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Username Post: Big block to small block tbi swap        (Topic#358428)
Mkswmp 
Poster
Posts: 4

Reg: 10-13-19
10-13-19 06:43 AM - Post#2777772    

Newcomer here and would like some much needed info. I've got a 1989 Chevy 3500 4x4 with a 454 tbi and a manual 4 speed tranny. I've recently spun a main bearing and want to replace the 454 with a 350 tbi. I'm pretty sure everything will bolt up as far as I know. But what about the computer? Will I have to get a computer for the 350 tbi or can the 454 one work?



Edited by Mkswmp on 10-13-19 06:43 AM. Reason for edit: No reason given.

 
CowboyTrukr 
"8th Year" Silver Supporting Member
Posts: 4281
CowboyTrukr
Loc: Salt Lake City
Reg: 06-20-09
10-13-19 08:28 AM - Post#2777775    
    In response to Mkswmp

At a minimum you will need the prom chip from a 350 truck. I’m not sure if the computers are the same, so you’ll need to at least check the wiring diagram pin configuration to make sure they’re the same.

Greg

'95 K1500 Z71 EC Short Step 5.7L+0.040/NV3500
'00 Explorer XLT 4.0 V6 Auto
'94 K2500 5.7 NV4500 ECLB - SOLD
‘87 GMC S15 SCLB 4.3 Auto - SOLD

"The only thing necessary for evil to triumph is for good men to do nothing" Sir Edmund Burke


 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3838
Chevytech
Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
10-13-19 12:34 PM - Post#2777794    
    In response to Mkswmp

The computer (ECM) in your truck should be a 1227747 which will work if you get the correct chip (prom).

For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If your vehicle has been altered from stock, let us know about that too.


 
Mkswmp 
Poster
Posts: 4

Reg: 10-13-19
10-13-19 07:01 PM - Post#2777829    
    In response to Chevytech

Does each tbi engine have it's own prom chip? Or will any prom chip for a 350tbi engine work?



 
bowtie44s 
Valued Contributor
Posts: 4239
bowtie44s
Age: 36
Loc: wv
Reg: 08-29-12
10-14-19 08:20 AM - Post#2777857    
    In response to Mkswmp

Why not rebuild the 454 instead of cutting the value of the truck in half?

Jeff

'88 Chevy K3500, aluminum head roller cam 511in³ stroker 10.5:1 compression, 96 NV 4500, 94-98 grille, 305/70-16 (33x12) BF Goodrich KM2s, 91 cluster swap


 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3838
Chevytech
Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
10-14-19 10:00 AM - Post#2777867    
    In response to Mkswmp

  • Mkswmp Said:
Does each tbi engine have it's own prom chip? Or will any prom chip for a 350tbi engine work?


The prom tells the computer which engine, transmission, rear axle ratio, vehicle weight...

For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If your vehicle has been altered from stock, let us know about that too.


 
65_Impala 
Very Senior Member
Posts: 4326

Reg: 12-29-02
10-14-19 10:34 AM - Post#2777870    
    In response to Chevytech

A '7747 in a 89 TBI only cares about the engine and it being a standard so it doesn't have a torque converter clutch. Nothing else about the truck really matters much. So, you need a prom from a 350 with a standard to get it working right.



 
scrambldcj8 
Silver Supporting Member
Posts: 2504
scrambldcj8
Loc: Belchertown, MA
Reg: 04-06-03
10-14-19 03:55 PM - Post#2777895    
    In response to 65_Impala

Make it a 383-406 and let the original comp think it's powering a 454...



 
Mkswmp 
Poster
Posts: 4

Reg: 10-13-19
10-15-19 10:08 AM - Post#2777942    
    In response to bowtie44s

I've thought about that, but I've had 350's in all my older trucks my whole life and they are just much cheaper to work on, buy parts for, etc. Besides, I wasn't really impressed by the performance of the 454. Even when I had it running perfect it just didn't impress me much compared to a good old 350 with an RV cam, flattop pistons and 305 heads on the block. I was expecting alot more power with that additional 100 cubic inches....it wasn't there.



 
Mkswmp 
Poster
Posts: 4

Reg: 10-13-19
10-15-19 10:14 AM - Post#2777943    
    In response to 65_Impala

I don't think I asked then question correctly.....are the proms engine specific? Like the vortec motors I think you have to have the exact computer with each motor or get it reflashed to work with that motor. This isnt a vortec it's tbi so will any prom for a 350 and manual tranny work? Or does every individual motor have its own specific prom?



 
65_Impala 
Very Senior Member
Posts: 4326

Reg: 12-29-02
10-15-19 12:08 PM - Post#2777950    
    In response to Mkswmp

Any TBI engine in that era ran basically the same heads, intake, exhaust and TBI so they're not really prom specific. Only reason would be something like a change in emissions devices on the engine.

Now, you're posting about a modified engine that isn't equal to a stock 350 TBI, which makes it a whole different thing.



 
jktucker92 
Silver Supporting Member
Posts: 317
jktucker92
Loc: West Richland, WA
Reg: 02-05-17
10-24-19 06:27 AM - Post#2778668    
    In response to 65_Impala

At a minimum, you need a chip from a 350 for the engine to run. I don't know all the differences between an auto TBI program and a manual TBI program, but at a minimum, the idle speed will be wrong and you'll end up with a check engine light on all the time with an auto PROM instead of a Manual PROM. That said, you're also talking about modifying the engine from stock. In order to make best use of those upgrades, you should have a custom PROM made. It's not hard to do, and there are several companies online that will offer custom chips. If you do a google search on TBI PROM programming, it will have many hits. There are many people who put the 454 TBI on a 350 to get more out of the 350. That would definitely require a custom prom, but since you already have the 454 TBI, it's something to consider.



 
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