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Tony Hanna
03-06-2007, 09:16 AM
I'm looking at the fuelfullthrottle table in a stock '89 TI cal trying to figure out the relationship between map and pulsewidth. I know this is probably a really stupid question, but how does pulsewidth in usec relate to % duty cycle? I'm trying to figure out at what point the stock injectors would hit 100% duty cycle if the pulsewidth was lengthened based on map above 14.7 psi.
I've got an idea kicking around in my head, but it all depends on how much the stock injectors have left by 14.7.

Thanks,

Frank
03-06-2007, 09:40 AM
Well the term duty cycle can be very easy read compared to u-sec or microseconds. Why? Well because it doesnt require math to figure out how much of the available off time can be used. In other words, it doesnt work well with mechanics. However most of the real meat of the equations is indeed u-sec.

If you want to calculate it, convert RPM to RPS, invert that to SPR, times by 2, and that is the number of seconds between injection points.



RPM Revs/sec Sec/rev Injection
Spacing
sec
250 4.1667 0.240000 0.480000
500 8.3333 0.120000 0.240000
750 12.5000 0.080000 0.160000
1000 16.6667 0.060000 0.120000
1250 20.8333 0.048000 0.096000
1500 25.0000 0.040000 0.080000
1750 29.1667 0.034286 0.068571
2000 33.3333 0.030000 0.060000
2250 37.5000 0.026667 0.053333
2500 41.6667 0.024000 0.048000
2750 45.8333 0.021818 0.043636
3000 50.0000 0.020000 0.040000
3250 54.1667 0.018462 0.036923
3500 58.3333 0.017143 0.034286
3750 62.5000 0.016000 0.032000
4000 66.6667 0.015000 0.030000
4250 70.8333 0.014118 0.028235
4500 75.0000 0.013333 0.026667
4750 79.1667 0.012632 0.025263
5000 83.3333 0.012000 0.024000
5250 87.5000 0.011429 0.022857
5500 91.6667 0.010909 0.021818
5750 95.8333 0.010435 0.020870
6000 100.0000 0.010000 0.020000
6250 104.1667 0.009600 0.019200
6500 108.3333 0.009231 0.018462
6750 112.5000 0.008889 0.017778
7000 116.6667 0.008571 0.017143



I hope that is right.

What you can do is figure how how much the change in duty cyle this will have. Let say that at 5000rpm in your cal, you bumped it up 100u-sec. That would mean you bumped it by 0.4%.

Tony Hanna
03-06-2007, 08:55 PM
Thanks for trying Frank, but I'm really confused now.:o
I wasn't even aware that I'd need to bring RPM into it.

I'll just go ahead and post my idea and maybe you or Rob or somebody can tell me if it's worth persuing. What I had in mind was a 2 bar stock injector cal with overboost protection disabled. I was thinking of increasing injector pulsewidth drastically above 14.5 psi in the FuelFullThrottle and FuelPartThrottle tables. Basically have the injectors give everything they've got at and above the point where the 2 bar map goes blind.
If it would work, it would be alot like kicking on an extra injector with a pressure switch but without all the external hardware and a person could then raise the boost with a MBC to make use of the additional fuel.

That's why I was trying to figure out how close to 100% duty cycle they are at 14.7. If there's not enough left to fuel for 18 psi or so safely, then this whole idea isn't worth giving anymore thought to.
Thanks,

cordes
03-06-2007, 09:09 PM
Rob had a great spreadsheet for figuring this out. It would give you the DC for a given injector vs. RPM etc. It is posted over on D-cal.

Tony Hanna
03-06-2007, 09:16 PM
Thanks! I'll check it out.

ShelGame
03-06-2007, 09:54 PM
Yeah, the DC is the ratio of the injector "on" time over the engine cycle time. The cycle time is obviously RPM dependant. So, the DC at 14.7psi boost is not a constant. The DC will be different at 3k rpm vs. 6k rpm. That's what Frank is illustrating in his table above.

FWIW, Geoff is incorporating the Speed-Density calculation (that my spreadsheet is based on) into ChEM2 - including a max DC line at redline.

cordes
03-06-2007, 10:42 PM
Yeah, the DC is the ratio of the injector "on" time over the engine cycle time. The cycle time is obviously RPM dependant. So, the DC at 14.7psi boost is not a constant. The DC will be different at 3k rpm vs. 6k rpm. That's what Frank is illustrating in his table above.

FWIW, Geoff is incorporating the Speed-Density calculation (that my spreadsheet is based on) into ChEM2 - including a max DC line at redline.

Looking at your spread sheet a while back made me think that it will be time to upgrade to some 72pph injectors in the omni, and then looking at the new chem with the lines on there made me really look at how hard some people are pushing the 52pph injectors.

Tony Hanna
03-07-2007, 01:01 AM
Yeah, the DC is the ratio of the injector "on" time over the engine cycle time. The cycle time is obviously RPM dependant. So, the DC at 14.7psi boost is not a constant. The DC will be different at 3k rpm vs. 6k rpm. That's what Frank is illustrating in his table above.

FWIW, Geoff is incorporating the Speed-Density calculation (that my spreadsheet is based on) into ChEM2 - including a max DC line at redline.

Ok, it all makes sense now. So, my idea might work at a lower rpm but likely won't as the rpms increase due to the need for larger injectors or higher fuel pressure to get the necessary ammount of fuel sprayed in the available time.
Thanks!

8valves
03-07-2007, 03:15 AM
Looking at your spread sheet a while back made me think that it will be time to upgrade to some 72pph injectors in the omni, and then looking at the new chem with the lines on there made me really look at how hard some people are pushing the 52pph injectors.

Many people on here seem to push their 52's farther than I would want to. I'd rather run an oversized injector and drop the DC and deal with having to be more precise with part throttle driveability.

I should really jump in on learning how to do our cals. I tune stand alone cars ranging from low-buck Chrome/Turbo-Edit and piggyback's to FAST XFI, AEM, Hondata... I would imagine that if I got to understanding which table represented what that it would be a breeze compared to making ignition and fueling maps from pretty much scratch.

cordes
03-07-2007, 12:40 PM
Many people on here seem to push their 52's farther than I would want to. I'd rather run an oversized injector and drop the DC and deal with having to be more precise with part throttle driveability.

I should really jump in on learning how to do our cals. I tune stand alone cars ranging from low-buck Chrome/Turbo-Edit and piggyback's to FAST XFI, AEM, Hondata... I would imagine that if I got to understanding which table represented what that it would be a breeze compared to making ignition and fueling maps from pretty much scratch.


Yeah, actually when I read that you went to 72s, was when I started reading up on it, and decided I should probably make the switch sooner than later. Of course now that we are getting an ethanol plant in town, I might need to go even larger to convert to E85 which I would love to do.

I would definaltly recommend checking out moparchem.com. It is really pretty easy, and if you already have experience with other systems you should catch on in no time flat.

Frank
03-07-2007, 12:48 PM
If someone were to bouce the injector signal thru another injector driver circuit, one could attach 2 FFV injector with a cut in half rail and a FFV regulator and consistant, perdictable alky injection and then just supplement the fuel curves.


Frank

Tony Hanna
03-07-2007, 07:53 PM
If someone were to bouce the injector signal thru another injector driver circuit, one could attach 2 FFV injector with a cut in half rail and a FFV regulator and consistant, perdictable alky injection and then just supplement the fuel curves.


Frank

That's a really good idea Frank! I wonder if you could set the secondary driver circuit up to come on with a pressure switch or at a certain map voltage? If a person did that and modified the ffv reg to be adjustable...:thumb:

cordes
03-07-2007, 07:55 PM
That's a really good idea Frank! I wonder if you could set the secondary driver circuit up to come on with a pressure switch or at a certain map voltage? If a person did that and modified the ffv reg to be adjustable...:thumb:

Geoff was talking about using the purge solenoid somehow in the code to turn on some injecotrs a little while back. That might be something to look into.