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Question Injector size (EFI)

Hey guys,

I am close to purchasing injectors for my EFI project and Im curious if you think 72# per Hr. injectors are too much? I have read many informative threads on this but none that have talked about my HP range. I am planning on trying to be in the neighborhood of 550 to 600 RWHP.

I have a 3.2 Litre built by Gordon Ledbetter, 8:1 CR, 964 cams, mild port and polish, Custom intake manifold, GHL headers, Single 3" exhaust (straight through design) magnaflow muffler, Spectre eMS-pro management, MSD DIS4 Plus, MSD two tower coils, Inovate wideband, full bay IC, Turbonetics Hybrid turbo, Tial 46mm wastegate, HKS BOV (vent to atmosphere)

Any thoughts, Don E? Steve Weiner?

Thanks in advance guys!

...............................................Chr is
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77 930 "P Zilla" 3.2 Litre w / EFI conversion
Old 06-14-2007, 12:15 PM
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If you're planning to be in that range, I think you'll need at least 72# injectors. You may want to go with Evo cams too.
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Old 06-14-2007, 01:04 PM
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I use 60lb Siemens and at WOT (520rwhp), they are around 72% duty cycle - the larger inj were around 65% duty cycle at WOT. The 60lb inj provide much better low end throttle response and idle than the 72lb Siemens used earlier. I just could not get the big injectors to provide a good spray pattern at 1.5ms (idle) like the 60lb inj can - I think they dripped rather than sprayed. I think your inj size will also be dictated on the ECU you use as well.
Old 06-14-2007, 06:54 PM
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Quote:
Originally posted by DonE
I use 60lb Siemens and at WOT (520rwhp), they are around 72% duty cycle - the larger inj were around 65% duty cycle at WOT. The 60lb inj provide much better low end throttle response and idle than the 72lb Siemens used earlier. I just could not get the big injectors to provide a good spray pattern at 1.5ms (idle) like the 60lb inj can - I think they dripped rather than sprayed. I think your inj size will also be dictated on the ECU you use as well.
This is VERY important - too large an injector will manifest itself with poor idle/off idle performance, especially if you use the Bosch pintle-style injectors. I think Siemens are disc style, which seem to work better at very short PWs, but in any case you need to balance this out if you're planning on street duty with your car.....
Old 06-14-2007, 08:07 PM
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I have the Siemens (Mototron) injectors also. Apparently they can deliver a lot of fuel at higher pressures, like 80lbs/hr, but I'm running them at about 40psi right now. I still haven't turned up the boost to see what my engine will put out so I don't know how much room I have on the injectors.

Are you planning to run over 1.0 bar to get that kind of power?
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Old 06-15-2007, 06:11 AM
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Fuel pressure is another variable with EFI that can be used to work with bigger (or smaller) injectors. With an adjustable regulator, you can lower the pressure and let a bigger injector use a longer PW at idle/low RPMs to improve response. Depending on your (or your tuner's) skill, the injector size parameter (in the ECU, not the motor) can be changed 10-20% to compensate for fuel pressure changes (ie the ECU sets PW based on a 60lb/hr injector, but the motor actually has a 72 lb/hr injector running at a reduced fuel pressure).

Also, ECUs are typically set up to run either high or low impedance injectors. Once you get over ~72lb/hr, there are no high impedance injectors available AFAIK. It is, however, fairly easy to set up a low impedance injector driver with a high impedance ECU.
Old 06-15-2007, 06:51 AM
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I have 72# injectors and EFI. I am getting 505 rwhp at .85 bar. I'll look in the software and see what the max % is, but I think it is low. My idle is very smooth once it gets warmed up. I do have a fragile (car may quit) for the first 30 seconds but ater that it is solid. I have been having troubles wiht my IAC so it may not be related to injectors.
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Old 06-15-2007, 07:24 AM
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I'm running 72 lb Siemens on my 3.3 with 38 psi fuel pressure. No idle problems but it did take a little fine tuning to balance variables at high vacuum and low rpm situations.
Old 06-15-2007, 07:39 AM
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Thanks guys, I will have my tuner review this thread and help me decide. My tuner is Scott Clark of Spectre Performance, he is the man that created my ECM and is a tuning guru. I'll be bringing the car down to him in LA on the 28th. If any Porsche guys are in the LA area and would like to meet up for dinner or something while Im down there I would love to meet some fellow Pelican's!

Please PM me if you are interested and want my mobile #

Thanks for all the help!...................................Chris
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77 930 "P Zilla" 3.2 Litre w / EFI conversion
Old 06-15-2007, 08:12 AM
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72lbs/hr = 700cc/min.

I believe 700cc shouldn't be the problem idle-wise as long as cams aren't wild and you use fuly-sequential peak-and-hold ECU with good PWD-resolution.

Batch/fully sequential injection usually doesn't matter power-wise but when it comes to fiddling with final idling characteristics it can matter a lot. To put it this way:

You have two engines. Both have same 92lb injectors but one is equipped with Megasquirt I for 200$ and other with kitted-out Autronic/motoronic/DTA/whatever. Both can be mapped for same top-end power, but MS will suffer when it's batch-fired injectors try to quirt small amounts of fuel at idle (and try to do it with low resolution).

If you still get rolling idle with sequential injection you can try to vary the injection phase. If that doesn't it's time to go to staged injectors (a twin set where second set is activated on demand).

But frankly, I don't believe you'll have problems as long as other things are taken care of. I saw four-bangers idling with 1600cc injectors.

Good luck!
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Old 06-15-2007, 08:45 AM
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Quote:
Originally posted by beepbeep
72lbs/hr = 700cc/min.

I believe 700cc shouldn't be the problem idle-wise as long as cams aren't wild and you use fuly-sequential peak-and-hold ECU with good PWD-resolution.

Batch/fully sequential injection usually doesn't matter power-wise but when it comes to fiddling with final idling characteristics it can matter a lot. To put it this way:

You have two engines. Both have same 92lb injectors but one is equipped with Megasquirt I for 200$ and other with kitted-out Autronic/motoronic/DTA/whatever. Both can be mapped for same top-end power, but MS will suffer when it's batch-fired injectors try to quirt small amounts of fuel at idle (and try to do it with low resolution).

If you still get rolling idle with sequential injection you can try to vary the injection phase. If that doesn't it's time to go to staged injectors (a twin set where second set is activated on demand).

But frankly, I don't believe you'll have problems as long as other things are taken care of. I saw four-bangers idling with 1600cc injectors.

Good luck!
Just remember that a 1600cc injector is low impedance, and there is no comparison WRT short PW operation between low and high impedance (700 cc Siemens). At 700cc you are on the ragged edge of high impedance use, and low PW operation will suffer. Low impedance injectors by nature will perform better at short PW, so it's not out of the realm to have better idle characteristics in a 2.0L 4cyl with 1600cc injectors than in a 3.3L 6cyl with 700cc injectors.
Old 06-15-2007, 09:07 AM
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Quote:
Originally posted by kellcats521
Just remember that a 1600cc injector is low impedance, and there is no comparison WRT short PW operation between low and high impedance (700 cc Siemens). At 700cc you are on the ragged edge of high impedance use, and low PW operation will suffer. Low impedance injectors by nature will perform better at short PW, so it's not out of the realm to have better idle characteristics in a 2.0L 4cyl with 1600cc injectors than in a 3.3L 6cyl with 700cc injectors.
Well I assumed that his 700cc injectors indeed are low-Z injectors. Frankly, I newer saw hi-Z injectors bigger then 500cc altough I heard that MSD had some special designs for sale.

There are lot's of factors influencing idle quality. To mention a few:

1. Cam timing
2. Injector design (pintle/disc)
3. Injector impedance
4. Intake design
5. Injector placement
6. Sequential/batch?
7. Injection phase.
8. Spray pattern

All in all, I still believe that 700cc low-Z injectors should idle properly if everything else is OK. Even in batch mode.
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Old 06-15-2007, 10:14 AM
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These are the 72lb units of which I 'thought' most folks here are using......

siemens 72

Also, I totally agree with your assessment of idle quality factors, and I also agree with your statement regarding the use of the 'correct' ECU - I'm not a fan of most of the low-end ECUs because of the limitied capability.

Pat K
87 930
Old 06-15-2007, 10:53 AM
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This is what I'm using http://www.racetronix.com/L107FM.html
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Old 06-16-2007, 05:51 AM
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Quote:
Originally posted by DRV2FST
I have 72# injectors and EFI. I am getting 505 rwhp at .85 bar. I'll look in the software and see what the max % is, but I think it is low. My idle is very smooth once it gets warmed up. I do have a fragile (car may quit) for the first 30 seconds but ater that it is solid. I have been having troubles wiht my IAC so it may not be related to injectors.
Heh,
I went thru 5 Tec3r's, all with non operable IAC circuits. I think I have one now that works. I am somewhat unimpressed with them as a company relating to their product, attitude and customer service. Of course everything was my fault.

Les
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Old 06-16-2007, 10:14 AM
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Thanks for the info here from everyone. I have decided to go with Delphi 75# injectors. My tuner has assured me he has been able to get good idle and off idle throttle response with the use of even larger injectors. The Spectre eMS-pro is very capable of controlling what I will be using.

Thanks again, I will keep you all posted on the end results.

.................................................. Chris
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Old 06-16-2007, 12:08 PM
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les, thanks for the information about the Tec3r. At least I know it is not just me.

kirk
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Old 06-16-2007, 02:01 PM
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Quote:
Originally posted by DRV2FST
les, thanks for the information about the Tec3r. At least I know it is not just me.

kirk
Ditto my friend. I was "glad" to hear someone else had the problem. Incidentally, I have it on Excellant authority that this problem was rampant. I told them that I coldn't be the only one after 5 straight in a row didn't work from day one. Now these rubes kept sending me non-functional units that "I" had to keep paying for the freakin' postage. They were rude, condescending, and basically *********S about the whole thing. They insisted I was the only guy having this problem and it was my install that was causing issues.
The way I got it fixed was to send it to Clewitt, and said, test it, confirm that it does not work, get it back , test it, confirm it works, send it to me. This resulted in the first functional unit I had. They also kept insisting that the one's I was sending to them had no flaws and functioned perfectly. That was BS also. I had a IAC tester that had not problem actuating the IAC valce. The tester also indicated signal failure on every unit they sent me. This problem went on for months. I really was ticked off at the way they treated me and won't buy anything from them in the future. YMMV.

Les
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Old 06-16-2007, 03:03 PM
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Hey Les and Drive to fast,

I used to have a crank sensor from Electromotive. I had to replace it 3 times cause they all failed. So whenever I get a chance to take a dump on Electromotive, I do.

Now I have a Ford sensor.

Have fun
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Old 06-16-2007, 04:41 PM
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Quote:
Originally posted by dean
Hey Les and Drive to fast,

I used to have a crank sensor from Electromotive. I had to replace it 3 times cause they all failed. So whenever I get a chance to take a dump on Electromotive, I do.

Now I have a Ford sensor.

Have fun
I talked to a lot of Folks there to Kinda escalate my issue. They pretty much all responded the same way. Kinda like I got your Money, deal with it.

Les
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Old 06-16-2007, 05:19 PM
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