3400 Impala Engine Mods

[Khipset]

I saw the pumps run up to 60 but that doesn't mean its the fuel pressure. If you find the rating on the regulator let me know.

Well, not many sources, but I finally came up with the Part number. FPR is Delphi FP10075, when I searched for it, I have found this site:
FP10075

and Napa

and this GrandAm Forum

Seems the FPR is 61.8PSI

[SappySE107]

I saw the pumps run up to 60 but that doesn't mean its the fuel pressure. If you find the rating on the regulator let me know.

[Khipset]

Did you test the fuel rail on a 4.2 or find the information somewhere? Google is giving me a bunch of stuff I don't need to know and i wasn't aware they ran at a higher pressure than 55 psi.

Google at some point in time. I thought it was a little high too. Unfortunately I didn't save my sources. I remember searching for the <year> (can't remember that either) TrailBlazer Fuel Pressure and having to go through a bunch hits for fuel pumps. I will see if I can come across some more reliable information.

[SappySE107]

Did you test the fuel rail on a 4.2 or find the information somewhere? Google is giving me a bunch of stuff I don't need to know and i wasn't aware they ran at a higher pressure than 55 psi.

[Khipset]

Khipset - I'm not positive about all of the exact numbers but the method of figuring rate of fuel flow appears to be correct. There are also online calculators to help with the math if you are deciding between multiple injectors and need quick answers.

I have been using
http://www.rceng.com/technical.aspx

http://www.injector.com/injectorselection.php

and

http://www.csgnetwork.com/presskpapsicvt.html

For the math help. Thank God for Google. Just trying to make sure that when I do the change out and tune it that I have the correct info to input.

[WrathOfSocrus]

I will try it... i'll go from 19 to 21# and i think it'll be fine. thats pretty much going from my stock injectors to the 2000+ style injectors for my malibu.. I think my stft will always be in the negative as well as my ltft, but i cant see 2 lbs being outside what the pcm can compensate for.. by the way, i know what a tps and a maf and and map and 02 and bla bla bla... etc etc.. are.

It isn't a matter of what the computer can compensate for with the oxygen sensor. The oxygen sensor only comes into play when in closed loop. When you start your car you are in open loop mode and the engine runs off of predefined tables. Based off of those tables it sends a pulse to the injectors that tells it to open a certain amount for a given RPM, throttle position, and so on.

Changing the amount of fuel entering the engine per pulse by either increasing the fuel pressure or using a larger injector will result in more fuel being added than the computer expects. Small changes such as adding a few PSI to the fuel rail or installing a slightly larger injector might not drastically affect closed loop operation but will likely result in a rich condition in open loop. How rich would depend on the amount of extra fuel added and if the engine was already starved due to engine mods. It could be that the increase matches what the engine needs but the best way to know that would be through computer tuning.

Khipset - I'm not positive about all of the exact numbers but the method of figuring rate of fuel flow appears to be correct. There are also online calculators to help with the math if you are deciding between multiple injectors and need quick answers.

[Khipset]

28# trail blazer injectors....

I am hijacking HotSauce's Thread here, but have been looking for information on this for a while.

I have an '05 Impala w/ the LA1. I first came across the idea of swapping in the Trail Blazer Injectors on a Grand AM forum I believe, and have been interested in doing it.

I have seen so many numbers, but no solid information as to which injectors are in the '05 3400. The last number I remember seeing is 22.5#/hr (rounded). I do not have a solid understanding of how they're rated. The most I know is that they open at a determined pulse width based on load, etc, etc. But am ignorant beyond that, if anything more to it then than.

Now for the ratings, to my understanding, but this is where I am unsure, injectors must have a certain amount of pressure behind them to achieve their rated flow. I know the Fuel pressure is lower in the 3400 than the TrailBlazer's I6.

Using this information:

LA1 -
22.5lb/hr injectors at 370kPa or 236.25cc/min at 53.7PSI

Trail Blazers -
28lb/hr injectors at 410kPa or 294cc/min at 59.5PSI

Using the LA1's pressure, I get
278.91cc/min or 26.54lb/hr

Yielding 15.22231% increase

Would this info be correct or is my logic a bit convoluted?

[HotSauce6226]

Any news?

[IanSzgatti]

I will try it... i'll go from 19 to 21# and i think it'll be fine. thats pretty much going from my stock injectors to the 2000+ style injectors for my malibu.. I think my stft will always be in the negative as well as my ltft, but i cant see 2 lbs being outside what the pcm can compensate for.. by the way, i know what a tps and a maf and and map and 02 and bla bla bla... etc etc.. are.

[HotSauce6226]

Do you have a link for the 3500 top swap?

[HotSauce6226]

Understandable. I do have a SLP Powerflo Catback Exhaust. So the headers should be all.
Can you define "big bump"?

[IsaacHayes]

That will provide a big bump in power. If you get the S&S headers then it will help a lot as well. Cam requires pulling the motor, or a skill full install through the fender well... So if you want cam, best to pull the engine and do heads/cam all at once I say. Or if you think that won't happen, then just swap the top end, and do more bolt on like headers and exhaust.

Either way you'll need an updated tune to take full advantage, and with a cam (depending how "hot" of a cam) one is needed to get it to run good like stock again.

And by tune I don't mean mail order. It might be possible if someone has tuned for the same mods before to save a tune and set you up with that, but for a cam or a good fine tune you'll need someone to ride a long and datalog and adjust from that.

[HotSauce6226]

Thank you. You guys are great. So this is what i might be looking at
3500 top end swap and have your 3400 UIM ported to match a 3500 LIM for an easy install. Wot can port you an upper to match a 3500 lower. This way you won't have the ugly 3500 UIM. And a 62mm Tb. Maybe a 65mm but i'm not sure you would benefit much from it.
Quoted from bombshell. How does that sound. I dont think its time for stage 2 yet. Dont have that kind money.

[IsaacHayes]

Ian, go throw some 36# GTP injectors in and see how well your car runs.... See if the ECM can adjust... LOL Or even 28# trail blazer injectors.... At idle you are not pulling more air even with a larger TB. And even with a larger TB you are not necessarily going to pull more air, you just are going to get more air for less pedal travel. The ECM will still read the MAF/MAP and do it's calc based on that. It doesn't go solely on TPS for fuel. TPS is will affect spark some and so it knows for PE and AE modes. If your heads/intakes/exhaust prevent you from using the full CFM from the larger TB then you could be breathing in the max amount of air you can take in before the throttle plate is even open all the way. The ECM won't know you have larger injectors, and while it may try to adjust some, it won't run right.

Say in it's table to adjust for X amount of richness, it pulls back 5 milliseconds of duty cycle. Well that might work for the stock injector to pull that much duty cycle and then you'd no longer be rich, but now you have say 36#/hr in there. So it pulls back 5ms on the 36#'ers, and well that doesn't make hardly a bit of difference with that large of injector in regards to get you to no longer rich. It still reads X rich. So it looks that up and pulls 5msec of duty according to it's tables once again. Which doesn't help a damn bit.... You need to tune the injector flow rate constant in the ECM so it can calculate correctly how much to pull. The stock ECM figures it has X#/hr injectors. Change that and it has no clue that change was made.

Plus as you go to a larger injector the duty cycle for idle and low throttle/cruise is going to be less and less. Say a small duty cycle 19#/hr injector has a somewhat linear curve of duty cycle per RPM/throttle/load. Now jump to a 36#hr/. Now it's going to look more of an inverse curve. Low duty cycle until you get close to WOT where you need more fuel for your high power motor. Say 19#/hr at idle would be (just relative # here) 20msec, but a 36#/hr would only be 2msec... It's just impossible to get a decent running engine by throwing in a different injector or fuel pressure without adjust the ECM for it. Too many tables and such need to be updated to work. The tables and flow rate of injectors are not linear or that might work by just swapping a bigger injector that is dead on for the application. But then we'd need injectors sized in 1lb/hr increments..

That explanation might not be 100% absolute, but it's relative in trying to compare how the things work.....

Trust me. Or go try it!

The ECM isn't a self calibrating instrument. If it was then it would come with a WBO2 sensor and a rough tune and the car makers would say "here go drive this for a few weeks then it will run good, oh and don't remove the battery!" haha Or I guess it could store it in NVRAM if they put that in there...


HotSauce: If you have really good ported 3400 stuff it probably will approach a stock 3500 top end. But the 3500 heads are designed a lot better according to all who have actually seen the ports and stuff.

[HotSauce6226]

That sounds like a great idea. I might jsut do that. I was just wondering is the 3400 lower and upper ported would be about the same as 3500 top swap. Ill talk to a few shops and see what they say about the install