[3000GT MR]

Posted this over the other place. Figured people could use it here as well.

I've had a lot of questions regarding some of my comments regarding PI injection.
I'm not even close to the most experienced tuner but i have done a lot in the past and have found things out the hard way

The quick down and dirty.

The #55 injectors that people are using flow 55lbs @ 43.5 (578cc/Min) (standard psi for fuel injector flow benchmark and 99% of EFI engines) and we are running them at 72psi ( So they really flow 744cc/min)

Take Josh's (MR2 Josh) for example 861WHP 100% e85 and 80% IDC and his HPFP is about 80% from what he said. That is a shit ton of fuel and still has a lot of head room (80% is a good peak IDC). This is way to much for anyone running less than 860whp. Even though they are considered secondary fueling they need to be power matched to the engine. You want to be around 75% idc at your peak power/rpm to leave some head room and not over work the injectors. This can easily be done with a few calculations.

Batch firing is what scares me when the injector is open for such a short period at such a high power and RPM. Terry is only at 30 or 35% at 600+ on straight E85. To me that injection window is way to short and i wonder if thats why he is having timing pulls and cant figure it out. Here is the secondary PI injector window based off Terrys published results.

RPM IPW IDC
4000 10ms 33.3%
5000 8ms 33.3%
6000 6.65ms 33.25
7000 5.7ms 33.25%

I know its not 33% across the board it probably starts off lower and rises, so technically these numbers would be even smaller.

Normal IPW is more than double that.

With race fuel these numbers would be in upwards of 30% less. If your barley using them and don't plan on making much more power I would defiantly go to a smaller injector and increase the IPW. That's just me though. It's not a one size fits all.

On batch firing each injector is spraying at 6 different phases of rotational event.

What would help greatly is if we knew what the stock HPFP puts out with a 1.00 scalar so that we can maintain HPFP headroom and calculate remaining flow for PI for given HP levels.
Any insight on this. I'm sure if i sat down and thought it out with some calculations we could come up with a good guesstimate

I wrote this up pretty quick and copied and pasted from PM's I've answered.

From my own tuning experience on normal EFI's, injector lag times and IPW are huge players in proper tuning. To each their own.

Please comment with any insight or added info.

[135Pats]

Excellent, excellent post Chris. Thanks for your insight


This weekend i'll be playing with the port fuel more, Terry thought the firmware may be off in which case it would be injecting on idle. That would probably explain why my car is so pissy at idle right now, but who knows.

[3000GT MR]

Originally Posted by 135Pats

Excellent, excellent post Chris. Thanks for your insight


This weekend i'll be playing with the port fuel more, Terry thought the firmware may be off in which case it would be injecting on idle. That would probably explain why my car is so pissy at idle right now, but who knows.

Do you happen to know what your idc is at a given point?

[Give_Em_The_DD]

Very nice info...trying to sort thru my PI issues as well tonight/tomorrow.

Thanks for the insight sir!

[TT-Tom]

I'll be tuning my friends car when it comes out of storage, we just installed bms pi with these injectors. I have a couple ideas and I agree completely with what you are saying. My idea, working with these injectors is to run a negative (sub 1.0 fuel scalar) using accesstuner, not sure if tuner pro actually recognizes the smaller numbers but cobb will. I will start by using the base map on the aic and set the scalar at 1.3 across the board using 100% e85 (i know it will run pig rich on a stage 2 turbo car) then work my way down with the scalar until i have the trims in the positive 15-20 range. My plan from there is to increase ipw on the aic until they hover around 5-10. If all else fails then try a smaller injector but i think this will work nicely and take a lot of load off of the hpfp

[TT-Tom]

overall though these would be a good fit for a 500-600 hp car http://www.atpturbo.com/mm5/merchant...Category_Code=

[3000GT MR]

Originally Posted by TT-Tom

I'll be tuning my friends car when it comes out of storage, we just installed bms pi with these injectors. I have a couple ideas and I agree completely with what you are saying. My idea, working with these injectors is to run a negative (sub 1.0 fuel scalar) using accesstuner, not sure if tuner pro actually recognizes the smaller numbers but cobb will. I will start by using the base map on the aic and set the scalar at 1.3 across the board using 100% e85 (i know it will run pig rich on a stage 2 turbo car) then work my way down with the scalar until i have the trims in the positive 15-20 range. My plan from there is to increase ipw on the aic until they hover around 5-10. If all else fails then try a smaller injector but i think this will work nicely and take a lot of load off of the hpfp

I wouldn't take away from the factory DI system. The DI's ability to cool, add pressure, and be precisely controlled by the DME has to many far advantages to take this away. The only reason we can run so much boost on such a high compression motor is because of DI. We dont need as big of injectors as one may think. I'd assume in the 250-350cc rated range for 600-650 100% e85 range

[3000GT MR]

Originally Posted by TT-Tom

overall though these would be a good fit for a 500-600 hp car http://www.atpturbo.com/mm5/merchant...Category_Code=

That should be a good fit. It will flow 315cc at our pressure

[135Pats]

Originally Posted by 3000GT MR

Do you happen to know what your idc is at a given point?

Not off the top of my head but if the Split Second or JB can log that, i'm happy to get some numbers for ya. Once this damn MAP sensor code/car cutting out idle nonsense is squared away, i'm going to be logging a ton.

Do you know what channels i'd be logging? I don't run the AEM so not sure if that's an option with the JB.