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Old 01-26-2008, 01:06 PM   #1
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454 TBI, yes/no good/bad idea?

The 454 that goes in our 1974 Argosy motorhome is in the shop to be rebuilt. I've heard various pros and cons to using Throttle Body Injection over a carburetor. So, is there a definitive answer to which is better and why? Should I decide to go with TBI I do have a computer already that came with the 4L80E transmission that was out of a 1994 Chevy box truck, although it was a fuel injected 350 and not a 454. Don't know if that makes any difference.

If I do decide to use TBI what needs to be purchased or replaced on the carburated 454?

Hoping for a lively discussion here

Thanks,

Brad
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Old 01-26-2008, 01:33 PM   #2
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I have really liked trucks that have had TBI.
More responsive and starts are easy.
There maybe more than just TBI to the system, like heads, cam and of course sending units.

If had the whole unit would consider.
Piece by piece may get tough.
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Old 01-26-2008, 01:43 PM   #3
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Replacing carbureted engines was easy. Now in computer era, when putting in different engine, the computers might cost more than the new engine.
Make sure you get mechanics who are really up to task and get firm quote.
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Old 01-26-2008, 02:16 PM   #4
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Don't forget the electric fuel pump in the gas tank, its part of the gasoline pickup assembly.
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Old 01-26-2008, 02:22 PM   #5
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Quote:
Originally Posted by klattu
I have really liked trucks that have had TBI.
More responsive and starts are easy.
There maybe more than just TBI to the system, like heads, cam and of course sending units.

If had the whole unit would consider.
Piece by piece may get tough.
You're right it would be tough doing it piece by piece. Knowing what pieces you need would be the biggest issue. Thats one of the things I'm hoping to get out of this thread, what pieces are really needed.

I'm hoping the computer that I have will work. So what else is there?!


Thanks!


Brad
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Old 01-26-2008, 02:23 PM   #6
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Quote:
Originally Posted by Beginner
Don't forget the electric fuel pump in the gas tank, its part of the gasoline pickup assembly.
Beginner
Now that might get kinda tough on a Classic motorhome! How would one go about installing an intank fuel pump in one of those 60 gallon tanks?

Thanks!

Brad
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Old 01-26-2008, 04:00 PM   #7
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Pump in Fuel Tank

Quote:
Originally Posted by bkahler
Now that might get kinda tough on a Classic motorhome! How would one go about installing an intank fuel pump in one of those 60 gallon tanks?

Thanks!

Brad
Brad, I am watching this thread. We are considering a crate/fuel injected motor packgaged with computer for a possible tow vehicle. I need to understand if If it wants electric fuel pump in the tank. JB
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Old 01-26-2008, 04:25 PM   #8
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Brad,

You can acquire an aftermarket external fuel pump to meet your requirements. You will need to make sure you have a fuel return line to your gas tank and that the lines are of sufficient size (I'm sure you'll find that info on the 'net).

My buddy put an aftermarket TBI from Holley on his engine and the difference it made is very noticeable. Easier cold starts, better fuel economy, cleaner when going through the pollution testing center, and not nearly as finicky as carbs get when running various types of gas on long trips. I believe his fuel economy increased by about 15 to 20%. He loves it and is "working" me to add one to my 455 Pontiac which I'll likely do.

The factory crate engines that come with TBI also include the correct computer and info on what's required for a fuel pump and line sizes and return lines so go talk to the local GM dealer and find out from them what is needed. You already have the engine/computer but the computer itself might require a different chip if it's from a throttle body injection unit. Actually, I'm not even sure you can use one from one type to the other.

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Old 01-26-2008, 08:40 PM   #9
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Hmmm, speaking of when I swapped my V6 Chevy Astro TBI with a 350 v8 TBI here.....
1) Computer - I'd make sure you have the right computer. Although you can use the 350 TBI engine computer, it may not be telling the injectors to give enough fuel to the unit. It's easy enough to swap the computers, so that's the least of your issues. (I might have one lying around for a 454... I'll check and pm you if I do).

2) Harness - This is probably the biggest issue. Advance Adaptors may make a new harness for you to use. I'd be wary of buying one out of a junker, those wires and the plugs are sometimes on the cheaper side. I'd be a nightmare trying to figure out where a loose connection or broken wire is.

3) The intake manifold is different for the TBI vs. the carb.

4) You could just make this easy by purchasing either a Holly or Edelbrock TBI conversion. I believe it comes with the harness and intake (computer too!).

However, it is a pricey item. Check Summitracing.com for it. I still get the impression from folks who have used it that it isn't just a turn key conversion though. I do think you have to use your laptop to dial it in.

When I was pulling my hair with idle problems with my swap, I really wished it had the ol fashioned carb....... : >
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Old 01-27-2008, 07:48 AM   #10
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TBI and 454 Conversion + 4L80E

I am also planning a TBI conversion. Have been researching for about a month now, so I can share a few things.

My primary reason for switching to TBI is for improved drivability, AND so that I can put in a computer controlled 4L80E transmission. The hot rod and off road crowd has been doing EFI conversions for years, mostly for drivability. Having driven fuel injected vehicles for years, I'm just tired of not being able to just start up my Argosy Motorhome without endlesss cranking and pedal pumping. My old '74 Cortez had the same fussiness.

SO...here's what I've learned so far:
TBI is the most economical way to go. There are several companies out there (small shops) that specialize in kits for these conversions. They use GM computers, sensors etc. so that parts can be replaced more easily in the future, and it keeps the costs down. They tend to use fuel injectors from Holley.

I'm planning to purchase a kit from Howell EFI (www.howellefi.com) I've spoken to them, and they always answer my questions. They have also provided kits to many of the GMC motorhome guys, and have been written up in some 4x4 mags.

To order the kit, you've got to tell them everything you know about your engine and driveline, and whether it has been modified. You've also got to decide on whether you want a computer controlled distributor (add $100-300) for adjusting timing. You've got to map out where the computer will be installed, because it may need a longer harness. You've also got to know tire size, circumference, and rear axle ratio. I'm still a bit uncertain as to whether I've got a 4.10 or 4.56 in mine, so I've got to jack up the rear and do some tire twirling.

You'll need a new air cleaner to clear the injectors, and if you are hoping to control the 4L80 tranny, you've got to tell them which year, because it determines both the computer and software selection, as well as the harness connectors. The electronic tranny also warrants either a new electronic speedometer, ($120-150) or some type of mechanical to electrical conversion apparatus, at $300-$400.

The transmission conversion will be the most challenging, I think, because the 4L80E is 2-3" longer than the TH400. That means either the tranny mounts moves back, or something needs to be fabricated. Also means the driveshaft needs to be shortened! The newer tranny also has different cooling line connectors.

I've purchased a 4L80E used MH tranny because I wanted to make sure it could handle the load, AND it was way cheaper than the Gear Vendors overdrive/underdrive kit. I also liked the idea of components that were less than 30 years old!

If you decide NOT to do the TBI, you can still get a computer to control the tranny, and even custom program it with a laptop. Dedicated TCMs are $700-1200.

I'd be very interested to hear from anyone in this community who has already done these. I've read a lot on the Jeep sites, and the GMC sites, but it would be great to have details that are specific to us.
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Old 01-27-2008, 08:56 AM   #11
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Another TBI thread exists, with good links

http://www.airforums.com/forums/f159...4-a-19421.html
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Old 01-27-2008, 07:55 PM   #12
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Barry, thats good news about the fuel pump. If I remember right there is a 5/16" and a 3/8" line coming from the fuel tank right now. Not sure which is the feed but I think its the 3/8" line. Hopefully those will be sufficient.

I'll consider aftermarket parts although I would prefer to use GM parts. Mainly due to ease of finding parts along the road if need be.

Marc, thats a good point about the computer. I guess I need to find out if there was a part number difference between the 350 and 454 installations for 1994 which is what year the 4L80E is.

So far it looks like I need to replace the manifold for certain and possibly the computer and obviously I would have to source the TBI hopefully from a salvage yard somewhere.

What about pistons, rods, heads, cam, etc. Lots of questions still

Sean, it sounds like we might be going down the same path. I got your PM and will definitely keep you in the loop if/when we make progress.

Thanks!

Brad
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Old 01-27-2008, 08:23 PM   #13
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I installed a 700R4 into my 24ft MH and didn't need a computer check out Bowtieoverdrives.com and you may not need computers I bought a kit to lockup my tourque converter without the computer but I guess you would need all that with the Electronic components on a TBI engine only been on two trips but about 10-12 mpg which is about 3+ better than I was getting
before I changed the engine and tranny. My old 454 finally just wore out.
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Old 01-27-2008, 11:44 PM   #14
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The rest of the engine should be fine with the TBI ... start modding with the camshafts, heads and etc, then you're really talking about needing to fine tune the computer.

You'll also need to have a knock sensor added to the block if it's not already drilled for one... not hard to do in the rebuild process.

TBI units can be had from any pick and pull around here. I found a local shop to rebuild my injectors, which flowed much better than the ones I bought "rehabbed" from the local Napa (and were cheaper too). I would suggest going and pulling a whole intake manifold and tbi unit as a whole. That way you'll see what kind of sensors you'll need for the engine. I just bought new ones and replaced as I went along... not too difficult to do. Thinking about it, I'd call Painless Wiring to see if they have a harness for the P30 chassis. My bet is they might... you'd need just a basic harness with A/C controls..... Painless Performance Fuel Injection Harnesses - summitracing.com these are what you need, but just for the 454.



My computer was for the 350 after all, so no help to you. I really don't know if they were the same or not for the 454 vs. 350. My guess is that they aren't. You also need a cover for the fuel pump on the side of block... no big deal.

You will llike the driveablily, but I'd stay close to stock with the engine to get it running, then MAYBE start swapping out things. Like I said, I had a hard time getting my engine to work with my mild cam swap.
Good luck!
Marc
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