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350 TBI -454 TBI conversion/Need help!

S

scoutillac

1/2 ton status
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OK, I posted yesterday that I had blue smoke blowin out the exhaust. Today I have the wife convinced I need more power to tow my scout around. So Should I go 383 or 454? If I go 454 what do I have to do to make it work? Will the motor mounts be the same? Will my 700R4 bolt to it? Will a computer from a 454 donor plug into my wiring or will that need to change too? Ipretty positive the radiator will need to be larger. Please give me all the good bad and ugly about this transplant.
 
If you go to a 454 your 700r4 will most likely die. Basically if you decide to go to a 454 I would just buy a complete ragged out truck and use all the parts from it or find a wreck in a junk yard for the parts. That way you know you have everything. The engine will bolt in, it will bolt to the trans but you might need a new flexplate on the engine if your converter does not bolt up. Not sure on the electronics that is why I would get everything. I should know more in a few weeks about this swap when I pick up my tow rig. I will be able to park the tbi350 and tbi454 right next to each other and compare. As far as the trans goes I would swap to a th400 or a 4l80e.
 
Hey if you would keep me posted. I would really appreciate it.

I know there has been a lot of conversation about 383 installs. If I remember right to do this I can run my factory set up, but need to chip it. Am I right? Are there any other things I might need to know? Would this be the easiest, and cheapest way to go?
 
You better think this through a bit more before you go ahead with it.. Can the rest of your drivetrain handle BBC power? Your 700r4 is a SERIOUS weak link...

I swapped in a TBI 454 inplace of my TBI 350 and will be more than happy to guide you through it...But beware, BBC's can (and will) break weak parts.

For the mechanical part of it, the 454 will bolt right in. I used my 350 motor mounts with polly inserts. It will bolt to your 700r4 just fine. BBC and SBC bellhousing bolt patterns are identical. The 700r4 TC will bolt up to a BBC flexplate with no issues at all.

Wiring this thing is another story. It can be as simple as plug and play (plug in the 454 ECM and hook up the connectors using you existing 350 TBI harness) or as complex at swapping in a new connectors and adding some wires on you existing harness. This is ALL dependeds on the year of the 454 and ECM you plan on swapping into you 88.

ECMs for both BBCs and SBCs that were used with TurboHydro transmissions OR manual trannies have the SAME pinout. Your truck has a 700r4 tranny and a 7747 ECM. A BBC ECM that had a 4l80e behind it WILL NOT plug into you existing harness. I believe 1991 was the year that the electronically controlled trannies were used in production. Do you options are getting a 454 ECM from 1987 thru 1990 (that had a TH tranny or a manual tranny) OR get a 1991-1995 ECM from a truck that had a manual tranny.

The other concern is all the connection on the 454. Will your existing harness plug into all the sensors? Again it depends on the year. I believe 1990 or so was the split for this. ON my 1987, I had to swap about 60% of the connectors so my 1992 454 would plug in.


The BEST thing to do is to get EVERYTHING you could possible need. I bought my 1992 BBC and it had the ECM, the wiring harness, complete motor cleaner to pan, all accessories, even the NV4500 bellhousing that hung off the motor...I kept my existing harness in the truck and just swapped in the correct connectors.


The ECM you are looking for is the 8747..GM#1228747 or something like that...

That is the TBI 454 ECM that will plug into your factory harness...

Feel free to contact me with any questions...It is second nature to me anymore.... /forums/images/graemlins/waytogo.gif /forums/images/graemlins/waytogo.gif
 
You seem to be a walking JtR manual. So as long as I get 88-90 top end and sensors, and throttle body everything should plug in. And the computer will work with my factory 350 harness as long as it is in the same time frame as well? Now, I understand the tranny will be my weak link, not to mention, all the half ton components. But, as long as I quit mashin the pedal to the floor it should be ok right? What are you guys opinions in using the 700R4 as a DD and part time tow rig?

I'm just pickin yer brains so I make an informative decision? Again, would I be better off with the 383 for simplicity and strength issue?
 
I don't think keeping a stock 700r4 is a good way to go. You can have them built to handle a big block so I would seriously consider doing that. Even with a pumped up 383 you should do something with the trans in my oponion. Also the rear 10 bolt is questionable. I bought my Burb to tow with and if something ever happens to it such as getting totaled I don't think I need to tell you where the 454 is going to wind up. /forums/images/graemlins/whistling.gif I already have the rest of the drivetrain to handle it though and you will probably have to do some of the same. Also remember the Burbs are pigs in the weight department which does not help any. Since you found somebody that already did the swap and seems to know his sh!t about it I'de listen to him.
 
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Now, I understand the tranny will be my weak link, not to mention, all the half ton components. But, as long as I quit mashin the pedal to the floor it should be ok right?

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Do you really have that much will power /forums/images/graemlins/whistling.gif /forums/images/graemlins/histerical.gif
 
Kennyw-No I don't have that much power. I'm still wishing for that.
So I think I can get some shmuck to buy the burb for 4k. I could use that on a down for a 3/4 or 1 ton /forums/images/graemlins/crewcab.gif.

fortcollinsram and wayne-Thanks dor your info. Now, I guess I will have to contemplate a rebuild of the stocker or sell for a 1 ton. /forums/images/graemlins/crewcab.gif

Anyone in Washington wanna trade? /forums/images/graemlins/histerical.gif /forums/images/graemlins/histerical.gif
 
Yes...I am unsure as to the splin in years for when the sensors changed. I am almost 100% sure taht all TBI 454 and TBI 350s share the same connectors from like 1987-1989 or 1990...The older TB connectors has like a big square four plug for the IAC and a big flat three plugg for the TPS. The newer TPS has a MUCH smaller plug with an offset 3 plug kinda like :. ANd the IAC is a SMALL round (I think!?!?) plug..It is dark out so I can't see jack under the hood on my truck.

If you can score the wiring harness w/ it, you can get ANY year TBI 454 and make it work...

Chris
 
A 383 will not neccessarily be easier on the drivetrain. And in reality, I think making a TBI 454 work will is easier than a TBI 383. With a 383, you have to deal w/ a custom chip and there are some variables that may cause driveability issues...The TBI 454 had AWESOME driveability from the factory. I have a hotter cam in my 454 and higher compression and couldn't be happier with its driveability.


If you BABY it, the 700 will last, but the 454 will break those axles in the blink of an eye if you and heavy with the skinny pedal...

My suggestion...? Get a 6-lug 14bsf axle and think about getting a GOOD high strength rebuild on the 700...The 14bsf will take the power MUCH better than the 10b.


Chris
 
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Today I have the wife convinced I need more power to tow my scout around.

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The heavy towing is gonna be the killer. I talked with the tech guys at www.bowtieoverdrives.com last year about using one of their beefed 700R4's in a 454 powered 'burb to be used as a tow vehicle. They said that the 700R4 just isn't up to dealing with that kind of abuse and recommended that I consider a 4L80E instead. /forums/images/graemlins/frown.gif
 
But then I run into even more money. I just remembered there is a 2wd burban with a 454 and a TH400 for sale. The guy wants 1200 for it. I wonder if I should get that for the 14 bolt, 454 core, radiator. The tranny would be a good thing too I guess if I can mate it to my 208 t-case. If not what would I need to make it work with my 203 sitting in the garage? I just sold my SM465 with 205 t-case. Or is the 203 worth it? I'm sure I could find a computer and heads from the local recycling yard to convert to TBI. Were there any TBI 454's put in front of TH400 non computer controlled? I know I ask a lot of questions. Thanks for all your help.
 
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I just remembered there is a 2wd burban with a 454 and a TH400 for sale. The guy wants 1200 for it.

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Is that the green one that's been sitting in Airway Heights for a long time?
 
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Were there any TBI 454's put in front of TH400 non computer controlled? I know I ask a lot of questions. Thanks for all your help.

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Yes from 1987 to 1991 the TH400 was still used
 
No I haven't heard it run. I am just exploring options.I was just talking with the wife about junking all the TBI crap and running the 454 with the TH400. I could yank the TBI stuff out and go for old school carb and raw power.
 
Thats what we did with my friend's yellow Suburban (was parked up at Ione). It's an '88 that had TBI, and we had taken it all off and put a carb on it.

Also, thats what I'm doing on my plow truck. The motor gave out, so I yanked the 454 and TBI stuff, sold it, and have a carbed 454 I'm going to put back in it.
 
I'm just torn on what to do. I've put so much time and money to get it the way it is now. You saw how well it does. I would hate to get rid of it now. But, on the otherhand, do I sink more money into it or trade/ sell it off for something a little newer and heavier duty. Either way I'm spending more money and sacrificing. What do you guys think. Junk the TBI and drop a carbed 454 in with a 14 bolt in the rear or get a 3/4 or 1 ton newer truck for towing? If I get a 2wd TH400 will the tail shaft section unbolt so I can bolt on a 4wd adapter and run my 208?
 
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Yes...I am unsure as to the splin in years for when the sensors changed. I am almost 100% sure taht all TBI 454 and TBI 350s share the same connectors from like 1987-1989 or 1990...The older TB connectors has like a big square four plug for the IAC and a big flat three plugg for the TPS. The newer TPS has a MUCH smaller plug with an offset 3 plug kinda like :. ANd the IAC is a SMALL round (I think!?!?) plug..It is dark out so I can't see jack under the hood on my truck.

If you can score the wiring harness w/ it, you can get ANY year TBI 454 and make it work...

Chris

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Don't mean to hi-jack, but I'm doing this same swap. I purchased a '95 454 complete with every harness that was attached to it before it was yanked. I plan on installing it in a '90 blazer. How would I find out the split years. You say it may be '89 or '90. From the info that I've gathered, it should be a almost a direct swap. I'm I missing anything? More questions later in my own post.
Thanks, Joe
Yes I've upgraded the 700R and my axles.
 
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