will run pig rich.

[Q45tech]

I just read the milliseconds open time from Consult ~~10-11msec and mentally calculate the possible time at what ever rpm I want.

At 6,000 rpm you have 20 millisecs per rpm, so 10/20=50% duty cycle at 7300 rpm you have 16.6 millisecs with 9.4ms @7300 rpm you have 56.6% duty cycle. Therefore 23% reserve [before 80%] ~~400 HP unless you need to run richer to cool chambers because fuel quality is inferior.Factory is a very rich 10.5ms at 6900 rpm [10.5/17.4=61%]JWT Nox system went to 80% [13.2 ms] for 375HP way too rich.

[INFINITI Q45]

With 6% more efficency than needed for a stock setup, sounds great. The calculations I find interesting, does any one know the total efficency of a 94 Q45 engine? For a race engine they are a 100% optimized, and most stock cars are only 80% efficent. Thanks

[RobertsnewQ]

If you're just revving the engine to 6k you are not putting any load on it and the PW will not be very high. Try it under load.

As for VE, Q engines are pretty good, you could actually calculate it if you know the mass of air entering the engine at a given RPM (use the MAF voltage and a transfer curve).

[Q45tech]

Of course you data log the engine injector time UNDERLOAD. Not some faked up dyno which doesn't load the engine properly.

I must have multi-hundreds of feet of Consult paper with all LOADED parameters. I've tested over 100 Q engines from idle to redline datalogging every parameter along the way. I test my Q at least every 90 days [40 times in last 9 years] to obseve changes.This is my method of assuring that things are OK and near to spec.....engine swaps and major rehab work, after chain guides, etc. for customers.

The Consult will store 4.00 secs in 0.03 sec increments or 130 lines of up to 15 parameters simultaneously.

Of course this work is mostly in 1st gear, although I have about 60 test in 2nd gear to 98 mph......too much traffic to exceed 80 mph on street.

We have a perfect level long bridge where no one can pull out in front of you. Start at 55 [4,000] end at 85+ [6300 rpm].......takes 2 runs because it is more than 4.00 seconds. Easy to do a 4,000 [30 mph] to 7300 [55mph]in first gear in much less than 4.0 seconds........still I do that twice to observe heat effects.

To far and too time consuming to chassis dyno each car with engine work during the field test. I stopwatch a 50-80 mph acceleration test on the same section of road [have developed a temperature correction chart to adjust times to fine tune data].

My entire field test takes 15 minutes and 15 minutes to look over data for anomolies.

Since the HP peaks at 6,000 this is the point where the longest injection time is other than of course the torque peak rpm.

Worries me that people don't understand that the torque peak [~~4,000 rpm] is where the engine [each cylinder] consumes the most air and fuel per rpm. As the rpm climbs above this point less air per gulp flows in therefore less fuel......shorter injector open time.

Sure 6,000 rpm consumes more air per minute [than 4,000] but not 50% more since the VE has fallen by 15%. By 7000 rpm the VE is down by 30%+.

The injector time should drop from 11msec at 4,000 to 9 msec at redline depending on exact MAF voltage...........these numbers will vary based on air temp [density] by at least 8% [32F>120F=8%]...........that could be 0.9 msec variance.

For protection stock ecu doesn't lean the alreasy too rich injectors after 6,000 rpm. Why JWT reprogram works: less fuel and more advance as VE declines.

[goody90q45]

VE?

[elwesso]

volumetric efficiency

[maxnix]

VE?

The loss in VE at higher RPM is mainly due to restrictions of the valve orifices in the head, not intake nor exhaust to any significant extent. Engine is optimized to deliver maximum efficiency at the torque curve peak, in part because it is so small for a 2+ ton vehicle geared as it is (constraint of 4 speed automatic and EPA target MPG).

[goody90q45]

Sorry, but I don't know what the arconym VE stands for. While you're at it how about BSFC? Thanks.

Good post by Dennis since I didn't know how the consult worked.

[elwesso]

Sorry, but I don't know what the arconym VE stands for. While you're at it how about BSFC? Thanks.

Good post by Dennis since I didn't know how the consult worked.

volumetric efficiency

[Q45tech]

Actually time is the VE enemy, as 248 degrees is only 248/720 =34.4% of 20 msec or 6.9 millisec worth of air flow. From the time the valve just cracks open till fully closed and worse than that the curtain area [the doughnut shaped flow area between the head and valve] doesn't flow much till 1/4 opened......9.3mm valve lift peak.

The injectors open just before the valve to give the fuel time to get from injector to the valve head just as it begins to open......the pressure forces it down long before the airflow would carry it along.

Hope I'm being clear that the injector is open before and thus longer than the intake valve:The injector must shut off before the intake closes or you get a 2nd puddle of fuel.....that sits there for for about 16 millisec until it's time to start the process all over.

It takes 1.2-1.5 millisecs after the injector begins to open before full rated flow is achieved! The ecu corrects open time based on alternator voltage and fuel temperature [density][guessed from coolant temp and air temp if equipt or from AC air temp sensor in case of Q].

The fuel displaces air in the flow to cylinder the 10-8% fuel at WOT means the cylinder gets 8-10% less air.Why direct injection creates more power the fuel is forced into 100% full of air cylinder AFTER the intake valve closes like a diesel.

[JedCoop]

How does volumetric efficiency change with intake and exhaust tuning on the Q? Every time the vales open or shut a strong sound wave is sent back up the intake, and is later reflect back down twoards the valves. My understanding is that the added air compression due to the reflected wave improves the air flow into the heads. For the exhuast the reflected wave arrives when the valve is closed. Are the intake lengths are tuned for around 4000 RPM?

[Q45tech]

Depending on AIR TEMPERATURE the 2nd harmonic appears to be at 3700 rpm. then 4,000. then 4600.

There are multiple tunes besides just runner length to plenum.

Start with this spread sheet:http://mgcgti.clarkeandclarke....n.xls

[BlackBirdVQ]

Our injectors are actually bout 395ccs, I have the flow charts of my 94Q injectors from Deatsche Werks after getting them cleaned, balanced and tested. I've had them balanced out to even 390cc all across. One of my injectors before the testing was actually at 401cc. With 390cc exacly all across, engine runs sooooooper smooth.