42# vs 50# high Z injectors for drivability?

The engine is to be a 383 with 195 AFR heads a 224/236 camshaft and a Vortech S-trim. The computer is a stock 95 OBD1 computer. Maximum rpm will be 6,000. Hoping for 550 HP at the wheels.

I was planning to run an FMU, but am thinking about trying to eliminate it by going to MSD 50# injectors.

How do the MSD 50# injectors work in a daily driven application?

I'm assuming that 42# injectors will be "nicer" on the street, but is there a difference between Lucas and Bosh(SVO) injectors?

My original plan was to run SVO 42# injectors with an FMU and perhaps see 65 psi of fuel pressure. Then I got info on a good deal on Siemens injectors ... I don't have any idea on what sort of injector offset table the Siemens injectors need in order to funtion well.

In a nut shell ... I'm ... :confused:

Any information or input is appreciated ...

LWM

As far as driveability there is no difference between 42# & 50# injectors. The computer adjusts for whatever your running. As far as 50# injectors without an fmu I would go with at least 70# injectors with a 383. I plan on selling my 50# injectors and using 82# with my new 383 with 8lbs boost.

I ran the MSD 50# injectors for a while - put in the correct injector constant and offset tables, and they will work/function just like the stockers in every aspect... Since the MSD/Holley injectors are make by rochester (same people that make the stock LT1 injectors), they look exactly like the factory 24# injectors... a definite bonus when you're trying to be sneaky.

Originally posted by EddieP
I ran the MSD 50# injectors for a while - put in the correct injector constant and offset tables, and they will work/function just like the stockers in every aspect... Since the MSD/Holley injectors are make by rochester (same people that make the stock LT1 injectors), they look exactly like the factory 24# injectors... a definite bonus when you're trying to be sneaky.

Sounds good, but just begs the question ... what are the correct injector constants for a 95 OBD1 computer.

So far I've located tables of injector constants for SVO injectors up to 42# and Lucas/Delphi 42#, but nothing in the MSD range.

LWM

Since the 50# injectors were the same design/type as the stock 24# injectors, I started with the factory offset table and kept multiplying the entire offset table by 5% until my idle BLM went back to ~128 (this took several attempts... the 50# had significantly longer open/close times than the stockers)... at that point, I didn't need touch the offset table - all the other cells turned out to be very close.



Originally posted by LWM
Sounds good, but just begs the question ... what are the correct injector constants for a 95 OBD1 computer.

So far I've located tables of injector constants for SVO injectors up to 42# and Lucas/Delphi 42#, but nothing in the MSD range.

LWM

Thx for the input, I'm starting to like the MSD 50# injectors.

Anyone else have something to add?

LWM

Originally posted by LWM
Thx for the input, I'm starting to like the MSD 50# injectors.

Anyone else have something to add?

LWM

I've learned something about offsets. I thought changing the offset adjusted the event timing of the injector pulse based on the intake valve opening/closing (sequential systems)...I only made adjustments after I re-cammed, not after changing injectors...I'm such an idiot. Where can I get the proper offsets for my injectors (holley 50#)? Thanks!

If what EddieP says is correct, then I believe that MSD, Holley and Delphi injectors are all made by the manufacturers of the injectors that GM uses ... Rochester ... He said you could use the stock 24# offset table and then add 5% to the entire table untill you got reasonable BLMs at idle, and that that would pretty much cover the entire RPM range.

I gather that Siemen injectors are somewhat different.
And also that Bosch/SVO injectors are also somewhat different.

At this point, I must confess, that when I installed my SVO 30# injectors, I did not touch the stock injector offset table, even though I did have a table for the SVO injectors. I logged a few runs with the trusty laptop and found the BLMs always around 126 - 128 ... and that to me was ... "good enough for Government work" ... :)

So when I got wind of some people having problems with the larger Hi Z injectors, I got concerned. The devil as they say is in the details.

Hope this helps and, hope I got it right ... :)

LWM

Originally posted by LWM
How do the MSD 50# injectors work in a daily driven application?

I went from stock to SVO 30 to MSD 50 to Delphi 75 and now Delphi 95. The MSD 50's easily had the worst "drivability". My idle and throttle response got much crisper after switching from the high-z 50's to low-z 75's. Which makes sense, since you have 4 times the electric current yanking open a low-z. I used stock offsets for the 75's.

Originally posted by 10secz
I went from stock to SVO 30 to MSD 50 to Delphi 75 and now Delphi 95. The MSD 50's easily had the worst "drivability". My idle and throttle response got much crisper after switching from the high-z 50's to low-z 75's. Which makes sense, since you have 4 times the electric current yanking open a low-z. I used stock offsets for the 75's.

Hmmm ... did you go through the process of adjusting the injector offset table when you tried the MSD 50# injectors.

Are you able to use the stock computer with the Delphi 75s and 95s??

So many questions ... sigh

Thx for the input

LWM

??? Very strange- I've used the stock, bosch, and MSD 50# injectors, and once the programming is done, I could not tell a difference... there was a off idle hesitation right after I installed the 50# (with the factory offsets), but I knew the offsets too small - once corrected, it would be difficult, if not impossible to tell the difference between the 50# injectors and the stockers.

NOTE! Just like the stockers, the MSD/Holley injectors don't like lots of fuel pressure - I figured I mention this, since this is the forced induction forum. Anyone wanting to run 65+ psi of fuel pressure would probably be better off with a low imp. injector or a 42# bosch or lucas injector.

Originally posted by LWM
Hmmm ... did you go through the process of adjusting the injector offset table when you tried the MSD 50# injectors.

Are you able to use the stock computer with the Delphi 75s and 95s??

Yes, I tinkered with the offsets quite a bit. The 50's are very sluggish and required large offsets to run decently. IIRC I was up around 1.0 ms at normal operating voltage.

Yes, I run the 75s and will run the 95s (when they show up) with the factory PCM.

<commercial>
What makes this possible is the Acceleronics Impedance Converter. See the link in my sig.
</commercial>

I tuned Hugh Lam's s-trim 396 on Saturday. Hugh is running Siemens 72's with my Converter. He made 600 rwhp on pump gas (598, actually) with an in-tank pump and stock fuel lines. What's even more impressive is how docile his car is in town despite the big injectors.

http://web.camaross.com/forums/showthread.php?threadid=101510&referrerid=24084
Check out the link above if you haven't.

Your setup will be similar to Allen’s (www.caspeed.com). He had stated before that with his MSD 50#/hr injectors he was at 80-85% duty cycle at 50psi and dyno tune to 510rwhp. He also has great information on his sites as well. And LJ also helped him with the tuning.

I went through exactly what you are thinking a while back and was really nervous to get LJ’s box and the 72#/hr injectors. I ended up getting because I wanted to do this right the first time about, and they worked out perfectly. With large enough injectors you are able to run at reasonable pressure (36 -50psi) so that you can maximize the stock fuel lines. On the other hand, if you try to squeeze by with smaller injectors like 50 and 42#, you will have to run at elevated fuel pressure (50-70psi) then you will face problems in stock fuel line and fuel pumps. Further, you know that you will not need to buy another set of injectors unless you want 1000hp like LJ.

My car idles like stock, then engages and runs smoothly to 600rwhp and I can drive that in CA traffic jam in 100F without a problem.

Good luck with your setup

Thx for the replies folks, at the end of the day, I'm still leaning to the 42#SVO injectors and the Super FMU which is already in place and has worked fine for 2 years.

How about the reliability of that impedance converter? Anyone ever had an issue with that?

LWM

Originally posted by LWM
How about the reliability of that impedance converter? Anyone ever had an issue with that?

Acceleronics has been selling Impedance Converters since Jan 2002, almost 40 units so far with exactly zero advertising or magazine exposure. There have been a couple of failures at installation time, but they have all been quickly resolved. I have received no reports of failures occurring anytime after the initial installation.

The box is very sturdy, there are no tall electrical components that could be affected by impact (such as dropping the box on the concrete floor), and the circuit board is covered with a silicone conformal coating that prevents problems caused by high humidity or water splash.