MSD injectors?

[1slickRED89]

You can support a whole lot of wHP with 48# if you increase your fuel pressure. 59 lbs of base fuel pressure with 48# injectors will support well over 600 cHP.

can you really just crank up the FP like that, what kind of supporting engine tune would you need?

 

[40BelowSummer]

Youd probably need to adjust your injector size scalars; not sure if you need to change any other settings.

So I should have no problem boosting the fuel psi a bit if needed, if I start running the injectors at a high duty cycle as I upgrade it? Basically any negative effects of running a higher fuel pressure vs. finding bigger injectors?

 

[sho_sc]

can you really just crank up the FP like that, what kind of supporting engine tune would you need?

Increasing the base FP just makes the injectors "bigger" in the scalars. I use a SCTurner. I don't have the forumla handy, but it's something to do with the the ratio of the new FP squared over the orginal FP squared.

However, as you raise the base fuel pressure, the Fuel Pump becomes less and less effecient. A little bump would be fine, say 7-10 psi increase, but much more than that .... remember you have to add the base increase with the amount of boost you run. 39 psi + 10 psi bump + 15 psi boost is 64 psi of fuel pressure drops that 255 lph pump to less than 200 lph if it is supplied with 14.5v at 12v it's something like 145 lph.

 

[1slickRED89]

Youd probably need to adjust your injector size scalars;

Increasing the base FP just makes the injectors "bigger" in the scalars.

alright, just curious because my FP, no vacuum, was 43+, and I thought i was boned. but sounds like the only side effect would be some richness. do you guys run a 255 regular or high pressure?

 

[Axianator]

Increasing the base FP just makes the injectors "bigger" in the scalars. I use a SCTurner. I don't have the forumla handy, but it's something to do with the the ratio of the new FP squared over the orginal FP squared.

However, as you raise the base fuel pressure, the Fuel Pump becomes less and less effecient. A little bump would be fine, say 7-10 psi increase, but much more than that .... remember you have to add the base increase with the amount of boost you run. 39 psi + 10 psi bump + 15 psi boost is 64 psi of fuel pressure drops that 255 lph pump to less than 200 lph if it is supplied with 14.5v at 12v it's something like 145 lph.

Ransom is correct. While a small bump in base fuel pressure can be desireable (and even beneficial), too much of a pressure increase over the factory figures can diminish the performance of even a 255lph hi-po fuel pump, especially when teamed with the teeny-tiny factory fuel lines. The problem becomes doubly-worse if said person is not careful with their fuel pressure adjustments and the proper support modifications have not been made, either of which can lead to a potential tuning nightmare.

alright, just curious because my FP, no vacuum, was 43+, and I thought i was boned. but sounds like the only side effect would be some richness. do you guys run a 255 regular or high pressure?

IMO, your best bet is to go with the high-pressure 255lph pump.

 

[1slickRED89]

The problem becomes doubly-worse if said person is not careful with their fuel pressure adjustments and the proper support modifications have not been made, either of which can lead to a potential tuning nightmare.

tuning nightmare? BTW I do have the high pressure version of that pump. I'm asking because I have a funny problem when the car is first started. for the first 20 minutes of driving lean cruise is like ~14.9:1 until about 1/2 hour in, it then dips to 11.5:1 at a regular 30% load cruise. I've been having great results with autolite racing plugs (stock heat range) but they foul a little bit when this happens.

I thought it was due to the FP being to high, about 45 no vacuum. I just ajusted it down to ~40 to see if that will help. also I leaned the base fuel tables to have a AFR of no less than 12.0 at any point. the scalers I am using for the FMS42#ers are 44/48 low/high, just on a guess.

I am slightly concerned because I have a race coming up on the 5th so I up-ed the boost to 10+ PSI to get a decent time (the WOT tune is OK), but I have to drive it over an hour to get to the track.

 

[Axianator]

tuning nightmare? BTW I do have the high pressure version of that pump. I'm asking because I have a funny problem when the car is first started. for the first 20 minutes of driving lean cruise is like ~14.9:1 until about 1/2 hour in, it then dips to 11.5:1 at a regular 30% load cruise. I've been having great results with autolite racing plugs (stock heat range) but they foul a little bit when this happens.

I thought it was due to the FP being to high, about 45 no vacuum. I just ajusted it down to ~40 to see if that will help. also I leaned the base fuel tables to have a AFR of no less than 12.0 at any point. the scalers I am using for the FMS42#ers are 44/48 low/high, just on a guess.

I am slightly concerned because I have a race coming up on the 5th so I up-ed the boost to 10+ PSI to get a decent time (the WOT tune is OK), but I have to drive it over an hour to get to the track.

Given that the factory D4U1 calibration was configured to run identical injector slope values (with values that are very close to the actual static flow rating), you should be able to get away with the same on your modified D4U1 calibration. That said, I would plug in a value of 42 for both of your injector slopes and then see what your datalogs show you after some detailed tuning and analysis.

Out of curiosity, what MAF are you using and how do you have it configured? Any pictures we could see?

 

[1slickRED89]

Out of curiosity, what MAF are you using and how do you have it configured? Any pictures we could see?

I had 42/42 for a while, till I read that the lightning truck that these came out of had a system pressure of 43+PSI. based on that, the real flow rate at 39 PSI should be less, so i just programed some values I read on EECTuning.org 40/44, then changed 44/48 as an experiment.

I used the tweecers' preloaded table for a 80mm lightning. as far as mounting it was glued into a 4" tube (the inside dimension left intact, just a packaging modification) and connected to a 4" inlet 9" long K&N (very lightly oiled). downstream from there a 3" tube has a 6" leg, 45* bend, another 45* and is reduced to 2.5", two 90's, about 4" of strait 2.5", and then the compressor. Pic

 

[Axianator]

I had 42/42 for a while, till I read that the lightning truck that these came out of had a system pressure of 43+PSI. based on that, the real flow rate at 39 PSI should be less, so i just programed some values I read on EECTuning.org 40/44, then changed 44/48 as an experiment.

IIWM, I would stick with 42/42 until I had a reason to change them (i.e. after detailed data logging and anaylsis).

I used the tweecers' preloaded table for a 80mm lightning. as far as mounting it was glued into a 4" tube (the inside dimension left intact, just a packaging modification) and connected to a 4" inlet 9" long K&N (very lightly oiled). downstream from there a 3" tube has a 6" leg, 45* bend, another 45* and is reduced to 2.5", two 90's, about 4" of strait 2.5", and then the compressor. Pic

Given the sheer number of functions and parameters that come into play even at light cruise/part throttle on the Gen 2 ATX (of which the '92-'95 MTX X2J computer does not have), it's difficult to say exactly what might be contributing to the problem without looking at your calibration file. That said, your air charge piping looks to be pretty-well laid out, especially WRT to sufficient air metering.

Out of curiosity, have you tried clocking your MAF in either direction to see if that helps with your mixture problems?