injectors

[Celica RA45]

if i have 720cc injectors running at the moment and these are causing stand off is that because they cant flow enough fuel in the required window and would i be better to go up to 1000cc and try to get this to fix it or will this only be a band aid fix
as 1 started with 720cc with 45lbs and stand off from 7000rpm .boosted fuel pressure up to 80 lbs stand off is now from 8300 up to rev cut of 9000
ideas

[oldcorollas]

fuel standoff is a product of reversion and injector placement, as well as bellmouth design, but i'm sure you know all that already. ie, fuel standoff is fuel sitting in air that is not being sucked into the engine.

if you are thinking to inject all the fuel when the valve is open, think abotu how long that window is, and what your duty cycle is..

ie 320deg cam = 44% duty (44% of one engine cycle), but you need the fuel in a smaller window that that, say 35-40% duty.

at 9000rpm, an engine cycle is 13.3ms, so you need injectors to flow the amount of fuel you need in about 5ms

720 is about 5.7ms (plus opening and closing time). 1000 is 4.1ms.
and need to get the injectors closer to valve..

[Celica RA45]

the 2stage gives me more power thats why it is there ,i could always just dissconnect the inboards and run out boards only as it make more torque and power any way was just trying to up the cc to see if i would have enough time to fill the cylinder up with out it coming back the 720cc are up to 50% duty cycle at the moment

[oldcorollas]

maybe you could try a plenum that reflects the sound wave back in, and pushes the standoff fuel back into the port?

[Celica RA45]

its in a 12 liter air box now with a 6inch hose and a super tourer air filter

[ed]

maybe you could try a plenum that reflects the sound wave back in, and pushes the standoff fuel back into the port?

plenums dont do anything harmonic stewy! dont be silly! but glenn knows this already

[oldcorollas]

..........

hmm, with my old carby 4K, i got rid of fuel standoff by making the exhuast/extractors better tuned
but i'm sure that is not the problem here...

just need to work out why there is stationary air sitting around.. and why manifold is throwing fuel backward... then fix that...

[Celica RA45]

i have tried 4 into 1 as well but the 4 2into 1 works best and makes more torque and power also the box has to be this big as the 2 stage bolts inside the air box with a long fuel rail and ram tubes as well
but i could rip it all off and go back to set up like edds and loose power with a 4 inch tube and small air box that makes heaps of torque over atmosphere

[ed]

just need to work out why there is stationary air sitting around.. and why manifold is throwing fuel backward... then fix that...

that there is the point

obviously there are some holes in the harmonic range. unless you can get the injection pulse to coincide with a VERY small window in the valve cycle, you wont avoid standoff without fixing/minimising the reversion

and glenn, i think you need to shift your thinkings on the role of a plenum

[Celica RA45]

obviously there are some holes in the harmonic range. unless you can get the injection pulse to coincide with a VERY small window in the valve cycle, you wont avoid standoff without fixing/minimising the reversion

thats why the bigger injectors, to squirt more in ,in a lesser milli sec and if this works move them them out another 60mm further out flush to the ram tube and see what happens

[JustenGT8]

I'd be inclined to just move the injectors around to see if that helps....should be fairly simple and reversable.

I can't see how changing the pulsewidth by using bigger injectors will help? 1stly, the period of time you have standoff for is far longer than the mS pulsewidth change. 2ndly, it is also a fixed point in time...ie it always exists at that rpm point so changing pulsewidth at that rpm will do nothing?

You are also degrading the perf of your injectors by trying to go bigger and running them at a lower duty cycle. Atomisation/spray pattern is not constant across duty cycle, hence you try not to use large injectors at low duties but pick an injector that is working at around 85% at peak fuel needs....Just look at the spray patter results from Ed's lastest test of the 7M injectors.

If you can't fix the standoff can you compensate by upping the duty on the non effected injectors at that load point...not optimum but might work?

[Celica RA45]

all im trying to do is keep some mist hanging around near the end of the ram tubes ,i just dont wont it to come out and wet the air box and create a fire so from 720cc with 45lbs had spray out from 7 to 8800rev cut up the fuel pressure to 80lbs and that has helped by moving stand off from 7 to 8300 up to rev cut

justin how do i increase duty cycle of the 720cc to get them up higher

[oldcorollas]

i think he is assuming you are using both sets of injectors at the same time.. so instead of having say, 30% on both sets, make the non-offending set 40% and the bad ones 20%, to reduce the mist.

do both the lower and upper injectors get standoff? do you run them both at the same time or have a switchover point? are the injector sizes same?

regardless, it is an intake tract problem (which could be due to pulses coming back from exhaust at certain rpm) causing enough energy to throw the heavy fuel droplets out, and then an intake tract problem in that you have stationary (ery?) air in front of bellmouth that is not going into engine... maybe end of bellmouth is too large?

do you see this with the plenum on? or only with plenum off? can you hold something near the bellmouths to see if it reduces the standoff, or if it just wets?

[Celica RA45]

just thinking of what you are saying i would have to go back to a smaller injector .been talking to motec and they agree that i should go up to the bigger 1s but they also said i might not have the resolution of putting fuel; where i wont to put it into the window
but these are not going, till after 3500 rpm any way so will have to try and see what happens

[Celica RA45]

stewy use 365cc for start up till about 3500 rpm then they start reducing and the 720cc take over from about 70% throttle they are 10%inboard and 90% out board
from 3500 they are 70/ 30 then 60/40 50/50 40/30 etc till thye get to the final