3400 Impala Engine Mods

[SappySE107]

I thought 99 3100 was 19# injectors.

[IanSzgatti]

I thought 99 3100 was 19# injectors.

i suppose you could be right.. a short pencil is better than a long memory, the latter of which I do not have.

I couldnt wrap my head around it though... from THIS site I learned that you'd need a tune for the larger injectors, yet im being told that it's the duty cycle thats important... that it's the same duty cycle, so it will flow more and be useable.

Since the 02 is detecting all the extra from the larger heads, intakes, etc, it will be able to keep the mixture correct.
Anyways, thats why im not even concidering tuning with only heads and intakes and some exhaust work. If those 3400 heads flow so nice I think i'll be happy with those.

thats why im suggesting to this guy that intakes and exaust would probably make him well enough happy... especially 3500 stuff and that big ole' 62mm. i've wanted one of those for over a year... but up in canada i cant get things shipped to easy.. it becomes really expensive

[IsaacHayes]

If you go to a larger injector, and don't adjust the duty cycle, then yes it will run poopy. If you can adjust the duty cycle to make it shorter for a larger injector, then great. If you don't, then if you have radical mods it might not starve it at WOT, but at idle and everywhere else it will run way rich.

[asylummotorsports]

Hey Ian. I'm in Hamilton and I have ordered lots of things from Ben for my 3500 swapped Beretta.

Service is excellant, and while shipping can be a little pricey, I have never had a problem with Ben at all.

[IanSzgatti]

Hey Ian. I'm in Hamilton and I have ordered lots of things from Ben for my 3500 swapped Beretta.

Service is excellant, and while shipping can be a little pricey, I have never had a problem with Ben at all.

hamilton eh? well we'll meet eventually... im originally from hamilton. I chose this town to work in because it's cool to go around town and see all the peoples cars you've worked on... it's still got that small town feel where people know you and you dont feel like a number...
anyways, i'd like to see what you've done some time.

[IanSzgatti]

If you go to a larger injector, and don't adjust the duty cycle, then yes it will run poopy. If you can adjust the duty cycle to make it shorter for a larger injector, then great. If you don't, then if you have radical mods it might not starve it at WOT, but at idle and everywhere else it will run way rich.

thats just the thing... your still getting more air in through a bigger tb (9% angle with a 62mm is more than 9% angle with a 52mm), and even at idle, your 02 sensor will know whats rich and whats lean...

if the duty cycle of the injectors in question are the same, then everything should be fine... i cant see a rich condition occuring... i can see the 02 sensors making the PCM cut back pulse width a little more than normal...

i only argue issac because i dont have a final and total understanding... it's mostly because I trust facts and figures rather than only what somebody says... no offence eh...

[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

[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]

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]

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]

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

[HotSauce6226]

Do you have a link for the 3500 top swap?

[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]

Any news?

[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?