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Tbi

4X4HIGH

4X4HIGH

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Is anyone here running a 350 engine with a 454 TBI unit using the 350 injectors?

I'm going to have my new engine done soon and was planning on using the larger 454 TBI unit but using the 350 injectors. The reason for this is so i can have the full potential of my engine. I'm assuming that the ECM will compensate the fuel requirements to match the air flow that would be required. Basically the 350 TBI unit will not flow enough air to support the torque and HP numbers but the 454 TBI unit will. The 454 injectors on the other hand would be too big to support my required needs. This brought me to the idea of using the 454 TBI unit with the 350 injectors. The injectors don't run at full potential i'm sure so there is some room for more injector pulse as would be needed.
 
So does no one have any experience with what i'm wanting to do or any advice as to if it will work or not?
 
All I've ever heard people talk about is duty cycle, and that's something that is figured out by getting the injectors to feed the fuel your engine needs, so kind of after the fact.

What size engine are we talking about? If it's in the 383 range, you will probably be hitting the "limits" of the 350 injectors at high load.
 
I'm talking about a 355 (350 + .030").
My thoughts are simply that the 350 TBI would not support enough air flow to use full potential of the AFR headed roller cammed engine. The 454 injectors would be too much injector though so i'm hoping that the ECM would allow enough "duty cycle" of the injecotrs to work with the larger CFM displacement of the 454 TBI.
 
To be honest, it seems that GM went pretty "light" on the injectors. Maybe others can chime in about stock 350 injectors on other than stock engines, but I know that with all the changes (still moderate IMO) on my 355, the stock setup couldn't compensate enough to keep it from running lean most of the time.

You can try it, I'd suspect if you could find a used 454 TBI, you could probably get one with injectors just in case?

Of course, more air means more fuel, you gotta keep the right mix. You can't have more airflow without more fuel, if the engine can effectively ingest more air, it HAS to have a like amount of fuel added. You may find that the vastly superior heads you have now will blow the stock injectors away when you get on it.
 
Well, i do have a 454 TBI with the injectors. I'm under the impression that the ECM will pulse the injectors to match the air flow up until the point of the cycle duy of the injector. If bigger injectors are going to be needed then i will step up to the 68 lb. hr. injectors that Turbo City sells. The factory 350 injectors are 61 lb. hr. and the 454's are 75 lb. hr.
 
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The ECM can actually only compensate so much from the "baseline", even if the injectors can handle the load. This is part of tuning of course, which I'm sure Southernspeed will chime in on...EBL probably fine tunes all of this for you. :)

You can somewhat compensate with fuel pressure, but that's not really "correct". You force more fuel through for the same injector pulsewidth, so the ECM really doesn't know how much is getting into the engine. Same concept of putting larger injectors in without adjusting the size of the injector in the PROM.
 
Sorry, unfortunately I don't know much about what your asking. I'm just curious about some specs on the motor your building. I have an '89 as well and I am thinking about building another motor. I have to deal with the wonderful smog here in CA and I'm wondering how your dealing with that ? Thanks!


Nick
 
Just sent you a PM. What part of California are you in? I'm also in northern Cali.
 
I am not running a 454 TB but I am running a bored out 350 TB. It flows aprox 580 CFM with stock flow matched 55lb hr injectors On a mild built 350. I still have the stock Chip. It runs the combo just fine. I have adjusted the fuel pressure and timing so it runs real good and gets good fuel MPG. I use an Auto X Ray scanner with real time readings to get my Integrator and BLM numbers right (128) with no knock counts. It took me about a week to tune it going back and forth to work 40 mile round trip. Making an adjustment letting the ECM learn the new adjustment. Checking the numbers then adjusting Timing and fuel pressure again and again. It takes time to tune but the ecm will learn and adapt to the changes as long as you are not running a wild cam or more than 10% above stock cubic inches displacement.. The problem most people have when tuning is they make an adjustment and never let the ECM learn how to deal with it. It takes 20 or so miles under normal city highway driving conditions for the ECM to learn and reset the cells to compensate for the higher fuel pressure and timing changes. I am running 13.5 PSI fuel and + 2* timing. This gives me around 18 MPG on the freeway and pretty good all around performance. If i go up to 14.5 PSI and 4* on timing I get better performance but gas milage takes a hit and I run rich all the time with a slightly choppy idle.

Beings you are running a 2" TB, AFR heads and a Roller cam you should get a new chip burned for your combo to deal with the greatly increased airflow.. Then adjust your fuel pressure and advance the base timing in small ammounts to fine tune it and help meet smog requirements.. Prolly would not hurt to go up in injector size to the cop car 65 lb hr.
You will have to rewire the IAC and most likely the TPS plugs to fit the 454 TB to your 350 harness.
Stock fuel pumps are a little weak. It would also be good if you upgraded your fuel pump to a 190 LPH pump. Walbro makes a good intank replacement pump for TBI for under $100.00
 
Thanks Thunder. I was hoping to stay away from needing a chip but if that's what i need then i'll do it. It's only money and i would rather spend the money than hurt my new motor. Too much money invested in it to damage it.
There are adapter harnesses for the IAC and the TPS switch so that's not an issue. I also already have swapped a different pump in the truck several years ago for a better one when the old pump crapped out on me.

PS: Who makes the best chips?
 
Who makes the best chips is you. :)

However, if you aren't willing to spend the time, money and effort, (which is understandable) TBIchips.com has a very good reputation, or a local dyno shop.
 
Well i haven't bought the adapter harnesses yet but yes Turbo City is who list them on their website.
 
Hey scott, mind sending me the specs on your motor. I've basically come to the conclusion to hold off on adding parts to my stock motor and just build a new one when I have the funds. I'm saving and have been so it shouldn't be longer than a couple months.

I'm also very eager to hear if the 454 tbi and 350 injector combo works out well.
 
I don't think you'll have any issues with the injectors, I run 350 injectors with a large throttle body on a 400 and with about 26 psi of fuel pressure the injectors are adequate with reasonable duty cycle. The problems you may run into:
1: Depending on your engine combination you may end up with a hesitation on heavy acceleration due to the additional airflow transition, easily fixed with a chip though.
2: What are you going to do to connect the TV cable? the big block t-body has no provisions.
By the time you get done buying a usable big block throttle body, harness adapters, and figuring out the linkage you're probably better off to buy a bored 350 t-body from cfm tech or the like.
Once you get your motor running make sure you hook up a scanner and make sure everything is happy, chips are a whole lot cheaper than motors.
 
bigblock72 said:
I don't think you'll have any issues with the injectors, I run 350 injectors with a large throttle body on a 400 and with about 26 psi of fuel pressure the injectors are adequate with reasonable duty cycle. The problems you may run into:
1: Depending on your engine combination you may end up with a hesitation on heavy acceleration due to the additional airflow transition, easily fixed with a chip though.
2: What are you going to do to connect the TV cable? the big block t-body has no provisions.
By the time you get done buying a usable big block throttle body, harness adapters, and figuring out the linkage you're probably better off to buy a bored 350 t-body from cfm tech or the like.
Once you get your motor running make sure you hook up a scanner and make sure everything is happy, chips are a whole lot cheaper than motors.
Click to expand...

I already talked with Brian from TBIchips.com and he advised me that i'm going to need to run the 454 injectors in order for me to get full potential from my engine. I already have two 454 TBI units with injectors.

As far as TV cable is concerned, i'm going to rob the throttle linkage plate from a 350 TBI and install it on the 454 TBI and i'm all set. I'm going to send out all 4 injectors from both TBI's to have them cleaned and flow matched so i know i'm starting with a good set of injectors.

Also, how are you running over double the fuel PSI of stock? I didn't know wthat was even possible and i'm sure it isn't good for your engine either.

Dennis, i'll get you specs on my new engine tomorrow when we PM with one another.
 
If you already have two throttle bodies with injectors then by all means use them, you will of course have to have a chip made, but you'll be happy with it in the end.
I changed the spring in the fuel pressure regulator to get the fuel pressure up that high. It won't hurt the motor at all, just have to have a pump capable of running the pressure/volume. In fact the 94-95 big blocks ran at 24 psi stock. Can't run the 350 injectors much over 30 psi they start to get a little flaky, I tried.
I would be interested in buying your leftover parts especially the injectors, I have some new parts coming for the 406 and will need some bigger injectors to support the new horsepower.
 
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